texts: How to make Poinsettia pigment into ink?

texts:
Like many families, this winter we had bought a red poinsettia plant to decorate our kitchen, and now that it's losing its leaves, I had the genius idea to extract the red pigment. The activity proved a success, and let my 5 yr baby girl amazed (and us too). The pigment was extracted by letting leaves soak in 96% alcohol overnight in a closed container in a hot spot, then filtering the solids and heating the solution until alcohol evaporated for the most part, also adding a few drops of lemon juice to increase acidity and transform the brownish liquid into a blood red tint the that now has the aspect of an ink. Unfortunately, we were unable to use this ink to basically anything, as most mediums like regular paper or white paint are neutral or high pH and turn the poinsettia ink from red to any other color, like blue or green.

As you might have gathered by now, I am not a chemist, and I have no knowledge in the matter beyond high school classes from the old days. I did understand thou after reading this article that changes composition and color with pH.

So what I ask for, if at all possible, is a method described in plain terms and using household accessible chemicals to stabilize this red ink in order to use it, for instance, to paint on paper without losing its intense red color. (at least for a few hours or days)


texts: I would like to know what is the difference between a chemical element and a type of atom? Can  anyone give the definition, please!


texts:
According to my chemistry textbook, heat is defined as "Energy that is exchanged because of a difference in temperature or a change in phase." My textbook also says, "Heat is a form of energy. Temperature, on the other hand, is a measure of how quickly the molecules (or atoms) in a substance are moving," implying that temperature is not a form of energy, just a measurement of a physical condition.

This seems all wrong to me. If heat is just a change in temperature, but temperature isn't energy, doesn't that imply that energy is created when two objects of different temperature interact, or is there potential heat energy in the temperature of an object?

Also, the textbook says that the reason we feel hot is because of heat from temperature change, and not temperature itself, but this doesn't explain why chemical reactions occur faster at different temperatures. Nor does it explain why there are different states of matter at different temperatures, or even why our bodies need to stay at a certain temperature at all. Where is the energy from heat and other chemical processes coming from, exactly?

Other sources online also say that heat is a change in temperature and temperature is not energy, only a measurement, so I don't think it's just my textbook. I feel like I'm missing something.


texts: Why ¹H–¹⁴N coupling is not observed in ¹H NMR

texts:
Since the nuclear spin value of $\ce{^{14}N}$ is $I = 1$, we should expect a coupling between $\ce{^1H}$ and $\ce{^{14}N}$. Hence, the proton peak in a primary amine $(\ce{-NH2})$ should split in a triplet ($2 × 1 × 1 + 1 = 3$).

But generally that is not observed. Is this because of lower gyromagnetic ratio of $\ce{^{14}N}$ that leads to very less population difference between ground and excited state, or is there some other reason behind it?


texts: Are there any free electrons in metal vapor?

texts: Metals contain free moving electrons, in both the solid and liquid state. Does this happen when it is in vapor form?


texts: If the standard state symbol means that the substance is pure (and at 1 bar) how is it possible to have a standard REACTION enthalpy?

texts:
For the reaction one mole of substance $A$ in equilibrium with one mole of substance $B$ the standard reaction enthalpy is defined:
$$\triangle_rH^{\theta}(T)=H_m^{\theta}(B;T)-H_m^{\theta}(A;T)$$
However, I have two issues with this.

Firstly: the standard state of a substance (denoted by the symbol $\theta$) is the pure material at a pressure of 1 bar. How can the reaction enthalpy be standard - the reactant have to be mixed (thus are not pure) to react.

Secondly: what is $H_m^{\theta}$? Surely nothing can have a molar enthalpy because only changes in enthalpy can be measured not absolute values. Am I right in thinking that is is because the enthalpy scale has no zero value?


texts: What is a kg.cal per gram, as a heat of combustion?

texts: I see heats of combustion given in kg [dot] calories per gram molecular weight (Handbook of Chemistry and Physics, 1969-1970). I don't know how that makes sense, as I don't know what a kg cal might be.  I would have expected units of energy per mass (calories per gram) or energy per mole.  What is a kg cal, and what is wrong in my thinking?


texts:
Pressure can be measured in $\pu{mmHg}$ which is equal to the pressure exerted by a “column of mercury” of a height expressed in $\pu{mm},$ at $\pu{0 °C}$ under Earth’s normal gravity.

Does the diameter of a tube that contains the mercury affect how high the mercury will rise? Why isn’t pressure measured in $\pu{mmHg^3}$ or some other unit of volume of mercury?


texts: Relation of Boiling Point and Melting Point with the reactivity of an element

texts:
When we look at the trends of periodic table, there is an interesting correlation to be noticed. Along a period, when we look at the trends in reactivity of an element( Both due to electropositivity AND electronegativity) the trend is that from the right to the left, first there is a decrease and then an increase; which is definitely sensible. The question that arises is due to this observation that same happens with the boiling point and the melting point of that particular element. It first decreases and then increases. So this leads to the intuition that the reactivity (ie combining capacity ) also affects the physical characteristics of that particular element. If such is the case, the WHY EXACTLY does this happen- what is the explanation behind this phenomenon. If this intuition is false, then correction would be highly appreciated.

Thanks and yes, you are awesome!


texts: Why Does an Area in Phase Diagram Considered as Having Degree Of Freedom=1?

texts:
Why did the area in the center are Considered as Having 1 Degree Of Freedom. Aren't we able to change the concentration and the temperature at the sametime without changing the Phase?

Here is the link to the document https://www.google.co.id/url?sa=t&source=web&rct=j&url=http://www.colby.edu/chemistry/PChem/notes/GibbsPhaseRule.pdf&ved=0ahUKEwjw7Laq7M3QAhXGQI8KHXwKB3sQFggcMAE&usg=AFQjCNHWRoz8CuB0BSOoLJm-K0iPayNvgQ&sig2=vYhsTSV_woeOd2_GPPLdEw


texts: Does the stoichiometry effect the value of the equilibrium constant of an equilibrium reaction?

texts:
Will be there any change in the $K_c$ values for same reaction, if we write stoichiometry as a fraction or as a integer? For example, assuming that we calculate $K_c$ at same temperature:

$$\begin{align}
&(1)  &&\ce{1/2A + 3/2B -> C}\\
&(2)  &&\ce{A + 3B -> 2C}\\
\end{align}$$

If we calculate $K_c$ for above two equilibrium reactions, do we get different answers?


texts: Finding membrane potential equation using the Nernst equation?

texts:
I am very new to electrochemistry and ion selective electrodes. The membrane potential of an ion selective electrode is given by $$E=\frac{RT}{nF}\ln{\frac{c_2}{c_1}}$$
Where R is universal gas constant, T temperature in kelvin, n the number of electrons transfered, F Faraday of electricity, $c_2$ the concentration of internal standard solution and $c_1$ is the concentration of the ion to be calculated.

But according to the Nernst equation
$$E= E^\circ -\frac{RT}{nF}\ln k$$
Can someone explain how to come up with the membrane potential equation using the Nernst equation?


texts: I've been practicing organic nomenclature and I was wondering if anyone could show me the proper way to approach naming this molecule. My guess would be methane-quadra-dioxyanol.


texts: Is there relation between “Plane wave basis” “Correlation-Consistent” basis and “Fourier basis”

texts:
This question is related to the following link I found while browsing the internet: http://www.gutenberg.us/articles/Basis_set_(chemistry) The question: Is there a relation between "Plane wave basis" "Correlation-Consistent" basis and "Fourier basis"?  Would anyone please add appropriate tags as well? Any comment would be appreciated.

One can think of Fourier basis as constructing the function with different frequencies. I was looking for constructing the function with vectors with same "correlation-consistent" . Is such concept possible? Is "correlation-consistent basis" is something similar?


texts: Why do the lanthanides and actinides have a 5d and 6d orbital, respectively?

texts:
I was taught in school that the rare earth metals were the $\mathrm{f}$-orbital group. Additionally, the Aufbau principle states that the order of orbitals based on energy levels is $\mathrm{6s4f5d}$ and $\mathrm{7s5f6d}$ for the lanthanides and actinides, respectively. However, upon inspection, both periods have 15 elements whereas the $\mathrm{f}$-orbitals can only hold 14 electrons. I was able to resolve this by assigning one electron to the $\mathrm{5d/6d}$-orbital, which is correct according to chemistry libretexts. Why does this occur for the rare earth metals?
Furthermore, according to libretexts, only some of the rare earth metals have a $\mathrm{5d/6d}$-orbital, whereas others have the $\mathrm{6s/7s}$-orbital and proceed to only fill their outermost $\mathrm{f}$-orbital. Why is this the case, and is there a way to determine which elements are like this short of simple memorization?


texts: What is the function of acetic acid as a solvent in EAS reactions?

texts:
I saw acetic acid being used in two reactions:

1.

2.

I was asked to predict the outcome of the first reaction but I couldn't, because nitration requires generation of $\ce{NO2+}$ which in turn requires an acid stronger than nitric acid. (acetic acid is weaker)

I would like to know how exactly is $\ce{AcOH}$ participating in these two reactions. Is it supporting the generation of electrophile? If yes, then how? I couldn't find any relevant information on the net. The second reaction is from Clayden's book and it doesn't highlight the role of $\ce{AcOH}$ there.


texts: Hygroscopic Substances and Drying Agents

texts:
My book says:

  Most of the hygroscopic substances are drying agents

Based on what I read on several websites, I think dehydrating agents also act as drying agents. If so, all dehydrating agents would also be drying agents and that would contradict my book's statement. So, is there another type of hygroscopic substances or is the book wrong, or is my information or logic wrong?

P.S. I don't think the tags I've used are suitable. I just put the following tags as Wikipedia said that hygroscopy is caused due to either absorption or adsorption. I would appreciate if anyone could help me out.


texts: Can you push a liquid and a gas into a container at different pressures?

texts:
I have a gas ($\ce{CO2}$ for example) and I want to infuse it into a liquid ($\ce{H2O}$ for example). I need a higher pressure of $\ce{CO2}$ to do this. So I push in water into a sealed container (at 7 psi) and add $\ce{CO2}$ (at 14 psi).

Is this possible? Will it back up? What if I use a check valve? Can I use a non-electrical actuator of some sort to let liquid in, and then add gas 'automatically'? What about something that functions like a carburetor?

I need to let the new solution out after it is mixed and also allow a consistent flow if I leave the exit open. If I have a liquid at 7 psi and a gas at 14 psi and I am trying to push them both into a sealed container, how is this done? Letting it out? Doing it on the fly?

I know you do NOT carbonate water at these pressures. Just an example with real gas/liquid.


texts: What value of temperature does T represent in Gibbs Free Energy Equation?

texts: Temperature before, or after reaction? Temperature change? Or what is it?


texts: Photoionisation microscopy of hydrogen - where are the p orbitals?

texts:
In this Physics Review Letters article, which was published in 2013, but I found recently, the authors report photoionisation microscopy images of hydrogen atoms in various electronic states.

  A. S. Stodolna, A. Rouzée, F. Lépine, S. Cohen, F. Robicheaux, A. Gijsbertsen, J. H. Jungmann, C. Bordas, and M. J. J. Vrakking, "Hydrogen Atoms under Magnification: Direct Observation of the Nodal Structure of Stark States,"
  Phys. Rev. Lett., 2013, 110, 213001; url: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.213001

Here are some non-paywall summaries of this work:

physicsworld.com http://physicsworld.com/cws/article/news/2013/may/23/quantum-microscope-peers-into-the-hydrogen-atom
APS Physics http://physics.aps.org/articles/v6/58
io9 http://io9.gizmodo.com/the-first-image-ever-of-a-hydrogen-atoms-orbital-struc-509684901

The imagery is compelling:

I see images that look like $1s,\ 2s,\ 3s,\ \&\ 4s$ orbitals with appropriate number of nodes.

The solutions to the Schrodinger equation for hydrogen-like orbitals include wavefunctions corresponding to $p$ oribtals. Why did the authors not observe images that appear to look more like the $p$-orbitals?


texts: How does one analytically quantify whether or not a compound is a SIRT1 activator?

texts:
So there has been a lot of noise over whether or not certain molecules activate SIRT1. Resveratrol was thought to be a specific SIRT1 activator, but many have argued against this claim.

Similarly, this has also happened to SRT1720 too.

My question is - why is it so hard to quantify whether or not a molecule is an SIRT1 activator? How would one go about doing this?


texts: I added urea to water and, predictably, observed a temperature drop (10 C).  I wanted to place the beaker under (reasonably) high vacuum (for a classroom) and recover the urea as a dry substance.  Well, I didn't.  It's been a couple of months now, and there's white scale all the way up the inside, and crystaline filaments on the bottom, with an unchanging fraction of the original H2O.  Is the substance still urea?  There's been no odor.  Is it ammonium carbamate? In either case, can I use vacuum to dessicate it?


texts: Why do many transparent plastics turn opaque when deformed?

texts:
Many transparent plastic materials, rigid or not, turn opaque (white) when subjected to stress, deformations or when folded (if not rigid) . The effect seems to be irreversible.

What is the cause?

I would have guessed that some internal crystalline structure is broken, but plastic (like glasses) have no crystal structure, no?


texts: Hydrogen + Fluorine Adiabatic Flame Temperature

texts:
The theoretical adiabatic flame temperature of Hydrogen and Fluorine in their stoichiometric mixture is often quoted at around $\pu{4300K}$, such as in this presentation on page 2, or this paper which is shown entirely in the pubs preview. However, this thermodynamics table from JANAF makes it seem as though the temperature should be much higher. I suspect I'm missing something, but after quite a lot of searching I can't find it! (So it's probably something very basic)

My work: The Gibb's energy for the reaction is quite negative even out to $\pu{6000K}$, so the combustion should happen effectively to completion regardless of temperature ($K = 307 = \exp\{--285.7\times1000/(8.314\times6000)\}$. The formation enthalpy is listed $\pu{-273kJ/mol}$, and we could either do the temperature integral of $C_p$, or scan down the H-H(Tr) column to find this puts us way beyond $\pu{6000K}$, let alone $\pu{4300K}$.

Anhydrous $\ce{HF}$ gas apparently does form dimers, trimers, etc. but these should only increase the adiabatic flame temp if present, and they (understandably) don't appear to be stable beyond a couple thousand K.

Thanks in advance for the help!


texts: How to calculate the sufficient ratio of acid and corresponding base of the indicator that allows to clearly observe the endpoint of a titration?

texts:
Ram can see the purple colour of an acidic indicator below pH = 5.5 only and the blue colour only above pH = 8.5. How many times that of acidic form must the concentration of the basic form at least be for him to be able to see the end point of the titration of HCl and NaOH.

Attempt at Solution

Since the indicator is acidic it is of the form $\ce{HIn}$ and dissociates as follows - $$\ce{HIn<=>H^+ + In^-}$$

where $\ce{HIn}$ is acidic form and $\ce{In^-}$ is basic form so we need to find the minimum value of $\frac{[\ce{In-}]}{[\ce{HIn}]}$. The colour change happens at ph 5.5 and 8.5

At the end of point of titration of HCl and NaOH ${pH = 7}$ which automatically falls within the pH range of indicator ( 5.5 - 8.5 ), so i don't know what to do.

Now from the Henderson Hasselbach equation we have, $${pH = pK_{In} + \log \frac{[\ce{In-}]}{[\ce{HIn}]}}$$ So I guess we put 7 in place of pH and then I again do not know what to do now.

Please help me out with this problem.

Answer in my book is 32


texts: Does the synthesis of beta-keto phosphonates from esters have a name?

texts:
Consider the Horner–Wadsworth–Emmons reaction; one of its reactants is a phosphonate, usually stabilised by a β-carbonyl group which is then deprotonated in α position (figure 1). These phosphonate esters can be synthesised in a Michaelis–Arbuzov reaction from a phosphorous acid triester and an alkyl halide (figure 2). Another viable way is to start from diethyl ethylphosphonate, deprotonate that (e.g. with n-BuLi) and let it attack a carboxylic ester much like a Grignard reagent would (figure 3).

Figure 1: Horner–Wadsworth–Emmons reaction. Image taken from Wikipedia, originally created by Wikipedia user ~K.

Figure 2: Michaelis–Arbuzov reaction. Image taken from Wikipedia, originally created by Wikipedia user ~K.

Figure 3: Alternative synthesis of HWE phosphonates. Image self-drawn.

Since about every reaction in organic chemistry has a name of some kind, is the reaction in figure 3 also a named reaction, and if so, what is the reaction’s name?


texts: What does the volume of a gas depend on?

texts: In my chemistry textbook, it states that the volume of a gas is directly proportional with the amount(number of moles) of that gas. However, it also mentioned before that the volume of a gas depends on its container. So if the volume of a gas depends on its container then wouldn't the volume not change as you add or take away gas molecules? As long as the container doesn't change wouldn't the volume of the gas stay the same?


texts: How can the torsional barrier of a polymer determined by molecular dynamics?

texts:
First consider a simple polymer, like polyacetylene:

Its torsional barrier can be determined by DFT calculations by considering "enough" units and performing a simple dihedral scan. "Enough" appears to be 5-7 units (J. Chem. Phys., 2014, 140, 054310)

But now I want to study a more complex polymer:

The same method does not work, because the structure is too flexible. Different values are obtained after multiple turns around the central unit. Is it possible to use molecular dynamics to find the effective/average rotation barrier?

My guess would be that we could simulate this polymer over a certain period of time, then make an histogram of the central dihedral angle. We could then calculate the torsional barrier by looking at the relative frequencies of the angles (e.g. if we get a flat distribution, the barrier is 0, if some angle is very disfavored, the barrier should be high. I'm not sure how to quantitatively calculate the barrier though)


texts:
Advanced Inorganic Chemistry: A Comprehensive Text on Pg. 228, Chapter 8 titled 'Boron' talks about three factors which appear to be responsible for the shortness of $\ce{B-X}$ bonds(where $\ce{X}$ is a halogen). The second point was stated as:

  Strengthening and hence shortening of the $\ce{B-X}$ bonds by ionic-covalent resonance, especially for the $\ce{B-F}$ and $\ce{B-O}$ bonds because of the large electronegativity differences. Evidence that this is important, in addition to the dative pπ-pπ bonding, is afforded by the fact that even in $\ce{BF3}$ complexes such as $\ce{(CH3)3N^+B^-F3}$ and $\ce{BF4^-}$, where the pπ-pπ bond must be largely or totally absent, the $\ce{B-F}$ bonds are still apparently shortened

What is this "ionic-covalent" resonance exactly? I tried looking it up,but found some unsatisfactory and vague answers here where it seems like they are presenting regular resonance as ionic-covalent. This answer on the other hand seems to be talking about compounds possessing both ionic and covalent factor although which is correct,does not really address the issue at hand.
So is this term really just refering to regular π-bond resonance, or is it an entirely different phenomenon?


texts: Does the electrochemical series reverse in electrolysis?

texts:
Are these two statements true?

In a galvanic cell at standard lab conditions (SLC), the strongest reductant is $\ce{Li (s)}$ and the strongest oxidant is $\ce{F2 (g)}$.
In an electrolytic cell at SLC, the strongest oxidant is $\ce{Li+ (aq)}$ and the strongest reductant is $\ce{F- (aq)}$.


texts: Why does adding a charged group to an organic molecule decrease its stability?

texts:
As I understand it, during glycolysis, glucose is converted into fructose 1,6-bisphosphate which greatly destabilizes the molecule. This is so it can be divided into pyruvates more easily.

Now I don't understand why adding charged groups such as phosphates destabilize molecules, what actually happens to the molecule when a charged group associates with it? Why does it become destabilized?


texts: Enthalpy of formation of ammonium bicarbonate

texts:
I'm helping with correcting lab reports, and one of the experiments the students did was heating of ammonium bicarbonate, $\ce{NH_3HCO_3}$ in powder form, over Bunsen burners, which turns the compound into water, carbon dioxide and ammonia (all gasses). They are supposed to say, in their report, whether this is an endothermic or exothermic reaction.

Now, I would be very surprised if this reaction turned out to be exothermic. An hour of googling seems to agree with me, but I can't find a definite answer. In the course we've talked about enthalpy of formation and Gibbs free energy, so it would fit into the curriculum if we could find the relevant data.

Unfortunately, it's apparently very difficult to find the enthalpy of formation of sodium bicarbonate through google. Many small tables do not list the chemical at all, and the other sources that I've found does not list enthalpy of formation. I've found one number, which is -32 kcal, without specifying whether it's per mole, g, kg, ounce or pound.

Does anyone have a source on the enthalpy of formation of solid $\ce{NH3HCO3}$ at room temperature?


texts: Is the water in an aqueous solution undergoing a reaction considered part of the system or surroundings?

texts:
System: In chemistry, a system is a chemical reaction. A system operates within its surroundings. Energy can move between the two.

Surroundings: The environment around a particular chemical reaction. The chemical reaction is the system.

Above are my textbook's definitions for system and surroundings.

For example, mixing two aqueous solutions to produce a precipitate. Although the water doesn't undergo any permanent chemical changes, it is still enabling the reaction (much like a catalyst). So is water then considered part of the system?


texts: Conservation of angular momentum in rotational spectroscopy

texts:
In spectroscopy, transitions between rotational energy levels obey the selection rule $\Delta J = \pm1$. The rule follows from the fact that the photon absorbed has an angular momentum of $\pm \hbar$, so the molecule must change its angular momentum for the total angular momentum to be conserved.

However, the angular momentum of a molecule is given by $\hbar \sqrt{J(J+1)}$, so the change in molecular ang. mom. is $\hbar\sqrt{(J+1)(J+2)} - \hbar\sqrt{J(J+1)}$. As $\hbar\sqrt{(J+1)(J+2)} - \hbar\sqrt{J(J+1)} \neq \hbar$, it seems that the total angular momentum is not actually conserved.

Questions:

Does the conservation of angular momentum apply to quantum systems?
If yes, what is the source of the contradiction above?


texts:
A cereal sample was analysed for Calcium content as follows: A 5g cereal sample was digested with HCl and the resulting mixture made up to 50ml in a volumetric flask. The absorbance of this solution was found to be 0.351. A 7ppm calcium solution gave an absorbance of 0.254. Assuming linearity between absorbance and concentration, calculate the calcium content of the cereal in mg Ca/100g cereal. (8 marks)

Seems so simple but is confusing me as when I take into account calcium content of the cereal in mg Ca/100g cereal.

A 5g cereal sample was digested with HCl and the resulting mixture made up to 50ml in a volumetric flask.

The absorbance of this solution was found to be 0.351.

A 7ppm calcium solution gave an absorbance of 0.254

7 ppm Ca solution/ absorbance 1 x absorbance 2 =

step 1: 7 ppm/ (0.351 x 0.254) = 78.515 ppm ca in final dilute sample.

step 2: 78.5158/50 ml  (of initial volume sample)= 1.57 ppm ca in the first solution.

Supposing the density of the first solution to be near that of water:

step 3: (1000g) x (1.57 x 10^-6) = 1564 g Ca

step 4: (1564 g ca / 5g) = 312.8 g/100 g

answer: 3.128x10^5 mg/100 g would be the initial answer I receive.

My second attempt looking at it a different way...

feeling that I have done step 1 correctly.  Starting at step 2

78.5158/(50 ml x 2) (multiplying initial volume by 2 to achieve 100 ml)
= .785158 ppm ca in 100 ml.

step 3: (1000g x 7.85x10^-4g)=7846 g ca /100 ml

7846000 mg ca / 100 ml

answer: 7.846 x 10^6 mg ca/ 100 ml

third attempt:

Seeing that the initial sample is 5 g and the question is looking for calcium content in a 100 g sample...

5g sample x 20 = 100 g

therefore other components are multiplied by 20

V= 50ml x 20 = 1000 ml

step 1: step 1: 7 ppm/ (0.351 x 0.254) = 78.515 ppm ca in final dilute sample.

step 2: 78.5158/1000 ml  (of initial volume sample x20)= 0.0785 ppm ca in the first solution.

step 3: (1000g) x (.0785 x 10^-6g) = 72.5 g Ca

step 4: (72.5 g ca / 100g) = .725 g Ca

answer: 725 mg Ca content/ 100 g cerial

I feel that I am missing a step in calculations.  I would prefer to read a resource of working this out myself than finding the answer.
I feel more confident in my third attempt of finding a correct answer.

This question is from a past paper.


texts: Is acetate a weak base due to its resonance structure?

texts:
I just read that acetic acid is an exception to the general idea that the conjugate base to a weak acid is a strong base.  The example says that the conjugate base of a weak acid will only be strong if the acid is a weaker acid than water.

What I'm curious about though, is if acetate is a weak base due to its resonance structure.  Does the resonance cause acetate to be more stable than hydrogen acetate?

Is this true in the more general case where some substituent can bond to the atoms involved in the resonance?

Thanks.


texts: When would the presence of lone pair result in a polar molecule?

texts: In what cases would the presence of a lone pair result in a polar molecule? For instance, O3 is polar despite only consisting of O atoms due to the presence of lone pair of electrons. However, O2 also has lone pair of electrons but is not polar, why? Also, for HAt, the electronegativity difference between H and At is 0, but is HAt polar or non-polar?


texts: Why are the mass ratios of O to KClO3 and O2 to KClO3 the same?

texts:
I just did a lab that involved heating KClO3 (with MnO2 as a catalyst) to decompose it into KCl and oxygen gas. That part is easy. What's throwing me is the % yield calculations.

The theoretical yield of O should just be the mass percentage of O in KClO3 (48.00/122.55 = KClO3 is 39.17% O by mass).

The actual yield of O2 (measured by subtraction) was 0.840 g out of a initial mass of 2.062 g KClO3, or 40.7%.

My question is this: Given that the theoretical yield was 39.17% based on moles of O (not O2) , why is the actual yield 40.7% (well with margins of error outlined by the professor) when it's based on O2? Shouldn't it be half as much? Or did I mess my calculations up?

Please feel free to edit tags, I'm out of my depth on this particular SE site in that area.


texts:
Picric acid has nitro groups in para and ortho positions, so it has great possibility to go for resonance, thus it is supposed to be a very good acid.
But a question arises! The $\ce{O}$ of $\ce{-OH}$ has intramolecular $\ce{H}$-bonding with ortho-nitro groups present on both sides. So will the firstly mentioned theory work well or is the answer something else?


texts:
This is 1,6-dimethyl-cyclohexene. Why cannot this same structure have the IUPAC name 1,2-dimethyl-cyclohexene. In the given picture the locant sum comes to 7 but in my case it comes to 3, implying that my answer is in accordance with the rules. Aren't the alkyl groups supposed to be given the lowest number as per lowest locant sum rule?

Please do clarify. Thanks!


texts: Will nitrate be able to oxidise mercury?

texts:
We have the following data:

\begin{align}
\ce{NO3- + 3 e- &-> NO} &\quad E^\circ_1 &= \pu{0.96 V}\\
\ce{Hg^2+ + 2 e- &-> Hg} &\quad E^\circ_2 &= \pu{0.86 V}
\end{align}

By the reasoning given in my book, nitrate oxidises mercury:

  ... of two substances, the one whose reduction $E^\circ$ value is greater, will be able to oxidise the other substance the other.

Then I tried calculating $E^\circ$ for overall reaction also taking into account number of electrons in each reaction. Or that we calculate $\Delta G$ for

$$\ce{NO3^- + Hg -> NO + Hg^2+}$$

$$\Delta G^\circ = -0.96 \cdot 2F + 0.86 \cdot 3  = 0.66F$$

So, $\Delta G^\circ$ is positive and so nitrate does not oxidise mercury. Which is correct?


texts: Is soap the natural form of Sodium Lauryl Sulfate?

texts: I was told that "Sodium Tallowate, sodium cocoate and sodium palm kernelate are the 'natural' forms of SLS".  Is this true?  I thought "natural" SLS would be SLS derived from a natural product such as coconut oil.


texts:
Can anyone show me how to find the masses of $\ce{NaH2PO4}$ and $\ce{Na2HPO4}$ needed to prepare $1.0~\mathrm{L}$ of a $0.1~\mathrm{M}$ phosphate buffer solution with $\mathrm{pH} = 7.4$ using the simultaneous equations method?

This is what I have so far:

$$\ce{NaH2PO4 + H2O <=> H3PO4 + NaOH} \\
\ce{Na2HPO4 + 2H2O <=> H3PO4 + NaOH + H3O+} \\
\ce{NaOH -> Na+ + OH-} \\
\ce{H3O+ + OH- <=> 2H2O} \\
\ce{H3PO4 + H2O <=> H3O+ + H2PO4-} \\
\ce{H2PO4^- + H2O <=> H3O+ + HPO4^2-} \\
\ce{HPO4^2- + H2O <=> H3O+ + PO4^3-}$$

The species present are: $\ce{HPO4^2-}$, $\ce{PO4^3-}$, $\ce{H2PO4-}$, $\ce{H3PO4}$, $\ce{Na+}$, $\ce{OH-}$, and $\ce{H3O+}$.

I have two equations:

$$\begin{align}
K_\mathrm{w} = [\ce{H3O+}][\ce{OH-}] &= 1.0 \times 10^{-14} \\
[\ce{OH-}] + 2[\ce{HPO4^2-}] + 3[\ce{PO4^3-}] + [\ce{H2PO4-}] &=  [\ce{H3O+}] + [\ce{Na+}]
\end{align}$$

I need 5 more equations for this system. How do I get them?


texts: When is it necessary to check wavefunction stability in density functional theory?

texts:
In Gaussian, there is a stable keyword that checks the stability of the wavefunction. Using stable=opt reoptimizes the wavefunction until a stable one is found if there is an instability.
My question is - when do you use this stability check? Presumably one must have some hunch in advance that the wavefunction may be unstable in order to use this keyword, but what insight would lead one to this conclusion?

To add some context, this question came to mind after following instructions on how to model a system with antiferromagnetic coupling (e.g. as shown here). When I tried this procedure on cupric acetate hydrate, which has a dinuclear structure of copper(II) atoms and is known to be antiferromagnetic, I had to use the stable=opt keyword to stabilize the wavefunction resulting from the "fragment guess job" otherwise it erroneously appeared that the antiferromagnetic singlet was higher in energy than the triplet. This made me wonder when I should be using stable=opt in general (perhaps outside the context of antiferromagnetic coupling calculations) and also what it is specifically doing.


texts:
I am using a Lennard-Jones potential in a computer simulation and I was wondering if i should place a cut-off for low distances since the potential blows up quickly   making the calculations quite difficult.
I am trying to simulate basic molecules ( few atoms ) , calculating bonds stretching , bond angle bending and lennard-jones interactions and trying to minimize the total energy to get an optimal structure prediction .


texts: Fabrication and/or Selection of a Single Crystal Ionic Conductor

texts:
I want to fabricate or buy single crystal ionic conductors for usage as solid state electrolytes in batteries testing. However, I am having trouble finding anyone that can sell appropriate materials.

From my understanding, lanthanium series elements typically have good ionic conductivities. Thus, it seems like Strontium Lanthanum aluminum oxide (SrLaAlO4) or lanthanum aluminum oxide-strontium aluminum tantalum oxide (LSAT) which are both sold in single crystal form, may be suitable. However, I'm having trouble determining if they are compatible with the lithium ion.

Meanwhile, I know that I have seen SiO2 and Al2O3 used as barriers in battery electrodes, and it's possible that single crystals of either of these may be possible to use. However, just because it is a barrier doesn't necessarily render it a solid state electrolyte. Meanwhile, it appears alpha-Al2O3 has previously been used as a separator, I'm unsure if this is truly because the alpha-Al2O3 can transport the lithium versus the pores of the material transporting the lithium. When trying to discover which was the case, I found this paper discusses the transport mechanism of lithium in Al2O3, but I am unsure if this applied to alpha-Al2O3.

Lastly, I can also find MgAl2O4 single crystals, which appear to be good ionic conductors of lithium but only if doped with lithium. However, I do not know a way to create single crystal LiMgAl2O4, starting with MgAl2O4 single crystal.
Does there exist a suitable single crystal material which can be easily fabricated or bought for my purposes?


texts: Titration of sulfuric acid with sodium hydroxide

texts:
$55.0~\mathrm{mL}$ of $0.250~\mathrm{M}~\ce{NaOH}$ is used to titrate $35.0~\mathrm{ml}$ of $\ce{H2SO4}$.
  What is the molarity of $\ce{H2SO4}$?

I know that the equation for this reaction is:
$$\ce{H2SO4 + 2NaOH <=> Na2SO4 + 2H2O}$$

I know that I have to use $$i_\mathrm a\cdot M_\mathrm a\cdot V_\mathrm a = i_\mathrm b\cdot M_\mathrm b\cdot V_\mathrm b$$ formula where $i$ is the number of ions, $M_\mathrm a$ and $M_\mathrm b$ are the molarities (of the acid and base, respectively), and $V_\mathrm a$ and $V_\mathrm b$ are the volumes of the acid and base (in milliliters).

I starting doing this problem and got up to this point:

$$i\cdot M_\mathrm a\cdot 35~\mathrm{ml} = 2\cdot 0.250~\mathrm{M}\cdot 55~\mathrm{ml}$$

So my question is:
What should I put for the number of ions on the left hand side? Is it three or two?


texts:
I am planning to use some of this to construct a transparent touch panel for a prototype of mine. It is PET plastic coated in Indium Tin Oxide.

My plan is as follows:

Use some of this UV-cure dry film, a transparency, and a fluorescent light fixture placed very close to it for a while to cure it (not sure if enough UV there at the right wavelength...I may get one of those UV LED nail spa cure things).
Develop the film, remove excess with water.
Use some of this 32% HCl to etch the ITO.
Remove the film.
Enjoy my completed touch screen.

The problem is, I'm not really a chemistry person. My background is electrical engineering and my experience is limited to one semester in a cleanroom class where we did a lot of SiO2 etching (BOE) and some aluminum and nickel etching.

My questions are as follows:

Will dry film work well for this application? I worry that since it is designed for use with PCBs, made of the relatively stable FR-4, the etchant and remover provided with the kit I linked to will be too harsh and damage the PET or ITO
This paper seems to note that $\ce{HCl}$ is quite slow at $20^{\circ}$C for etching ITO. I estimate the molarity of the solution above is probably between 8-12M, giving me an etch rate of ~2-4angstroms/sec. I'm not sure what the thickness of the film is on the plastic, so I could be there a while. How can I determine the thickness of the ITO given its sheet resistance of 50 ohms? (What I'm really asking is how to determine the resistivity so I can solve for the thickness of the film.) I don't have access to anything fancy like a 4-point probe.
This chemical information sheet states that PET plastic does great with $\ce{HCl}$ at 10%, but terribly when "concentrated" (whatever that means). Am I going to destroy the PET during this process?
Is my plan fundamentally flawed? Is it likely not going to work? Do I need to use a different photoresist or etchant (aqua regia is terrible to PET according to that info sheet)?

I'm not too concerned with overetching or overdeveloping since the pattern doesn't need to be incredibly precise (this is a one-off thing and the contacts are around a half-inch square each).

Assume that I don't have access to a laser for ablation, fancy deposition equipment, or any complex measurement equipment (I've got a multimeter and oscilloscope). I can acquire basic glassware through amazon and such AFAIK.


texts: How to convert an organic carbonate to its formate ester?

texts:
I'm currently working on a chemistry project in which I need to convert ethyl methyl carbonate to ethyl formate.

I only have a simple background in organic chemistry (and I haven't seen anything about reaction mechanisms yet), but I was guessing water could be used in this reaction, to produce $\ce{CH3OH}$ and replace the $\ce{-OCH3}$ group by an $\ce{-OH}$ group. Then the next step would be to remove the oxygen from the  $\ce{-OH}$ group. I've seen that compounds such as $\ce{LiAlH4}$ can do this, but I'm looking for a catalyst to make the process more economically viable, in case the proposed synthetic path is correct.

Does anyone know how to perform the conversion, or even by following another synthetic path? I've got no idea whether this process is correct. I'm also trying to keep the process as low energy-consuming as possible.

I agree it would be better to start from ethanol and formic acid, but I have to start with this molecule.


texts: Can the amount of shielding in proton NMR caused by ring currents be predicted?

texts:
My textbook (Organic Chemistry, 2nd Ed. Hornback, Joseph) states that if a hydrogen is located near the center of an aromatic ring it will experience an (often quite sizable) upfield shift, as seen in these images (borrowed from aforementioned textbook):

Theoretically it all makes sense - the ring current of the aromatic system shields these protons rather strongly. But is there a way to estimate what the actual upfield shift will be? For example, if provided with structure 1 and asked to estimate the chemical shift of the red hydrogen, how could you do so? Or do you just run the NMR and find out? My book doesn't give any advice on how to figure this out, just that it happens.


texts: Why are electrons added in the ionic counting method?

texts:
Why do we add one electron to the ligands that have an odd electron number?

For example the cyclopentadienyl ligand has five electrons that can be donated to the metal but when we count the electrons by the ionic method we add one, so it become total of 6 electrons donated to metal.


texts: Galvanic cells/redox - confused regarding diagram

texts:
I'm not sure if I got this wrong because I interpreted the cell incorrectly. When they have an arrow pointing in to the tube for $\ce{O2}$, does this imply that $\ce{O2}$ is a reactant? If so then B is definitely wrong, which was my answer.

Is there any other reason why B is wrong? I wasn't sure if it was right or wrong when I did this question.


texts: What does this dashed and curved line mean in pyruvate molecular graph?

texts: Hi all, I came across this while researching a gene sequencing assignment and I cannot find out what the curved/dashed line means. Can anyone tell me please? Is it something to do with the negative symbol? Thanks


texts: Does the stability of the radical affect the product for Birch Reductions?

texts: I am working on the Birch reduction on this question. I am thinking that 1) happens because the product for it has the most substituted alkenes. However I noticed that the radical for 2) would be more stable. So I was wondering if that radical in 2) be more likely to form therefore giving the second product?


texts:
Why does the graph of $\ln[\ce A]$ vs $t$ produce a straight line for the first order rate law?

Also why does the graph of $t$ vs $\frac{1}{B}$ produce a straight line for the second order rate law?


texts:
I just have a question on how you handle polyprotic bases.
Question:

Show how oxalate ion can be a polyprotic base

My answer:

My question is whether we stop doing the reaction until the oxalate ion has no charge or do we keep going on as below:

Another question I have is ;why hypochlorite ion would be a monoprotic base, rather than a polyprotic base?


texts: What is the effect of Helium-based surroundings (99% Helium) on electrochemical gas sensors?

texts:
I am currently working on a project measuring gas composition of car exhaust. In order to dilute the gas concentration down to something electrochemical sensors can read, I diluted the sample with pure helium.

The following is true for these sensors:

  Importance of Oxygen. The reactions at the sensing electrode (anode) for some gases are as follows:
  \begin{align}
\ce{CO + H2O &-> CO2 + 2H+ + 2e-} \\
\ce{H2S + 4H2O &-> H2SO4 + 8H+ + 8e-} \\
\ce{NO + 2H2O &-> HNO3 + 3H+ + 3e-} \\
\ce{H2 &-> 2H+ + 2e-} \\
\ce{2HCN + Au &-> HAu(CN)2 + H+ + e-}
\end{align}
  Simultaneously, the reactions at the counter electrode (cathode) need oxygen molecules to complete the process:
  $$\ce{O2 + 4H+ + 4e- -> 2H2O}$$
  An inadequate supply of oxygen to complete the reaction will shorten the life of the sensors, hence the sensors will not operate properly.

Does this mean that doing what I intend is going to affect their performance and damage them?


texts: Are there any other (meta)stable oxygen molecules beyond O3?

texts: Apart from Ozone, are there any longer oxygen molecules that are at least stable for short amounts of time? What configurations would that be?


texts: Comparing bond strength by IR frequency: symmetrical modes

texts:
In literature the stretching mode of $\ce{CO}$ is often said to be the diagnostic criteria for strength of back-donation by virtue of weakening the $\ce{CO}$ bond. However, when speaking about homoleptic carbonyls, the vibrations of individual $CO$ ligands interact, forming symmetric and asymmetric modes with considerably different frequencies.
For example, let's say I want to compare strength of back-donation in $\ce{Cr(CO)6}$ and $\ce{Fe(CO)5}$ and compare it with a free molecule?

$\ce{Cr(CO)6}$ has modes $2119 (A_{1g}), 2027 (E_{g}), 2004(T_{1u})\ cm^{-1}$
$\ce{Fe(CO)5}$  has modes $2121 (A_{1}^{'}), 2041 (A_{1}^{'}), 2034 (A_{2}^{''}), 2013 (E_{1}^{'})\ cm^{-1}$
free $\ce{CO}$ vibrates at $2143 cm^{-1}$ )

What modes I should use for comparison?


texts: An alternative basis set for analytical computation of two electron integrals

texts: It is well known that the usage of the Gaussian basis set, in contrast to Slater basis set, leads relative simple semi-analytical expressions for the two electron repulsion integral $(ab|cd)$. Could you propose any other basis sets allowing simple computations of two-electron integrals? This is quite general questions meaning that these functions should not fit atomic orbitals well (the problem is formulated for wider class of potentials rather than for the Coulomb one only).


texts: failed simple experiment with surfactant

texts: I wanted to show my son the effect of a surfactant.  So I filled two small glasses with tap-water, added a squirt of RinseAid to one and stirred.  Then I sprinkled powdered flour on both.  My hypothesis was that the powdered flour would sink much more quickly in the water-RinseAid mixture compared to the water because the RinseAid would lower the surface tension.  In fact, the experiment was a flop-- I could not see any difference in how fast the flour particles sank in the two glasses.  What went wrong?


texts:
PV=nRT. Hence, T=PV/nR.Let's consider a gas containing in a
bulb in a way that  its pressure,volume and number of moles of gas can be changed.So if I want to attain a certain temperature for n moles of a gas in the bulb,I can adjust the PV value in the equation so as to fit to the value of T.Theoretically this can be done with above equation.But is this experimentally possible?


texts:
Why is $\ce{CH3CH2NH3Cl}$ acidic?

I know that it has something to do with how it is formed from a weak alkaline, but I cannot identify which acid and base it is formed from.


texts:
First of all, though I think that my question is related to this society, if you think reverse, tell me to delete the question:

I would like to know if carbohydrate alcohol is inebriant; Can anyone reference me to some valid source?


texts: What type of test can I do to show that water is one of the products in a neutralisation reaction?

texts:
I've completed an acid base titration experiment of $\ce{HCl}$ and $\ce{NaOH}$. This forms salt + water

$$\ce{HCl + NaOH -> NaCl + H2O}$$

Indicator was used and we evaporated the water to get the salt.

I've been asked to design a test to show that water was the other product of this reaction. I'm not sure what to do here. I'm thinking maybe a distillation type test but not sure where to go with this question …

I'm a middle school student and would like an answer that is of a middle to high school level if possible. Could you provide some examples of tests I could do, and explain how they work?

EDIT -

I really appreciate the answers guys/gals. I'm not going to pretend like they did not go over my head though!

I think the issue might be the wording of the question in the textbook. What I've written above is exactly how it was asked in the textbook but I get the feeling that the expected answer is much simpler considering the level of chemistry I'm dealing with. Even though I don't expect you to read all of this I've gone ahead and scanned the book page anyway. Below is the experiment I completed, and question 4 in the discussion section which is highlighted is what I am trying to answer.


texts: Why is the addition of methanol during the prepartion of the liquid crystal cholesteryl benzoate necesary

texts:
Here's one way to prepare cholesteryl benzoate crystals:

Step 1 Dissolve 1.0 g of cholesterol in 3 cm3
 of pyridine in a conical flask.

Step 2 Add 0.40 cm3
 of benzoyl chloride.

Step 3 Heat the mixture on a steam bath for about 10 minutes.

Step 4 Cool the mixture, and add 15 cm3
 of methanol.

Step 5 Collect the solid cholesteryl benzoate by suction filtration. Rinse the flask and the crude crystals with a little cold methanol.

Step 6 Recrystallize the cholesteryl benzoate using ethyl ethanoate as the solvent.

The methanol is said to be added to react with the benzoyl chloride. Why is this required?

Usually, in a preparation such as that of 1-bromobutane, some substance such as sodium carbonate is added in order to allow for separation of the aqueous substances from the organic layer. That makes sense. However, in the case of the above preparation, by adding methanol the substances within the conical flask go from benzoyl chloride, pyridine and cholesteryl benzoate to HCl, pyridine, methyl benzoate and cholesteryl benzoate. What's the point? Either way, both mixtures are going to eventually be separated from the cholesteryl benzoate by suction filtration.


texts: Formation of tetrazoles from ketones in Schmidt reaction

texts:
Normally in schmidt reaction of ketones, amides are formed however for some reason here further reaction takes place and a tetrazole is formed. Here is my try for this reaction mechanism,
(if my mechanism attempt is wrong please point out the mistakes and the proper mechanism.)

relating to the mechanisms I have the following doubts:

is this a special case of reaction or are tetrazoles formed with many different ketone reactions? if not, what makes this case special?

what are the driving forces in each step? is the aromaticity the main reason?

thanks!


texts: UV-spectrophotometer analytical method for doxycycline hyclate and tylosin tartrate powder

texts:
I am trying to detect tylosin tartrate from the mixture of doxycycline hyclate using $\pu{0.01 M}$ $\ce{HCl}$ as solvent, and waveleghth of $\pu{290 nm}$ for detecting tylosin tartrate in UV-spectrophotometer but the method fails

The aim is  finding an analytical UV-spectro photometer  method to detect tylosin tartrate in mixture of doxcycline hyclate ?


texts: Fluorescence Intensity and Fluorescence Quantum Yield

texts:
I plan to use ImageJ to analyze some fluorescence experiments where the pH changes. I will be using fluorescein as the indicator for the pH changes and it will be present in low concentration (like is typically the case when any indicator is used to measure a pH change).
As I understand it, I can get the relative fluorescence intensity from the grayscale intensity in ImageJ.  From the literature I have a chart of relative fluorescence quantum yield for fluorescein versus pH.  If I conduct two experiments, one at pH 12 and another at a lower pH (which is unknown), I think I can determine that lower pH simply from the grayscale intensities in ImageJ and the literature chart that I mentioned.  If the ratio of intensities is equal to the ratio of quantum yields in the literature chart, then I should be able to read the pH from the literature chart.
Assume all conditions for determining the grayscale intensity in ImageJ are identical, except that the pH of the liquid is different. So I'm going to assume that the molar absorptivity, path length, source power and concentration of fluorescein (all ionic and non-ionic forms) remain unchanged. For discussion purposes, let's say the Image J grayscale intensity at a pH of 12 is equal to 100 and at the unknown pH is equal to 60.  The ratio of these intensities is 0.6.  The question is can this ratio of 0.6 be assumed to be equal to the ratio of relative fluorescent quantum yields on the literature chart? So essentially, can a ratio of intensities from ImageJ be considered to be equal to the ratio of quantum yields, under the assumptions that I have outlined, so that I can read the pH from a chart that plots pH versus fluorescence quantum yield.


texts: Why is the Friedel-Crafts alkylation of nitrobenzene disfavoured?

texts:
Suggest a synthetic route to m-nitrotoluene, starting from benzene.

The conversion can be achieved in two ways:

$\hspace{10 mm}$

or:

However, the first route is not possible as the Friedel-Crafts reaction does not yield a meta-substituted product. Why is that so?


texts: How does Palladium dissociate H₂ so easily?

texts:
If I understand correctly, $\ce{H2}$ in the presence of $\ce{Pd}$ readily dissociates as it dissolves into the metal. With the dissociation energy for the $\ce{H—H}$ bond being so large, how is this possible?

At first I thought that the $\ce{H}$ atoms were falling to a lower energy level in the $\ce{Pd}$ that was somehow only available if they were monatomic, but if that were true wouldn't some heat be generated by the absorption?


texts: Will the current at the inversion potential of a CV trace asymptotically approach zero?

texts: Reading up on the theory of cyclic voltammetry, I note that the current at the inversion potential (that is, the point at which the applied potential goes negative) in every reversible CV trace I have seen is nonzero. My intuition says that this is related to the finite speed of enlargement of the depletion zone around the working electrode and suspect that given sufficient time this current will drop away to zero as the bulk solution homogenises. Is this correct? If not, what accounts for the current?


texts: How to separate sulfur and carbon powders?

texts:
How can someone separate two elemental solids, in powder form, that are mixed together?

If I have a powder, and its mass is 60% carbon and 40% sulfur, how do I separate one from another in a high school level laboratory?


texts: Urban air pollution and the smell of freshly cut lawn grass?

texts:
Recently, all the lawns in the apartment complex that I live in have had their lawns cut - giving that pleasant smell of freshly cut lawn.

Now, I am aware that the smell arises from a chemical distress signal from within the plant itself - are the chemicals from freshly cut lawn contributors to urban air pollution?

Related: How to determine source of air pollution


texts: Why is zinc not considered to have a noble gas configuration?

texts:
I am wondering why we say that, for example, zinc does not have a noble gas configuration?

I would like to say beforehand that this question may has its origin in a confusion about the word "shell" or "outer shell". Wikipedia states that:

  The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence electrons is considered to be full.

Ok, so argon is a noble gas and its configuration is: $\ce{1s^2 2s^2 2p^6 3s^2 3p^6}$. When we speak of a shell we mean the principle quantum number $n$. In this case, the highest principal quantum number is $n=3$. However, for $n=3$ there is also the $\ce{3d}$ subshell available, which is not filled by argon.

So I conclude that "filled shell" does not mean that all available subshells for a given principal quantum number (here $n=3$) have to be filled. Because the $\ce{3d}$ subshell is empty here. Instead, I conclude that "filled shell" means, that whenever we start to fill a subshell (here $\ce{3s}$ or $\ce{3p}$), they must be filled. If there is another subshell with $n=3$ available, it has to be completely empty (like $\ce{3d}$).

But when we look at zinc, we find the configuration: $\ce{[Ar] 3d^{10} 4s^2}$.

Again, for the highest principal quantum number (here $n=4$) we have a filled subshell (here $\ce{4s}$). Additionally, all shells of the $n=3$ are also filled. There is no subshell (neither for $n=3$ nor for $n=4$) which is partially occupied. So, according to the definition from Wikipedia, what is missing for zinc to be in a noble gas configuration?

Again, let me stress, that I am not asking for what a noble gas is (I know that zinc is neither a gas nor a noble gas). I am asking what I am doing wrong, when I conclude that zinc obeys the definition of a noble gas from Wikipedia?


texts: Is this statement valid for reactions of all orders?

texts:
My textbook (not an international standard) states that for the first order reactions only

The quantity of reactant remaining after $n$ half lives is
$$A_n = \frac{A_0}{2^n},$$
where $A_0$ is the initial concentration and  $A_n$ is the concentration after $n$ half lives.

Shouldn't this statement be true for all orders of reaction?
Upon calculation (for 0 order reaction), I observed that half life time reduced with progress of reaction.
Doing same calculation for First order reaction, I observed that half life time remained constant with progress of reaction.
So, is it this(inconsistency of half life time period) due to which Half life concept is not extended to other order of reactions?
I only wanted to confirm regarding concentration after n half lives,
as in a single half life of any order reaction, concentration of reactant reduces to half of its initial value.


texts: Heat energy vs. electrical energy in a galvanic cell or in an electrochemical reaction

texts:
How can someone determine heat energy released during an electrochemical reaction?

Let's assume a simple galvanic cell at standard environment:

$$\ce{Zn(s) -> Zn^2+(aq) || Cu^2+(aq) -> Cu(s)}$$

Electrical energy can be derived from the electrode potential and electron flow, but how the heat release can be calculated? What's the heat release when $\ce{Zn(s)}$ gets solvated to $\ce{ZnSO4(aq)}$, and whats the heat release when $\ce{Cu^2+}$ ions gets plated to the electrode?

I'm using term "heat release", because I get confused about the enthalpy in electrochemical cells, since some of enthalpy seems to be connected to electrical work as well.


texts: 2017 Nobel Prize; What does Cryo-electron microscopy data actually look like?

texts:
It was just announced that the 2017 Nobel Prize for Chemistry has been

  awarded to Jacques Dubochet, Joachim Frank and Richard Henderson "for developing cryo-electron microscopy for the high-resolution structure determination of biomolecules in solution".

What does the data that Cryo-electron microscopy produces when examining the structure of "biomolecules in solution" actually look like? Is it electron transmission images of the molecules, or a diffraction pattern produced by single molecules, or something different? Are the molecules still in liquid solution when they are measured, or are they actually frozen by the time the data is collected?

Including an example image or diffraction pattern or some representation of the type of data obtained from a biomolecule in solution would be greatly appreciated!

From this Nobel Prize tweet:


texts:
PubChem compound 6140 is L-phenylalanine in its neutral (not zwitterionic) form.  According this PubChem, this molecule has the following SMILES and InChI indentifiers:

SMILES: C1=CC=C(C=C1)CC(C(=O)O)N
InChI: InChI=1S/C9H11NO2/c10-8(9(11)12)6-7-4-2-1-3-5-7/h1-5,8H,6,10H2,(H,11,12)/t8-/m0/s1

PubChem compound 6925665 is the zwitterionic form of L-phenylalanine (protonated amine and deprotonated carboxylate).  Pubchem has decided that this species should be called "(2S)-2-azaniumyl-3-phenylpropanoate".  The SMILES and InChI identifiers are:

SMILES: C1=CC=C(C=C1)CC(C(=O)[O-])[NH3+]
Inchi: InChI=1S/C9H11NO2/c10-8(9(11)12)6-7-4-2-1-3-5-7/h1-5,8H,6,10H2,(H,11,12)/t8-/m0/s1

Confusion.  My confusion is why these different compounds have different PubChem entries (CIDs), and different SMILES identifiers...but the same InChI structure.  The different SMILES identifiers each appear to reflect the respective structures displayed by PubChem, but the single InChI identifier given for both compounds seems to reflect only the neutral form.  I even put the InChI into rdkit and converted it back to InChI.  The result was the same and rdkit interpreted this InChI as the neutral (not zwitterionic) species.  What is the reason for this discrepancy between InChI duplicity yet structural uniqueness?

Here are some possibilities:

PubChem is in error.  They should change the InChI for the zwitterionic compound.  (If so , to what?)
PubChem is right but is using definitions of compound and CID that are different than mine.
I have some kind of fundamental misunderstanding of the purpose of InChI, which I had thought would uniquely specify a molecular structure.  But InChI is designed to handle ambiguities like zwitterion vs. neutral.
rdkit interprets InChIs weird.
Something else.


texts: Does chemical compound with formula N₄O₁₀ exist?

texts: I do not know if a dimer of $\ce{N2O5}$ (dinitrogen pentaoxide) exist, and if its formula is $\ce{N4O10}$. Can you explain me that please? I do not know where to search for this information.


texts: Does anything like this covalent concerted bond exchange reaction exist?

texts:
I'm wondering if any reaction pathway exists (not involving enzymes) to do the following in aqueous solvent at temperatures < ~100°C:

To clarify, it's important however that the reaction is concerted, and that the W - X and Y - Z bonds are not broken until both the W-Y and X-Z bonds are formed.  Bonds here must be covalent, but otherwise can be of any type.  Any kind of catalyst can be used.  Of course, it would be nice to know of an efficient reaction with minimally exotic conditions or reagents (i.e. it would be nice to avoid heavy metals for oxidative-addition type reactions), but I won't push my luck.

Does something like this exist?


texts:
Since its isothermal, $\delta U$ is zero. But enthalpy change $\delta H$ is $\delta U + \delta n(\text{gaseous})RT$ or $\delta H = \delta U + \delta (pV)$.

For reversible isothermal expansion of ideal gas, what is the $\delta H$, is it positive, negative or zero.

Ref: I've checked my study material and it says positive, which makes sense but my exam worksheets state it to be zero.


texts: Formating chemical equations for proteins binding in hugely complex configurations

texts:
In a previous question I asked about a simple case, I'm now trying to write equations for proteins that bind multivalently. In the simplest case proteins $A_1$ and $A_2$ can bind to up to two $L$ proteins. This gives a massive chemical equation:
`

where $(AL_1AL_2)_r$ is a tetramer where $A_1$ and $A_2$ are both bound to both of the $A$ proteins in a ringlike structure. But this diagram misses out one possible state, $A_1LA_2$ which is connected in this way:

.

I can't see a way of joining this extra state to the above chemical equation without arrows crossing each other.

What is the best way of formatting these kinds of complex protein reaction equations?


texts: What would be the most suitable solvent for a single-solvent recrystallization?

texts:
The compound in question is acetanilide, and
the solvents in question are: water, ethanol, and ethyl acetate

I was thinking all three would be suitable since upon experimentation, acetanilide dissolved in all three solvents when heated.

Is it possible to rank the suitability?
As, well could someone provide an explanation as to why one is more suitable than the other ?


texts: Is there any formula for finding out probable distance of orbitals or do I just remember the values?

texts: Like, do I need to just remember that it is less in 3d than 3s and so on?


texts: How to test if white powder is lime fertilizer?

texts:
I found two buckets (white and black) containing a very light grey powder in the basement. The label is partially removed, but it probably originally contained lime fertilizer.

However, I am not sure if the current content is still lime or if it got refilled with something else?

How can I proof that the powder is calcium oxide or something similar that I can throw on my lawn to make the grass greener?

I already tried to dissolve the powder of both buckets in water, there are a few grains like sand that stay, but the rest seems to dissolve or rather suspend, the water becomes milky.

Adding normal household vinegar, the powder from the black bucket did not react any differently than with water, but the powder from the white bucket dissolved and created bubbles, so I assume the reaction with acid produces carbon dioxide.

What further tests which I can perform using household stuff would you recommend to make sure I have a bucket of lime fertilizer or anything else?


texts: Maximum temperature attainable by thermite reaction

texts:
In the thermite reaction
  $$\ce{2Al(s) + Fe2O3(s) -> 2Fe(l) + Al2O3(s)}$$
  what is the maximum temperature attainable by the products? Assume reactants at $25\ \mathrm{^\circ C}$ and $1\ \mathrm{atm}$ and that all heat capacities remain constant.

I started by using Hess's law to find the enthalpy change of the reaction. I couldn't find a heat of formation for liquid iron so I assume I have to find that out. I just wrote out the equation
$$\ce{Fe(s) + heat + enthalpy of fusion -> Fe(s)}$$
and figured the heat of formation for liquid iron at $25\ \mathrm{^\circ C}$ is around $-302.71\ \mathrm{kJ/mol}$.

To find the max temperature I used
$$\Delta H_\mathrm r=\Delta T\cdot C_\mathrm p(\text{products})$$
and came out with an equation like
$$-14445\ \mathrm{kJ/mol}=0.147\ \mathrm{kJ/(mol\ K)}\cdot T_\text{max}$$
This gives me a negative temperature, so I assume it is wrong. Even if I were to take the absolute value, the answer seems awfully high. I was expecting something around a few thousand degrees not near ten thousand.


texts:
I have been investigating the iodine-clock reaction for my chemistry project. I have done a great deal of research on the titration of iodate ions, iodide ions and sodium thiosulfate using HCl. But, I still don't get the use of this reaction. Where can this type of reaction be used in our lives.

I read articles that said iodine clock reaction can be used to determine the concentrations or pH. But where can it be used? What are the real-life applications of the iodine clock reaction?


texts: Is it possible to synthesis adenine, thymine, cytosine, or guanine at home?

texts: I'm wondering if there is any way to create adenine, thymine, cytosine, or guanine from chemicals available to anyone, using basic lab equipment.


texts: Dependence of the rate of a catalysed reaction on substrate concentration?

texts:
In my answer to this question: Master equation for catalyst and substrate binding?. I made the assumption along the following lines:

If we have a substrate concentration $[S]$ then the rate of binding of any substrate molecule with a given enzyme is proportional to $[S]$. Such that $$\text{rate}=\alpha [S]$$
I have however, read that it is rather a hyperbolic relation. So are there any (and if so what) assumptions required so that we can assume that the rate is proportional to $[S]$ rather then it been a hyperbolic relation?


texts: Are some alkali metals better conductors than others?

texts: I want to know if there is any difference at all between the alkali metals as far as conducting electricity goes.


texts: Gel electrophoresis separates proteins on the basis of what property?

texts:
In SDS-PAGE for separation of proteins, SDS is an ionic detergent that coats the unfolded protein to mask its native charge and give at a uniform charge to length ratio. Since the length of the protein is proportional to its molecular weight, the charge to mass ratio of all the loaded proteins is the same.

To quote this site:

  Since the SDS-coated proteins have the same charge to mass ratio there will be no differential migration based on charge.

Similarly in a DNA agarose gel electrophoresis, the charge to mass ratio remains constant. So what is the separation based upon?

Proteins having larger size will have more SDS bind to it and thus more negative charge than to the smaller proteins. While proteins of higher molecular weight also have lower mobility in the gel. So is this some kind of a trade off between the charge and the size? If charge to mass is constant, what is the property that separation is based on?

What does the above quoted statement mean? Why not differential migration based on charge? Doesn't mobility through gel depend on the quantity of charge?


texts: Why doesn't acetic acid affect the formation of beta-nitroamine in nitro-Mannich reaction?

texts:
In a nitro-Mannich reaction, if we deprotonate a nitroalkane species with a strong base, then add acetic acid followed by an imine species, the reaction still proceeds giving the $\beta$-nitroamine.
Why is that the case and why wouldn’t we get protonation of the nitro anion species hindering a subsequent reaction with the imine?


texts: Hydrogen donor without hydrogen acceptor?

texts:
Is there a molecule that can donate a hydrogen to a hydrogen bond but not accept one? It would seem that since the donated hydrogen needs to be bonded to an electronegative atom, that electronegative atom will always have lone pairs available to accept a hydrogen bond.

For example, in ethanol, the H in the OH can participate in hydrogen bonding since the the O is electronegative. Then the oxygen with its two lone pairs can also accept hydrogen bonds.

In reverse, things like diethyl ether can accept but not donate hydrogens because the oxygen is surrounded by carbons, not hydrogen.

Are there any exceptions to this apparent rule?


texts: Is it possible to find the ratio of isotopes only given the mean mass number?

texts:
Three isotopes of an element have mass numbers $(M)$, $(M+1)$ and $(M+2)$. If the mean mass number is $(M+0.5)$, then the ratio of the amounts of the three isotopes is?

Let amount of $(M)$, $(M+1)$, and $(M+2)$ be $x$, $y$ and $z$ respectively.
$$\frac{(M)x + (M + 1)y + (M + 2)z}{x + y + z} = (M + 0.5)$$

After further simplification, I got $x-y=3z$.

I don't know how to proceed further. Can someone give me a hint, or reassure me that this question can't be solved with the given data?

The answer is given as $x:y:z=4:1:1$.


texts: Why does pH decrease when diluting a base?

texts:
Take a strong base such a sodium hydroxide
Adding water will result in adding a hydroxide ions as well as hydronium ions to the solution
However if the pH decreases this means that the hydronium ion concentration will increase , hence the hydroxide ion concentration decreased
Why is this so ? What about all the hydroxide ions that were added from the water
I understand the mathematics behind it , but it doesn't intuitively make sense


texts:
It is intuitive to me that for a spontaneous process involving any system i.e. one occurring without constant human interaction $$ \text{d}S \geq 0 $$ as I can observe increasing energy dispersal in everyday life, for example my tea turning cold.

What is not intuitive to me is that for all systems $$ \text{d}S \geq 0  ⇔\text{d}G = \text{d}H-T\text{d}S-S\text{d}T  \leq 0 $$

Why is this? I imagine that the explanation requires an understanding behind the origin of the definition of Gibbs free energy, G = H - TS.


texts: Bond dissociation energy order for C−C, N−N, O−O and F−F single bonds

texts:
Data from Chemistry LibreTexts — Strength of Covalent Bonds, Table 8.8.1: Average Bond Energies (kJ/mol) for Commonly Encountered Bonds at 273 K:

$$
\begin{array}{cr}
\hline
\text{Bond} & D/\pu{kJ mol-1} \\
\hline
\ce{C-C} & 346 \\
\ce{N-N} & \approx 167 \\
\ce{O-O} & \approx 142 \\
\ce{F-F} & 155 \\
\hline
\end{array}
$$

I couldn't understand the trend of bond dissociation energy of various single bonds. Why

$$D(\ce{C-C}) > D(\ce{N-N}) > D(\ce{F-F}) > D(\ce{O-O})?$$

I had mugged up the trend the now, and according to me BDE should continuously increase while going from left to right in a period due to decrease in size and increase in ENC. Why this irregular trend?


texts: Where does the 9th electron go in a N=O bond?

texts:
In the first resonating structure you can see 5 unpaired electrons and 4 shared electrons on nitrogen, then isn't this a extended octet? If it is so, then in which orbital that 9th electron is revolving?
In the second resonating structure you can see that oxygen has 5 unpaired electrons on nitrogen and 4 shared electrons, then isn't this a extended octet? If it is so, then in which orbital that 9th electron is revolving?
Can anyone explain completely about the above questions? If this question is already been asked please comment me the link of that question. Thank you in advance.
Please explain with boxes if you can.


texts: Why does sodium sulfate have an unusual solubility-temperature curve?

texts:
For many salts there are solubility curves as a function of temperature that are smooth (don't have any kinks). Sodium sulfate, however, has a kink in the solubility-T curve at 30 degrees as shown below:

What happens when the temperature is about 30 degree?


texts: Analytical solution to first-order rate laws

texts:
Does anyone know the analytical solutions to the following rate laws:

1) $\frac{\mathrm{d}\rho_\text{W}}{\mathrm{d}t} = -\rho_\text{W} \cdot (K_1+K_2+K_3)$

2) $\frac{\mathrm{d}\rho_\text{T}}{\mathrm{d}t} = \rho_\text{W} \cdot K_2 - (K_4+K_5) \cdot \rho_\text{T}$

3) $\frac{\mathrm{d}\rho_\text{C}}{\mathrm{d}t} = \rho_\text{W} \cdot K_3 + \rho_\text{T} \cdot K_5$

As an example, I have determined the following analytical solution for this rate law:

$\frac{\mathrm{d}\rho_\text{W}}{\mathrm{d}t} = -\rho_\text{W} \cdot (K_1+K_2+K_3) \qquad \Rightarrow \qquad \rho_\text{W} = \rho_{\text{W}0} \cdot \operatorname{e}^{-(K_1+K_2+K_3) \cdot t}$

where $\rho_{\text{W}0} = $ initial density, $K = $ reaction rate constant, $t =$ time

The scheme for the reactions are:

$\ce{wood} \xrightarrow{K_{1}}{} \ce{gas}$
$\ce{wood} \xrightarrow{K_{2}}{} \ce{tar}$
$\ce{wood} \xrightarrow{K_{3}}{} \ce{char}$
$\ce{tar} \xrightarrow{K_{4}}{} \ce{gas}$
$\ce{tar} \xrightarrow{K_{5}}{} \ce{char}$

Any help with the three rate laws above would be greatly appreciated.


texts: Tertiary carbanion in more alkylated alkene

texts:
Saytzeff rule says that more alkylated alkene is more stable and the reason is hyper conjugation.
Going by this, 2,3 Dimethyl but-2-ene should be most stable alkene due to 12-alpha hydrogen.
But on drawing hyper conjugative structures of the molecule and a less alkylated alkene, say 2-Methyl propene; there was formation of a tertiary carbanion in 2,3 Dimethyl but-2-ene! and not in 2-Methyl propene. Instead in this molecule there is a primary carbanion which is much more stable than tertiary. I know that there will be 12 hyper conjugative structures in 2,3 Dimethyl but-2-ene rather than 6 structures but isn’t a tertiary carbanion poorly stable and make overall molecule less stable than 2-Methyl propene?

Can anyone please prove me wrong?

Thanks in advance


texts: Chemical Reactions at the Cathode of the Leclanche Cell

texts:
In the dry cell, the overall reactions that occur are:
$$\textbf{anode:}~~~ \ce{Zn -> Zn^{2+} + 2e^-}~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~$$
$$\textbf{cathode:} ~~\ce{2NH4+ + 2MnO2 + 2e- -> Mn2O3 + 2NH3 + H2O}$$
I have read that the overall reaction at the cathode actually consists of two separate reactions. However different sources have conflicting chemical equations for these two reactions.

Some sources says that the hydrogen is ammonium gets reduced first and then there is a separate redox reaction between the manganese dioxide and hydrogen gas:
$$\ce{2NH4 + 2e- -> 2NH3 + H2}$$
$$\ce{2MnO2 + H2 -> 2Mn2O3 + H2O}$$
While other sources say that the manganese first gets reduced and then the produced hydroxide ions are neutralised by the ammonium:
$$\ce{2MnO2 + H2O + e- -> Mn2O3 + 2OH-}$$
$$\ce{NH4+ + OH- -> NH3 + H2O}$$
Which of these reactions are correct?

Also, if the first set of equations are correct, does the redox reaction between the manganese dioxide and hydrogen gas also contribute to the voltage produced by the battery, or is it only the the redox reaction between the ammonium and zinc that contribute to the $1.5\ \mathrm{V}$ that is produced.


texts:
Instead of going for the normal free radical mechanism for Wurtz reaction, What reasons prevent us from believing in the following ionic mechanism?

\begin{align}
\ce{R-X + 2Na &-> R^--Na+ + NaX}\\
\ce{R-X + R^--Na+ &-> R-R + NaX}\\
\ce{2R-X + 2Na &-> R-R  + 2NaX}
\end{align}

Related but doesn't answer my question here


texts:
I did a lab about spectrophotometry and right now I need the molar absorptivity(ε) of thymol blue in acidic solution and also in basic solution. I have tried looking online but I haven't found the data I need.

What is the molar absorptivity of thymol blue in acidic solution and in basic solution?
 information
The specific wavelength is 540.27 nm for the acid and 601.88 nm  for the base.


texts: basic chemistry alkaline test for flavonoids!!! with reference please

texts: What is flavanoid physical and chemical properties, and how alkaline reagent test for flavonoids gives yellow coulour?


texts: Why does diesel have a higher energy density than gasoline?

texts:
One of the primary reasons why hydrocarbons produce energy is the production of water during the combustion process.

I've been trying to find out why diesel is considered to have a higher energy density compared to gasoline and I can think of a couple of reasons:

Higher molar mass (more carbon/hydrogen to burn)
Easier to burn diesel since it is heavier (weaker bonds)

I think I'm on the right path but I don't have a clear picture of the situation.


texts: Do we use volumes of both solutions if they have different densities to find cocentration of ions

texts:
So essentially lets say I am given a mixture of  hexane, water and nickel chloride(masses also given) in a beaker, and am asked to find the concentration of the chloride ions in the aqueous layer of the mixture.

Now, I know what we should first do is find the mols of NiCl2(using the given mass)
mass of NiCl2/molar mass of NiCl2

However, knowing that hexane is less dense than water, hexane will not "mix" and instead float on top of the nickel chloride solution (Sorry for my poor/incorrect terminology!).

So my question here is, when we find the concentration using c=m/v, do we include the volume of the hexane as well? Or only the volume of the water in which the nickel has dissolved in. Thanks in advance!


texts:
Is it possible to use CI3TMS (a carbon with three iodo groups and a trimethylsilyl protecting group) and three equivalents of an ethyl grignard reagent to prepare 3-ethylpentan-3-ol? By deprotecting the product after the grignard reaction using tributylammonium fluoride, is it possible to produce the desired product? I have studied a more lengthy method of arriving at the product; however, I cannot find any reference to my proposed mechanism, which seems shorter and more efficient. Is there some sort of flaw in my mechanism, or would it theoretically work?

CI3TMS --- 1) BrMgEt, diethyl ether 2) TBAF --->  3-ethylpentan-3-ol


texts: Lowering the freezing point of a lipid by adding another lipid

texts:
I'm trying to stop bacon grease from congealing in the fridge by adding another lipid with a lower freeze point to it, but I'm not sure how much to add, as I'd like to keep the ratio as bacon-grease heavy as possible.

Of the oils I have available, corn oil has the lowest freeze point at -11C (http://www.veganbaking.net/articles/tools/fat-and-oil-melt-point-temperatures), and bacon grease has a freezing point of 26C (https://www.doesitgobad.com/does-bacon-grease-go-bad/). I need to bring the freezing point down to 5C or lower.

Can I calculate the melting point of the mixture simply by finding the average melting temp between the two according to their ratios? So for corn oil:

T = (26b + -11c) / (b + c)
Where T=Freezing temp. of resulting mixture, b=# parts bacon grease, and c=# parts corn oil

If not, how should I calculate the ratio of corn oil to bacon grease to bring the freezing point to 5C? Can I calculate it the same way if I use cottonseed oil (-48C freezing point) instead of corn oil?


texts:
I was studying catalytic poisoning and read that in temporary poisoning, the poisoners are held at active centres by weak forces.

What is an 'active centre' in this context?


texts: How to set the memory for the Gaussian 09 cubegen utility?

texts:
I am connected to a supercomputer via SSH and my cluster uses Linux Scientific, I am using the Bash (Unix Shell), I load the modules of Gaussian 09 and Gaussview. I am trying to print orbital densities for a very large tetramer system, but when I try to generate the orbitals on Gaussview, the system crashes because of insufficient memory. On the internet, I found that using the "cubegen" keyword I can generate the cube files of the orbitals. The keyword gives me the power to modify the amount of memory but I do not know how. I go to interactive mode so I can use computational resources directly and on the command shell I do the following:
 (I try changing Gaussian's memory's environmental variable directly at the folder I am at)

GAUSS_MEMDEF=16gb

then,

cubegen 16000000 MO=HOMO xxx.fchk xxx.cub 0 h

But it still crashes with the following message,

Out-of-memory error in routine DecCub-RdMO (IEnd=      34279201 MxCore=      33546152)
Use %mem=33MW to provide the minimum amount of memory required to complete this step.
Error termination via Lnk1e at Wed Sep 28 16:41:41 2016.
Segmentation fault (core dumped)

How can I solve this problem? How can I allocate memory to Gaussian from the command window (I do not know where Gaussian folders are located since I just load it as a module, given that the software is already installed on the system)


texts: Why there is no bichloride or binitrate ion like bicarbonate or bisulphate?

texts: I have been thinking lately that if there is bicarbonate why there is no bichloride or binitrate, please someone  give an easy explanation.


texts: Proposal: Optically Activating Ellagic Acid

texts:
Hey all,
I’m currently drafting a proposal to research the antioxidant claims of ellagic acid. My working hypothesis for the experiment is to expose the Ellagic acid to peroxides generated from UV in water to simulate biological oxidative stress and that the Ellagic acid would lose a Pi bond in the process of reducing radical species and thus lose some of its Absorbance in the visual spectra.
In terms of instrumentation, I’m working with an Evolution 300 UV-Vis spectrometer with 10.0 mm polystyrene curettes.  I’m just trying to determine an adequate indicator reagent to assess the change bonding as a response to reduction.
Please offer suggestions or ideas.


texts: Explanation for the reaction of gold and iodine(iii) solution

texts:
The Experiment
A few days ago I saw a video of dissolving gold in the condition of $\ce{ICl3/HCl(aq)}$. In the video, $\ce{ICl3(s)}$ is added to a test tube, followed by adding conc. hydrochloric acid. The solid is dissolved in the solution and the solution turned yellow. No green color was shown.
A gold wire is then placed in the solution for a short period of time. Putting the wire on the starch indicator produces a color of blue.
As a comparison, a piece of titanium was placed in the solution and then indicated by starch. No blue was produced.
The Speculation
After adding $\ce{HCl(aq)}$ to $\ce{ICl3(g)}$, I can think of 3 types of reactions may occur.
1) Lewis acid-base reaction.$$\ce{ICl3(g) +Cl-(aq)<->ICl4-(aq)}$$ As I'm not sure whether $\ce{ICl3}$ is a strong Lewis acid and whether $\ce{HICl4}$ is a strong acid (I suggest it is), I don't know it may present as a molecule in the solution.
ii) Disproportionation. As no purple color was seen, which leads to no iodine was produced.
iii) Hydration. $$\ce{ICl4-(aq) +5H2O(l)<->HIO2(aq) +4Cl-(aq) +3H3O+(aq)}$$
This reaction is unlikely to occur as $\ce{HIO2(aq)}$ is unstable and will disproportionate but no disproportionation production could be observed.
The OP of the video claimed that the equation of the reaction of gold and the solution is $$\ce{2HICl4 +2Au->2HAuCl4 +I2}$$

  Questions
  a) Does the solution of iodine(iii) really contains much $\ce{ICl4-}$, and it is the cause of oxidation of the gold wire?
  b) Does the equation claimed above really occur?
  c) Is there any paper that investigates the electrode potential of $\ce{ICl4-/I2}$? Hence we can support the correctness of the equation thermodynamically.


texts: Haemoglobin literature spectra does not match

texts:
I am studying haemoglobin absorption spectra in its oxygenated and deoxygenated state and I compiled values from different sources including:

A PhD thesis by van Assendelft [1], using extinction coefficients in (mmol/L)-1/cm

A book compiling almost one century of research on the topic by the same laboratory that helped standardizing the haemoglobin cyanide standard [2]. Extinction coefficients in the same unit as [1], numerical values are very close.

Coefficients compiled by Scott Prahl[3]. The unit is the same but there is a factor 3.7 up to 4.0 between his data and that of Assendelft and Zijlstra.

Coefficients measured by Kolyva[4].

All the published coefficients are defined as base 10 extinction coefficient. That is if I
is the light intensity, they are expressed in Beer-Lambert law as:
$I = I_0 \cdot 10^{-c\cdot \varepsilon \cdot l}$
Where $l$ is the light path length (cm), $c$ the concentration in absorbing compound (mol/L) and $\varepsilon$ the molar extinction coefficient (L/mol/cm).
How comes there is a 3.7-4.0 factor between Prahl and Kolyva data on the one hand and Assendelft and Zijlstra on the other hand?
At first I thought of some $log(10)\approx2.3$ difference, as if some of the author forgot to precise that they used base $e$ extinction coefficient at some point but it does not fit. If anyone has an idea on the topic, the help would be most appreciated.

Further information
The cyanmethaemoglobin method is often used for the determination of the haemoglobin concentration of a solution. In particular, its absorbance at 540nm is known to be 11.00L/mmol/cm[5] which is in agreement with Assendelft and Zijlstra published data.
References

O.W. Assendelft, Spectrophotometry of Haemoglobin Derivatives, 1970. ISBN: 902320560X.
W.G. Zijlstra, A. Buursma and O.W. van Assendelft, Visible and Near Infrared Absorption Spectra of Human and Animal Haemoglobin, 2000. ISBN: 9067643173.
Scott Prahl, Optical Absorption of Hemoglobin, 1999, https://omlc.org/spectra/hemoglobin/
C. Kolyva, Systematic investigation of changes in oxidized cerebral cytochrome c oxidase concentration during frontal lobe activation in healthy adults, 2012. DOI: 10.1364/BOE.3.002550. Coefficients are in MEDIA 1.
F. Meng, Determination of extinction coefficients of human hemoglobin in various redox states, 2017. DOI: 10.1016/j.ab.2017.01.002. Table 1.


texts: Why is the F-F bond in fluorine a p-p sigma bond?

texts: Won't the lone pairs hybridize to $\mathrm{sp^3}$ making it an $\mathrm{sp^3}$-$\mathrm{sp^3}$ $\sigma$ bond? If it still is $\mathrm{p^\sigma}$-$\mathrm{p^\sigma}$  bond what is the spatial location of the lone pairs?


texts: How to determine the pH of citrate buffer system

texts: I used this table (http://microscopy.berkeley.edu/Resources/instruction/buffers.html) to make a citrate buffer system. The Pka value is 6.4, and I multiplied the solution by ten to make a larger batch. I used 137ml of citric acid and 363ml sodium citrate in distilled water to make a buffer system with pH of 5.6. Now I'm trying to work backwards to prove this was correct, and using the equation pH = pKa + log(A-/HA) I am getting 6.4 + log 0.0137/0.0363 = 5.97, when it should be 5.6. Anyone know what I'm doing wrong? Thanks!


texts: Does lead(II) chloride dissociate into Pb²⁺ and Cl⁻ ions in HCl?

texts:
While solving JEE Advanced 2020 (Paper 2) questions, I came across this particular question:

Q.10 Choose the correct statement(s) among the following.
(A) $\ce{SnCl2 · 2 H2O}$ is a reducing agent.
(B) $\ce{SnO2}$ reacts with $\ce{KOH}$ to form $\ce{K2[Sn(OH)6]}.$
(C) A solution of $\ce{PbCl2}$ in $\ce{HCl}$ contains $\ce{Pb^2+}$ and $\ce{Cl-}$ ions.
(D) The reaction of $\ce{Pb3O4}$ with hot dilute nitric acid to give $\ce{PbO2}$ is a redox reaction.

According to the final answer key, its answer is options (A), (B).
Coming to the option (C), after doing some research, I have been able to conclude the following:

$\ce{PbCl2}$ is sparingly soluble in water.
$\ce{PbCl2}$ + little amount of dil. $\ce{HCl}$ decreases its solubility due to common ion effect.
Upon further addition of dil. $\ce{HCl}$ or $\ce{PbCl2}$ + conc. $\ce{HCl}$ leads to formation of soluble lead complexes: $\ce{[PbCl3]-}$ and $\ce{[PbCl4]^2-}.$
Hence, option (C) is incorrect as in one case, $\ce{PbCl2}$ doesn't dissociate at all and even in the other, $\ce{Pb^2+}$ and $\ce{Cl-}$ ions are not formed (so the dilemma of the $\ce{HCl}$ doesn't exist anymore as this option is incorrect regardless of the $\ce{HCl}$ being dilute or concentrated).

Are the above four points accurate? It'd be appreciated if someone could add more details and correct the above points if needed.


texts: I've noticed that chalcogens never form binary acids, and instead end up like water, with very little acidity. Why is this? Or am I wrong and there's a counterexample, if so please give it.


texts:
$$\ce{NaOH +H2O->H2 +O2 +NaOH}$$
We know that $\ce{H+}$ and $\ce{OH-}$ go  to the cathode and anode, but how can I write the total reaction?
Is it: $$\ce{2NaOH +2H2O->2H2 +O2 +2NaOH}$$
I've put NaOH both sides because if the mass of NaOH is given, how can I find the mass of H2 for example?


texts: How can I distinguish whether a metal that I have is tin ($\ce{Sn}$)? I am specifically looking for a chemical reaction that will happen only with tin and not with other metals such as $\ce{Al,~Cu,~Fe,~\ldots}$. Do such reactions exist? What are they?


texts: Molybdenum ditelluride (MoTe2) single and few-layer liquid exfoliation?

texts: In 2D nanomaterials like Transition Metal Dichalcogenides (TMD) exfoliated using liquid exfoliation methods, the solvent will play an important role in determining the final thickness and quality of layers we get out of this process. For instance, Gas sensors based on 2D materials like Molybdenum ditelluride can be prepared by exfoliating single or few layers of MoTe2 from the bulk crystal using liquid exfoliation by probe sonication, this process needs the 2D material powder to be dispersed in specific solvents before being sonicated. In this regard the chosen solvent should have low surface tension and low boiling point, the boiling point of the solvent will play a vital role for the usage of the yielded exfoliated nanosheets in Gas Sensing applications. For that, what are the preferred solvents when exfoliation MoTe2 powders using Liquid exfoliation for the application of Gas Sensors.


texts: Change in gas phase reaction equilibrium when not all product and reactant are increased

texts:
$$\ce{2NOCl <=> 2NO + Cl2}$$
What will be the effect on equilibrium concentration of $\ce{NOCl}$ when equal moles of $\ce{NOCl}$ and $\ce{NO}$ are introduced in the mixture at constant temperature?
Now this is what I think
Increasing the moles will result in increased concentration of both $\ce{NOCl}$ and $\ce{NO}$. But there also lies a second product $\ce{Cl2}$. Since there's an increase in $\ce{NO}$ and $\ce{NOCl}$, there should be an equal increase in the concentration of $\ce{Cl2}$ to keep the equilibrium-constant constant. But since there's no addition of $\ce{Cl2}$ molecules there should be a decrease in $\ce{NOCl}$ concentration which will decompose further to increase the molar ratio of $\ce{Cl2}$ and hence achieve equilibrium. Please enlighten me where my logic is flawed.

From comments (edit by BuckThorn): The reported answer is that the position of equilibrium remains unchanged and hence the concentration of $\ce{NOCl}$ remains constant.


texts: What is meant by a 'hydrophilic' sphere?

texts:
So, I know that a hydrophilic material is defined as those with a special affinity for water, opposite to
hydrophobic, those that naturally repel water.

I am investigating the impact of spheres with water surfaces, and the splashes caused by them. However, one research paper focuses on the difference between the fluid dynamics of hydrophilic spheres and hydrophobic spheres, and the difference in the cavities they make when they sink underwater.

I understand what a hydrophobic sphere is, but what is a hydrophilic sphere? Like a rolled up ball of tissue paper? Or the water absorbing waterbeads/orbeez that get bigger(the ones children play with)?


texts:
I'm seeking a $\ce{S_N1}$ reaction that happens in a polar aprotic solvent.
Do you know any good simple $\ce{S_N1}$ reactions which satisfy the condition?


texts: Should I round an experimentally determined reaction order to an integer?

texts:
For a lab experiment I did, I'm calculating the reaction order for one of the reactants using data from two trials, both rates and the concentration of that reactant during each.

$$
\frac{\text{Rate}_1}{\text{Rate}_2} = \left(\frac{[A]_1}{[A]_2}\right)^x
$$

The number I got from that for the reaction order for reactant a was 0.967. DO I put that exactly as the reaction order, or just round and say it's a first order reaction, and the little bit of different is just a result of the number I get from my calculations not being perfect?

I'm also trying to calculate $K_\mathrm{eq}$, and need to know if I should use $[A]^1$ or $[A]^{0.967}$ in the calculation of $K_\mathrm{eq}$.


texts: What makes dimethyl compounds so extreme?

texts:
I've noticed that dimethyl compounds tend to have extreme reactive, including bioreactive, characteristics.

Am I being misled by anecdotal selection bias, or is this generally true.  And if generally true, are there clear theoretical explanations as to why?

Examples that come to mind:

Dimethyl sulfoxide (DMSO) readily penetrates skin, and can carry lots of things across the skin barrier along with itself.
Miniscule amounts of dimethyl mercury will not only penetrate skin and many common PPE but are also irreversibly lethal.
Many dimethyl-metals are pyrophoric (i.e., they auto-ignite in a standard atmosphere).


texts:
Are the following two compounds isomers or not?
I feel they are enantiomers(non-superimposable mirror images) however my book states that they are not isomers?
I cannot understand why?


texts: Magnesium powder mixed with CuSO4 solution

texts: $\ce{Mg}$ powder is stirred into $\ce{CuSO4}$, what is the balanced molecular equation for this reaction ? I have $\ce{Mg + CuSO4 -> Mg2SO4 + Cu}$. Also, is the ionic equation the same as the net ionic equation? I believe it is not, because Copper would act as a spectator ion, however, I am not too sure.


texts: Why does calcium oxide react with sulfur dioxide?

texts:
Which of the following compounds reacts with calcium oxide, $\ce{CaO}$?
  (a) $\ce{K2O}$
  (b) $\ce{Na2O}$
  (c) $\ce{SO2}$
  (d) $\ce{MgO}$

I thought that since sodium is higher in the reactivity series than Ca, then it would be B. However, the answer is C, and I'm not quite sure why. Can anyone enlighten me?


texts: How to order the reactivity of t-butyl iodide and neopentyl bromide for SN2

texts:
The relative leaving group ability of iodide is better than that of bromide but steric crowding is more important as the neucleophile will attack the back lobe of carbon atom.
So how should I order the steric hinderance produced by t-butyl and neopentyl groups?


texts: Quantitative Analysis of Urea in aq. solution

texts:
What would be a good way to assay Urea in aq. solution? The test doesn't need to be super accurate. 1% accuracy is fine.

But it needs to be relatively fast & robust to carry out.

NaHCO3 is a co-dissolved impurity so the test needs to tolerate NaHCO3 interference.


texts: How much time does sulfur dioxide take to oxidize to trioxide in air?

texts: I saw that $\ce{NO2}$ is oxidized really fast, but if I put $\ce{SO2}$ in a jar with air at STP, will it take hours, days or years to react into $\ce{SO3}?$


texts:
What factors go into selecting an appropriate material for an inert electrode for electrolysis?

It looks to me like metal oxides or platinum/platinum-coated titanium are the preferred options. However, I'm not really clear why platinum should be a good option since it doesn't have a particularly high standard electrode potential (1.188V). Lead oxide, gold, and silver all have higher standard electrode potential and are all cheaper, so why are they not preferred?


texts:
How should we name this compound by IUPAC system?
Is it

2,3-dimethylcyclohexene
 (or)
 1,6-dimethylcyclohexene?

In the first case locant position adds to 2+3 = 5, while in second it is 1+6 = 7. However, in second case, first substituent gets lower position, i.e., 1 , while in first case it gets 2.


texts: What would be the best combination to clean polyurethane

texts:
I am struggling to find the best composition to clean old golf balls and make them white again.
The balls are made out of different types of coating, e.g. polyurethane or an isomer.

I have found hydrogen peroxide to be so far a good candidate.
I cover the balls in hydrogen peroxide and expose them to UV light.
What I'm trying to figure out is how to find a good process or accelerator to the compound.

For example, should the balls only be soaked for 10 seconds or do they have to be in for 5 hours due to the material?

Would any other item (e.g. bleach or oxi washing powder) add to the cleaning power of hydrogen peroxide?

Any insights on a chemical level of what should be the best process forward or suggestion on how to evaluate my methods?


texts: How is solid PVA filament (for 3D printing) synthesized?

texts:
Polyvinyl alcohol (PVA; also referred to as: PVOH, PVAl) filament--the sacrificial support polymer filament used in 3D printing, how is that made?  All the reactions I've seen that make PVA create a gel-like substance that could be used as a glue or perhaps a film.  But it's not solid.  (See image with beaker.)

The reactions I've seen use an alcohol (ethanol or methanol) and an alkaline catalyst (sodium hydroxide) which are combined with polyvinyl acetate.  Here's the reaction that was used to make the beaker's gel PVA:

Another preparation can be seen in this video.

Is there some kind of coagulation/further reaction I must do to the gel to solidify its structure, or is the trick to do something during the first reaction, such as varying the temperature or pressure?

To clarify, I don't actually need/want it in the typical extruded filament form that would be needed for a 3D printer.  A simple solid blob of the stuff would suffice. I'm very new to materials science and only a novice in chemistry, but I'd love any answers you wonderful folk could provide, even if they are dense scholarly articles. Thank you for your time!


texts: Can sodium carbonate-sodium bicarbonate buffer be used for EDTA titration of calcium?

texts:
I am planning to measure general/total hardness (calcium and magnesium) of aquarium water using EDTA titration with Eriochrome Black T indicator. From what I understand, the unknown solution must be kept basic, at pH 10, for the EDTA to work in chelating the calcium ions off of the dye indicator complex. The procedures I can find online all use ammonia-ammonium chloride buffer. I would prefer using another buffer if possible as I find ammoniacal solutions difficult to handle and relatively hard to source.

Can I use a sodium carbonate-sodium bicarbonate buffer? Will it interfere with the titrant: will the EDTA form chelates with sodium ions?

From a similar titration procedure for exclusively determining calcium ion concentration using EDTA but with a Patton-Reeder indicator (calconcarboxylic acid), pH was raised to 12.5 using sodium hydroxide to precipitate magnesium off the solution. I suppose sodium will not interfere then?

Thank you!


texts: Do bidendates occupy cis position always?

texts:
https://chem.libretexts.org/Core/Inorganic_Chemistry/Coordination_Chemistry/Properties_of_Coordination_Compounds/Isomers/Stereoisomers%3A_Geometric_Isomers_in_Transition_Metal_Complexes

In example 1.1, it is written that en which occupy only adjacent positions.....is it true for any bidendate for octahedral isomer?