texts:
We have,

$$\theta = \frac{Kp_\mathrm a}{1+Kp_\mathrm a}$$

where, the fractional coverage $\theta$ is defined as the number of sites occupied by adsorbate $A$ over the total number of sites. $p_\mathrm a$ is the partial pressure of the adsorbate and $K$ is the equilibrium constant.
$$\theta = \frac{[A_{\text{ad}}]}{[S_{\text{total}}]}$$

I need to plot the following data to verify the monolayer adsorption of $\ce{CO}$ on 1 g of $\ce{Pt}$ powder.

$$\begin{array}{cc}
\hline
\text{Equilibrium Pressure (P)/mmHg} & \text{Adsoprtion Amount(V)/ mmHg} \\ \hline
 2.50 & 0.507\\
5.00 & 0.92\\
10.0 & 1.51\\
15.0 & 1.97\\
20.00 & 2.32\\
30.00 & 2.75\\
40.00 & 3.13\\ \hline
\end{array}$$

The question gives me the following hint

  Because adsorption amount $V$ is proportional to $\theta$, $\theta$ can be expressed as $\frac{V}{V_\mathrm m}$ where $V_\mathrm m$ is the adsorption amount at $\theta = 1$

I generated the following graph in Mathematica, simply by plotting $V$ vs $P$

I don't quite understand what the hint wants me to do? Does that require that I normalise the data fashion, i.e by dividing by a particular $V_\mathrm m$, so instead of having $V$ on the y-axis, I have $\theta$ varying from 0 to 1.

Is $V_\mathrm m$ something I obtain from the data/graph by calculating, or is it a tabulated value that I can look up in table somewhere.


texts: How do I extract anthocyanin from a blueberry?

texts: I am doing a school project to extract anthocyanin from a fruit. I chose blueberry. What is a step by step method to extract the anthocyanin? I have to do it in school so hopefully its not a very complex procedure. Also, im not allowed to use methonal as it is flammable. From what i have researched, i should use ethanol and hydrochloric acid. But i do not know what else to add. Thank you.


texts: What is the hybridisation of trifluoromethyl free radical?

texts:
Having three σ bonds in a similar manner to $\ce{CH3^·}$ free radical, $\ce{CF3^·}$ should also have $\mathrm{sp^2}$ hybridisation. However, if we look at its shape, it is pyramidal and not planar like $\ce{CH3^·}$ free radical (which is $\mathrm{sp^2}$-hybridised), which signifies that $\ce{CF3^·}$ should have $\mathrm{sp^3}$ hybridisation.

But how is this possible because the three σ-bonds will bond with three hybrid orbitals? Where does the third p-orbital come?

If its hybridisation is $\mathrm{sp^3},$ then why is it?


texts: Why does an increase in Kinetic Energy increase the likelihood of successful collisions?

texts:
As far as I understand bond formation, bonds must be broken between reactant particles to allow reactant particles to form new bonds and create product particles. This involves increasing the potential energy of the reactant particles, such that the attractive forces between say, reactant A and reactant B > the attractive forces between reactant A particles.

My textbook states that reactant particles must have sufficient kinetic energy so the collisions are energetic enough to break reactant bonds. What I don't understand is how the KE of the particles is related to breaking bonds. KE describes the energy needed to shift a body from rest to a given velocity, not the magnitude of a distance between particles (potential energy). So my question is: how is KE related to collisions, potential energy and product formation?


texts: Orbital correlation diagram for the cleavage of cyclopropylmethylene carbene

texts:
In the last exam we were asked to rationalize the mechanism of the cyclopropylmethylene carbene cleavage into acetylene and ethylene.

In the lecture we discussed pericyclic reactions (cycloadditions, electrocyclic reactions, sigmatropic reactions, ene reactions). I don't think it's a con-/disrotatory ring opening, because in my view only a $\sigma$-plane is conserved over the entire reaction coordinate. What type of ring opening is this; is it a concerted or radical based C-C bond cleavage? Because there is highly probable an elongation of the bond length (as drawn in the stretched cyclopropane moiety), I don't assume it to be concerted but rather radical based.

I tried to classify the reaction in terms of symmetry along its entire reaction coordinate. Because from the task, a singlet carbene, I know it's a $sp^2$ hybrid, so I strongly assume the empty p-orbital to be in conjugation with the Walsh orbitals, more precisely with the Möbius type orbitals.

The problem is very similar to cyclopropylcarbinyl cation:

In the exam I was asked to draw the orbital correlation diagram. For me it looks like two radicals forms the double bond of ethylene and the "biradical" like centers recombines with the "biradicaloid" (in $sp^2$ orbital). I call a carbene a diradicaloid or biradicaloid because the two radical electrons share the same orbital.

To correlate reactants with products I need to combine orbitals with the same symmetry. We only draw the orbitals which are involved either in bond braking or in bond making. How should I account for the biradicaloid singlet $sp^2$ orbital in the orbital correlation diagram? (It is forming the triple bond of acetylene, so there must be a change of hybridization.) For me it looks like to have no symmetry (neither A' nor A'' because it lies in the mirror plane, because it is eclipsed with the $\alpha$-carbon-H.

If it's a radical mechanism I assume the Möbius orbital of A'' symmetry (depicted in green) to correlate with the $\pi^*$ of ethylene.

I assume, the cleavage happens preferently with light, because in this way I can put a photon from A'' (green) into the orbital of A'' symmetry on the reactant site and therefore lowering the activation energy for the reaction.

I assume the orbital correlation diagram to look something like this:

There are some points unclear to me:

Has the empty p-orbital A'' symmetry ?
For me it looks somehow ugly to correlate orbitals which don't have symmetry labels (I think this procedure is not allowed and I need to build a proper set.) How can I build a linear combination in this particulate case, so that the orbital correlation from red to red makes sense?
There is a "$\pi^*$ orbital acetylene,2" unused (not correlated). Did I miss an orbital from the reactant site? (because there is one orbital too many on the product site)


texts: Wave and particle properties of protons and electrons

texts: Do both electrons and protons have wave and particle properties and if they do, do they show them at the same time?


texts: "Drinking water" plastic - can I store beer in this?

texts:
This is an outdoors & chemistry question.

I have an old and functional water bladder, shown below. On it, there are markings that coffee, beer, wine, hot drinks etc. must NOT be stored inside, only water.

While I realize that wine is acidic, damaging the bladder and becoming poisonous, beer seems to me quite close to water. Furthermore, I indend to test it with weisbeer, which does not contain such a large amount of gases as to explode.

Would be safe for me to store non-fizzy beer for up to a day every day in a "do-not-store-beer-inside" water bottle and then safely drink it?


texts:
I have a file with smiles and I'd like to convert the SMILES to SDF and tag the properties of each molecule, so I can use the SD file in another tool. Here is my code:

pp = pd.read_csv('anti.smiles', names=['Smiles', 'BA'])
pp =  PandasTools.AddMoleculeColumnToFrame(pp,'Smiles','Molecule')
PandasTools.WriteSDF(pp, pp_out, molColName='Molecule', properties=list(pp.columns))

And the error I get is this:

NameError: name 'pp_out' is not defined

Kindly assist


texts: Is there a stable molecule with total number of electrons equal to 13? Molecule can be either organic or inorganic


texts: Can a liquid turn to a solid by applying pressure?

texts: When pressure increases, volume decreases. If an extremely high pressure is applied to a liquid, is it possible to reduce it's volume to an extent where the molecules are very tight together, hence becoming a solid? Or do changes in pressure and volume not alter the physical properties of the substance and the liquid remains liquid?


texts: Alloy-component weight based on desired molecule

texts:
I'm a gold smith and I want to start experimenting with non-standard metal-alloys. Now high school is a long time ago for me so while I think I've got this right, I'm just not as sure as I should be when working with precious metals costing 40 dollar a gram. So could anyone confirm that what I'm doing is right:

I have two metals
Metal X, with an atomic-weight of 20
Metal Y, with an atomic-weight of 3

If I want to create an intermetallic alloy of $\ce{XY2}$, where one atom of X is combined with two atoms of Y and I'd want 10 grams of that alloy. I would alloy (20*10)/26=7.692g of metal X and (6*10)/26=2.308g of metal Y, correct?


texts:
According to Arrhenius acid/base theory, a base is a substance which when dissolved in water furnishes $\ce{OH-}$.

But $\ce{CuO}$ is insoluble in water and does not produce $\ce{OH-}$, so why do we consider it a base?


texts: Counting the number of conjugated pi bonds in a complex aromatic molecule

texts:
So for multiple bonds to be conjugated, they must be in an alternating
double bond – single bond – double bond, etc arrangement. However, do they need to be continuous? In my textbook, they count the number of conjugated multiple bonds like this:

However, for other molecules such as 9,10-Bis(phenylethynyl)anthracene :

Would I count the number of conjugated multiple bonds as a total of 13 or as 7? In other words, do the bonds need to be continuous to be counted as conjugated pi bonds?


texts: Could An Equivalence Point Be Calculated or Deduced Based on Limited Data with Accuracy?

texts:
I have recently been tackling a problem from one of my A-Level chemistry exercises on the topic of acids and bases, particularly with strong base and weak acid titration curves:

  A titration is carried out in which $\pu{25 cm3}$ of $\pu{0.08 mol dm-3}$ propanoic acid $\ce{CH3CH2COOH}$ of pH 2.5 is put in a conical flask. Sodium hydroxide solution of concentration $\pu{0.1 mol dm-3}$ is added from a burette until $\pu{50 cm3}$ has been added.

One of the sub-questions asked to state the equivalence point of the pH, but I do not know whether drawing a rough sketch (as the exercise had suggested) would be validly sufficient to deduce this. From my reading of theoretically calculating such a point, a $\mathrm{K}_b$ constant is required such as that used in a solution in a similar conundrum: https://socratic.org/questions/calculate-the-ph-at-the-equivalence-point-for-the-titration-of-0-20-m-hcl-with-0 But the exercise does not provide such a value.

While the volume of the strong base, sodium hydroxide, required to reach the end-point is easy to calculate, as...

$\pu{0.1 mol dm-3} = \frac{\pu{2 * 10^-3 mol}}{v}$

$v = \pu{0.02 dm3} = \pu{20 cm3}$

...I am still unsure what would be the best way to tackle such a problem in which a roughly accurate answer could be obtained.


texts: What does it mean to take reading up to 0.05 mL?

texts: In titration we usually take burette reading upto $0.01~\mathrm{mL}$, but my teacher says that we need to take reading up to $0.05~\mathrm{mL}$. What does that mean? Does it mean if I read $23.56~\mathrm{mL}$ that I should record it as $23.60~\mathrm{mL}$ and if I read $23.44~\mathrm{mL}$ I should record it as $23.40~\mathrm{mL}$?


texts: What does acidity of para-alkyl substituted phenols depend on?

texts:
Problem

Arrange the following organic compounds in decreasing order of acidity.

Answer

 S, R, Q, P.

Question
According to my knowledge the answer should be P, Q, R, S. As we proceed from P to S we are increasing the number of methyl groups, and so the number of electron donating groups increases, decreasing the polarity of of the C−O bond, which is the opposite to the answer. This obviously means that whatever I'm thinking is the right reason is the wrong logic, but I'm not sure how.


texts: Calcium concentration in NMDARs e Nitric Oxide Synthase

texts:
My question is related to calcium $\ce{Ca^{2+}}$ concentration in NMDA receptors and nitric oxide synthase. I've found a very simple model that describes how the time change of calcium can be related to the NMDA current (http://www.pnas.org/content/98/22/12772.full.pdf, Appendix B), but, however, I would like to find some relationships between the time derivative of $\ce{NO}$ concentration and the time derivative of $\ce{Ca^{2+}}$.

Does exist an expression that could solve this problem?


texts: Reaction of cyclohexene with hydrochloric acid

texts:
What happens when cyclohexene reacts with concentrated hydrochloric acid?
I formed the carbocation intermediate by protonating cyclohexene.
But now I am stuck. I know the end product will be a dimer.
I tried to form a bond between the intermediate and cyclohexene like this.

Then through rearrangement the plus charge will shift to 3 degree carbon.
In the answer there is a double bond between the two rings.
That's where I am stuck . I can not think anything further.


texts: Software/server for calculation of protonation states of small molecules depending on pH

texts: For docking calculations at different values of pH, I am working with flavonoids and would like to know about any software/server that can prepare ligands depending on the pH. Up to now I read about Maestro (Schrodinger) but it is too expensive for us. I wonder if you could suggest other alternatives.


texts: What causes the "Gd break" in the trend of lanthanide-EDTA formation constants?

texts:
Smith and Martell obtained a series of data for the binding of trivalent lanthanide ions, $\ce{Ln^3+}$, with various carboxylic acid ligands (amongst them the well-known EDTA).1 A graph of the formation constants is attached ($K_\mathrm{f} = [\ce{Ln(edta)-}]/[\ce{Ln^3+}][\ce{edta^4-}]$):

Due to the contracted nature of the 4f orbitals, the lanthanide ions characteristically do not exhibit covalency in metal-ligand bonding, which is strongly reflected in their chemistry. Therefore, the almost linear increase in $K_\mathrm{f}$ going from $\ce{La^3+}$ to $\ce{Lu^3+}$ is entirely to be expected. The ionic radius decreases going across the 4f block, and consequently, the interactions with the ligand (primarily electrostatic in nature) become stronger.

However, as the title suggests, I'm interested in the slight blip at gadolinium ($\ce{Gd^3+}$). The value of $K_\mathrm{f}$ seems to be lower than would be expected, and the astute reader will notice that this applies not just to the EDTA complexes but also for some of the other ligands investigated.

Is there a reason for this anomaly?

There is a review by Moeller et al. from 1965,2 which wrote:

  For all ligands which have been studied, the gadolinium complex is less stable than would be expected from the simple electrostatic model. This behavior has been called the “gadolinium break” and cannot be explained, as was originally attempted, by assuming a steric effect, since it is still apparent in ligands for which there should be no steric interference.

Of course, this is more than half a century ago. I would be grateful if anybody could provide either a sound theoretical explanation for why the Gd formation constants should be smaller or a newer reference that explains this effect.

References:

Smith, R. M.; Martell, A.E. Critical stability constants, enthalpies and entropies for the formation of metal complexes of aminopolycarboxylic acids and carboxylic acids. Sci. Total Environ. 1987, 64 (1–2), 125–147. DOI: 10.1016/0048-9697(87)90127-6.
Moeller, T.; Martin, D. F.; Thompson, L. C.; Ferrús, R.; Feistel, G. R.; Randall, W. J. The Coordination Chemistry of Yttrium and the Rare Earth Metal Ions. Chem. Rev. 1965, 65 (1), 1–50. DOI: 10.1021/cr60233a001.


texts: Cobalt Oxalate / Potassium Permanganate Titration

texts:
My class just did a lab today where we mixed cobalt oxalate with $40~\mathrm{mL}$ of $\ce{H2SO4}$ and then titrated it with $\ce{KMnO4}$ (potassium permanganate). I need the mole ratio of cobalt oxalate and $\ce{KMnO4}$ and am not sure how to set up the equation. She provided us with this formula with 3 variables A,B,C -
Co(a)(C2O4)(b) * (c)H2O
but I am not sure what to do with it. I am also confused as cobalt oxalate appears as $\ce{CoC2O4}$ in her equation yet Google says it's $\ce{H2C2CoO6}$.

My table in my lab book is asking me for "Moles Oxalate Present" , "Mass of Oxalate in Sample" , and "Percent Mass of Oxalate in Sample (%)". It is also referring to the "Mass of transition metal oxalate used" which we took during the actual lab. (I guess this lets me know that it solely wants oxalate and to calculate these values aside from cobalt oxalate?)

I am very confused and if any part of this question needs to be cleared up I can certainly do so.

I can provide any/all data that I took during the lab, but explaining conceptually will still do me some good here. I really just don't know where to start with all this data.

My book also gave me this formula for the reaction of oxalate ions with permanganate ions:

$$\ce{5C2O4^{2-} + 2MnO4- + 16H+ -> 10CO2 + 2Mn^{2+} + 8H2O}$$

Will this factor at all into my calculations?


texts: Does knowing the ratio of masses of the elements in a compound lead to the unique chemical identity of the compound?

texts: I was posed this question from a friend, however I am not necessarily sure. I think: yes, because a molecule of any compound is composed of a whole-number ratio of atoms of its elements, per the law of definite proportions. However, I feel as if I am wrong.


texts: Unknown yellow substance from mixing ascorbic acid, baking soda, and rubbing alcohol, then boiling

texts:
So lately I've been using ascorbic acid (very very tiny amounts) to neutralize the chlorine and chloramine in my tap water (temporary solution to improve flavor in lieu of a proper filter).

Just for fun, I decided to react a solution of ascorbic acid with some sodium bicarbonate in an attempt to make a sodium ascorbate solution. Then I got to thinking, how can I get the ascorbate out of the solution?

I figured boiling would do the trick, but for some reason, I thought that adding isopropyl alcohol to the solution might do something, maybe precipitate the crystals out? That probably sounds completely stupid, but forgive me, it's been years since I studied any kind of chemistry (and I wasn't planning on ingesting the solution, so I figured it couldn't hurt to try).

Anyway, the alcohol did nothing visible, so I figured I'd go ahead and book off the solution (figuring the alcohol would dissipate quickly with its low boiling temp).

All went well for some minutes, the alcohol seemed to have boiled off (the smell was gone), and the liquid level was going down so I expected to see some white precipitate forming after a while. Instead what happened surprised me, the solution started turning yellow, then darker as more water boiled off. I did eventually start seeing some cloudiness at the bottom which I assume was the sodium ascorbate, but I didn't boil all of the water off because the color intrigued me.

Here's what it looked like after boiling about 2/3 of the water off:

Any ideas what this could be? My first thought was some contamination, but the pan I used was washed and rinsed very thoroughly.

Some more details on the solution:

about 1/2 teaspoon ascorbic acid
about 1/4 teaspoon sodium bicarbonate
mixed in roughly 2oz water and added a bit more sodium bicarbonate until everything stopped bubbling
when the solution was completely clear and not bubbling, added about 1oz isopropyl alcohol (maybe less)
boiled off about 2/3 of the solution

I eyeballed a lot of this and added stuff as I went (wasn't sure exactly how much ascorbic acid would dissolve) so those amounts may be quite a bit off, but the solution was crystal clear and not bubbling at all after I was done adding everything.

Hope someone with more knowledge than I can offer some insight!


texts: Which compound is responsible for the borax bead test?

texts:
When borax is heated, the reaction that takes place is :

$$\ce{Na_2B_4O_7.10H_2O \ce{->} 2NaBO_2 +  B_2O_3 + 10H_2O}$$
And the compounds that are responsible for the colors are $\ce{M_x(BO_2)_y}$ salts, like $\ce{Co(BO_2)_2}$. My question is, does this $\ce{BO_2}$ come from $\ce{NaBO_2}$ or from $\ce{B_2O_3}$ or do both of them react?


texts: How many particles are necessary to observe a well-defined state of matter?

texts:
The three ordinary states of matter $-$ solid, liquid, gas $-$ can usually be distinguished by a function of the strength of interparticular forces and distance. A shorter distance and a stronger force results in a solid whereas the opposite will yield a gaseous state. In other words, the states of matter are describing macrostates.

With clarity in mind, let us define a practical limit to observing different phases.

  Definition. A practical limit of particles is such that a phase transition is concievably observable by experiment. This is the smallest number of individual particles that when probed give us the traditional phase diagrams (omitting different solid phases).

What is the practical limit for most purposes? I am probably looking for a 'number' of the form $10^a\ldots10^{a + \approx2.5}$ where $a$ is a positive integer.

So while an individual particle under standard conditions can be described as gaseous, it does not fit the definition.

An alternative wording (equivalent as far as I can tell) to this question is given by the Clapeyron equation. Apostrophes mark different phases.

$$\frac{\mathrm{d}P}{\mathrm{d}T} = \frac{\Delta H}{T\left(V'' - V'\right)}$$

In which range of the number of particles do the entalphy of transition and difference in volumes of phases become measurable? This does not definitively mean that $\Delta H$ has to be a constant w.r.t. $T$ but rather a function of temperature $\Delta H = \Delta H\left(T\right)$ that has predictive capability.


texts: Are there art supplies that create a new color by mixing through a chemical reaction?

texts:
When two elements or compounds react together, they form new compounds, which more often than not assume new colors. If the two elements or compounds don't react, they form uniform or non-uniform mixtures, in which case the new color which results from the mixing is the result of the direct combination of the light of emitted by the original elements or compounds. These colors affect the red, green, and blue light receptors inside human eyes, producing a perceptual sensation of color.

I want to know, are there any safe colored substances or color media, which can be used together by an artist, notably a typical artist working from home on paper, cardboard, or canvas materials, and which when mixed together to form a new color, as artists do, actually generates a color resulting from a chemical reaction rather than substance mixing, and, above all, the chemical reaction is safe in terms of not causing damage to the eyes or skin.


texts: Trying to displace iron from ferrous sulphate heptahydrate using aluminium foil but nothing has happened

texts: I started by dissolving the sulphate into water and filtering it as I noticed there was a dirty residue lying at the bottom. (I am using ferrous sulphate that is commonly used in gardening.) I then poured this solution into a jar along with torn pieces of tin foil (tin foil being a common name; the foil is made of aluminium). At the start the solution was fairly clear and greenish in colour. A few days later there is no sign of iron collecting at the bottom of the jar and there has been a slight change in colour. The solution is now slightly cloudier and looks more like apple juice. The orange colour makes me think there must be iron oxide being produced. I need to know whether my method for displacing the iron is correct and if elementary iron will be produced.


texts: Can a ferrite magnet be impregnated with polymer to reduce its fragility?

texts:
Ferrite magnet is a ceramic material and consists of agglomerated crystalline domains with spinel structure. Like other ceramic materials, ferrite magnets are brittle. For example, here is a photo of newly manufactured $\ce{Sr_xBa_{1-x}FeO2}$ tablet which already has chips and sharp fragments stuck on a surface:

This is one of the primary reasons as to why ferrite magnets for the consumer market are sold wrapped in plastic shells or coated with resin. There are also flexible magnets, a composite material consisting of a polymer matrix impregnated with ferrite magnet powder. Flexible magnets do not crumble and are more  impact-resistant, but they are also significantly weaker due to lower density of magnetic domains.
Would it be possible to do the opposite, i.e. impregnate the ferrite ceramic body with polymer to create a less brittle composite material still retaining magnetic properties comparable with those of a bulk permanent magnet?
I suppose the main difficulty stems from the fact that the manufacturing technology requires sintering at the temperatures around 1000 °C which limits the variety of binders and polymers to choose from. If there is no alternatives to currently used inorganic salts, can the impregnation be done afterwards? One suggestion could be creation of a slight increase in porosity of ferrite and filling the voids with polymer in vacuo at lower temperatures, but I didn't find any sources as to how legitimate or cost-efficient this approach can be.


texts: NaHCO₃ + HNO₃ → NaNO₃ + H₂O + CO₂ ... but something weird happens to me in practice

texts:
I put 98% white fuming nitric acid and then I pour some sodium bicarbonate expecting $\ce{NaNO3}$ being formed, I'm not really using much water because it will make evaporation takes ages, even so $\ce{NaHCO3}$ should give $\ce{NaNO3}$ when in contact with $\ce{HNO3}$ and it seems so, $\ce{CO2}$ is formed very quickly so I suppose the reaction is happening... and I can see those white crystals (as the solution is over-saturated of $\ce{NaNO3}$) I shake, shake and shake, and pour more Sodium bicarbonate tills $\ce{HNO3}$ gets a pH around 7 (usually a bit less like 5 or 2) when I notice that it doesn't want to react anymore, however, I try to add mol per mol.

I know there's some unreacted $\ce{HNO3}$ but it should decompose into $\ce{H2O} + \ce{NO2}$ so I put it to start drying in a hot plate, and then the solution becomes yellow (decomposing) it's suddenly brown... and then my "supposed" $\ce{NaNO3}$ is yellowish/pink... and I wonder that seems like a $\ce{NaNO3} + \ce{NaNO2}$ mix but it makes no much sense, I tried with $\ce{NaOH}$ instead $\ce{NaHCO3}$ and it's the same ending color; it's not working... what did I do wrong? how to do it properly?


texts: How to figure out which phase on a phase diagram will be the most dense?

texts:
If I am given a phase diagram, how can I determine which phase will have more density?

What should I consider to solve these kinds of questions?

Does the answer have to do with the area that each phase occupies?  Or the more area a phase occupies, the more the density?


texts: What red and blue area represent in a orbital software?

texts: I have a software in my android device named hydrogen atom. It show orbital of hydrogen we have to set the quantum numbers and probability of finding particle. But what the blue and red colour area in below pictures represent.


texts: Pressure of two flasks connected to each other at different temperatures

texts:
Two flasks of equal volume connected by a narrow tube (of negligible volume) are at $\pu{27 °C}$ and contain $\pu{0.7 mol}$ of $\ce{H2}$ at $\pu{0.5 atm}$. If one of the flasks is then immersed into a bath kept at $\pu{127 °C}$ while the other remains at $\pu{27 °C}$. What is the final pressure?

Will the pressure of the two flasks which are now kept at different temperatures be the same or will they have different pressures?
In the solution I found of this question, the pressure of the two flasks at different temperatures are taken to be equal. Can someone please explain why this is so?


texts: Why don't molecules of ionic compounds exist?

texts:
My book says:

  As single ions of a metal are not associated in the solid with single ions of a non metal, separate units of ionic compounds do not exist. It is, therefore, wrong to talk of a molecule of an ionic compound.

I know ionic solids exist in form of crystal lattice but why can't we isolate a single molecule of ionic compound?


texts: Does naphthalene in moth balls really sublimate or does it evaporate?

texts: The triple point of naphthalene is $\pu{-56 °C}, \pu{1.05 kPa}$ (which is much less than $\pu{1 atm}$). So how can a naphthalene ball sublimate at $\pu{1 atm}$, when considering that its melting point at $\pu{1atm}$ is $\pu{78.2 °C}$ (and the boiling point is $\pu{218 °C}$)?


texts: Number of grams of CO2 released from a carbonated water

texts:
The partial pressure of $\ce{CO2}$ gas in a bottle of carbonated water is $3.84\mathrm{~atm}$ at $25\mathrm{~^\circ C}$.  How much $\ce{CO2}$ gas (in g) will be released from $0.5\mathrm{~L}$ of the carbonated water when the partial pressure of $\ce{CO2}$ is lowered to $1.04\mathrm{~atm}$?  $25\mathrm{~^\circ C}$, the Henry’s law constant for $\ce{CO2}$ dissolved in water is $1.65 \times 10^3\mathrm{~atm}$, and the density of water is $1.0\mathrm{~g/cm^3}$.

First, I found the number of moles of $\ce{CO2}$ using this formula:

$$n = \frac{PV}{k}$$

So the answer that I found which is $0.000351$, can I multiply it by a molar mass of a $\ce{CO2}$ to get the number of grams inside the bottle? This approach seems too easy for me, but at the same time it makes sense.


texts: The oxidation state of iodine in iodoxybenzoic acid

texts:
I am slightly puzzled by this seemingly trivial question. The idea behind assigning oxidation states is simply to treat every single bond made by the atoms as ionic bonds. That is to say, both the electrons of a covalent bond in a molecule would go to the more electronegative atom. For example, in the case of the $\ce {O-I}$ bond, the bond electrons would go to the oxygen atom, leaving the oxygen atom with a negative charge while the iodine atom incurs a positive charge. Based on this, we would say that the oxygen atom doubly bonded to the $\ce {I}$ atom has an oxidation state of -2.

However, I am slightly confused as to why various sources assign the oxidation state of $\ce {I}$ in IBX as +5, rather than +3. On the Pauling scale of electronegativity, it is shown that $\ce { I (2.66)}$ is indeed slightly more electronegative than $\ce {C (2.55)}$. Based on this premise, we would reasonably assign the $\ce {I}$ atom in IBX with a +3 oxidation state as the pair of electrons in $\ce {C-I}$ bond would go to $\ce {I}$ rather than to $\ce {C}$.

Image taken from here


texts:
I've been conducting some experiments to determine the temperature dependence of a reaction. To do this, I've been conducting the experiments at different temperatures and generated a graph of $\ln{[\ce{X}]}$ (where $[\ce{X}]$ is the concentration of the product) vs $T^{-1}$. I was told in a passing comment that because the reaction is first order the gradient of this graph is equal to $E_\mathrm a/R$ in the Arrhenius equation

$$
\ln{k} = \ln{A} - \frac{E_\mathrm a}{RT},
$$

but I don't understand why I can substitute $\ln k$ for $\ln [\ce{X}]$.
Any help is much appreciated.


texts: Cyclopentyl to cyclohexyl carbocation rearrangement

texts:
Here is my problem. The mechanism seems pretty straightforward, but I am having trouble converting the cyclopentane to a cyclohexane. During a synthesis problem, does the starting material add the extra C onto its chain during carbocation rearrangement or a methyl/hydride shift?

As for the problem at hand, I believe the first step is for the pi bond to attack the $\ce{H+}$, and that will leave me with a carbocation at the more substituted carbon. From there, I know $\ce{HOCH3}$ will attack, but somehow, the molecule needs to rearrange its format in order for the $\ce{HOCH3}$ to come in. What needs to happen here?


texts: I keep seeing the term cropping up, but cannot seem to find a definition for it. My understanding is that it is an environment in which, when the isomers interact with the environment, the two enantiomers can be distinguished. The only example I can think of is with the human body, where one type of enantiomer can form an enzyme-substrate complex and the other cannot. I can't think of any other examples though. Can you create a chiral environment in a lab?


texts: Is s-p mixing referring to hybridization or is it the mixing of one atoms s orbital with the other's p orbital?

texts:
According to molecular orbital theory s and p orbitals can mix if they are close enough in energy to each other. For period 2 diatomics, this occurs for $\ce{Li}$, $\ce{Be}$, $\ce{B}$, $\ce{C}$ and $\ce{N}$ - in the case of oxygen and fluorine the s and p orbitals are two far apart in energy. The effect can be seen by realizing that s-p mixing causes the $2\sigma_\mathrm{g}$ orbital to be higher in energy than the $1\pi_\mathrm{u}$ orbital.

My question is: Does the mixing of the s and p orbitals occur between the orbitals of one atom (basically hybridization right?) or does the s orbital of one atom mix with the p orbital of the other (and vice versa)?

This has confused me because I realize that concept of hybridization is widely used and functions well so I initially believed that the mixing should occur in one atom - forming hybrid atomic orbitals - and  then bonding. However, after I thought about it some more I began to doubt that this is the case. Firstly, the s and p orbitals on one atom do not have the correct symmetry to mix effectively (the s orbital would simultaneously constructively interference with one lobe of the p orbital and destructively interfere with the other). Also, the molecular orbital diagram of carbon monoxide reveals that s-p mixing must be occurring since the  $3\sigma$ orbital is higher in energy than the $1\pi$ orbital.

This also seems to contradict the idea that the s and p orbitals mix on the same atom because in $\ce{O_2}$ there is no s-p mixing so why would oxygen mix its s and p orbitals when it's bonding with carbon.


texts: Chaotic melting points of n-alkyl carboxylic acids

texts: Is there any trend here at all? This seems very chaotic as a trend.


texts: Why does [H3O+] of a buffer change very slightly when diluted?

texts:
I am confused as to why the [H3O+] of a buffer changes very slightly when diluted (at least in an intuitive sense).

Consider:

$\ce{HNO2 + H2O <=> H3O+ + NO2-}$

[$\ce{HNO2}$] = 0.45 M and [$\ce{NO2-}$] = 0.30 M yields [$\ce{H3O+}$] of $6.8 \times 10^3 M$. After solving: $4.5 \times 10^{-4} = \frac{x(0.30+x)}{0.45-x}$ where the ionization constant of nitrous acid is $4.5 \times 10^{-4}$

If these concentrations were to be divided by two (the solution is diluted by a factor of 2)

[$\ce{HNO2}$] = 0.225 M and [$\ce{NO2-}$] = 0.15 M yields [$\ce{H3O+}$] of $6.7 \times 10^3 M$. After solving: $4.5 \times 10^{-4} = \frac{x(0.15+x)}{0.225-x}$

Mathematically this makes sense, but I can not intuitively reason why a buffer would behave this way in the "real world." Why can buffers resist changes in pH so effectively when diluted?


texts: What's a good chemistry book for a practical man

texts:
Yesterday I picked up my old organic chemistry book and started to read it from the first chapter. After a couple of minutes I realized that I don't understand the concepts at all.

The first chapter mentions the reason behind polarity of covalant bonds because of difference in electronegativity of different elements, flourine being the highest. Now chemistry is a practical science and all these concepts have been theorized by observing reactions. Is there a chemistry book which gives a detailed explanation of the experiments which led to the formulation of theories we read in school?


texts:
I recently have a lesson about quantum chemistry, and in one lesson we spoke about hyperfine stucture of elements.

The teacher give us something which looks to be an extract of Moore's tables here for the carbon. He said there are thousands of this tables which give the energy levels of many atoms.

But I search on the net and I only found things about electronic such as transistors et caetera... can you tell me the real name of this tables or how can I find them ?

Thank you in advance


texts: Does gravity affect the rate of a chemical reaction?

texts: For example, on planets with lower gravity, would the rate of reactions be lower because the reactants are slower to mix with one another?


texts: Can I add citric acid to KCl for iron removal in a water softener?

texts:
I recently installed a water softener and having a fair amount of clear iron in our water, I've been using Morton Rust Remover pellets which are basically NaCl with citric acid added as an additive.  I'm guessing the iron removal function has something to do with the citric acid since it's the only notable difference between this salt and regular water softener salt.

At some point I'd like to stop using NaCl and switch the KCl since it seems to be more environmentally friendly.  However, I really notice a difference using the iron removal pellets and I've been unable to find an equivalent product for sale which uses potassium.

Can I simply mix some citric acid in with the potassium in the water softener to achieve the same result?  Or do the citric acid and the sodium have some special relationship which helps with the iron removal?


texts: Are ethyl iodophenylundecylate and Ethyl-10-(Iodophenylundecanoate) the same compound?

texts:
I have no understanding of chemistry, so these to chemical formulas mean nothing to me. What I am trying to ascertain is are these compounds the same? If not, what differences are there especially if injected into the CSF [which they were]?

Known as Ethyl Iodophenylundecylate:

CH3
I   (CH2)8 COOC2 H5
CH

Known as Ethyl-10-(Iodophenylundecanoate)

CH3
I -CH2 (CH2)6 CH2 COOC2 H5
CH


texts:
Do ions also form special electron configurations? (just as Copper and Chromium do)

I know that because copper has 1 electron in its s-orbital (highest) because it wants to have a full d-orbital (d^10)

But do ions also act this way?


texts: How was the pKa value (-1.7) for the oxonium ion determined? Why does it correspond to the minimum pH value accessible in water? What reaction does it represent?


texts: Why does the temperature of the gas in a container moving with constant velocity does not change?

texts:
Systematic changes do not affect thermodynamic equilibrium.

What does this mean? And what kind of systematic changes are allowed?

The container with gas is stationary till some time then its given a constant velocity and the final temperature is asked , the answer says that systematic changes dont affect thermodynamic eqiulibrium and temperature remains constant .


texts: Energy-efficiency aside, what are the chemical constraints on CO₂ capture and methanation?

texts:
Synthesising $\ce {CH4}$ from air and water (in a non-biological process) has been proposed as one form of energy storage. What are the chemical constraints at play here? That is to say, what sort of catalysts might be used, and what are the performance / lifetime issues with them?

More specifically:

$\ce {CO2}$ capture and recycling (CCR) has been suggested as one form of round-trip electricity storage, with a round trip being:

electricity
$\to$ something that can hang around for hours to months
$\to$ electricity some time later

The proposal goes something like this: capture the $\ce {CO2}$ produced from the combustion of $\ce {CH4}$ in air in a gas-turbine electricity plant, and store it. Then, when there's surplus electricity, use it to synthesise $\ce {CH4}$ from the $\ce {CO2}$ plus water (I'm guessing electrolysis of water and a Fischer-Trop / Sabatier type reaction). And next time there's a deficit of electricity, burn the $\ce {CH4}$ to generate electricity, and capture the $\ce {CO2}$, and go around again. So, for the sake of this question, I'm specifically interested in the non-biological synthesis of methane.

And let's put aside for one moment the issue of energy efficiency, as that's effectively an economics question. (The question being "is the round-trip efficiency less than the ratio of off-peak to peak electricity prices?") Let's just agree that round-trip energy efficiency is one of the factors that influences the economics, and leave it at that for now.

So the question is: what sort of catalysts might be used, and what are the performance / lifetime issues with them?


texts: Melting point and boiling point in isomers

texts:
We know, that cis isomers are less stable than trans isomers. What I don't get is why the boiling point is changing as opposed to the melting point. The change is melting point makes sense to me considering the stability.

Also the difference of mp and bp in iso and n-butene is not clear to me. How can I possibly explain the change in these physical properties?


texts: Justify this statement whether correct or incorrect . He2^+ has the same energy as two isolated He atoms

texts: My explanation : how can a stable molecule be at the same energy level as two isolated inert gas atoms?? Is this even possible?


texts:
I need a good book that explains the basics of chemistry in a lucid and importantly, systematic manner. Most books on this subject are not comprehensive and assume that the reader is well acquainted with certain topics. Also, most chemistry books have references to later chapters. And later chapters, references to earlier ones. This makes it very confusing.

I would like a book that assumes (effectively) no prior knowledge and builds up the basics needed to understand chemistry (structural theory, acid-base theory, electrode potentials) to a level adequate to understand undergraduate level organic and inorganic chemistry.

The reason I need this book is because frequently, while studying inorganic and to a certain extent organic chemistry, I am unable to understand the rationale behind a certain reaction. And most textbooks do not take the effort of explaining it. So, chemistry, for me,  just reduces to memorizing a set of reactions. I think solid basics should remedy that.


texts: Why are all 3 of propane, butane and isobutane used in deodorant sprays?

texts:
Here are the back ingredient labels of a few popular commercial alcohol-based deodorant sprays.
As one can clearly see, they all have many things in common, but the 3 which are of importance in lieu of this question are-

Butane
Isobutane
Propane

After a quick search on the internet, one can find all 3 have the same common function i.e. acting as a propellant to give a perfect aerosol spray.
My questions lies, why are all 3 of them used together when they have the same function? There are also many deodorant sprays that use only butane as the propellant. Is it something related to pressure factors or its ability to be used in different conditions(hot/cold weather)?
If there's no such strong reason behind it, and if cost effectiveness isn't harmed either, then why not just use one of the 3? And if so, what would be the best of the 3 alternatives?
Image source: Google Images 1
2
3
4


texts:
How many stereoisomers are possible for following compound (1,3,4,6-tetramethylcyclohex-1,4-diene)?

My Approach
the 1,4 methyl groups lie in the plane, whereas 3,6 are possible chiral centers. However it doesn't seem like enantiomers are possible due to centre of symmetry, one structure can be meso. Apart from this I don't see any possibility of Geometric isomers as well. However the answer given is:

3

What am I missing in this?


texts: Does this set of quantum numbers have a unique solution?

texts:
I received the following question:

  Complete the missing values for the four quantum numbers:
  $n=?$, $\ell = 2 , m_\ell = 0$ , $m_s= ? $ .

The problem is that I think $n$ can be any number greater then 2, and $m_s$ can be $\frac{1}{2} $ or $-\frac{1}{2}$, so there seems to be no unique solution to this problem.

Is this correct?


texts: Equation for collision frequency of molecules/ions in aqueous solution?

texts: There are equations that describe collision frequency in the gas phase, but I am wondering if this collision theory has been extended to describe the collisions of molecules and/or ions that are dissolved in water. I would imagine this equation would incorporate the aqueous diffusion coefficients of the species in some way and also not have the gas constant (R) in the expression.


texts: What is the logic behind the terminology lyophilic and lyophobic colloids?

texts:
Its given in my text book that-

  Colloidal dispersions of starch,rubber,proteins etc are lyophilic colloids whereas colloidal dispersions of metals,sulphides etc are lyophobic in nature.

But even the protein molecules have both hydrophilic as well as hydrophobic ends. And metals being ionised have strong affinity for polar dispersion medium. They why is it given that metals sols are lyphobic whereas sols generated from macromolecules are  lyophilic colloids.

Is it because we can create protein or other macromolecular sols just by simply shaking in dispersions medium and generation of metal sols require certain chemical and mechanical means.

What is the real definition for lyophilic colloids and lyophobic colloids?


texts: How can the ketone in a β-ketoester be protected during hydride reduction?

texts:
I am supposed to find what X is. I know that $\ce{LiAlH_4}$ will convert all carbonyl groups to alcohols, and the ester group is being reduced. The only way of ending up with a ketone that I can think of is by a pinacol reaction.

However, the answer given was that X was $\ce{HOCH2CH2OH + H+}$. How does this work?


texts: Should equiatomic iron–cobalt alloy be written as FeCo or CoFe?

texts:
I have an alloy made of 50% iron and 50% cobalt. I see occasionally in the literature this is written as FeCo alloy.
But shouldn't it be CoFe alloy since the chemical symbols are supposed to be arranged in alphabetical order?
Is there somewhere where these rules are written down?


texts: Is there a proof for Markovnikov's Rule? Specifically, why does the H bond to the carbon with the most hydrogen atoms already bonded to it?


texts: How to get a precise answer to a textbook precipitation problem?

texts:
This question concerns a textbook problem* on precipitation. Briefly, there are $2\cdot10^{-4}$ of Mn$^{2+}$ and Cu$^{2+}$ ions in a liter of solution with $0.003$ M HClO$_4$. This solution is then saturated with H$_2$S. The solubility of H$_2$S is given as 0.1 mol/L and assumed independent of the presence of other substances in solution. K$_{sp}$ for MnS is $3\cdot 10^{-14}$, K$_{sp}$ for CuS is $8\cdot 10^{-37}.$  K$_1$ and K$_2$ for H$_2$S are given as $1.0\cdot 10^{-7}$ and $1.2\cdot 10^{-13}$ respectively.

In part one of the question it is found that Mn remains in solution and  Cu$^{2+}$ will precipitate because the product [Cu][S] = $2.6\cdot 10^{-20}$ far exceeds K$_{sp}$ of CuS. In part two the problem is to determine how much Cu remains in solution.

The solution begins by stating that "most of the Cu$^{2+}$ will precipitate" and explains that a corresponding increment of [H$^+$] will be added to the solution from the H$_2$S which has lost S to precipitate, requiring a correction which leads to $8\cdot 10^{-21}$ moles Cu remaining in solution vs. $6\cdot 10^{-21}$ moles without the correction.

To make the correction the text assumes all the Cu precipitates, so here is my question.

The question being asked is: How much Cu remains in solution? To answer the question, it is assumed that none remains in solution...(!) This leads to a slight correction (from $3\cdot 10^{-21}$ % to $4\cdot 10^{-21}$ %) Cu remaining. The text does ignore the small change in [S] that accompanies the change in [H$^+$].

  If there is a situation in which this very small difference matters, what is the right way to find it?

My guess is that there would be a simple ODE governing this problem--but I'm not sure.

The details above are included for completeness but the answer I think does not depend on the numbers here.

*The source of this problem is Shaum's College Chem. (10 ed.), 18.13-14.


texts: Why are least electronegative elements usually in center of lewis structure

texts:
Many sources state that one of the primary rules for molecular structures is that the least electronegative element is in the center. However, none of them explain why this is the case.

Is this because it is most conducive to sharing electrons and forming bonds, or is it the most stable, or is there a better reason?

Also, why are many molecules symmetric. Is there a reason why symmetry in nature and in chemistry is preferred over non-symmetry?


texts: What would Kp be if there is no gas reactant

texts: What would $K_\text{p}$ be if there is no gas reactant but the reaction produces gas. I found something confusing: $$K_\text{p}=\frac{P_\text{gas product}}{P_\text{gas reactant}}$$ If there is no gas in the reactant side, then the partial pressure of the reactant gas is 0 so the $K_\text{p}$ would be infinity.


texts:
What's the chemistry behind only charging a Lithium-ion battery to 80% capacity at most, to increase its lifespan?

Over on the Skeptics StackExchange, a question has come up about charging Lithium-ion cells to just 80% of their maximum, in order to extend their lifetime.

Is there a sound basis in chemistry for such a recommendation, and if so, what is it?


texts: Molybdenum/Tungsten alloy armor piercing round

texts: As we all know, the military's use of depleted uranium in armor piercing rounds and shells is very dangerous as far as health concerns, and an alternative is needed. Tungsten is already a very dense metal, but molybdenum is widely used to harden metals, and also has a very high density. Would a molybdenum and tungsten alloy work for armor piercing capabilities? If so, why not?


texts: In UV photoelectron spectroscopy why are filled orbitals seen at a higher binding energy?

texts: I understand that the partially filled Ni intersects the Fermi level as there is a change from filled to unfilled orbitals. But what is the explanation for the lower binding energy of the filled 3d Cu orbital. Surely there would be greater electron-electron repulsion resulting in higher kinetic energy of the electrons due to more shielding, which corresponds to a lower binding energy?


texts: Predicting color of a TMB derivative affected by peroxidase

texts:
The ELISA test on HIV works by verifying the presence of peroxidase within samples. The verification process is done through the enzymatic reaction that said peroxidase has on TMB (3,3',5,5'-tetramethylbenzidine) in an environment that contains $\ce{H2O2}$. This reaction leaves the enzyme untouched and transforms the $\ce{H2O2}$ into $\ce{2H2O}$ by adding two hydrogen atoms taken from the TMB. This also transforms the TMB into another compound, 4-(4-imino-3,5-dimethylcyclohexa-2,5-dien-1-yl)-2,6-dimethylcyclohexa-2,5-dien-1-imine, which has a blue color in that specific case.

Therefore my question is, how could one predict from the structure of the one product that it is going to have a blue color in that situation? I know that it probably comes from the conjugated double bonds but how do their count relate to the absorbed wavelength(s)?


texts: How can the standard deviation for a set of experimental value be interpreted in terms of precision?

texts:
I have read from many websites that the sample standard deviation can be used to measure the precision of experimental values. I understand that the lower the standard deviation the better, as it would mean that the values are close together (precise). But what standard deviation is small enough to be considered precise?

As an example, in a redox titration experiment I obtained titrant values of $16.3$, $16.4$, $16.5$ and $\pu{17.1 mL}$.

From these four measurements, I thus calculate an average of $\pu{16.58 mL}$ and a standard deviation of $\pu{0.35 mL}$.  The uncertainty of the burette is $\pm\,\pu{0.05 mL}$.

From this standard deviation, would this experiment's results be considered precise?

If not, why not, and how would I interpret it?

Is there a better method for quantifying precision?


texts: What is relationship between molecular weight distribution of PE and its strength?

texts:
I'm trying to figure out the relationship between the molecular weight distribution of a polyethylene plastic and its strength and heat sealability.

(The molecular weight distribution is described as being narrow, which apparently is helpful in terms of strength and heat sealability).


texts:
According to my chemistry manual meso forms are "a particular case of of stereoisomers" implying that they are isomers, anyway right after this sentence the manual states that if you rotate the 2 forms of tartaric acids (the green ones in the image) you obtain the same molecule... so they're not isomers.
Is that correct? Are the green forms the same molecule? In this way it would be senseless to speak about isomers...

I'm not asking if these 3 formulas are isomers, because they obviously are. I'm asking whether the green forms (the last 2 forms starting from left) are to be considered isomers (that means they have a different structure) or they are totally (in every aspect) the same molecule with a different drawing.


texts: What's the chemical nature of a dishwasher's rinsing agent?

texts: It seems that a rinsing agent helps the dishes in the dishwasher dry much better than they do without it (which I recently noted on my new dishwasher). What molecules are used in the composition of these rinsing agents? How do they help the plates dry?


texts: How does the pH of fresh glacial meltwater compare to marine seawater?

texts: How does the pH of fresh glacial meltwater (at the time of melting, so it has not travelled downstream for example) compare to marine seawater? I assume that glacial ice is more neutral since it cannot uptake as much alkalis into its structure. Any insight would be helpful.


texts: How do we find the oxidation state of individual carbon in Mg₃C₂. Explain with the help of structure if possible. For the average oxidation number, we can exploit the fact that the molecule will be electrically neutral, but what about the individual atoms of carbon?


texts: Multiday lab courses in classic chemistry

texts:
This time of the year I usually get some extra income I can use on interesting courses. Usually rescue or sport courses. However, I also have a master degree in chemistry, and would like to spend some days or a week just to do some old fashioned chemistry with a great teacher. But I have never found a "summer school" or something like that.
Does anyone has a any suggestion? I can gladly expand "classical chemistry" in any direction, as metallurgy or microbiology.


texts: Stereochemistry of cycloalkanes having substituents

texts:
My teacher said that from $3$ to $6$ member cycloalkanes having any number
  and type of substituents we can always draw the planar structure and
  decide the specifics of stereochemistry like:

  Are they optically active or not?
  Are they meso compunds or not?
  Do they have a plane of symmetry/centre of symmetry/axis of symmetry/alternating axis of symmetry or not?

But I feel that the molecules are hardly in planar form. It would be incorrect to assume they are planar and find the specifics of stereochemistry. Only for cyclopropane the points should be correct as it is always planar. Maybe my teacher said that mistakenly in a hurry.

So regarding points $(1),(2)$ and $(3)$ who is correct? Why? Or are we both partially correct? I need a slightly detailed answer.


texts: 1H NMR impurity peaks don't align across samples

texts:
I have a series of four 1H NMR spectra for a polymer I'm synthesizing under different reaction conditions. However, the acetone and chloroform peaks are shifted relative to each other across the samples - see the attached images, where if the spectra are calibrated to the chloroform peak, the acetone peaks do not overlap.

I'm relatively a novice at NMR, so I apologize if the answer is obvious, but what could be causing something like this? Is it a common observation?


texts: Adding cyanide vs nitrite for nucleophilic substitution and why does it change when we use silver salts for it

texts:
On adding $\ce{NaCN}$ to $\ce{RX}$, we get

$$\ce{NaCN + RX -> RCN + NaX}$$

And not $\ce{RNC}$. Clayden gives the explanation as follows:

  Although linear cyanide (which is isoelectronic with $\ce{N2}$) has a lone pair on nitrogen and a lone pair on carbon, the nucleophilic atom is usually anionic carbon rather than neutral nitrogen as the $\mathrm{sp}$ orbital on carbon is of higher energy than that on the more electronegative nitrogen, and therefore constitutes the HOMO.

So according to Clayden, Carbon being less electronegative, has a higher HOMO than Nitrogen, thus it's lone pair attack the LUMO, to form a bond as the less the difference in energy between HOMO and LUMO, the stronger is the bond

But when we consider the same case with $\ce{NaNO2}$, so according to Clayden, nitrogen being less electronegative than oxygen, Nitrogen should have a higher energy HOMO and thus in a nucleophilic substitution reaction it is from the nitrogen side, that  the reaction should take place but ...
$$\ce{NaNO2 + RX -> RONO + NaX}$$

The reaction takes place from the oxygen side. Why?

Also when we have the silver salts of them, e.g., $\ce{AgCN}$, the reaction becomes:
 $$\ce{AgCN + RX -> RNC + AgX}$$
Similarly,
 $$\ce{AgNO2 + RX -> RNO2 + AgX}$$

Why does it change?


texts: What is the difference between steric strain and torsional strain?

texts:
I know that in ethane, the extra energy present in the eclipsed conformer is caused by torsional strain.

In butane, the gauche conformation experiences steric strain. But the eclipsed conformation at 0 degrees has substantial amounts of both steric strain and torsional strain.

What is the difference?


texts:
The equilibrium constant for the reaction:
  $$\ce{2NO(g) <=> N2(g) + O2(g)}$$
  is $2.60 \cdot 10^{-3}$ at $\pu{1000^\circ C}$. If $\pu{0.820 mol}$ of $\ce{NO}$ and $\pu{0.223 mol}$ each of $\ce{N2}$ and $\ce{O2}$ are mixed at $\pu{1100^\circ C}$, what are the concentrations of $\ce{NO}$, $\ce{N2}$ and $\ce{O2}$ at equilibrium?

I'm really stuck, because with these types of questions usually the concentration of at least one reactant or product at equilibrium is provided, so I know the direction of the equilibrium shift.

Usually I allow the variable $x$ to equal the change in concentration of each product/reactant, where I subtract or add different ratios of it from the initial concentrations of the reactants and products (depending on the direction of equilibrium shift).

However, since I do not know the direction of equilibrium shift, how am I supposed to know whether to subtract or add $x$ to the reactants/products?


texts: Propan-1-ol Heats Objects Faster than Propan-2-ol. Is this an anomaly?

texts:
After conducting a practical revolving around burning alcohols, I found that propan-1-ol heated the 50 mL of water to 60 °C about 1 min faster than propan-2-ol.

The experiment was controlled as much as possible, including the temperature escaping the setup.

I know that propan-2-ol is more volatile than propan-1-ol, so I have a reason to believe that this is tied to the slower heating. On the other hand, I have yet to find any sources to verify this.

If I do not find any more about this, I will have to call this out as an anomaly.

If anyone knows anything about the relationship between the position of the $\ce{OH}$ bond in an alcohol and the heat output/speed of heating, please explain this to me.


texts: Estimating standard Gibbs free energy of a molecule

texts:
In order to estimate the standard Gibbs free energy of a molecule at room temperature and normal pressure, we use Maxwell Boltzmann average over  rotational conformers.

Question

Should we consider cis/trans isomers besides rotational conformers? Is there any criterion for it?


texts: Generating mol files from a molecular structure image?


texts: Spontaneous reaction between chromium(III) and aluminum

texts:
I'm trying to rationalize this problem. It's been a while since I've done redox problems. So here goes, and any input would be great. Basically - am I right?

Here is what happens when you store chromium ion in an aluminum container:

$\ce{Cr^3+ + Al -> Cr + Al^3+ ~~~~~~E^{o}_{cell}=}$ ${+ 0.94}$$\ce{V}$

$\ce{Cr^3+}$: oxidizing agent

$\ce{Al}$: reducing agent

$\ce{Cr}$: conjugate reducing agent

$\ce{Al^3+}$: conjugate oxidizing agent

This reaction is spontaneous because we are going from strong to weak (just like in a spontaneous acid-base reaction).

So if we are going from strong to weak, all these statements are true:

$\ce{Cr^3+}$ is a stronger oxidizing agent than $\ce{Al^3+}$.

$\ce{Al}$ is a stronger reducing agent than $\ce{Cr}$.


texts: How does aluminium amalgam work as a reducing agent?

texts:
I can't seem to find much information on this topic but how does aluminium amalgam work as a reducing agent?

Could it be used to deoxygenate a carboxylic acid or amino acid to the corresponding alcohol or alkane?

If not , why not?


texts: What does the equilibrium equation look like when calculating the solubility from Ksp?

texts:
For example, given a reaction

$\ce{NaCl -> Na+ + Cl-}$

and its $Ksp$ value, I know that you can set up
$$Ksp\; =\; \left[ \ce{Na^{+}} \right]\left[ \ce{Cl^{-}} \right]$$ and solve from there.

My question is why do you not put $\ce{[NaCl]}$ in the denominator, as isn't that part of the equilibrium expression also?


texts:
Can good quality crystal meth really be made as in Breaking Bad?
Can a pharmaceutical drug really be reverse-engineered?


texts: Why do we use [H⁺] and [OH⁻] in balancing redox reactions instead of using [H₃O⁺] and [OH⁻]?

texts: For what reason is it universally agreed upon that we use $$\ce{H+ + OH-}$$ ions in balancing water on either side of the reaction, but not the $$\ce{H3O+}$$ ions?


texts:
My question is simple, If chlorine ($\ce{_17Cl^35^.^5}$) and nitrogen ($\ce{_7N^14}$) have similar values of electronegativity, and chlorine has way more lone pairs than nitrogen, what prevents it from forming hydrogen bonds ?

(other than in chloral dihydrate $\ce{CCl3CH(OH)2)}$


texts: Reconciling these different solubility values

texts:
In a review article [1] on the solubility of CaCO$_3$(calcite), the solubility is reported to be on the order of 1 gram/litre.

Since CaCO$_3$ has a molar mass of about 100, this solubility is equivalent to $10^{-2}$ M.

The solubility product is the square of this, $K_\mathrm{sp}=10^{-4}$.

However, the solubility product of calcium carbonate (according to various sources, like Wiki) is actually $\sim 10^{-9}$ which is 5 orders of magnitude smaller.

What am I missing?

[1] Miller, John P. "A portion of the system calcium carbonate-carbon dioxide-water, with geological implications." American Journal of Science 250.3 (1952): 161-203.


texts: How to determine the dimensions of a bixin molecule?

texts:
I need the dimension of a bixin molecule.  I do not know where to look or how to calculate this information.

I understand that this molecule has several rotational axes and conformation, so there is no uniform size to be determined. But I am interested in the standard method for the determination of the molecule's dimensions.

I am doing a series of refractive and scattering experiments in a concentrated bixin medium. I need to determine the most probable cross section area normal to its principal axes.


texts: Calculations on an irreversible adiabatic expansion

texts:
A $\pu{5.00 L}$ sample of $\ce{CO_2}$ at $800\ \mathrm{kPa}$ underwent a one-step irreversible adiabatic expansion against a constant external pressure of $\pu{100 kPa}$. The initial temperature of the gas was $300\ \mathrm{K}$

  An alternative path between the initial and final states consists of a reversible isothermal expansion
  from $5.00\ \mathrm{L}$ to the final volume $V$, followed by (reversible) constant volume cooling to the final temperature $T$.

  a) Give the equations for $\Delta U$, $q$ and $w$ for all three processes in terms of $V$ and $T$

  b) Calculate the final volume and temperature of the gas

My Attempt

Adiabatic Expansion

$q = 0$ since it is adiabatic. $w = -100 \times (V-5)$. $\Delta U = q + w = -100 \times (V-5)$

Isothermal Expansion

$\Delta U = 0$. $w = -q = -\mathrm{nRT}\times \ln\frac V5$ = $-4000 \times \ln\frac{V}{5}$

$q = 4000 \times \ln\frac{V}{5}$

Reversible Cooling

$w = 0$. $\Delta U = \mathrm{c_v \Delta T = c_v \times (T -3oo)}$

$q = \mathrm{c_v \Delta T = c_v \times (T -3oo)}$

Part b)

$-100 \times (V-5) = \mathrm{c_v \Delta T = c_v \times (T -3oo)}$ since $\Delta U$ is a state function

$\mathrm{V = \frac{nRT}{p}} = 0.133T$  Now I am not sure if this step is correct. I used that $p = \pu{100 kPa}$. Is that right? From there I can solve for $T$ and hence for $V$.

Could someone please check if above working out is correct?


texts: I have learned that non-bonding MOs are lone pairs. However when considering the MO diagram for the $O_2$ molecule, I do not see any non bonding orbitals yet there are two  lone pairs on each oxygen atom. Where do these come from?


texts: Relative humidity above various mixtures of table salt and water

texts:
I heard that if I saturate some water with NaCl and put it in a closed box, the relative humidity near the water surface should be around 75 % at room temperature.

I am using this to calibrate some electronic sensors measuring relative humidity.

If a saturated solution gives 75 % RH, how can i know which RH more diluted mixtures should result in?

--

My setup is a small 1l plastic container where in I put a mixture of table salt (iodized) and tap water (about 150 ml). The sensor is hanging a few cm above the water surface and measures for a day or so.

The solutions I use are:

Fully saturated water (Plenty of undissolved salt crystals)
75 % saturated water (3 parts saturated, 1 part pure water)
66 % saturated water (2 parts saturated, 1 part pure water)
50 % saturated water (1 part saturated, 1 part pure water)

I am also monitoring the temperature in the container, and it is usually swinging a few degrees below 20 °C.


texts: Why are B-O-H and B-O-C angles in B(OH)3 and B(OCH3)3, respectively are higher than normal?

texts:
In Concise Inorganic Chemistry by JD Lee (4th edition; adapted by Sudarshan Guha), page 77 under the topic "Back Bonding" it is given:

  The $\mathrm{2p}\pi$-$\mathrm{2p}\pi$ back bonding in $\ce{B(OH)3}$ and $\ce{B(OCH3)3}$ explains why  $\ce{B-O-H}$ and $\ce{B-O-C}$ angles are $112°$ and $113°$, respectively.

Based on the above statement I arrived at the following:

Due to back bonding in $\ce{B(OH)3}$ and $\ce{B(OCH3)3}$ there is a partial double bond character in the bond between boron and oxygen in both the compounds. The oxygen in both compounds is $\mathrm{sp}^3$ hybridised and ideal bond angle is $109°28'$. But due to the partial double bond character and as we know the repulsion between a double bond and single bond is greater than between two single bonds the bond angles $\ce{B-O-H}$ and $\ce{B-O-C}$ are larger than the ideal $109°28'$.

Kindly tell whether my understanding is correct or not. If not, kindly give an explanation for the observed bond angles and their deviation from ideality.


texts: Non-cyclic alkenes can be oxidized to carboxylic acids in presence of hot alkaline $\ce{KMnO4}$ and quenched with dilute $\ce{H2SO4}$ to form carboxylic acids. I suddenly got a thought. Can cycloalkenes be oxidized to form carboxylic acids? For example: can cyclohexene be oxidized to cyclohexanoic acid using the same conditions?


texts: Smoke Bomb with Potassium Nitrate and Sucrose (Or is it caramel?)

texts:
I've scoured the internet for a proper chemical reaction between caramelized sucrose and Potassium Nitrate for the past few days. So far, every chemical reaction I see drawn out is between pure sucrose and potassium nitrate, while the smoke bomb in question requires caramelized sucrose, an entirely different thing altogether that probably will give you a different reaction.

Am I over-thinking this, or is Caramelen/Caramelan the reactant, instead of sucrose? If someone could be so kind as to draw out the chemical equation between the two, that'd be awesome, too. (Heat is part of this equation, as the substance is lit to produce the smoke)


texts: I read in a west African chemistry textbook (New School chemistry by Osei-Yaw Ababio) that aluminium trioxocarbonate (IV) (aluminium carbonate) does not exist. I need verified confirmations or oppositions.


texts: Gibbs Free Energy: Exothermic, low temperature & reduced system entropy - such reaction is spontaneous or not?

texts:
According to $\ce{\Delta G^\mathrm{o}= \Delta H^\mathrm{o} -T\Delta S^\mathrm{o}}$, if a reaction

a) is exothermic,

b) reduces system entropy, and

c) the temperature is low,

then it is spontaneous.

Consider the combustion of hydrogen gas, with $$2\ce{H2}+\ce{O2}\to 2\ce{H2O}.$$ This reaction is exothermic, and the system's entropy decreases. So does it mean that:

1) this reaction is spontaneous at low temperatures?

2) this reaction is not spontaneous at high temperatures?

If so, it seems counter-intuitive that placing the reagents in a high-temperature environment will not cause spontaneous combustion. Can you explain why this should be the case?

I really appreciate your help!


texts: Remove formalin from food using chemical found in kitchen

texts:
In some parts of the world food is stored with formalin so it looks fresh forever! This is astonishing, but true (See refs here). As formalin is very bad for health and damages kidneys and liver very quickly, I am looking for a way to remove it.

When I buy fish, I know it has formalin in it. Every fruit I bought has formalin. I remember I bought 2 kilgrams of apples once. And it lasted for 1 month, looking fresh whole time. Then I threw it away.

My question is: how can you remove formalin from food? (Especially fish and fruit). It's best if we can use a chemical found in the kitchen. If not, I'd think one that is found at a chemical store.


texts: How there are 7 enolizable hydrogens in 2‐methylcyclohex‐2‐en‐1‐one?

texts:
49. How many enolizable hydrogens are there in the following compound?

(a) 2
(b) 4
(c) 5
(d) 7

I know that enolate ion is the anion formed when an α-hydrogen in the molecule of an aldehyde or ketone is removed as a hydrogen ion.
In the above question I find only two α-hydrogens which can participate (denoted with red color):

But the answer is (d) 7.
Where am I getting wrong?


texts: Can a metallic bond with a sea of electrons form inside the human body?

texts:
I’m interested if atoms or ions can for a metallic bond inside the human body?
I’m talking about a metallic bond as described here: https://www.britannica.com/science/metallic-bond
So I’m thinking of a metallic bond where the valence electrons of the atoms or ions are not associated with specific atoms or ions of the metallic bond. My understanding is that this is described as a sea of electrons.
If such a metallic bond can not form inside the human body, I would be very interested in the reason why. Thank you very much.


texts: Classification/Nomenclature of aroma and flavour compounds - terpenes, aldehydes, and alcohols, etc

texts:
I'm collating different types of aroma compounds but the nomenclature and classification structure is confusing. How do you classify flavour compounds that can belong to different groups (e.g. terpenoids and aldehydes)?
Citral (lemony smell), for example, is a mixture of neral and geranial. Citral seems to be generally referred to as a terpene, but is a mixture of aldehydes. This previous post refers to it as an aldehyde: What happens when deodorants or perfumes expire , but is generally referred to as a terepenoid.

Similarly, Citronellal is a terpenoid, but is it not also an aldehyde?

Is there a way to prioritise the classifications of aroma/flavour compounds - i.e. does a terepenoid structure take priority over presence of an aldehyde or alcohol group?


texts: What is the name of the diagram in this question? How do you read it?

texts: My teacher calls it an 'orbital diagram' but every time I search for information something completely different pops up. I assumed it was a fancy Bohr diagram, but the electron placement is always weird. I understand electron configuration , but I cannot understand why each electron goes where on this diagram. This example is really simplistic, but other ones that I've seen make no sense in terms of electron placement.


texts:
At equilibrium, the rates of the forward and backward reaction become equal. In a reaction
A(s) giving B(g) + C(g)
Increasing the surface area of A increases the rate of the forward reaction, but the backward reaction is between two gases and is unaffected. By the time the rate of the backward reaction becomes equal to that of the forward reaction, more of A must have converted into B as compared to how much it did when there was less surface area. Since the activity of a pure solid is unity, it doesn't appear in the expression for K. So K must have increased. The equilibrium constant on the other hand depends on the ∆G standard for a reaction. The standard ∆G is unchanged, so K must be unchanged. How does one resolve these two?


texts: Do certain cumulated dienes present geometric isomerism?

texts:
Let's take, for example: 2,3-pentadiene.

Can't this compound present geometrical isomers, like 2-butene?


texts: What is a good method to measure the redox potential of a cellular system?

texts:
I know how to measure the concentration of free thiols, which is reflective of the redox-potential of cellular compartment such as the cytoplasm or a lysosomes.

What other methods exist?


texts:
I have a question about anti-solvent precipitation in organic chemistry:

Is it possible to precipitate lycopene or other carotenes using this method?

I have been extracting carotenes like lycopene by Soxhlet method using acetone as solvent. I was wondering if it's possible to precipitate these compounds using the anti-solvent method.

If it's possible which anti-solvent would be more accurate, in the documents that I have been reading , it was mentioned methanol and other alcohols but I'm not sure if the acetone that I used in the extracting part would cause any interference.


texts: How to prepare solutions of different concentrations of potassium from stock solutions with different concentartions?

texts:
I need to prepare different concentrations of $\ce{K+}$ ($10$, $20$, $30$, $40$, $\pu{50 mM}$) by diluting a solution of $\pu{100 mM}$ $\ce{K+}$ with an isotonic buffer of $\pu{5 mM}$ $\ce{K+}$.
I need $\pu{4 mL}$ of each concentration.

I really don't remember how to calculate this. Because I need to consider the $\ce{K+}$ within the isotonic buffer right, because they will also add amount of $\ce{K+}$? If I would have diluted the $\pu{100 mM}$ $\ce{K+}$ with just water, then I understand how to do.


texts:
Last week I was discussing with a friend how we thought the stripeless cleaning of windows is achieved when using a cleaner like Windex Glass Cleaner as opposed to just using hot water, in which case you do get stripes left behind.

At first we thought that the stripeless nature was caused by surfactants in the cleaner that allow the (polar) dirt on the windows to be collected in the water through micellation. However, when we use normal cleaner not specifically designed to clean glass/windows, we also get the stripes even though we are sure that there are also surfactants in the normal cleaner.

The question is: what is the difference between the glass cleaner and the regular cleaner that makes sure that windows become stripeless clean?

One thought we considered but couldn't really work out was that the stripe formation would be something caused by a combination of the marangoni effect and evaporation, similar to the coffee-stain effect which can be overcome by specific tuning of the surfactants as shown here.

Could someone explain how the stripeless cleaning works? Can fluid dynamics explain what happens or is it really something chemical going on?

When searching I also ran into a solution that (at least the manufacturers claim) will also give stripeless clean windows. The interesting thing is that they use pure $\ce{H2O}$ so without any surfactants but also without any dissolved salts like regular tap water has.

Cross-post: https://physics.stackexchange.com/q/56800/7433


texts: Permanent ink from urethane, 99% IPA, and pigment?

texts:
I’m an artist and I started working with recycled plastic bottles as a material recently. I want to paint the plastic and retain its transparency, but acrylic paint won’t stick without priming and generally looks bad. Permanent markers are good, but they leave streaks over large swathes of color and are expensive.
I want to make alcohol ink, which is basically bulk highly pigmented permanent ink that you can paint with or do whatever. I could buy permanent markers and make my own (again, expensive), but I have
solvents (99% iso, mineral spirits, naphtha--no toluene or xylene, though) and lots of dyes and pigments, as well as experience with epoxy resins.
I’ve read that permanent markers are simply a resin (urethane) dissolved in a solvent and pigment is added. I have resin-friendly pigments and was looking at spar (has more resin) or poly urethane as possibly a good choice for the resin. Before I invest in another experiment I can't afford to fail, I was wondering if this would even work or if the two-part epoxy resin I have would work, too.
So my questions are:

What resin should I use?
What solvent for that particular resin?
What ratio of solvent:resin:pigment?

I know thinning epoxy resin can weaken it, but my work is purely decorative. I just need it to stick to the plastic and be ok with low heat for shaping purposes.


texts: Stereochemical outcome after elimination followed by addition

texts:
One of the following diastereomeric chlorides undergoes racemization on heating whilst the other is returned unchanged. Explain.

From the reaction conditions I can see that there must be an elimination of $\ce{HCl}$, presumably via E2 with the base being the amine group on another molecule. Then addition back to the double bond.
However, I have a couple of questions-
Firstly, wouldn't $\ce{HCl}$ add back onto the alkene the other way around so as to form the more stable tertiary heteroatom stabilized carbocation? Which would then be attacked by the chloride ion thereby inducing racemization, and thus it should be impossible to be "returned unchanged".
Secondly, why would one isomer undergo racemization and the other remain the same?


texts: Textbooks and the online reference differ about this and there are more than two answers.


texts: Is the mole fraction used in Raoult's law calculated initially or at equilibrium?

texts:
Raoult’s law states that:

The partial pressure of any volatile constituent of a solution at a constant temperature is equal to the vapour pressure of pure constituent multiplied by the mole fraction of that constituent in the solution

My question:
Is the mole fraction of the constituent of the solution to be considered at the time when equilibrium between vapours dissolving into the solution and rate of evaporation has been achieved or at the beginning when the solution is just formed and evaporation has just begun change the mole fraction of the constituent which we have just calculated?
Also, experimentally, is there much difference in the mole fractions at equilibrium and at the beginning when there is apparently no vapour pressure (for zero vapour pressure in the beginning, I think  we can just close the lid of the container)?


texts: How to analytically quantify a chemical's potential to intercalate DNA?

texts:
This shows that polyphenols (like quercetin) have the potential to intercalate DNA, but at potency 100x less than that of ethidium bromide. How does one analytically measure/quantify "100x weaker"?

I'm also interested in how this could apply for the compound 9-fluorenol (hydrafinil) - and of the relative potency of 9-fluorenol and quercetin in intercalating DNA.


texts: What is sprayed on chromatography paper when developing?

texts: When developing the chromatography paper, what chemical will you use to spray on the chromatography paper?


texts: It is said that $\ce {H2O2}$ behaves like a reducing agent in an external oxidizing environment but along with $\ce {H2SO4}$ a strong oxidizing agent it oxidizes $\ce {FeSO4}$ to $\ce {Fe2(SO4)3}$ in acidic medium. How and why?


texts: Range of distance for Van der Waals force

texts:
Is there any range of distance between the nuclei of the atoms (in Angstrom, say between 4 to 12 Angstrom) within which there will be an occurrence of Van der Waals force (attraction) between them?
For example, say within a distance of 4 A between two atoms of same type, there will van der Waals attraction present. Can such a certainty be obtained? If two atoms are very far apart, then there will be not Van der Waals attraction between them, this is known. So my question is how close should the nuclei of two atoms be so that one can say with certainty that there will be Van der Waals attraction?


texts: Can't nobelium form compounds like other lanthanides/actinides do?

texts:
Over the past week I've been browsing through WebElements just to find out some interesting facts/properties about certain elements in the Periodic Table.

I've just come across the uncommon element nobelium and it looks like it doesn't form compounds with anything despite being an actinide. For example, actinium can form Actinium Trichloride and promethium can form Promethium(III) Fluoride.

Is there a reason why nobelium is so 'special'?


texts: What is the IUPAC name of n-propylbenzene? Is it propylbenzene or 1-phenylpropane, i.e. should the ring or the chain be considered the substituent?


texts: Why are alkanes also called as paraffins?   Is it because they are mainly found from petroleum and natural gas?


texts: So guys, very quick question: Why does bromination occur at exactly this position on the aromatic ring? Has it something to do with the substituents and their respective electronic effects?


texts: Comparing ionic character of group 1 elements

texts:
According to Fajan's rule ionic character should increase down the group as the size of cation increase.
So it must be
$$\ce{LiH < NaH < KH < RbH < CsH}$$
However, the following two sources provide two different opinions. Which one is right?
Source 1

Explanation: As the size of the metal cation increases down the group, the lattice energy of the hydrides decreases down the group. Consequently, the reactivity of the alkali towards hydrogen decreases down the group.
iii. The ionic character of the alkali metal hydrides increases from Li to Cs.
Explanation: Since ionisation enthalpy of alkali metals decreases down the group, tendency to form cations as well as the ionic character of the hydrides increases.

Source 2

But it we are asked to compare the ionic character of hydrides (LiH, NaH, KH, RbH, CsH), we can not use the Fajan's rule. This is because, here the anion is very small ($\ce{H-}$) as compared to the cations (alkali metal cations). The ionic character is this case can thus be compared on the basis of Lattice energy.
Since lithium ion and the hydride ion are approximately of same size, the charge density is high between the two, thus the ionic bond so formed will be very strong and hence more will be the lattice energy.
On coming down the group, the difference in the size of cation and anion increases, thereby making the ionic bond weaker, thus reducing the lattice energy.
Also, lesser will be the lattice energy, lesser will be the ionic character.
Thus, down the group, the ionic character of the hydrides decreases.


texts: Does hyperconjugation and induction always have the same effect?

texts:
My professor does not believe in the hyperconjugative effect. Instead, we only consider inductive effects.

So do both effects have the same general effect? I know for methyl groups both have the same effect; both hyperconjugation and induction can be invoked to explain the electron donating tendencies of the methyl group.

Are there any cases in which the hyperconjugative effect and the inductive effect have opposite effects?


texts:
Enthalpy change of formation means the heat change when 1 mol of the compound is formed from its elements under standard condition.
For example, the enthalpy change for the formation of carbon dioxide gas  is -393.5 KJ/mol

But, I'm confused as the enthalpy change of any element under the standard condition is zero, so shouldn't the enthalpy change of formation of carbon dioxide is also zero as well?

I am missing something but I just couldn't figure out what it is


texts: Do eta-4 benzene ligands participate in Diels Alder or other cycloadditions?

texts:
While refreshing myself on denticity to answer another question, I started to read about hapticity, which is the coordination of a ligand through multiple continuous atoms. A famous case is ferrocene (bis[$\eta^5$-cyclopentadienyl]iron, $\ce{Cp2Fe}$), where all five carbon atoms in each cyclopentadienyl ligand (Cp) are coordinated to the iron center.

Benzene can also be a polyhaptic ligand, forming $\eta^4$ or $\eta^6$ complexes depending on the oxidation state of the metal. In particular, bis(benzene)ruthenium complexes can undergo redox shuttling, where one benzene ligand switches between $\eta^4$ and $\eta^6$.

In the $\eta^4$ complex on the right, the top benzene ligand is now bent out of planarity, implying a break of aromaticity. This compound looks like a good dienophile for a Diels-Alder reaction. The article linked in the Wikipedia page on this switching phenomenon is published in Angewandte Chemie, International Edition, which is behind a paywall for me.

  Does coordination of benzene to a metal in the $\eta^4$ mode activate it toward cycloadditions? Because of paywalls, I would appreciate summaries of articles in addition to links to them. My attempts to find articles using Google Scholar led me to articles about the construction of benzenes by metal mediated cycloadditions, and not to reactions of benzene itself.


texts:
In the observation tables provided in books and websites two different colors are assigned to a specific borax+salt bead in both oxidising and reducing flames. Not all basic radicals show this trend but some like Cu$^+$$^/$$^+$$^2$ does. It appears green in hot condition and blue in cold condition when made using oxidising flame.

My question is what is done to actually reduce the temperature of the borax bead? Is it held under running tap of water or just outside the flame?


texts: Does the alpha effect apply to third row elements?

texts: Alkylperoxy anions are stronger nucleophiles than alkoxides (the so-called alpha effect), but would an alkyldisulfide anion be a better nucleophile than an alkylthiolate anion?


texts: Calculating the percentage of (+)-2- butanol in the sample

texts:
Specific rotation of (+)-2-butanol is 12.5$^{\circ}$ . A sample of 2-butanol containing both the
enantiomers was found to have specific rotation value of –2.8$^{\circ}$ . What is the percentage of (+)-2- butanol in the sample?

I attempted it by letting the percentage of (+)-2-butanol be $x \%$ and therefore percentage of enantiomers in the mixture would be $2x \%$ due to equal contribution by (-)-2-butanol. Since the net specific rotation of the mixture is given to be negative, we know that percentage of excess of (-)-2-butanol would be $(100-2x)\%$. It is also given that specific rotation of pure (+)-2-butanol is 12.5$^{\circ}$, but I am unable to understand how is that useful here.
In it's solution, they have calculated the percentage of (-)-2-butanol as $\dfrac{2.8}{12.5} \times 100=22.4 \%$ and thus percentage of (+)-2-butanol came out to be $\dfrac{100-22.4}{2}=38.8\%$.
I didn't understand this last step, why is the division of 2.8 and 12.5 giving the percentage of (-)-2-butanol?


texts: What is the main difference between Quantum Clusters and Nanoclusters?

texts: I know that Quantum Dots have high quantum yield and ranges from 2nm-10nm, and Nanoclusters have high fluorescence and ranges from 1nm-10nm. But the difference between them is that Quantum Dots exhibits red shift as the size gets larger while vice versa for Nanoclusters. My guess is Quantum Clusters is the combination of both, size is less than 2nm and exhibits red shift as size gets larger. Is this correct? Are there more things that distinguish them to each other?


texts: Are the bonding orbitals in methane equivalent - photoelectron spectrum

texts:
The low energy portion (the part dealing with the $\ce{2s}$ and $\ce{2p}$ electrons) of the photoelectron (PE) spectrum of methane is reproduced below.

(image source)

The reaction being examined is the following one-photon process
$$\ce{CH4 + ~h\nu~ -> [CH4]^{+} + ~e^-}$$

The fact that 2 peaks in roughly 1:3 intensity are observed is often used to argue against the $\ce{sp^3}$ hybridization model for methane. Simply put, how can a model with 4 equivalent $\ce{sp^3}$ bonds produce 2 peaks in the PE spectrum.  The argument then goes on to point out that, according to MO theory, methane has one triply degenerate bonding MO and a second single bonding MO and these two nonequivalent orbitals would explain the 2 peaks in the PE spectrum with their 1:3 ratio (see p. 827 here for an example of such an MO-based explanation).

The PE spectrum of methane shows 2 transitions with 1:3 intensity.  How does one know that it is the methane ground state that is responsible for producing two peaks with a 1:3 ratio in the PE spectrum?  Why couldn't one argue that it is $\ce{[CH4]^+}$, where we clearly have 3 $\ce{C-H}$ bonds containing a pair of electrons and one $\ce{C-H}$ bond with one electron - two different types of $\ce{C-H}$ bonds in a 1:3 ratio - that is responsible for the two peaks in the PE spectrum?

Can the PE spectrum of methane really be used as evidence to argue against the hybridization model?

EDIT:

Poking around on the internet, I came across this Wikipedia article on Orbital Hybridization - Photoelectron Spectroscopy.

It says,

  "There is a popular misconception that the concept of hybrid orbitals
  incorrectly predicts the ultraviolet photoelectron spectra of many
  molecules. While this is true if Koopmans' theorem is applied to
  localized hybrids, quantum mechanics requires that the (in this case
  ionized) wavefunction obey the symmetry of the molecule which implies
  resonance in valence bond theory. For example, in methane, the ionized
  states (CH4+) can be constructed out of four resonance structures
  attributing the ejected electron to each of the four sp3 orbitals. A
  linear combination of these four structures, conserving the number of
  structures, leads to a triply degenerate T2 state and a A1 state.[16]
  The difference in energy between each ionized state and the ground
  state would be an ionization energy, which yields two values in
  agreement with experiment." (emphasis mine)

The bold face portion seems to support my contention (if I'm understanding it correctly) that it is the energy differences between the ground state and the excited state that is responsible for the spectrum.  Therefore, orbital splitting and orbital degeneracies in the excited state are likely an explanation for the observed spectrum.


texts: Why does methane have 4-different bond dissociation energies?

texts:
I will elaborate on my question here.
In my Lecture Notes it is mentioned that for methane, there are 4 different $\text{C-H}$ bond energies. I plotted a quick graph of the bond energies to analyse the trend.

Here the vertical axis represents the bond dissociation energy while the horizontal axis represents the bond dissociation number. Looking at the graph, there is no clear trend so I decided to turn my attention to the structure.
$\text{CH$_4$}$ has the following structure

It is from here that I am unable to proceed. Here are my questions.

Am I barking up the wrong tree by looking at the structure and how do I account for the changing bond energies
Is there a VSEPR structure for molecules like $\text{CH$_3$}$ $\text{CH$_2$}$ $\text{CH}$? If so how do I figure it out.
Why am I even learning about bond energies in the first place? Is there a way I can link this to a bigger picture? I find this topic very interesting and I want to tie up my knowledge neatly here.


texts: For an electron arrangement diagram, is it necessary to show the inner electron shells or is it customary to only show the valency electrons?

texts: Which electron arrangement diagram is correct? The one that shows all electron shells or the one that only shown the valence electron shell?


texts:
I'm simple man who doesn't know much about anything. I just enjoy my life. Lately I like chemistry a lot. I want to learn chemistry at home. How do you recommend I do it?

Do i need to do chemical experiments to become good at chemistry?

I can learn about reactions with books. For example:

O + H2 -> H2O

Also organic chemistry like

C2H5OH + O2 -> CO2 + H2O

What else do I need to learn? What do chemists do all day if all formulas can be calculated on paper?

How does chemist invent new materials?

Can I be theoretical chemist?

Is this a good hobby choice?


texts: Kinetics of the conversion from metal oxide to metal hydroxide in water

texts: How long can a metal oxide such as magnesium oxide remain in solution before being converted to the metal hydroxide?


texts: What happens to iron electrodes (attached to a battery) in copper(II) sulphate solution?

texts:
After a few hours, the following observations were made:

The solution turns green. My guess: $\ce{FeSO4}$ is formed.
There are reddish-brown and black powder deposits on both the electrodes.
The deposits fall down easily when the set-up is shaken a little.

What are the reactions that are occurring?

According to me, the copper is displaced from the $\ce{CuSO4}$ and is deposited on the iron electrode (the cathode), and $\ce{FeSO4}$ is formed as a green solution. What is getting deposited on the anode? Are there ferrous and ferric oxides/hydroxides being formed?


texts: Using osmotic pressure to find the molar mass of a compound

texts:
Working on-board a research vessel somewhere at sea, you have (carefully) isolated 12.5 micrograms $(\pu{12.5E-6 g})$ of what you hope is pure saxitoxin (a non-electrolyte) from a poisonous (and quite cross) puffer fish. You dissolve this sample in $\pu{3.10 mL}$ of water and determine that the osmotic pressure of
  the resulting solution is $\pu{0.236 Torr}$ at $\pu{19 °C}$ $(\pu{760 Torr} = \pu{1.00 atm}).$ What is the molar mass of the compound?

I am having trouble reaching the correct answer of $\pu{310.8 g/mol}$ for this question. I first found the pressure to be $\pu{0.0003105 atm}$ and plugged numbers in for the formula $\Pi = MRT.$ I got $\pu{2.04E-5 mol L-1}.$ I used this to find the amount of substance and got $\pu{6.3E-8 mol}.$

Lastly, I divided $\pu{12.5E-6 g}$ by $\pu{6.3E-8 mol}$ and got $\pu{1.98E-14 g/mol}$ which is not the right answer.

I feel like I have the right process so if you can help show me where I messed up, I would appreciate it.


texts: How can I identify whether a substance is KOH or NaOH?

texts: I've bought $\ce{NaOH}$ or $\ce{KOH}$ (I don't remember which one!) for my electrolyzer and I've tested it. Now I want to improve its performance and I was searching for a better electrolyte when I realized I've forgotten what my current electrolyte is! It is white and has crystal shape, but which one is it, $\ce{KOH}$ or $\ce{NaOH}$? If they are both white how can I know?


texts: Distinguishing Brown Ring Test for Nitrates and Nitrites

texts:
My question is how will one detect the presence of nitrates by brown ring test when nitrites are also present in the solution?

Brown Ring Test for Nitrite
$\ce{NO_2^- + H+ -> HNO2}$
$\ce{3HNO2 -> H2O + HNO3 + 2NO}$
$\ce{FeSO4 + 6H2O -> [Fe(H2O)6]SO4}$
$\ce{[Fe(H2O)6]SO4 + NO -> [Fe(H2O)5NO]SO4 + H2O}$

Brown Ring Test for Nitrate
$\ce{2NO_3^- + 6Fe^2+ +4H2SO4 -> 6Fe^3+ + 4SO4^2- + 2NO + 4H2O}$
$\ce{FeSO4 + H2O -> [Fe(H2O)6]SO4}$
$\ce{[Fe(H2O)6]SO4 + NO -> [Fe(H2O)5NO]SO4 + H2O}$

Note: I personally think that it may have something to do with preventing oxidation of nitrites to nitrates and the release of NO (nitric oxide). But I am not quite sure how to go about that.


texts: Any suggestions for a shock induced material that would illuminate and be capable of being visible for a minimum of three seconds? Non-toxic and minimal heat production would be optimal.


texts: Reactions between enantiomers in a racemic mixture

texts:
As a follow up to this question I started thinking about another question. During racemization, enantiomers are mixed in a equal ratios to form an optically inactive mixture.

What type of reactions can take place between the enantiomers and how would this affect the mixture, if at all?


texts: I was thinking: Could we could make a strong acid-strong base buffer solution? Take, for instance, a mixture of 1 L $\ce{HCl}$ (0.1 M) and 1 L of aqueous salt, $\ce{Na_2SO_4}$ (also 0.1 M), note that $k_2=0.012$ for the polyprotic acid. How can the pH of the mixture be calculated? Additionally, would it be "stable" like a buffer?


texts: Why isn't Mg deposited on the cathode after electrolysis?

texts:
Well here's a question from my book:

A solution containing one mole per liter of each $\ce{Cu(NO3)2}$, $\ce{AgNO3}$, $\ce{Hg2(NO3)2}$ and $\ce{Mg(NO3)2}$ is being electrolysed by using inert electrodes. The values of standard electrode potentials in volts (reduction potentials) are:

$\ce{Ag+/Ag} = +0.80$,
$\ce{Hg2^2+/Hg} = +0.79$,
$\ce{Cu^2+/Cu} = +0.34$,
$\ce{Mg^2+/Mg} = -2.37$

The sequence of deposition of the metals on the cathode will be?

The answer to the above question is: $\ce{Ag}$, $\ce{Hg}$, $\ce{Cu}$.
Why isn't Mg deposited on the cathode? Is it because the reduction potential is negative?
If yes, what exactly is the reason?