Nicolau Saker Neto
  • Member for 8 years, 9 months
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When pigments absorb light only around a single particular wavelength, why aren't they still white?
5 votes

As others have brought up, indeed the absorption features of most compounds with electronic transitions in the visible light range are rather broad, and this breadth is important in generating a ...

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What is an example of an exothermic reaction with negative ∆S?
10 votes

A very simple reaction which is readily accessible for study is the dimerisation of nitrogen dioxide: $$\ce{2 NO2(g) -> N2O4 (g)}$$ This process is has a standard reaction enthalpy change of $\rm{\...

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What is the error in the number of aromatic isomers of C7H8O?
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9 votes

You are completely correct - the furan derivatives you've drawn display unquestionable aromatic character, though the "strength" of their aromaticity is somewhat lower than various other ...

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Is stoichiometric imbalance in polymerization important if the process has an evaporation step?
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0 votes

Yes, in theory, an idealised step-growth AA/BB monomer polycondensation is exquisitely sensitive to an imbalance in the ratio of the functional groups A and B present in the reaction mixture, as is ...

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What is the strongest oxidising agent?
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31 votes

Ivan's answer is indeed thought-provoking. But let's have some fun. IUPAC defines oxidation as: The complete, net removal of one or more electrons from a molecular entity. My humble query is thus - ...

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Reaction of cyclooctatetraene with sulfuric acid
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9 votes

This is a rather unusual and interesting case of aromaticity, which has been given a special name: homoaromaticity. The Wikipedia page does a quite nice job of explaining what's going on. As you state,...

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What is hydrogen-rich water?
12 votes

I was completely unaware of the concept of hydrogen-rich water, and although there is a lot of misinformation and quackery around it, a quick search on Google afforded an article (whose quality I ...

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Why is chemistry unpredictable?
37 votes

Let me contribute two more reasons which make chemistry hard to analyse from a purely theoretical standpoint. The first one is that, viewed very abstractly, chemistry essentially relies on the study ...

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Finding the equivalent point of a weak polyprotic acid when reacted with a strong base
3 votes

A simple way to determine whether an equivalence point in a titration is the last one is to figure out the volume of titrant added for the first titration point, then realize all subsequent ...

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Shortcut for calculating pH of mixtures
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9 votes

Case 1: Mixing equal volumes of two solutions with a pH difference of 1. Initially we have: \begin{array}{|c|c|c|} \hline &[\ce{H+}]& \mathrm{pH} &n_\ce{H+}\\ \hline a& x & \log x ...

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What does radioactive decay look like?
6 votes

If you somehow magicked into existence a macroscopic solid cube of some radioisotope with a half-life in the range of minutes to hours, you would probably see the cube become blindingly white-hot then ...

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Do strong acids actually dissociate completely?
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12 votes

Yes, for sufficiently strong acids, in sufficiently dilute conditions, in sufficiently basic solvents. However, things are hazier than you might expect, and depending on your definition, "clear-...

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Question about null space balancing method
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4 votes

Fortunately this issue was just caused by a small oversight. In the midst of so many coefficients, you accidentally skipped the second nitrogen atom in $\ce{NH4NO3}$, which changes the fifth element ...

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Electron configuration of iron(I) cation
3 votes

Isolated in a vacuum, in the absence of external fields, the first configuration is correct - $[\ce{Ar}]\mathrm{(3d)^6(4s)^1}$ is the ground electronic state of the iron(I) cation $\ce{Fe^{+}}$. More ...

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Can carbon dioxide be reduced to carbon monoxide and oxygen to produce energy?
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20 votes

Unfortunately, the question as stated is thermodynamically impossible. Let's look at the proposed reaction: $$\ce{CO2(g) -> CO(g) + O(g)}$$ This reaction is simply a bond dissociation (specifically,...

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Non-computational theoretical chemistry
5 votes

I think I can answer this in the affirmative. There are articles which find connections between abstract mathematics and chemistry, sometimes even bypassing physics altogether. Of course, these kinds ...

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Is benzene a polymer of ethyne?
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17 votes

The scientist who coined the term polymer, Jöns Jacob Berzelius, used the word to refer to different substances which had the same empirical formula. In this sense, benzene is a polymer of ethyne (...

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Why is the overall change in entropy of Photosynthesis positive?
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3 votes

To answer this question, we need to be clear whether we are talking about the change in entropy of the system, the surroundings and the Universe. With regards to the entropy of the Universe, the ...

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Why is the melting point of p-dichlorobenzene higher than those of o-dichlorobenzene and m-dichlorobenzene?
5 votes

I had some comments to make, but they're too large to actually fit into the comments, so I'm making another answer. I'll take the opportunity to give a bit of background, which may be going a little ...

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Amine vs Amide Solubility
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5 votes

The mixing of two compounds is a process which requires consideration of three types of interactions: solute-solvent, solvent-solvent and solute-solute. You make a good argument for the solute-solvent ...

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Is the Henderson–Hasselbalch equation volume independent?
8 votes

For a much shorter and clearer explanation of this problem, look here. The Henderson-Hasselbalch (HH) equation is not to blame here. It is an approximate equation, with a certain region of validity. ...

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On heating in the Earth's atmosphere, can magnesium react with nitrogen to form magnesium nitride?
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23 votes

A large pile of grey magnesium powder, when lit in air, produces a smouldering pile which cools down to reveal a crusty white solid of magnesium oxide. However, if you break apart the mound, you can ...

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In aminobenzoic acid, do we have three different pKa's?
7 votes

The two acidity constants in 4-aminobenzoic acid are due to the loss of $\ce{H^+}$ from the protonated form of 4-aminobenzoic acid (the 4-carboxyphenylammonium cation), transforming it into 4-...

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In acid/base chemistry, are there amphoteric substances that undergo something that resembles disproportionation in redox chemistry
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5 votes

As I mentioned in the comments, I know of one case where a polyprotic acid has a second proton which is more acidic than the first: the aqueous pervanadyl complex, $\ce{[VO_2(H_2O)_4]^+}$. According ...

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How to switch Mercury-vapor lamp between UVA and UVC bands?
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9 votes

TL;DR - You need two different lamps, one that has a phosphor to absorb the 254 nm light, and one that doesn't. Alternatively, you can use one lamp, and use a filter to select the wavelengths. ...

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What is the correct value of the Avogadro constant? And how was it derived?
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24 votes

Whenever you're looking for accurate fundamental physical constants, CODATA recommended values are the way to go. As of May 20, 2019, Avogadro's constant is now truly an exact value, with infinite ...

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Does hydrogen really have seven isotopes?
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28 votes

Yes, there are seven known isotopes of hydrogen, though only two ($\ce{^1H}$ and $\ce{^2H}$) are stable with respect to nuclear decay, and only three ($\ce{^1H}$, $\ce{^2H}$ and $\ce{^3H}$) exist/can ...

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What are some other gases that liquify at around the same temperature as ammonia?
1 votes

Wikipedia has a large list of gasses in ambient conditions here as well as a list of refrigerants here. You can sort them in order of boiling point by clicking on the small black triangles just ...

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Which gas is a oxidizing agent as well as a reducing agent?
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11 votes

I'm guessing your teacher is looking for sulfur dioxide as the answer, but I don't see how or why you're supposed to be able to arrive to this answer logically. Either you'd need to read about it ...

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Transition metals and their ability to form coloured ions
2 votes

Edit: In this answer I've focused on solid solutions of transition metals, which are kind of half-way between pure transition metal solid compounds, and aqueous solutions of transition metal compounds ...

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