New answers tagged

1

Well, interesting question, I would re-word your question as "How can one determine an atomic mass with high accuracy using gravimetric analysis? Precision simply implies that you repeated a measurement and it agrees very well with itself even though it may be wrong. What we desire is high precision and high accuracy. Almost all the naturally occurring ...


4

As Buck Thorn and I commented elsewhere, the antioxidant activity of carotenoids has been determined using $\ce{DPPH}$ radical ($\ce{DPPH^.}$)(Refs 1 & 2). According to Ref.1, antioxidant activities of the isolated α- and β-carotene have been analyzed in five different concentrations of 0.001, 0.005, 0.01, 0.05, and 0.1% ($w/v$) using several assays: The ...


2

It is not always a good idea to focus only on $\ce{^{13}C}$-$\mathrm{NMR}$ when you are doing structure elucidation on unknown compound using spectral data. Yes, $\ce{^{13}C}$-$\mathrm{NMR}$ gives you valuable info, so does FTIR to some extent. Yet, $\ce{^{1}H}$-$\mathrm{NMR}$ gives the most info about the compound as I depicted in following diagram: All ...


2

The test is administered by breathing through a tube, and the results become apparent immediately. Indeed, this has something to do with oxidation of alcohol. As soon as the alcohol in the exhale reaches the contents of the test tube, the latter changes its color, and the police guys put you in the handcuffs. Or it doesn't, and they don't. That's a wonderful ...


6

Since there were no further suggestions, I decided to use the references from my comment in an answer, which, I believe, is element 99, einsteinium. Both single crystal x-ray diffraction (SCXRD) and powder x-ray diffraction (PXRD) have certain sample requirements/limitations: Mass/amount PXRD: lower limit is in micrograms region, ideally at least a couple ...


3

In this case, cerium(IV) sulfate is a strong oxidising agent, hence, using $\ce{HCl}$ would likely be oxidised to form $\ce{Cl}$ of higher oxidation state. Therefore, the titre would be vastly higher than expected. $\ce{HNO3},$ on the other hand, is an oxidising agent and would oxidise $\ce{Fe}$ to a higher oxidation state than expected (of $\ce{Fe^3+}$). ...


4

For "burning" of paper by sulphuric acid, the better term would be "aggressive dehydration". Note that aqua regia is rather a diluted acidic mixture without significant dehydrating or oxygen based oxidation behaviour, but manifests aggressive chloration behaviour, that dissolves precise metals. Cellulose has quite good endurance against chlorine, which is ...


1

Concentrated and strong acids like sulfuric acid are substances that extracts water anywhere and everywhere to react with and make H3O+ ions. They are even able to extract water from the cellulose of the paper, as cellulose is made of carbon plus water. So a drop of sulfuric acid on paper burns it, or rather transforms it into charcoal. The word "burn" is ...


5

Structure elucidation from spectrocopic analysis needs some experience. I have feeling that you are novice to this field by your explanation of the structure. You cannot determine the molecular formula by the data given and, hence you cannot determine the degree of unsaturation of the molecule. Yet, based on $\ce{^1H}$-$\mathrm{NMR}$, you can propose there ...


4

My personal opinion is: screw IR, it does not give useful information – but NMR does. The first thing to check in the proton NMR is the integrals of your signals (I used a ruler on my PC screen – which interestingly enough seems to be good enough for this case!). You have clearly aromatic protons, one singlet at around $\pu{5 ppm}$ and one larger one at ...


3

Do you think this is the correct molecule? No, for three main reasons: As Ezze states in the comment, there are strong indications for phenyl groups in the NMR spectra. One phenyl group corresponds to 4 double bond equivalents, which is incompatible with your molecular formula (too many hydrogen atoms). The H-NMR has too few multiplets for your proposed ...


1

The distance between two peaks is characterized not by $\Delta m$ but rather by mass resolution. The distance between the peaks is often referred to as $\Delta m$ and assumes that the $z = 1$, but this is not always the case. IUPAC addresses this in detail: Resolution, DOI: 10.1351/goldbook.R05318 (10 per cent valley definition): Let two peaks of equal ...


6

I wanted to back up my comment and make sure it's justified, so I decided to flip through Gross'Mass spectrometry: a textbook [1] and it looks like there are indeed basically two possible variations, including distance between $m/z$ values, as you suggested: {Distance | difference | mass difference} between {peaks | signals | peak tips} {Difference in $m/z$ ...


0

Hmm, I haven't heard about such a term. After a quick search in the IUPAC suggested terminilogy I haven't found anything either. Perhaps there simply is no name for this quantity. I guess you can simply call it separation of the peaks.


1

When you ask for a precision of 0.1 ppm, I assume you actually mean the detection limit? A very common method for quantitative analysis of peroxide content is iodometric titration: the peroxides react with potassium iodide forming free iodine which is subsequently titrated with thiosulfate. It is basically at straight forward method, which only requires ...


0

You can recognize Fe(III) by adding some thiocyanate ion to the solution, which must be at least a little acidic. If it contains Fe(III) ions, it will turn dark red. This test is specific to iron. Copper(II) ion can be recognized by adding some potassium iodide to its solution, which must be at lest a little bit acidic. A brown precipitate should appear ...


Top 50 recent answers are included