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# Tag Info

8

While calcium sulfate is usually termed insoluble, it is not the ‘sitting at the bottom like a rock’ type insoluble; rather, it is the ‘there’s no practical way for me to get the two ions into the same solution without precipitation, but I’m still able to identify both ions in solution’ type insoluble. Those sentences don’t really help, so let’s look at ...

6

I would probably also use the method Buck has suggested, but let’s say the NMR broke down or somebody is measuring a $\ce{^13C}$ of $\pu{2.5mg}$ meaning it will be blocked until tomorrow; in this case, we can still extract more information from the mass spectrum. In addition to the molecule peak at 122, you have: a chlorine-containing fragment $m/z=93$ a ...

6

Being an NMR fan myself I would inspect that NMR spectrum: The integrals suggest you have 11 $\ce{^1H}$ or a multiple thereof (the number under each peak is the normalized integral, which is proportional to the number of protons represented by the multiplet). That leaves you with $\pu{87 Da -11 Da}=\pu{76 Da}$ to explain. If you throw in an oxygen you ...

5

To answer this question, we have to assume that the given buffer solution is an ideal solution of which the total volume of it always equals to the summed volumes of sodium ethanoate ($\ce{NaOAc}$) and $\ce{HCl}$ solutions when they are added together. It should also be assumed that $\mathrm{p}K_\mathrm{a}$ of ethanoic acid (acetic acid; $\ce{HOAc}$) is ...

4

Intensity is (in general) proportional to sample concentration, so yes, if you are performing IR in solution, then an overly dilute sample would have less intense peaks. But solution IR is somewhat uncommon; I suspect you are either doing IR on your sample in neat form (using an ATR stage) or in a pressed KBr plate? If the latter, you may not have used ...

3

I think all modern teaching labs use attenuated total reflectance (ATR)-FTIR systems... you place some crystals and then collect the spectrum right away. ATR is least sensitive technique because the IR penetrates only only a few nanometers of the sample. In good old school times, one would dry the sample-literally bone dry, then oven-dried KBr was ground ...

2

I like both answers provided before me where one has used exclusive use of internet to suggest structure by NMR spectrum, and the other has used thorough analysis of mass spectrum. Although these two are valuable techniques, I feel OP needs to analyse step by step analysis of spectra given to predict the structure since he/her seemingly in a graduate course, ...

2

First, the aniline is converted to a diazonium halide salt in the presence of acid and sodium nitrite, per this reference. Then, the diazonium salt reacts with the phenol to give an azo compound, per this reference (see the section entitled Coupling reactions of diazonium ions Note that the diazonium ion is shown reacting with the para position of the ...

2

Generally, ashes of natural samples (e.g. plant material or soil) do not actually contain chemical compounds like $\ce{Na2O}$, $\ce{P2O5}$, $\ce{SO3}$, $\ce{K2O}$ etc. These are just the reference compounds for the calculation of results of the elemental analysis.

1

You are right about the limitations of century old Lassaigne's method. Why are they still teaching it? Modern day CHNSO elemental analysis is done with gas chromatograpy systems. If you are quoting from a book, provide a reference. This is an excerpt from a 1953 work Sulfur in Organic Compounds, by a Modified. Lassaigne's Method ACTA CHEMICA SCANDINAVICA 7 (...

1

In electrospray ionization, a molecule can end up with an extra proton or an extra cation. Either one of these +1 charged species is accelerated and detected in the mass spectrometer (negative charged particles or neutral species are not; if there are multiple cations, they would supposedly repel each other once the solvent is gone, and not fly together). ...

1

Proton NMR (1D) acquisition time can vary by orders of magnitude depending on concentration (sample amount), instrument sensitivity and relaxation times. For a standard experiment it is on the order of minutes.

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