Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

A range of analytical methods is used to assemble an overall picture of complex molecules. By itself, each method supplies different details about complex molecules, but together they can provide useful structural information.
(a)[3]

Complete the table by naming the technique that can supply the correct structural information for: • three-dimensional arrangement of atoms and bonds in a molecule • chemical environment of protons in a molecule • identity of amino acids present in a polypeptide.

(b(i))[1]

One general way of separating organic molecules is chromatography. Briefly explain the chemical principles behind paper chromatography.

(b(ii))[1]

One general way of separating organic molecules is chromatography. Briefly explain the chemical principles behind thin-layer chromatography.

(c(i))[2]

Mass spectrometry together with NMR spectroscopy is often sufficient to determine the structure of a simple organic compound. The organic compound N gave a mass spectrum in which the ratio of the M:\(\text{M}+1\) peaks was \(5.9\!:\!0.20\), and which had a \(\text{M}+2\) peak of similar height to the M peak. Calculate how many carbon atoms are present in one molecule of N.

(c(ii))[1]

Deduce which element, other than carbon and hydrogen, is present in N.

(c(iii))[1]

Explain how many atoms of this element are present in one molecule of N.

(c(iv))[2]

The NMR spectrum of N is shown. State the empirical formula of N and, using the NMR data, suggest the structural formula of N, explaining your reasons.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: X-ray crystallography for three-dimensional structure

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