A2 LEVEL CHEMISTRY

4.3.1 CHROMATOGRAPHY
4.3.2 SPECTROSCOPY

ASSESSED HOMEWORK

Answer all questions
Max 44 marks

	
Name		…………………………………………………………..

Mark		……../44	……....%	Grade ………

1.	α-Amino acids are found in human sweat. A student had read that chromatography could be used to separate and identify the amino acids present in human sweat.
	The student used Thin-Layer Chromatography (TLC) to separate the α-amino acids in a sample of human sweat and discovered that three different α-amino acids were present.
(i)	Name the process by which TLC separates α-amino acids.
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[1]
(ii)	The chromatogram was treated to show the positions of the separated α-amino acids.
	Explain how the student could analyse the chromatogram to identify the three
α-amino acids that were present.
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[2]
(iii)	Several α-amino acids have structures that are very similar.
	Suggest why this could cause problems when using TLC to analyse mixtures of α-amino acids.
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[1]
[Total 4 marks]

2.	Chromatography is a versatile technique that may be used to separate and identify compounds.
(i)	Name a type of chromatography that is used to separate and identify dissolved substances.
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(ii)	State what quantitative value may be determined from the chromatogram to identify the substances present in the solution.
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(iii)	Sketch a chromatogram to show how the value in (ii) is determined.

[1]
[Total 3 marks]
 
3.	(a)	Gas-liquid chromatography is used to separate and identify gases and liquids.
(i)	State what quantitative value is normally used to identify the components in this type of chromatography.
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[1]
(ii)	Sketch the chromatogram to show how the value in (i) is determined.

[1]
(b)	State the physical process on which the separation used in gas-liquid chromatography depends.
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[1]
[Total 3 marks]
4.	A mixture of tripeptides can be analysed by using gas chromatography, coupled with mass spectrometry.
	Summarise how each method contributes to the analysis.
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[3]
[Total 3 marks]

5.	In this question, one mark is available for the quality of use and organisation of scientific terms.
	The structural formulae of three isomers of C3H9NO are shown below.

	Describe the similarities and differences you would expect to see when comparing the
•	infra-red spectrum of each isomer
•	mass spectrum of each isomer.
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[5]
Quality of Written Communication [1]
[Total 6 marks]

6.	In this question, one mark is available for the quality of the use and organisation of scientific terms.
	Describe and explain the different ways that a high resolution n.m.r. spectrum can give information about a molecule.
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[7]
Quality of Written Communication [1]
[Total 8 marks]

7.	Unknown compounds are often identified by n.m.r. spectroscopy.
	Part of the n.m.r. spectrum of butanone is shown on the axes below.

(i)	State which part of the butanone molecule is responsible for peak A at d = 2.1.
	Explain your reasoning.
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[2]
(ii)	Explain why peak B is split into a quadruplet.
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(iii)	Predict the remainder of the n.m.r. spectrum of butanone by sketching it on the axes above.
[2]
(iv)	Write the relative peak area above each of the peaks on the completed spectrum of butanone.
[1]
[Total 6 marks]

8.	Lactic acid produces an n.m.r. spectrum in D2O with peaks at chemical shift values of 1.4 ppm and 4.3 ppm.
(i)	On the axes below, sketch the high resolution n.m.r. spectrum of lactic acid in D2O.
	Show any splitting patterns and state the relative areas of the two peaks.

[4]
(ii)	How many peaks would you expect if the n.m.r. spectrum of lactic acid was run in an inert solvent rather than in D2O? Explain your answer.
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[2]
[Total 6 marks]

9.	Thua nao is a traditional sauce made in Northern Thailand by fermenting cooked soybeans. Its unique flavour is due to a range of volatile compounds formed during the fermentation.
	One of these volatile compounds is 3-hydroxybutanone.
	
(a)	State the meaning of the term volatile.
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[1]
(b)	Several hydroxyketones with similar boiling points can be separated from the fermentation mixture.
	Describe a method, which does not involve spectroscopy, that could be used to distinguish 3-hydroxybutanone from the other hydroxyketones.
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[4]
[Total 5 marks]