A2 LEVEL CHEMISTRY

CHROMATOGRAPHY
SPECTROSCOPY

TEST

Answer all questions
Max 48 marks

	
Name		…………………………………………………………..

Mark		……../42	……....%	Grade ………

1.	Chromatography is an important analytical technique used to separate mixtures into their individual components.
(a)	Define the following terms used in chromatography.
Rf value ..........................................................................................................
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retention time .................................................................................................
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[2]
(b)	Volatile organic compounds that enter soil via waste disposal sites affect the quality of the soil.
	A preliminary step in analysing soil quality involves separation of these volatile components using gas/liquid chromatography.
(i)	What name is given to the process by which components in a mixture are separated during gas/liquid chromatography?
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[1]
(ii)	What are the roles of the gas and liquid in gas/liquid chromatography?
role of gas .............................................................................................
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role of liquid ..........................................................................................
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(iii)	Draw a diagram of a gas/liquid chromatogram for a mixture containing two components.
		
[1]

(iv)	Explain how the gas/liquid chromatogram could be used to determine the percentage composition of each component in the mixture.
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[3]
[Total 9 marks]

2.	This question is about the use of spectrometry in helping to gain information about the structure of organic molecules.
	The major peaks in the mass spectra of two hydrocarbons A and B are shown below.
Compounds A and B have the same empirical formula.

(i)	Deduce the molecular formula of each compound.
Compound A .............................
Compound B .............................
[2]
(ii)	Draw the structural formula of compound A.

[1]
(iii)	Suggest the species responsible for the peak at m/e 41 in the spectrum of compound B.
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[2]
[Total 5 marks]

3.	An industrial chemist discovered five bottles of different chemicals (three esters and 
	two carboxylic acids) that were all labelled C5H10O2.
	The different chemicals had the structural formulae below.
	CH3CH2COOCH2CH3              (CH3)3CCOOH              CH3COOCH(CH3)2
	(CH3)2CHCH2COOH                           (CH3)2CHCOOCH3
(a)	The chemist used both infrared and 13C NMR spectroscopy to identify the two carboxylic acids and to distinguish between them.
	How do both types of spectra allow the carboxylic acids to be identified and distinguished?
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[3]
(b)	The chemist analysed one of the esters by 1H NMR spectroscopy. The spectrum is shown below.

	Analyse the splitting patterns and the chemical shift values to identify the ester.
	Give your reasoning.
	In your answer, you should use appropriate technical terms, spelt correctly.
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[6]
[Total 9 marks]

4.	Compound G can be extracted from sugar-cane and is commonly used in ‘rejuvenating’ skin creams because it helps to remove some of the dead cells from the skin surface.
	The molecular formula of G is C2O3H4 and the compound contains two different functional groups containing oxygen atoms.
	The infra-red and mass spectra of G are shown below.

(a)	After inspection of the mass spectrum of G, an analyst wrote the comment:
	‘The molecular ion peak appears to be missing from the spectrum.
The base peak is due to a fragment ion with m / e = 31.’

(i)	Explain what is meant by the following terms.
molecular ion peak ...............................................................................
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base peak .............................................................................................
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[2]
(ii)	Suggest why the molecular ion peak is missing from the spectrum.
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[1]
 (b)	The structure of compound G is shown below.
		
	Show how the infra-red and mass spectra confirm this structure. In your answer, you should suggest a possible structure for the ion that gives the base peak at
m / e = 31 in the mass spectrum.
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[4]

(c)	The structure of compound G is shown below.
		
	Sketch the 1H n.m.r. spectrum of compound G and label the relative peak areas. Label any peaks that would be lost from the spectrum on shaking with D2O.

[4]
[Total 11 marks]

5.	Forest fires release a large number of organic compounds into the atmosphere. These include alcohols and carboxylic acids. An environmental chemist is trying to identify one of these compounds in a sample of air.
	The unknown compound X is thought to be a carboxylic acid with empirical formula C2H3O2.
(a)	Mass spectrometry is used to help deduce the molecular formula of compound X.
(i)	Describe how the mass spectrum of compound X is used to determine its relative molecular mass.
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[2]
(ii)	The relative molecular mass of compound X is shown to be 118.
	Explain how this relative molecular mass and the empirical formula are used to deduce that the molecular formula of compound X is C4H6O4. Show any working.
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[2]

(b)	The two dicarboxylic acids with molecular formula C4H6O4 are shown below.
	
	N.m.r. spectroscopy is used to deduce which of these is the unknown compound.
	The environmental chemist obtains an n.m.r. spectrum of compound X and then adds some D2O and obtains a second n.m.r. spectrum.
(i)	What difference would you expect between these two n.m.r. spectra?
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[1]

(ii)	The n.m.r. spectrum of compound X in D2O is shown below.

		Use this spectrum to identify which of the two carboxylic acids is compound X.

•	Draw the correct structure in the box above the spectrum

•	Use labels to show which protons in the structure are responsible for 
			which peaks in the spectrum

•	Explain your reasoning by referring to the relative peak areas and the 
	spin-spin splitting patterns of the peaks

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[6]

(iii)	Predict the number of peaks and any spin-spin splitting expected on the n.m.r. spectrum of a solution in D2O of the other acid with formula C4H6O4.
	Explain your reasoning.
	(The two possible structures of compound X are shown again below.)
		
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[3]
[Total: 14 marks]