Organic Analysis (AQA A Level Chemistry)

Exam Questions

3 hours45 questions
1a2 marks

This question is about halide ion tests.

i)
Give the formula of a reagent that would produce a cream-coloured precipitate when added to an aqueous solution of magnesium bromide.

ii)
The identity of the anion may be confirmed by testing the solubility of the cream-coloured precipitate in ammonia solution, as shown in Table 1.

Table 1

 

Solubility in dilute ammonia

Solubility in concentrated ammonia

A

insoluble

insoluble

B

insoluble

soluble

C

soluble

insoluble

D

soluble

soluble


State which pair of responses helps to confirm the identity of the anion from Table 1.

1b2 marks

Chemical tests can be used to distinguish between different organic molecules.

State the chemical tests and any observations a student could use to distinguish between the following molecules.

CH3CH2CH2CH2CH2OH and CH3C(CH3)(OH)CH2CH3

1c1 mark

Three qualitative tests are carried out on a solution of an unknown compound.

Test 1: On heating with NaOH (aq), a pungent smelling gas evolves which turns red litmus paper blue.

Test 2: On addition of AgNO3 (aq), a white precipitate forms which is soluble in dilute NH3(aq).

Test 3: On addition of Na2CO3 (aq), there is no visible reaction.

State the identity of the unknown compound.

1d1 mark

Under certain conditions, butan-1-ol can be oxidized to the compound with infrared spectrum shown in Figure 1.

Figure 1

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State the name of the compound that has produced the spectrum shown in Figure 1

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2a1 mark

State what the molecular (parent) ion, M+ peak, in the mass spectrum of a hydrocarbon containing 12C and 1H represents.

2b2 marks

Ethane-1,2-diol is commonly used as anti-freeze in cars. Ethane-1,2-diol very quickly oxidises to ethanedioic acid, (COOH)2, even under the conditions shown in Figure 1.

Figure 1

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Ethane-1,2-diol reacts in a similar way to ethanol. However, ethanol requires stronger oxidising conditions to be converted into ethanoic acid.

Explain how you would change the apparatus shown in Figure 1 to achieve this oxidation of ethanol.

2c2 marks

Geraniol is an organic molecule that contains alkene and alcohol functional groups.

Give one chemical test that you could use to confirm the presence of each of the two functional groups and predict a result for each test.

2d2 marks

The mass spectrum of geraniol is shown in Figure 2 below.

Figure 2

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i)
State how this mass spectrum can be used to confirm the molar mass of geraniol.

ii)
Give the formula of an ion that could be responsible for the peak at m/ z = 69.

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3a1 mark

A sample of propanone, CH3COCH3, was heated under reflux with potassium dichromate (VI) acidified with sulfuric acid, and then the mixture was distilled.

Apart from the peaks due to the C—C and C—H bonds, what peak(s) would be present in the infrared spectrum of the distillate.

3b2 marks

Compounds A and B shown in Figure 1 can be analysed to obtain infrared and mass spectra.

Figure 1

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Suggest the molecular formulae of two ions responsible for peaks in the mass spectrum of A that are not in the mass spectrum of B.

3c3 marks

This question is about organic compounds containing fluorine and chlorine.

The use of chlorofluorocarbons as refrigerants has ceased due to concerns about their effects on the ozone layer. One such compound is dichlorodifluoromethane.

A different refrigerant contains 34.0% chlorine and 54.5% fluorine by mass, with the remainder being carbon.

Calculate the empirical formula of this compound.

3d2 marks

The mass spectrum in Figure 2 was obtained for the compound mentioned in part (c).

Figure 2

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i)
Use the mass spectrum in Figure 2 to show that the empirical and the molecular formulae of the compound mentioned in part (c) are the same.

ii)
Suggest the species responsible for the peak at m/z = 69. 

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4a2 marks

This question is about some isomeric alcohols with molecular formula C5H12O.

Some alcohols were heated with potassium dichromate (VI) and sulfuric acid. The organic compounds were separated from the reaction mixtures and purified.

The infrared spectra of two of these organic compounds are shown in Figure 1.

Figure 1

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Deduce, using Table 1 from the Data Sheet, the type of compound responsible for each spectrum.

Include in your answer references to wavenumbers and their corresponding bonds.

4b2 marks

State what is meant by the term ‘fingerprint region’ on infrared spectrums and explain how this can be used to identify between primary, secondary and tertiary halogenoalkanes.

4c1 mark

Figure 2 shows the infrared spectrum a student obtained of an organic molecule which contains carbon, hydrogen and oxygen atoms.

Figure 2

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Use information from the infrared spectrum to explain how the student deduced that the spectrum shows the presence of a carbonyl group.

4d1 mark

Group 2 metals can react with sulfate ions, SO42-. The formulas of Group 2 sulfates are shown below.

BaSO4             SrSO4              MgSO4            CaSO4

Place the sulfates in order of decreasing solubility.

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5a2 marks

A technician was asked to identify the contents of an unlabelled bottle of chemicals. They believed that the contents may contain either sodium nitrate or sodium sulfate.

i)
State the reagents the technician would need to use to determine if sodium sulfate was present.

ii)
Describe the observations they would see if the bottle tested positive for sodium sulfate.
5b1 mark

State the ionic equation, including state symbols, for barium reacting with sodium sulfate.

5c2 marks

In an experiment to prepare a sample of ethanal, CH3CHO, ethanol, C2H5OH, is reacted with acidified potassium dichromate (VI) and the reaction mixture is distilled. The infrared spectra for ethanol and ethanal are shown in Figure 1.

Figure 1

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yRyC0~xM_10

 

i)
State the bonds that give rise to the absorption in the ethanol spectrum at 3400 cm-1 and the absorption in the ethanal spectrum at 1720 cm-1.

ii)
Explain why the absorption at 3400 cm-1 in the ethanol spectrum does not appear in the spectrum for ethanal.
5d2 marks

The reaction mixture in part (c), was left for several days and another infrared spectrum taken. It was observed that a new absorption was present between 2500 - 3000 cm-1.

Using Table 1 from the Data Sheet, explain this observation.

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1a3 marks

The following two compounds will both react with sodium hydroxide to produce the same product.

Figure 1

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i)
Draw the structure of the product formed when the compounds in Figure 1 react with dilute aqueous sodium hydroxide. 

ii)

State which compound would be converted into the product more quickly, if the reaction was done at the same temperature with the same concentration of sodium hydroxide. Explain your answer.

1b1 mark

State how you could use infrared spectroscopy to determine that the reaction in part (a) had taken place.

1c2 marks

1-chloro-3-methylbutane underwent the same reaction as is stated in part (a), and produced a product which is a structural isomer of the product in part (a).

Name the product of the reaction following the IUPAC rules and draw the structural formula of the product.

1d5 marks

A group of students are trying to determine the identity of three isomeric organic compounds, R, S and T.

All three compounds were prepared from the dehydration of 2-chlorobutane, have the same molecular formula, and will all decolourise bromine water. S and T have the same structural formula.

Use this information to draw the displayed formula of R, S and T. Suggest the type of isomerism which is shown between R and S and between S and T.

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2a2 marks

You are provided with the following selection of organic compounds, to investigate using test-tube reactions.

Figure 1

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State the simple test-tube reaction which could be done to distinguish between Compound B and Compound C, including the observations that could be made.

2b4 marks

State the simple test-tube reactions that could be done to distinguish between Compound A and Compound D from part (a), including the observations that could be made.

2c5 marks

Compound D in part (a) can be formed from an alcohol if the correct reagents and conditions are used for the reaction.

i)
State the reagents, conditions and any observations that would be made during the above reaction.

ii)
Give the IUPAC name of the alcohol which would need to be used and write an equation using structural formulae for the reaction. 
2d3 marks

A student claims to have fully oxidised a different primary alcohol than that in part (c). The student analysed their product and obtained the following IR spectrum.

Figure 2

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Use the spectrum in Figure 2 to suggest whether full oxidation has taken place.

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3a6 marks

A group of students are asked to distinguish between four samples of different organic compounds.

The four samples are as follows:

  • A primary alcohol
  • A tertiary alcohol
  • An aldehyde
  • A carboxylic acid

Describe how the group of students could distinguish between the four types of organic compounds stated above, using the minimum number of tests necessary on each sample.

3b2 marks

One of the students wanted to distinguish between three compounds using mass spectrometry. The three compounds are shown below in Figure 1.

Figure 1

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Explain why determining the exact mass using mass spectrometry would not help in distinguishing between the samples of X, Y and Z shown in Figure 1.

3c2 marks

The three compounds from Figure 1 in part (b) were analysed using IR spectroscopy. The spectrum of one of the compounds is shown below:

Figure 2

yRyC0~xM_10


Identify which of the three compounds X, Y or Z this spectrum belongs to. Justify your choice.

3d2 marks

Explain why infrared spectroscopy alone could not be used to distinguish between the compounds X and Y from Figure 1 in part (b).

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4a2 marks

Infrared spectroscopy is a common analytical tool used in chemistry, to identify or distinguish between different organic compounds.

State how an IR  spectrum could be used to prove that a ketone was butan-2-one. 

4b2 marks

Breathalysers are used to test whether someone has been drinking alcohol while driving. Early models of breathalysers used chemicals which changed colour during an oxidation reaction.

Inside the breathalyser, ethanol was oxidised to ethanoic acid using the same reagents and the same oxidation reaction which would be completed in a lab.

State the reagents which are used to cause this oxidation and state the colour change which would be observed.

4c6 marks

The mass spectrum of the ketone, hexan-2-one has a large fragment ion at m/z = 43.

i)
Suggest two possible structures for this fragment ion.

ii)
Write an equation for the formation of each structure from the molecular ion.
4d7 marks

An organic molecule, J, has the following composition by mass.

  • 62.1% carbon
  • 10.3% hydrogen
  • 27.6% oxygen

In the mass spectrum of J, the molecular ion peak has a value of m/z = 116.

i)
Use this information to determine the molecular formula of J.

ii)
State how an IR spectrum could be used to prove that compound J is a carboxylic acid.

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5a2 marks

A student was investigating the structure of three hydrocarbons, L, M and N.

L and M are isomers.

L has two stereoisomers, but neither of the other compounds do.

Define the term stereoisomer and explain the key feature which must be present in L for it to show stereoisomerism.

5b2 marks

The homologous series that L and M belong to have the general formula CnH2n and the homologous series of N has the general formula CnH2n+2.

State a simple test-tube reaction that could be done to distinguish between L and N, including the observations you would see.

5c2 marks

Simple test-tube reactions like those in part (b) can also be used to distinguish between the following organic compounds.

2-bromopropane and hexane.

State the test-tube reaction which could be used and any observations that would be seen.

5d2 marks

Simple test-tube reactions like those in part (b) and part (c) can also be used to distinguish between the following pair of organic compounds.

Pentan-3-ol and 3-methyl-pentan-3-ol

State the test-tube reaction which could be used and any observations that would be seen.

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1a3 marks

The organic compounds labelled A to E in Figure 1 are all produced by living organisms.

Figure 1

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The infrared spectrum of one the compounds A to E is shown in FIgure 2.

Figure 2

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Analysis of the same compound showed it have the following percentage composition by mass: C = 78.94%; H = 10.53%; O = 10.53%. 

Use the information above to identify which compound A to E is present.       

1b6 marks

Some students are investigating the identity of four unlabeled lab chemicals, W, X, Y and Z, whose labels have fallen off the bottles.

The students completed a number of simple investigations. Their findings are given below.

Compound W can be oxidised to form compound Y.

Compound Z can be reduced to form compound X.

Compound Y and compound Z share the same molecular formula, C3H6O.

Compound Y was the only compound to give a silver mirror when warmed with Tollens’ reagent.

Use the information obtained by the students to identify compounds W, X, Y and Z giving each of their IUPAC namesJustify your answers for W and X.

1c2 marks

Clenbuterol, shown in Figure 1, is considered a performance enhancing drug and is believed to increase short term work rate and cardiovascular output.

Figure 1

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Determine the m/z value of the molecular ion, M+, of clenbuterol. Explain your answer.

1d5 marks

Two students, P and Q, were provided with the mass spectrum of an alkane, shown in Figure 3.

Figure 3

24


Student P analysed peaks a and b and concluded that the alkane was one of two structures.

Student Q analysed peaks a, b and c and was able to identify one possible alkane structure.

Analyse the peaks and explain why the two students obtained different conclusions.

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2a1 mark

Propanal, CH3CH2CHO, and propanone, CH3COCH3, are carbonyl compounds. When these compounds are compared using analytical methods, which of the following statements is not correct?

A         The compounds produce different patterns in the fingerprint region of the IR spectrum.

B         The carbonyl groups absorb at frequencies in the same region of the IR spectrum.

C         The compounds produce different fragmentation patterns in a mass spectrum.

D         The compounds have molecular ion peaks at different mass to charge ratios in a mass spectrum.

2b6 marks

This question is about compounds with the molecular formula C4H8O.

Three different compounds, A, B and C, have the molecular formula C4H8O.

All three compounds have infrared absorptions at about 3500 cm-1.
Only the infrared spectra of A and B each contain a peak at about 1650 cm-1.
A is the only branched carbon chain.
B is the E-isomer of a pair of stereoisomers.

Deduce a possible displayed formula for each of the compounds A, B and C.

You must use all of the data and the information in the Data Sheet to justify each of your structures.

2c4 marks

A student analysed the spectrum in Figure 2 and correctly deduced that the image was that of butanal.

Figure 2

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Suggest why this spectrum cannot be that of butanoic acid, but-1-ene or butan-1-ol. Justify your answer.

2d2 marks

The mass spectrum of 2-methylpropan-2-ol is shown in Figure 3. The relative molecular mass of 2-methylpropan-2-ol is 74.

Figure 3

26

i)
Give a possible reason why there is no molecular ion peak in the mass spectrum of 2-methylpropan-2-ol.

ii)

Draw the displayed formula for a species that could be responsible for the peak at m / z = 59.

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3a3 marks

The compound 2-bromopropane was heated at high temperatures under reflux with concentrated potassium hydroxide dissolved in a mixture of water and ethanol. There were two organic products, P and Q, formed in this reaction. P and Q belong to different homologous series.

After separating P and Q, their spectra were obtained.

The mass spectrum of P shows peaks at m/z = 45 and at m/z = 60.

Use this information to identify P. Justify your answer.

3b2 marks

The infrared spectra of P and Q (from part a) are shown in Figure 1.

Figure 1

27

28


Explain how each spectrum shows the homologous series to which each product belongs.

3c3 marks

A student predicted that the rate of hydrolysis must decrease as you go down Group 7. Fluorine is the most electronegative element in group 7 and must therefore react the fastest with the nucleophile.

Explain whether you agree or disagree with their conclusion. Justify your answer.

3d5 marks

Another student wanted to measure the rate of hydrolysis of three haloalkanes: 1-chlorobutane, 1-bromobutane and 1-iodobutane.

Explain what chemical tests the student could carry out to prove their conclusions were correct from part (c). Include in your answer any relevant observations and overall equation.

3e2 marks

Another student wanted to measure the rate of hydrolysis of three haloalkanes: 1-chlorobutane, 1-bromobutane and 1-iodobutane.

In a second experiment, the student used three structural isomers of C4H9Br, shown in Table 1 and noticed these isomers also hydrolysed at different rates. State the trend in the different reaction rates and explain your ideas.

Table 1

Formula of bromoalkane

CH3CH2CH2CH2Br

CH3CH2CH2BrCH3

(CH3)3CBr

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4a6 marks

Compound F is a trans stereoisomer which is a useful intermediate in organic synthesis.

Analysis of compound F shows it to contain 68.6 % carbon, 8.6 % hydrogen and 22.8 % oxygen. The infrared spectrum of compound F is shown in Figure 1.

Figure 1

29


In the mass spectrum, shown in Figure 2, the peak with the greatest relative intensity is caused by the loss of a functional group from the molecular ion of compound F.

Figure 2

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Determine the structure of compound F. Explain your reasoning and show your working.

4b6 marks

Crotonaldehyde, CH3CH=CHCHO, occurs in soybean oils.

Table 1 shows the reagents that crotonaldehyde will be reacted with in four separate reactions.

Table 1

Reaction

Reagent

Product

A

Br2 in an inert organic solvent

 

B

H2 and Ni catalyst

 

C

NaBH4

 

D

K2Cr2O7 / H+

 


Complete Table 1 by writing the structural formulae of the organic compounds and stating any colour changes you would expect to observe for each reaction.

4c1 mark

Use the information from part (b) to draw the skeletal formula of crotonaldehyde.

4d2 marks

Crontonaldehyde can be formed from alcohols.

State what reagents and conditions are needed for this reaction.

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5a2 marks

An alcohol can be prepared by hydrolysing the halogenoalkane C2H5CHBrCH3 with aqueous sodium hydroxide.

The infrared spectrum for C2H5CHBrCH3 is shown in Figure 1 with the C–Br bond absorption labelled.

Figure 1

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Outline how IR spectroscopy will change as a result of the above reaction.

5b1 mark

The mass spectrum of (CH3)2CHCH2OH is shown below in Figure 1.

Figure 1

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Determine which ion is responsible for the peak with the greatest relative intensity.

5c3 marks

This question is about the identification of an alcohol, X.

Alcohol X has the following percentage composition by mass:

  • Carbon, C = 68.2%
  • Hydrogen, H = 13.6%
  • Oxygen, O = 18.2%

The molecular ion peak in the mass spectrum for alcohol X occurs at m/z = 88.

i)
Use all of the data to show that the molecular formula for alcohol X is C5H12O.
Include your working.

ii)
When alcohol X is oxidised, a carboxylic acid can be formed.

State what information this gives about alcohol X.

5d7 marks
i)
Using information from part (c), draw the displayed formulae and give the systematic names of the four possible structural isomers that could be alcohol X.

ii)

The mass spectrum of alcohol X has a major peak at m/z = 45.
Draw the structure of the species that could give this peak.

iii)

Alcohol X has a branched chain.
Identify alcohol X and state the name. Explain your reasoning.

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