Analytical Techniques (OCR AS Chemistry A): Exam Questions

This question is about haloalkanes and their products.

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

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

[1]

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.

[2]

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

1-chloro-3-methylbutane underwent the same reaction as is stated in part (a). A structural isomer of the product in part (a) was formed. 

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

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.

This question is about analytical techniques.

A student wanted to distinguish between the following three compounds using mass spectrometry. 

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

Compounds X, Y and Z were analysed using IR spectroscopy. The spectrum of one of the compounds is shown below.

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

Explain why infrared spectroscopy alone could not be used to distinguish between compounds X and Y.

Explain how mass spectrometry can distinguish between compounds X and Y.

This question is about analytical techniques.

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. 

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.

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.

[1]

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

[2]

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.

[5]

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

[2]

This question is about analytical techniques.

Infrared spectroscopy and mass spectrometry are used in the search for extra-terrestrial organic compounds.

Compound X was analysed using both techniques. The infrared spectrum and mass spectrum are shown below.

 What evidence is there to support that compound X is a hydrocarbon?

How does the mass spectrum support that compound X has a molecular formula of C₄H₁₀?

Draw the displayed formulae of two possible isomers for compound X.

Use the fragment ions at peaks at m/z 15, m/z 29 and m/z 43 in the mass spectrum to name compound X. Explain your reasoning.

This question is about the identification of an organic compound.

An unknown saturated organic compound contains carbon, hydrogen and oxygen only.

Analysis of 1.00 g of the unknown compound showed it to contain 0.133 g of hydrogen and  0.600 g of carbon.

The infrared spectrum and mass spectrum of the unknown compound are shown below.

Calculate the empirical and molecular formulae for the unknown compound.

Using the infrared spectrum, suggest two structural formulae for the unknown compound. Explain your reasoning.

Using the mass spectrum, suggest a structure for the unknown compound. Explain your reasoning.

This question is about the determination of the structure of an unknown compound, B.

Compound B is a trans stereoisomer that is a useful intermediate in organic synthesis. 

Analysis of compound B shows it to contain 68.6 % carbon, 8.6 % hydrogen and 22.8 % oxygen.

The infrared spectrum of the compound B is shown in Figure 1.

Figure 1

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 the compound B.

Figure 2

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

This question is about the analysis of reaction products.

2-Bromopropane was heated under reflux with concentrated potassium hydroxide dissolved in a mixture of water and ethanol.

The organic products, G and H, formed in this reaction belong to different homologous series.

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

Identify compound G, showing your reasoning.

The infrared spectra of products G and H are shown below. 

Product G

 Product H

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

This question is about analytical techniques.

An alcohol can be prepared by hydrolysing the haloalkane C₂H₅CH(Br)CH₃ with aqueous sodium hydroxide. The C-Br bond is labelled on the IR spectrum below.

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

The mass spectrum of 2-methylpropan-1-ol is shown below. 

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

The IR spectrum of butanal is shown below. 

Explain why this spectrum cannot be butanoic acid, but-1-ene or butan-1-ol. 

Clenbuterol, shown below, is a performance-enhancing drug that is believed to increase short-term work rate and cardiovascular output. 

Determine the m/z value of the molecular ion, M⁺, of clenbuterol, giving your reasoning.

This question is about the identification of an alcohol.

An alcohol I is analysed, using a combination of techniques. The analytical data is shown below.

Elemental analysis by mass

• C = 68.2%, H = 13.6%, O = 18.2%

Mass spectrum

• Molecular ion peak at m/z = 88.0

Determine the molecular formula of alcohol I.

Alcohol I oxidises to form a carboxylic acid. State what information this gives about alcohol I.

Draw the displayed formulae and give the systematic names of four possible structural isomers that could be alcohol I.

The mass spectrum of alcohol I has a major peak at m/z = 45. 

Draw the structure of the species that could give this peak.

Alcohol I has a branched chain. Identify alcohol I, showing your reasoning.