Basic Concepts (OCR A Level Chemistry A): Exam Questions

Oleic acid, shown below, is a fatty acid which occurs naturally in different animals and plants. It is also widely produced in industry, for its uses as an emulsifying agent and in the pharmaceutical industry.

i) State the type of formula shown in the diagram of oleic acid.

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ii) Deduce the molecular formula of oleic acid.

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iii) Draw the displayed formula of oleic acid.

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The structure of another fatty acid commonly found in milk is shown.

Name the fatty acid.

Crotonic acid is another fatty acid which has a similar structure to oleic acid. The molecular formula of crotonic acid is C₄H₆O₂.

i) State the empirical formula of crotonic acid.

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ii) Crotonic acid has a carboxylic acid functional group. Draw the displayed formula of the position and chain isomers of crotonic acid.

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iii) Draw the cyclic functional group isomer of crotonic acid.

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Two students, Student A and Student B, discuss the properties of oleic acid and crotonic acid. 

Student A claims that both compounds belong to the same homologous series and Student B claims that both compounds have similar chemical properties.

Are either of the students correct? Explain your answer.

Crude oil consists of a mixture of hydrocarbons, which can be separated by fractional distillation.

The shorter hydrocarbons are more useful as fuels such as gasoline and diesel fuel, so longer hydrocarbons are often converted into shorter ones in a process called cracking.

Cracking of hydrocarbons results in the formation of shorter alkanes and alkenes.

A hydrocarbon with molecular formula C₁₂H₂₆ is cracked to form octane and one alkene.

i) Write an equation for this cracking reaction.

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ii) Draw the skeletal formula of the functional group isomer of the alkene formed in this reaction.

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iii) Draw the displayed formula of the chain isomer of the alkene formed in this reaction.

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The reaction mechanism for the reaction of but-1-ene with hydrogen bromide forming compound X is shown below, with errors:

i) What does the curly arrow going from the C=C bond to the H in H-Br represent?

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ii) State and explain corrections for the errors in the mechanism.

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Give the IUPAC name of compound X.

Compound X can also be formed from the reaction of butane with bromine using ultraviolet light.

CH₃CH₂CH₂CH₃ + Br₂ → CH₃CH₂CHBrCH₃ + HBr

The mechanism for this reaction occurs in three steps:

1. Initiation

2. Propagation

3. Termination

State what type of reaction this is and the type of bond fission involved.

A chemist is analysing a collection of organic compounds. The formulae of these compounds are shown in the table below:

Compound	Formula	IUPAC name
1	CH3CHCClCH2OH
2
3
4

 Give the IUPAC name for the compounds to complete the table.

Draw the skeletal formula for a straight chain isomer of compound 2.

State the empirical formula of compound 1, CH₃CHCClCH₂OH.

Compounds 1 and 4 can react in a similar fashion with some chemicals, while other chemicals can be used to distinguish between them.

Compound 1

Compound 4

i) Describe one chemical test, including expected observations, that both compounds 1 and 4 will give a positive test for.

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ii) Describe one chemical test, including expected observations, that can distinguish between compounds 1 and 4.

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The compound 2,2-dimethylpropane can be represented using different types of formula.

Its structural formula can be shown as (CH₃)₄C.

i) Give the empirical formula of 2,2-dimethylpropane.

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ii) Draw the skeletal formula of 2,2-dimethylpropane.

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iii) Draw the displayed formulae of the two isomers of 2,2-dimethylpropane.

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Pentane belongs to the homologous series of alkanes.

i) Define the term homologous series. 

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ii) State the general formula for the homologous series of alkanes.

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Pent-1-ene (C₅H₁₀) is a member of the homologous series of alkenes. 

i) State the general formula for the homologous series that pent-1-ene belongs to.

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ii) Draw the skeletal formula of pent-1-ene.

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Pent-1-ene (C₅H₁₀) has structural isomers but no stereoisomers.

i) Define the term structural isomerism. 

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ii) Give the IUPAC names of any possible functional group isomers of pent-1-ene.

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iii) Draw the skeletal formula of the position isomer(s) of pent-1-ene.

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This question is about the structure of organic compounds.

The structure of an alcohol Y is shown below.

i) Give the IUPAC name for alcohol Y.

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ii) What is the general formula of the homologous series of alcohols, which contain only one -OH group per molecule?

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iii) State the empirical formula of alcohol Y.

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2,3-dimethylpentan-1-ol is distilled with acidified potassium dichromate(VI) solution. During this distillation, 2,3-dimethylpentan-1-ol is oxidised to an aldehyde. 

i) Name the aldehyde formed by the oxidation of 2,3-dimethylpentan-1-ol.

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ii) Draw the displayed formula of this aldehyde.

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1-Bromopropane reacts with aqueous sodium hydroxide according to the following reaction mechanism.

i) State the type of reaction that is occurring.

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ii) Draw the skeletal formula of compound X.

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1-Bromobutane can also react via a free-radical substitution mechanism as shown. 

Explain how the butyl and bromine radicals are formed.

This question is about organic compounds

Terpenes are a class of organic compounds widely used as fragrances in products such as perfumes. For example, one of the simpler terpenes, nerol is found in many essential oils such as lemongrass and hops. The structure of nerol is shown in Figure 1 below.

Figure 1

i) Deduce the molecular formula of nerol. Use your answer to calculate the molar mass of nerol in g mol⁻¹.

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ii) Draw the displayed formula of nerol.

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Figure 2 shows the skeletal formula of a type of fuel.  

Figure 2

i) Give the IUPAC name of the compound shown in Figure 2.

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ii) State the number of monochloro isomers which would be possible for the molecule in Figure 2.

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iii) Draw the skeletal formulae of these monochloro isomers. Don’t include chain isomers but only move the position of the chlorine atom.

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A compound with a molar mass of 72.0 g mol^-1 is composed of 66.63% C, 11.18% H, and 22.19% O. 

i) Calculate the molecular formula of this compound.

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ii) Draw and name the skeletal formula of the isomers of this compound which contain a carbon-oxygen double bond.

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This question is about ethers.

Ethers are a homologous series of organic compounds containing the R−O−R functional group.

The structures and names of two ethers are shown in Figure 1.

Figure 1

i) Draw the skeletal formula of the ether, 2-ethoxy-2,3-dimethylbutane.

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ii) Determine the molar mass of 2-ethoxy-2,3-dimethylbutane.

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Ethers can be prepared by nucleophilic substitution of haloalkanes with alkoxide ions, RO⁻. 

Alkoxide ions can be prepared by reacting sodium with an alcohol. A gas is also formed.

Write an equation for the formation of methoxide ions from sodium and an alcohol.

Methoxyethane, shown in part (a), can be prepared by reacting bromoethane, CH₃CH₂Br, with methoxide ions, CH₃O⁻.

Outline the mechanism for the nucleophilic substitution of CH₃CH₂Br with CH₃O⁻ using skeletal formulae.

Your answer should include relevant charges, dipoles and the products formed.

In this mechanism, CH₃O⁻ ions have acted as a nucleophile.

i) Explain how CH₃O⁻ ions have acted as a nucleophile.

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ii) A student commented that this is an example of homolytic fission.

Explain whether the student is correct.

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This question is about saturated hydrocarbons.

Compound A is shown in Figure 1.

Figure 1

The reaction of compound A with excess fluorine forms compound D, which has a molar mass of 140 g mol⁻¹.

Draw a possible structure for compound D and write the equation for its formation from compound A. Use molecular formulae in the equation.

The hydrocarbon propane can be reacted with chlorine to prepare 2-chloropropane, CH₃CHClCH₃, by free radical substitution.

i) Write the overall equation and state the conditions for this reaction.

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ii) Outline the mechanism by naming and providing relevant equations for each step in the formation of 2-chloropropane.

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iii) Describe the limitations of this method of preparation.

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Oxybenzone is a UV light-absorbing chemical which is found in certain sun creams. The structure of oxybenzone is shown in Figure 2 below.

Figure 2

Oxybenzone contains an ether functional group, C-O-C. Identify the other functional groups present in oxybenzone.

One of the starting molecules used in the synthesis of oxybenzone is shown in Figure 3 below.

Figure 3

Draw the skeletal formula of two other structural isomers of this molecule.

This question is about molecules containing hydroxyl groups.

A student named the alcohol molecule shown in Figure 1 as E-1,3-dichlorohex-2-ene-6-ol.

Figure 1

State the errors the student has made in naming the molecule and give the correct IUPAC name.

Aspirin is an ester of salicylic acid, HOC₆H₄CO₂. Aspirin is formed when an ester bond is created between the salicylic acids OH group and ethanoic anhydride, (CH₃CO)₂O, in the presence of an acid catalyst, as shown in Figure 2. Ethanoic acid is also formed as a product.

Figure 2

i) Draw the skeletal formulae for both products of this reaction.

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ii) Determine the molar mass of aspirin.

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The organic compounds in Figure 3 below can be termed aliphatic, alicyclic or aromatic.

Figure 3

Each response may contain more than one letter for the questions below.

i) Identify, using letters E, F, G, H, I, and J, the compound(s) which are aliphatic.

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ii) Identify, using letters E, F, G, H, I, and J, the compound(s) which are alicyclic.

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iii) Identify, using letters E, F, G, H, I, and J, the compound(s) which are aromatic.

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i) Using Figure 3 in part (c), state which compounds E, F, G, H, I, and J can be categorised as aliphatic but not alicyclic.

Justify your answer.

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ii) Describe a simple test that the student could carry out to confirm the presence of the functional group in compound H.

Draw the structure of the organic product from the test.

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This question is about organic compounds found in living organisms.

Two structural isomers of C₁₀H₁₈O are linalool and geraniol. They are unsaturated alcohols with similar chemical properties and are both used in perfumes. 

The IUPAC names for both linalool and geraniol are shown in Table 1.

Table 1

Draw the skeletal formulae for these two isomeric alcohols.

The organic compounds below in Figure 2 are all made by living organisms.

Figure 2

i) State the IUPAC name for compound A.

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ii) Compound D reacts readily with hydrogen chloride in an addition reaction.

Two products are formed in this reaction, but one of the products is formed in much greater amounts than the other.

Draw the structures of both possible addition products of this reaction.

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5.175 g of compound D (from part C) is reacted with an excess of hydrogen chloride. The mixture of products contains 90% by mass of one product and 10% by mass of the other product.

Calculate the mass of each product formed.