Alcohols (OCR AS Chemistry A): Exam Questions

Ethanol which is formed from the fermentation of glucose must be separated from its aqueous mixture. Draw and label the apparatus needed to separate and collect ethanol once it has been produced. 

Explain how the apparatus you have drawn is used to collect a sample of ethanol and state the name of this separation technique. 

The boiling point of ethanol is 78 °C yet the boiling point of ethane is -89 °C. This is due to the differences in intermolecular forces. 

Draw how two molecules of ethanol interact with one another and explain how the strongest type of intermolecular force arises.

A chemist has access to alcohol A (CH₃)₃CCH(OH)CH₃, acidified potassium dichromate(VI) and concentrated sulfuric acid.

i) Draw the skeletal formula of alcohol A and give its IUPAC name. 

ii) Draw the skeletal formula of the organic product formed when alcohol A is heated under reflux with acidified potassium dichromate(VI).

iii) When alcohol B, (CH₃)₃CCH₂CH₂OH, is heated under reflux with acidified potassium dichromate(VI), a different organic product is formed.

Draw the displayed formula of this product and explain why this product is different to the one formed in part (ii).

2-bromobutane can be prepared by the following reaction:

CH₃CH(OH)CH₂CH₃ + Br^- → CH₃CH(Br)CH₂CH₃ + OH^- 

i) Name the type of reaction occuring.

ii) Suggest suitable reagents for this reaction.

Ethane-1,2-diol is an alcohol which is often used in antifreeze. Antifreeze is added toccooling systems of motor vehicles so that the coolant mixture does not freeze during the winter when temperatures are very low.

i) State the molecular formula of ethane-1,2-diol and draw its skeletal formula.

ii) State whether ethane-1,2-diol is a primary, secondary or tertiary alcohol. Explain your answer.

The chemist reacts 3,3-dimethylbutan-2-ol with hot, concentrated sulfuric acid to form product B. She then measures the boiling point of product B and compares it to the boiling point of alcohol 3,3-dimethylbutan-2-ol. 

i) Which of the two substances is likely to have the higher boiling point?

ii) Name and outline the mechanism for this reaction

iii) State the name of the product according to IUPAC rules

The chemist wants to conduct some further research into the reactions of the alcohols, and decides to use isomers of 3,3-dimethylbutan-2-ol.

i) Name an isomer of 3,3-dimethylbutan-2-ol which would not be oxidised by acidified potassium dichromate(VI) . Give a reason why it cannot be oxidised.

ii) Name an isomer of 3,3-dimethylbutan-2-ol which would not react with hot concentrated sulfuric acid. Give a reason why it will not react with the acid.

The chemist also has propan-1-ol which she wants to oxidise to propanal using potassium dichromate(VI). The oxidation of this alcohol may however also produce a second product C depending on the reaction conditions used.

The boiling points of propan-1-ol, propanal and product C are summarised in the following table

i) State the IUPAC name of product C.

ii) Describe the reaction conditions needed to form product C and why these reaction conditions are necessary.

iii) Describe how the chemist can obtain propanal from a mixture of the three compounds. Include a description of the apparatus used and state how the loss of propanal can be minimised.

A student wants to convert an alcohol P (CH₃)₃CCH(OH)CH₂OH to a compound which contains an aldehyde functional group only. The student has access to all other chemical reagents.

i) State necessary reagents and conditions for the conversion of an alcohol to an aldehyde.

ii) State whether the alcohol P is a suitable reagent for this reaction. Explain your answer using an equation for this reaction.

A mixture of alkenes is produced when butan-2-ol is reacted with hot concentrated sulfuric acid. One of the isomers formed is but-1-ene.

Name and outline the mechanism for this reaction that forms but-1-ene.

Propane-1,3-diol is a preservative in cosmetics and pharmaceutical products such as conditioner, lotion, shampoo, sunscreen, makeup, hair spray, and other products.

Explain why propane-1,3-diol is soluble in water.

Propane-1,3-diol is refluxed with acidified potassium dichromate. Draw the structure of the compound formed in this reaction.

When pentan-2-ol reacts with concentrated phosphoric acid under reflux, there alkenes are formed, X, Y and Z. X and Y are stereoisomers of one another.

Draw the skeletal structures of alkenes, X, Y and Z.

State how the stereoisomers formed in part (a) arise.

The dehydration of an alcohol produces an alkene. The addition polymerisation reaction of this alkene results in the formation of the polymer is shown below

Name and draw the alcohol from which only this polymer is formed.

Alcohols with short carbon chains such as ethanol are more soluble in water than those with longer chains. Explain why the solubility decreases with carbon chain length.

Compounds W, X and Y are all carbohydrates with X and Y each containing five carbons. Compound W and a by product, compound Z, are formed from the reaction between compound X and Y. Compound X can be fully oxidised by the reaction with acidified potassium manganate(VII) to give compound Y. 5.508 g of compound Y contains 0.054 moles.

Using the information given, state the name of compound Y and justify your answer.

Draw the full displayed formula of compound W and explain how compound Z is formed in the reaction.

Compound X will oxidise to compound Y if allowed to fully oxidise. Explain how a student could stop the full oxidation of compound X.

State the formula of an isomer of compound X that will not react with acidified potassium manganate(VII).

Using your knowledge of bonds present in the oxidation products of different classes of alcohols, suggest why the isomer you have drawn will not react with acidified potassium manganaate(VII).

Propan-1-ol has a relatively high boiling point. 

Draw how two molecules of propan-1-ol interact with one another and explain how the strongest type of intermolecular force arises.

A student states that the product of dehydration of propan-2-ol will exhibit E / Z isomerism.

Is the student correct? Justify your answer.

Explain the trend in solubility of primary alcohols with increasing carbon chain length. 

The following reaction pathway shows some of the reactions of butan-2-ol. 

Compound A is a stereoisomer of cis-but-2-ene.

i) Draw the structure of the stereoisomer of cis-but-2-ene.

[1]

ii) Explain why compound A is less soluble than butan-2-ol.

[2]

The reaction to form 2-chlorobutane produces three products.

i) State the name of reagent C.

[1]

ii) Give the formula of the two other products formed in this reaction. 

[2]

Give the equation for the overall reaction between butan-2-ol and phosphorus tribromide which occurs at room temperature.

Draw the structure of compound B and identify reagent E.

Ethanol can be converted to ethene only under harsh conditions, concentrated sulphuric acid at 450K. In contrast, 2-methylbutan-2-ol is dehydrated on treatment with acid at 298K.

In this reaction, two products are formed. 

i) Draw the skeletal formula of both products from the dehydration of 2-methylbutan-2-ol.

[1]

ii) Explain why less extreme conditions are required for the dehydration 2-methylbutan-2-ol compared to the dehydration of ethanol.

[1]

Menthol can be made synthetically or extracted from various kinds of mint plants. It can be used to treat mild aches and pains by causing the skin to feel cool and then warm.

The structure of menthol is shown in Figure 1.

Figure 1

State the empirical formula of menthol.

The final step in the synthetic production of menthol is to form the alcohol group from the ketone group in the molecule. 

State the formula of the ketone containing compound that will form menthol.

Describe the oxidation of 2-methylpropan-1-ol and cyclohexanol when using a suitable oxidising agent.

In your answer explain how the different reaction conditions control which product can be formed.

Include observations, and equations in your answer using [O] to represent the oxidising agent.