Alcohols (AQA A Level Chemistry)

Ethane-1,2-diol is an alcohol which is often used in antifreeze. Antifreeze is added to cooling 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.

Ethanol is an alcohol which can be industrially produced in three different ways, as shown in Figure 1.

Figure 1

i) Name the processes that occur in reactions 1 - 3.

ii) State the reagents and conditions required for the processes occurring in reactions 1 and 2 only.

The ethanol which is formed in reaction 3 must be separated from the aqueous mixture. 

i) Draw and label the apparatus needed to separate and collect the ethanol.

ii) Explain how the apparatus is used to collect a sample of ethanol.

iii) State the name of this separation technique.

Outline the mechanism for the process occurring in reaction 2 in Figure 1.

Ethanol is one of the most important alcohols and has a wide range of uses. Some of its uses include as an intermediate in the synthesis of other organic chemicals, as a solvent, in the manufacture of drugs, and in alcoholic beverages and ink.

Ethanol can be made industrially by fermentation of sugars.

i) Write down the symbol equation for the fermentation of glucose to form ethanol. Include state symbols.

ii) Explain why air is kept out of the reaction vessel during the fermentation.

iii) Explain why a temperature of about 35 C is used for this fermentation reaction.

The fermentation reaction described in part (b) only occurs at a temperature between 30 and 42 C.

State two other conditions which are essential for this reaction to occur.

The ethanol produced by fermentation cannot be used straight away as a biofuel as it first needs to be separated by fractional distillation.

i) State the meaning of the term biofuel.

ii) Which property of ethanol allows it to be separated from the fermenting solution by fractional distillation?

Ethanol can be produced from crude oil by cracking and hydration, or from sugars by fermentation. Though the use of biofuels has many advantages, there are also environmental and ethical issues linked to the use of biofuels.

i) State two advantages of growing crops and using them as raw materials for the production of ethanol from glucose rather using crude oil.

ii) State one disadvantage of producing ethanol by fermentation.

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).

The chemist then heats alcohol A from part (a) with a concentrated sulfuric acid catalyst to form product C. She then measures the boiling point of product C and compares it to the boiling point of alcohol A.

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 alcohol A.

i) Name an isomer of alcohol A which would not be oxidised by acidified potassium dichromate (VI). Give a reason why it cannot be oxidised.

ii) Name an isomer of alcohol A 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 D depending on the reaction conditions used.

The boiling points of propan-1-ol, propanal and product D are summarised in Table 1.

Table 1

i) State the IUPAC name of product D.

ii) Describe the reaction conditions needed to form product D 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.

iii) State whether the student can distinguish between the product formed in this reaction and (CH₃)₃CCOCH₃ using Fehling’s solution. Explain your answer.

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.

The reaction described in part (b) forms a pair of stereoisomers.

State how these stereoisomers arise.

The dehydration of an alcohol produces an alkene. The addition polymerisation reaction of this alkene results in the formation of a polymer is shown in Figure 1.

Figure 1

Draw the structural formula and name the alcohol from which the polymer in Figure 1 is formed.

Many internal combustion engines will run on ethanol or mixtures of petrol and ethanol. Ethanol can be made from ethene which is obtained from crude oil or by fermentation.

i) Write equations for the production of ethanol by fermentation and for the complete combustion of ethanol.

ii) State why either too low or too high temperatures are inappropriate for this reaction and which other two conditions are essential for the fermentation process.

Give an advantage of producing ethanol by fermentation over the hydration of ethene which is obtained from crude oil.

Despite the many disadvantages of producing ethanol by fermentation, this method is often promoted as it is claimed that the ethanol obtained in this way is a carbon-neutral biofuel.

One of the disadvantages of this process is that the ethanol produced is impure.

i) State how the contamination of ethanol formed by fermentation occurs and a method to separate the ethanol from these contaminants.

ii) State the meaning of the term carbon-neutral in this context of ethanol as a biofuel.

iii) Write equations to support the statement that ethanol produced by fermentation is a carbon-neutral fuel.

Local farmers are against the decision of the company to produce ethanol by fermentation as they claim carbon is not a carbon-neutral biofuel.

State and explain any arguments that the farmers may have to support their statement.

Two reactions involving compound A and compound B are shown below in Figure 1. Compound B is an alcohol that does not show a colour change when reacted with acidified potassium dichromate.

Figure 1

i) State the reagents and conditions for Reaction 1.

ii) Draw the skeletal structure of compound B.

A student suggested that the formula for compound B, in part (a) is more likely to be CH₃CH(CH₃)CHOHCH₃.

Is the student correct? Justify your answer using a suitable mechanism. 

Cold, dilute potassium permanganate, KMnO₄ is used for Reaction 1 was used as an alternative set of reagents and conditions. Potassium permanganate, KMnO₄ is a strong oxidising agent that is widely used in chemical industries and laboratories. It can also be used in medical procedures for cleaning wounds and as a disinfectant.

i) State the name of compound B.

ii) Using the information given in part (a) explain why these are not the correct reagents and conditions.

Explain what is meant by the term dehydration and identify a suitable catalyst for Reaction 2.

Use the reaction scheme in part (a) to illustrate your answer. You should include an equation in your answer.

Compounds W, X and Y are all carbohydrates with X and Y each containing five carbons.

Compound W and a byproduct, compound Z, are formed from the reaction between compound X and Y.

Compound X can be oxidised by the reaction with acidified potassium dichromate to give compound Y.

2.754 g of compound Y contains 0.027 moles.

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

Draw the skeletal 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 dichromate, H⁺ / K₂Cr₂O₇.

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 dichromate, H⁺ / K₂Cr₂O₇.

Propan-2-ol has a relatively high boiling point. Draw how two molecules of propan-2-ol interact with one another and explain how the strongest type of intermolecular force arises.

Propan-2-ol can undergo oxidation to form a compound which has the formula C₃H₆O.

i) Write the balanced symbol equation, using [O] to represent the oxidising agent, to show the oxidation of propan-2-ol.

ii) Suggest a chemical test for this reaction and give the results that will identify the product.

iii) In terms of the metal ions present in the chemical test, explain the results.

Propan-2-ol can be dehydrated to propene using concentrated sulfuric acid, H₂SO₄, at a temperature of 170C.

Name and outline the mechanism of the dehydration of propan-2-ol showing the sulfuric acid molecule is involved in the reaction.

The structure of sulfuric acid is shown below in Figure 1.

Figure 1

A student states that the product of dehydration of propan-2-ol will exhibit geometric isomerism. Is the student correct? Justify your answer.

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 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.

The structure of ascorbic acid is shown in Figure 2.

i) Explain why this molecule can form a carboxylic acid on oxidation.

Figure 2

ii) Identify the position where a carboxylic acid group will form with an ‘X’ on the diagram.

Grignard reagents as shown above the arrow in Figure 3 are powerful reagents for organic synthesis. The formula for a Grignard reagent can be simplified to R-Mg-X. They can react with esters to produce alcohols.

Figure 3

i) State the name of the alcohol produced and identify which class of alcohol to which it belongs.

ii) In an experiment, 5 g of the ester were reacted with a Grignard reagent to produce 8.3 g of the alcohol.

A student states that the percentage yield for the reaction is 70%. Is the student correct?

Justify your answer.

Ethanol has many uses such as industrial solvent and a raw material to produce a variety of compounds. It can be manufactured on a large scale by two different processes.

Give equations reagents and conditions for both of these processes.

Compare the two methods outlined in part (a) to manufacture ethanol. In your answer make reference to the atom economy, raw materials and the energy required.

The first production car that ran on biofuel was manufactured in Brazil in the 1970s.

Explain which method of production of the ethanol outlined in part (a) can be identified as carbon neutral.

In your answer explain what is meant by the term carbon neutral and give the extent to which your chosen process can be classed as carbon neutral.

Ethanol is 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 2-methylbutan-2-ol.

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