Alcohols (Cambridge (CIE) O Level Chemistry): Exam Questions

Propane reacts with chlorine to form a mixture of chloropropanes. This is a photochemical reaction.

i) What is meant by the phrase photochemical reaction?

[1]

ii) The products of this reaction include two isomers, one of which has the following structural formula.

   Draw the structural formula of the other isomer.

[1]

iii) Explain why these two different compounds are isomers.

[2]

Bond breaking is an endothermic change and bond forming is an exothermic change. 

Bond energy is the amount of energy in kJ / mol needed to break one mole of the specified bond.

Use the following bond energies to determine whether this reaction is exothermic or endothermic. You must show your reasoning.

i) Chloropropane can be hydrolysed to propanol, CH₃CH₂CH₂OH, by sodium hydroxide.

Write the equation for this reaction.

[2]

ii) Propanol can be dehydrated. It loses a water molecule to form a hydrocarbon.

Give the name and structural formula of this hydrocarbon.

[2]

iii) Propanol is oxidised to a carboxylic acid by acidified potassium manganate(VII).

Deduce the name of this acid.

[1]

Propanol reacts with methanoic acid to form the ester propyl methanoate.

CH₃CH₂CH₂OH + HCOOH → HCOOCH₂CH₂CH₃ + H₂O

4.0 g of methanoic acid was reacted with 6.0 g of propanol.

i) Calculate the M_r of methanoic acid.

[1]

ii) Calculate the M_r of propanol.

[1]

iii) Determine which one is the limiting reagent. Show your reasoning.

[2]

iv) Calculate the maximum yield in grams of propyl methanoate, M_r = 88.

[1]

The alcohols form a homologous series.

i) Give three characteristics which all members of a homologous series share.

[3]

ii) Give the name of the third member of this series.

[1]

iii) Deduce the molecular formula of the alcohol whose M_r = 158. Show your working.

[2]

Explain why the following two alcohols are isomers.

This question is based on typical reactions of butan-1-ol.

i) When butan-1-ol, CH₃–CH₂–CH₂–CH₂–OH, is passed over the catalyst silicon(IV) oxide, water is lost.

Deduce the name and the structural formula of the organic product in this reaction.

[2]

ii) Suggest the name of the ester formed from butanol and ethanoic acid.

[1]

iii) Butan-1-ol is oxidised by acidified potassium manganate(VII).

Deduce the name and the structural formula of the organic product in this reaction.

[2]

Alcohols can be made by fermentation or from petroleum.

Ethanol can be made by the fermentation of glucose.

C₆H₁₂O₆ (aq) $\stackrel{\mathrm{yeast}}{\to }$2C₂H₅OH (aq) + 2CO₂ (g)       exothermic reaction

Yeast are living single-cell fungi which ferment glucose by anaerobic respiration. This reaction is catalysed by enzymes from the yeast.

i) What are enzymes?

[1]

ii) Suggest a method of measuring the rate of this reaction.

[1]

The following observations were noted.

• When a small amount of yeast was added to the aqueous glucose the reaction started and the solution went slightly cloudy.

• The reaction rate increased and the solution became cloudier and warmer.

• After a while, the reaction rate decreased and eventually stopped, leaving a 14% solution of ethanol in water.

i) Why did the reaction rate increase?

[1]

ii) Suggest an explanation for the increase in cloudiness of the solution.

[1]

iii) Give two reasons why the fermentation stopped.

[2]

One use of ethanol is in alcoholic drinks.

Give two other uses of ethanol.

Alcohols can be made from petroleum by the following sequence of reactions.

alkanes from petroleum → alkene → alcohol

Describe the manufacture of ethanol from hexane, C₆H₁₄. Include in your description an equation and type of reaction for each step.

The structural formula of a butanol is given below.

CH₃—CH₂—CH₂—CH₂—OH

Butanol can be made from petroleum and also by fermentation.

i) Describe the chemistry of making butanol from petroleum by the following route.

petroleum → butene → butanol

[3]

ii) Explain, in general terms, what is meant by fermentation.

[3]

Butanol can be oxidised to a carboxylic acid by heating with acidified potassium manganate(VII). Give the name and structural formula of the carboxylic acid.

Butanol reacts with ethanoic acid to form a liquid, X, which has the sweet smell of bananas. Its empirical formula is C₃H₆O and its M_r is 116.

i) What type of compound is liquid X?

[1]

ii) Give the molecular formula of liquid X.

[1]

iii) Draw the structural formula of X. Show all the individual bonds.

[2]

The alcohols form an homologous series.

Give three characteristics of a homologous series.

The following two alcohols are members of the series and they are isomers.

CH₃—CH₂—CH₂—CH₂—OH and (CH₃)₂CH—CH₂OH

i) Explain why they are isomers.

[2]

ii) Give the structural formula of another alcohol which is also an isomer of these alcohols.

[1]

Copper(II) oxide can oxidise butan-1-ol to liquid X whose pH is 4.

i) Name another reagent which can oxidise butan-1-ol.

[1]

ii) What type of compound is liquid X and what is its formula?

[2]

The alcohol ethanol can be made by fermentation. Yeast is added to aqueous glucose.

C₆H₁₂O₆ (aq) → 2C₂H₅OH (aq) + 2CO₂ (g)

Carbon dioxide is given off and the mixture becomes warm as the reaction is exothermic. The graph shows how the rate of reaction varies over several days.

i) Suggest a method of measuring the rate of this reaction.

[2]

ii) Why does the rate increase initially?

[1]

iii) Suggest two reasons why the rate eventually decreases.

[2]

iv) Why is fermentation carried out in the absence of air?

[1]

The alcohols form a homologous series. Two characteristics of a homologous series are that the physical properties of the members vary in a predictable way and they have similar chemical properties.

Complete the table.

Give two other characteristics of a homologous series.

Draw a diagram showing the arrangement of the valency electrons in one molecule of the covalent compound methanol.

Use x to represent an electron from a carbon atom.
Use ● to represent an electron from an oxygen atom.
Use o to represent an electron from a hydrogen atom

Alcohols can be oxidised to carboxylic acids by heating with acidic potassium manganate(VII).

i) Draw the structural formula of the carboxylic acid formed by the oxidation of propan-1-ol. Show all the bonds.

[1]

ii) Describe how ethanol could be oxidised to ethanoic acid by fermentation.

[2]

Propan-1-ol and ethanoic acid react together to form an ester. Give its name and structural formula.

The alcohols form a homologous series. The first four members are methanol, ethanol, propan-1-ol and butan-1-ol.

One characteristic of a homologous series is that the physical properties vary in a predictable way. The table below gives the heats of combustion of the first three alcohols.

i) The minus sign indicates that there is less chemical energy in the products than in the reactants. What form of energy is given out by the reaction?

[1]

ii) Is the reaction exothermic or endothermic?

[1]

iii) Complete the equation for the complete combustion of ethanol.

[2]

iv) Determine the heat of combustion of butan-1-ol by plotting the heats of combustion of the first three alcohols against the number of carbon atoms per molecule.

[3]

v) Describe two other characteristics of homologous series.

[2]

Give the name and structural formula of an isomer of propan-1-ol.

Methanol is made from carbon monoxide.

CO (g) + 2H₂(g)$\rightleftharpoons$ CH₃OH (g) the forward reaction is exothermic

i) Describe how hydrogen is obtained from alkanes.

[2]

ii) Suggest a method of making carbon monoxide from methane.

[2]

iii) Which condition, high or low pressure, would give the maximum yield of methanol?
Give a reason for your choice.

[2]

For each of the following predict the name of the organic product.

i) reaction between methanol and ethanoic acid

[1]

ii) oxidation of propan-1-ol by acidified potassium manganate(VII)

[1]

iii) removal of H₂O from ethanol (dehydration)

[1]

Fig. 12.1 shows the alcohols ethanol and butan-1-ol.

Fig. 12.1

Describe the manufacture of ethanol from ethene.

Ethanol is used as a fuel.

i) State one other use of ethanol.

[1]

ii) Construct a symbol equation to show the incomplete combustion of ethanol.

[2]

Ethanol is oxidized to form ethanoic acid. State the name of a reagent that is used for this oxidation.

Draw the displayed formula of a different alcohol that is an isomer of butan-1-ol.

Butan-1-ol is heated with concentrated sulfuric acid which acts as a catalyst. But-1-ene and one other compound are formed.

i) Draw the structural formula of but-1-ene.

[1]

ii) Deduce the other compound formed in the reaction.

[1]

But-2-ene, CH₃CH=CHCH₃, is polymerised to give poly(but-2-ene).

i) State the type of polymerisation that occurs.

[1]

ii) Draw the structure of poly(but-2-ene) showing at least one repeat unit.

[1]

The fermentation of glucose can be carried out in the apparatus shown below. After a few days the reaction stops. A 12% aqueous solution of ethanol has been produced.

i) Complete the equation.

C₆H₁₂O₆ .........................

→ + ...................................

glucose carbon dioxide

[2]

ii) Why must air be kept out of the flask?

[1]

The ester methyl butanoate is found in apples. It can be made from butanoic acid and methanol. Their structural formulae are given below. 

butanoic acid	methanol

Use the information given above to deduce the structural formula of methyl butanoate showing all the bonds.

Proteins are natural macromolecules. Draw the structural formula of a typical protein. Include three monomer units. You may represent amino acids by formulae of the type drawn below.

Butan-1-ol is used as a solvent for paints and varnishes, to make esters and as a fuel.
Butan-1-ol can be manufactured from but-1-ene, which is made from petroleum.

Biobutanol is a fuel of the future. It can be made by the fermentation of almost any form of biomass - grain, straw, leaves etc.

But-1-ene can be obtained from alkanes such as decane, C₁₀H₂₂, by cracking.

i) Give the reaction conditions.

[2]

ii) Complete an equation for the cracking of decane, C₁₀H₂₂, to give but-1-ene. C₁₀H₂₂ →

[2]

iii) Name the reagent that reacts with but-1-ene to form butan-1-ol.

[1]

i) Balance the equation for the complete combustion of butan-1-ol.

...... C₄H₉OH + ...... O₂ → ...... CO₂ + ...... H₂O

[2]

ii) Write a word equation for the preparation of the ester butyl methanoate.

[2]

The fermentation of biomass by bacteria produces a mixture of products which include biobutanol, propanol, hydrogen and propanoic acid.

i) Draw the structural formula of propanol and of propanoic acid. Show all the bonds.

[2]

ii) Why is it important to develop these fuels, such as biobutanol, as alternatives to petroleum?

[1]

How could you show that butanol made from petroleum and biobutanol are the same chemical?

Ethanol and propan-1-ol are members of the alcohol homologous series.

i) State the general formula of the alcohol homologous series.

[1]

ii) Name the unbranched alcohol that contains exactly four carbon atoms per molecule.

[1]

Draw the displayed formula of a structural isomer of propan-1-ol. Show all of the atoms and all of the bonds.

Ethanol can be manufactured by the catalytic addition of steam to ethene, also known as hydration. State two conditions required for this reaction.

Ethanol can also be manufactured by fermentation. State two advantages of manufacturing ethanol by fermentation rather than by the hydration of ethene.

Ethanol reacts with compound X to form the ester ethyl propanoate and compound Y. Identify compound X and compound Y.

compound X:

compound Y :

An unknown alcohol, A, has the following composition by mass: C = 37.5%; H = 12.5%; O = 50.0%

Determine the empirical formula of compound A. Show all your working.

empirical formula = .......................

An unknown ester, Z, has the empirical formula CH_2​O. Its relative molecular mass, M_r​, is 60. Determine the molecular formula of ester Z.

molecular formula = ........................

Ethanol can be manufactured by the fermentation of aqueous glucose or by the catalytic addition of steam to ethene.

The table gives information about two countries, P and Q.

Country P plans to build a factory to manufacture ethanol.

Deduce which method Country P should use.

Justify your answer using two pieces of data from the table.

Country Q also plans to manufacture ethanol.

Suggest which method Country Q should use.

Give a reason for your answer using data from the table.

One of the two methods of manufacturing ethanol is a batch process and the other is a continuous process.

Explain one consequence of this difference for the mass of ethanol a factory can make each year.

State the conditions used for the catalytic addition of steam to ethene.

Explain which of these conditions makes the process expensive to run.

Country P grows a large amount of sugar cane, but it still imports some of the ethanol it uses.

Suggest two reasons why Country P does not manufacture all of its own ethanol by fermentation.

Propan-1-ol, C₃H₇OH, is used as a fuel.

Write the equation for the complete combustion of propan-1-ol.

Propan-1-ol burns to form carbon monoxide and water as the only products.

Write the equation for this reaction.

When ethanol is burned, the flame is yellow and a solid is deposited on the outside of the container being heated.

Name the solid.

State which reactant is in short supply when it forms.

Burning one mole of an alcohol in a limited supply of air releases less energy than burning one mole of the same alcohol in excess oxygen.

Explain why.