Carboxylic Acids (Cambridge (CIE) O Level Chemistry): Exam Questions

Methanoic acid is the first member of the homologous series of carboxylic acids.

Give two general characteristics of a homologous series.

In some areas when water is boiled, the inside of kettles become coated with a layer of calcium carbonate. This can be removed by adding methanoic acid.

i) Complete the equation.

............ HCOOH + CaCO₃ → Ca(HCOO)₂ + ................. + .................

[2]

ii) Methanoic acid reacts with most metals above hydrogen in the reactivity series. Complete the word equation.

zinc + methanoic acid → ............................................ + ............................................

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iii) Aluminium is also above hydrogen in the reactivity series.
Why does methanoic acid not react with an aluminium kettle?

[1]

Give the name, molecular formula and empirical formula of the fourth acid in this series.

name ..........................................................................................................

[1]

molecular formula .......................................................................................................

[1]

empirical formula ........................................................................................................

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The ester linkage showing all the bonds is drawn as

or more simply it can be written as –COO–.

i) Give the structural formula of the ester ethyl ethanoate.

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ii) Deduce the name of the ester formed from methanoic acid and butanol.

[1]

Draw the structural formula of the polyester formed from the following monomers.

HOOCC₆H₄COOH and HOCH₂CH₂OH

You are advised to use the simpler form of the ester linkage.

Esters can be used as solvents in chromatography. The following shows a chromatogram of plant acids.

An ester was used as the solvent and the chromatogram was sprayed with bromothymol blue.

i) Suggest why it was necessary to spray the chromatogram.

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ii) Explain what is meant by the R_f value of a sample.

[1]

iii) Calculate the R_f values of the two samples and use the data in the table to identify the plant acids.

[2]

The alcohols form a homologous series. The first member of this series is methanol, CH₃OH.

i) Give the general formula of the alcohols.

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ii) The mass of one mole of an alcohol is 116 g. What is its formula? Show your reasoning.

[2]

ii) Draw a diagram showing the arrangement of the outer (valency) electrons in one molecule of methanol.

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

[3]

Methanol is manufactured using the following method.

CH₄ (g) + H₂O (g) → CO (g) + 3H₂ (g)   reaction 1
CO (g) + 2H₂ (g) CH₃OH (g)    reaction 2

The conditions for reaction 2 are:

The forward reaction is exothermic.

i) Why is high pressure used in reaction 2?

[2]

ii) Explain why using a catalyst at 250 °C is preferred to using a higher temperature of 350°C and no catalyst.

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Methanol is oxidised by atmospheric oxygen. This reaction is catalysed by platinum.

i) The products of this reaction include a carboxylic acid. Give its name and structural formula.

[2]

ii) Deduce the name of the ester formed by the reaction of methanol with the carboxylic acid named in (i).

[1]

Propenoic acid is an unsaturated carboxylic acid. The structural formula of propenoic acid is given below.

i) Describe how you could show that propenoic acid is an unsaturated compound. 

Test:

Result:

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ii) Without using an indicator, describe how you could show that a compound is an acid.

Test:

Result:

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Propenoic acid reacts with ethanol to form an ester. Deduce the name of this ester. Draw its structural formula.

Name of ester:

Structural formula showing all bonds:

An organic compound has a molecular formula C₆H₈O₄. It is an unsaturated carboxylic acid. One mole of the compound reacts with two moles of sodium hydroxide.

i) Explain the phrase molecular formula.

[2]

ii) One mole of this carboxylic acid reacts with two moles of sodium hydroxide.
How many moles of –COOH groups are there in one mole of this compound?

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iii) What is the formula of another functional group in this compound?

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iv) Deduce a structural formula of this compound.

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Propanoic acid is a carboxylic acid. Its formula is CH₃–CH₂–COOH. 

i) Propanoic acid is the third member of the homologous series of carboxylic acids.

 Give the name and structural formula of the fourth member of this series.

  Name ..............................................................

  Formula ..............................................................

[2]

ii) Members of a homologous series have very similar chemical properties.

  State three other characteristics of a homologous series.

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Carboxylic acids can be made by the oxidation of alcohols.

 i) Draw the structural formula of the alcohol which can be oxidised to propanoic acid. Show all atoms and bonds.

[1]

ii) Name a reagent, other than oxygen, which can oxidise alcohols to carboxylic acids.

[2]

Complete the following equations for some of the reactions of propanoic acid.

The salts of this acid are called propanoates. 

i) Zinc + propanoic acid → ........................... ........................... + hydrogen

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ii) Calcium oxide + propanoic acid →........................... + ...........................

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iii) LiOH + CH₃CH₂COOH → ............................... + ...........................

[1]

A piece of magnesium was added to 100 cm³ of an aqueous acid. The time taken for the metal to react completely was measured.

This experiment was repeated using different aqueous acids. The same volume of acid was used in each experiment and the pieces of magnesium used were identical.

In one experiment the reaction was carried out at a different temperature.

Explain the following in terms of collision rate between reacting particles.  

i) Why is the rate in experiment C slower than the rate in experiment A? 

[2]

ii) Why is the rate in experiment B faster than the rate in experiment A?

[2]

iii) Why is the rate in experiment D faster than the rate in experiment A?

[3]

Structural formulae are an essential part of Organic Chemistry.

Draw the structural formula of each of the following. Show all the bonds in the structure.

i) ethanoic acid

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ii) ethanol

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Ethanoic acid and ethanol react to form an ester.

i) What is the name of this ester?

[1]

ii) The same linkage is found in polyesters. Draw the structure of the polyester which can be formed from the monomers shown below.

HOOC—C₆H₄—COOH and HO—CH₂—CH₂—OH

[3]

iii) Describe the pollution problems caused by non-biodegradable polymers.

[2]

Two macromolecules have the same amide linkage. Nylon, a synthetic polymer, has the following structure.

Protein, a natural macromolecule, has the following structure.

How are they different?

Carboxylic acids contain the group

Ethanoic acid is a typical carboxylic acid. It forms ethanoates.

i) Complete the following equations.

Mg + ......CH₃COOH → ............................... + ...............................

[2]

sodium hydroxide + ethanoic acid → ........................  ........................ + ........................

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ii) Ethanoic acid reacts with ethanol to form an ester. Give the name of the ester and draw its structural formula. Show all of the bonds.

[2]

Maleic acid is an unsaturated acid. 5.8 g of this acid contained 2.4 g of carbon, 0.2 g of hydrogen and 3.2 g of oxygen.

i) How do you know that the acid contained only carbon, hydrogen and oxygen?

[1]

ii) Calculate the empirical formula of maleic acid.

Number of moles of carbon atoms = ................................
Number of moles of hydrogen atoms = ................................
Number of moles of oxygen atoms = ................................
The empirical formula is ......................................................................................

[3]

iii) The mass of one mole of maleic acid is 116 g. What is its molecular formula?

[2]

iv) Maleic acid is dibasic. One mole of acid produces two moles of H⁺. Deduce its structural formula.

[2]

Esters, fats and polyesters all contain the ester linkage.

The structural formula of an ester is given below.

 Name two chemicals that could be used to make this ester and draw their structural formulae. Show all bonds. 

names ......................................................... and ..............................................................

[2]

   structural formulae

[2]

i) Draw the structural formula of a polyester such as Terylene.

[2]

ii) Suggest a use for this polymer.

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