The Characteristic Properties of Acids & Bases (Cambridge (CIE) O Level Chemistry): Exam Questions

Sulfuric acid is a strong acid. In aqueous solution, it ionises as shown below.

H₂SO₄  → 2H⁺ + SO₄^2–

i) What is meant by the term acid?

[1]

   Sulfurous acid, H₂SO₃, is a weak acid.

ii) State the difference between a weak acid and a strong acid.

[2]

Sulfurous acid forms salts called sulfites and contain the ion SO₃^2-

When barium nitrate solution is added to aqueous sulfurous acid, a white precipitate, A, forms. Bromine water changes from brown to colourless when added to aqueous sulfurous acid. 

Bromine oxidises sulfurous acid. When this solution is tested with acidified barium nitrate a different white precipitate B is formed. 

i) Identify the white precipitate, A.

[1]

ii) Identify the white precipitate, B.

[1]

iii) Write an ionic equation for the reduction of the bromine molecule.

[1]

iv) Name the product formed by the oxidation of sulfurous acid.

[1]

Complete the following word equations.

i) magnesium hydroxide + dilute sulfuric acid

   ........................................................................................................

[1]

ii) zinc + dilute sulfuric acid

   ........................................................................................................

[1]

iii) copper carbonate + dilute sulfuric acid

   ........................................................................................................

[1]

Write equations for the reaction of dilute sulfuric acid with each of the following.

i) ammonia

[1]

ii) sodium hydroxide

[2]

iii) iron

[2]

Match the following pH values to the solutions given below

1    3    7    10    13 

The solutions all have the same concentration.

Explain why solutions of hydrochloric acid and ethanoic acid with the same concentration, in mol/dm³, have a different pH.

Measuring pH is one way of distinguishing between a strong acid and a weak acid.

Describe another method.

method ....................................................................................................................................................................................................................

results ....................................................................................................................................................................................................................

Four bottles were known to contain aqueous ammonia, dilute hydrochloric acid, sodium hydroxide solution and vinegar, which is dilute ethanoic acid. The bottles had lost their labels. The pH values of the four solutions were 1, 4, 10 and 13.

Complete the table.

When nitric acid is added to water the following reaction occurs.

HNO₃ + H₂O → NO₃^– + H₃O⁺

Give the name and the formula of the particle which is transferred from nitric acid to water.

name

formula

This question is concerned with the following oxides.

i) Which of the above oxides will react with hydrochloric acid but not with aqueous sodium hydroxide?

[1]

ii) Which of the above oxides will react with aqueous sodium hydroxide but not with hydrochloric acid?

[1]

iii) Which of the above oxides will react both with hydrochloric acid and with aqueous sodium hydroxide?

[1]

iv) Which of the above oxides will react neither with hydrochloric acid nor with aqueous sodium hydroxide?

[1]

Sulfuric acid is a strong acid. Hexanesulfonic acid is also a strong acid. It has similar properties to sulfuric acid.

The formula of the hexanesulfonate ion is C₆H₁₃SO₃^–.

The formula of the barium ion is Ba²⁺. What is the formula of barium hexanesulfonate?

Complete the following equations.

i) Magnesium + hexanesulfonic acid → ............................. ......................... + ......................... 

[1]

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

[1]

iii) .....C₆H₁₃SO₃H + Na₂CO₃ → ............................. + ............ + ............

[2]

i) Sulfuric acid is a strong acid. You are given aqueous sulfuric acid, concentration 0.1 mol /dm³ , and aqueous hexanesulfonic acid, concentration 0.2 mol /dm³. Describe how you could show that hexanesulfonic acid is also a strong acid.

[2]

ii) Deduce why, for a fair comparison, the two acid solutions must have different concentrations. 

[1]

iii) Explain the terms strong acid and weak acid.

[2]

A student investigates the reaction of small pieces of zinc with dilute sulfuric acid at 20 °C. The zinc is in excess. Sulfuric acid is a compound.

Define the term compound.

State the formula of the ion that is present in an aqueous solution of all acids.

A few drops of the indicator methyl orange are added to aqueous dilute sulfuric acid. State the colour change observed

from orange to ____________________

The formula of sulfuric acid is H₂SO₄.
Complete Table 1 to calculate the relative molecular mass of sulfuric acid.                                                                                   

Table 1

Aqueous sodium hydroxide is a base.

Complete this sentence about the different types of bases. Bases are metal hydroxides or metal _______________________

Describe the reaction of aqueous sodium hydroxide with:

i) A named acid

ii) An ammonium salt

Ammonia is a soluble base.
Draw a circle around the pH value of aqueous ammonia.                            

pH 1    pH 5    pH 7    pH 10

Magnesium, calcium and strontium are Group II elements.

Calcium reacts with cold water to form two products:

• a colourless gas, P, which ‘pops’ with a lighted splint

• a weakly alkaline solution, Q, which turns milky when carbon dioxide is bubbled through it.

Name gas P.

Identify the ion responsible for making solution Q alkaline.

Suggest the pH of solution Q.

Write a symbol equation for the reaction of calcium with cold water.

Separate: Chemistry and Extended Only

Sulfuric acid has many uses. Sulfuric acid is a strong acid.

Define the term acid.

Separate: Chemistry and Extended Only

Define the term strong acid.

Ammonia reacts with water to form ions.                                      

NH₃ + H₂ONH₄⁺ + OH^–

How does this equation show that ammonia, NH₃, behaves as a base?

Aqueous ammonia is described as a weak base. Suggest the pH of aqueous ammonia.

Aqueous sodium hydroxide, NaOH (aq), is a strong alkali that reacts with dilute sulfuric acid exothermically. What type of reaction is this?

Ethanoic acid is a weak acid and hydrochloric acid is a strong acid. Both ethanoic acid and hydrochloric acid dissociate in aqueous solution.

Define the term acid.

The chemical equation shows the changes which occur when the strong acid, hydrochloric acid, is added to water.  

                                    HCl (aq)H⁺ (aq) + Cl^– (aq)

Complete the chemical equation to show the changes which occur when the weak acid, ethanoic acid, is added to water.

CH₃COOH (aq)  ______________________________

Hydrogen reacts with the halogens to form hydrogen halides.

Bond energy is the amount of energy, in kJ, that must be supplied (endothermic) to break one mole of a bond.

Use the above data to show that the following reaction is exothermic.

H─H + Cl─Cl → 2H─Cl

They react with water to form acidic solutions.

HCl + H₂O  H₃O⁺ + Cl^–

HF + H₂O  H₃O⁺ + F^–

i) Explain why water behaves as a base in both of these reactions.

[2]

ii) At equilibrium, only 1% of the hydrogen chloride exists as molecules, the rest has formed ions. In the other equilibrium, 97% of the hydrogen fluoride exists as molecules, only 3% has formed ions.

 What does this tell you about the strength of each acid?

[2]

iii) How would the pH of these two solutions differ?

[1] 

Ethylamine is a weak base and sodium hydroxide is a strong base.

i) In terms of proton transfer, explain what is meant by the term weak base.

[2]

ii) Given aqueous solutions of both bases, describe how you could show that sodium hydroxide is the stronger base. How could you ensure a ‘fair’ comparison between the two solutions? 

[3]

Ethylamine reacts with acids to form salts.

CH₃CH₂NH₂ + HCl → CH₃CH₂NH₃Cl                
ethylammonium chloride

i) Complete the equation for the reaction between sulfuric acid and ethylamine.

......CH₃CH₂NH₂ + ............ → .........................

Name the salt formed.

[3]

ii) Amines and their salts have similar chemical properties to ammonia and ammonium salts.

Suggest a reagent that could be used to displace the weak base, ethylamine, from its salt ethylammonium chloride.

[1]

Gases diffuse, which means that they move to occupy the total available volume.

i) Explain, using kinetic particle theory, why gases diffuse.

[2] 

ii) When the colourless gases hydrogen bromide and ethylamine come into contact, a white solid is formed.

CH₃CH₂NH₂ (g) + HBr (g) → CH₃CH₂NH₃Br (s)                

white solid

The following apparatus can be used to compare the rates of diffusion of the two gases ethylamine and hydrogen bromide.

Predict at which position, A, B or C, the white solid will form. Explain your choice.

[3]

Sulfuric acid and malonic acid are both dibasic acids. One mole of a dibasic acid can form two moles of hydrogen ions.

H₂SO₄ → 2H⁺ + SO₄^2–

Dibasic acids can form salts of the type Na₂X and CaX.

Malonic acid is a white crystalline solid which is soluble in water. It melts at 135 °C. The structural formula of malonic acid is given below. It forms salts called malonates.

CH₂(COOH)₂ or HOOC–CH₂ –COOH

i) How could you determine if a sample of malonic acid is pure?

Technique used ..........................................................................................................

Result if pure .........................................................................................................

[2]

ii) What is the molecular formula of malonic acid?

[1]

iii) When malonic acid is heated there are two products, carbon dioxide and a simpler carboxylic acid. Deduce the name and molecular formula of this acid.

[2]

iv) Malonic acid reacts with ethanol to form a colourless liquid which has a ‘fruity’ smell. Its structural formula is given below.

What type of compound contains the group which is circled?

[1] 

i) Suggest why a solution of malonic acid, concentration 0.2 mol /dm³, has a higher pH than one of sulfuric acid of the same concentration.

[1]

ii) Describe a test, other than measuring pH, which can be carried out on both acid solutions to confirm the explanation given in (b)(i) for the different pH values of the two acids.

[2]

Complete the following equations for reactions of these two acids.

i) sodium hydroxide + malonic acid → ........................ .......................... + ....................

[1]

ii) CuO + H₂SO₄ → .................... + ....................

[2]

iii) Mg + CH₂(COOH)₂ → .................... + ....................

[2]

iv) K₂CO₃ + H₂SO₄ → .................... + .................... + ....................

[2]

Ethylamine, CH₃–CH₂–NH₂, is a base which has similar properties to ammonia.

In aqueous ethylamine, there is the following equilibrium.

CH₃–CH₂–NH₂ + H₂O CH₃–CH₂–NH₃⁺ + OH^–

Explain why water is behaving as an acid in this reaction.

Given aqueous solutions of ethylamine and sodium hydroxide, describe how you could show that ethylamine is a weak base like ammonia and not a strong base like sodium hydroxide.

Ethylamine, like ammonia, reacts with acids to form salts.

CH₃–CH₂–NH₂ + HCl → CH₃–CH₂–NH₃Cl                                                         ethylammonium chloride

Suggest how you could displace ethylamine from the salt, ethylammonium chloride.

Explain the chemistry of the following reaction:

When aqueous ethylamine is added to aqueous iron(III) chloride, a brown precipitate is formed.

Silicon(IV) oxide, SiO₂, and zirconium(IV) oxide, ZrO₂, are both macromolecules. They have similar physical properties but silicon(IV) oxide is acidic and zirconium(IV) oxide is amphoteric.

Define the term macromolecule.

i) Predict three physical properties of these two oxides.

[3]

ii) Name an element which has the same physical properties as these two oxides.

[1]

i) Name a reagent that reacts with the oxides of both elements.

[1]

ii) Name a reagent that reacts with only one of the oxides.

reagent ..........................................

oxide which reacts .........................................

[2]

Sulphuric acid is a typical strong acid.

Change the equations given into a different format.

i) Mg + H₂SO₄ → MgSO₄ + H₂

Change into a word equation.

[1]

ii) Lithium oxide + sulphuric acid → lithium sulphate + water

Change into a symbol equation.

[2]

iii) CuO + 2H⁺ → Cu²⁺ + H₂O

Change the ionic equation into a symbol equation.

[2]

iv) Na₂CO₃ + H₂SO₄ → Na₂SO₄ + CO₂ + H₂O Change into a word equation.

[1]

When sulphuric acid dissolves in water, the following reaction occurs.

H₂SO₄ + H₂O → HSO₄^– + H₃O⁺

Explain why water is behaving as a base in this reaction.

Sulphuric acid is a strong acid, ethanoic acid is a weak acid.

Explain the difference between a strong acid and a weak acid.

The major use of sulfur dioxide is to manufacture sulfuric acid.

Complete the following description of the manufacture of sulfuric acid.

Sulfur dioxide reacts with .............................. to form sulfur trioxide.

The above reaction is catalysed by ................................................. .

The optimum temperature for this reaction is .............................. °C.

i) Define the term acid.

[1]

ii) Sulfuric acid is a strong acid. Ethanedioic acid is a weak acid. Given solutions of both acids, how could you show that sulfuric acid is a strong acid and ethanedioic acid is a weak acid?

Method

[1]

   Result for each acid

[1]

20.0 cm³ of sulfuric acid, concentration 0.30 mol / dm³, was added to 40 cm³ of sodium hydroxide, concentration 0.20 mol / dm³.

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

i) How many moles of H₂SO₄ were added?

[1]

ii) How many moles of NaOH were used?

[1]

iii) Which reagent is in excess? Give a reason for your choice.

Reagent in excess 

[1]

Reason

[1]

iv) Is the pH of the final mixture less than 7, equal to 7 or more than 7?

[1]