Strong & weak acids

This question is about hydrogen chloride (HC l) and hydrogen chlorate (HOC l).

Hydrogen chloride and hydrogen chlorate both form acids when dissolved in water.

Hydrogen chloride gas dissolves in water to form hydrochloric acid.

Give the state symbols for:

• hydrogen chloride

• water

• hydrochloric acid.

A solution of hydrochloric acid has:

• a concentration of H⁺ ions of 3.16 × 10⁻³ mol/dm³.

What is the concentration of H⁺ ions in a solution of hydrochloric acid that has a pH of 3.5?

Figure 5 shows the outer shells in one molecule of hydrogen chlorate (HOC l).

Complete the dot and cross diagram to show the electrons in the outer shells.

Figure 5

Hydrogen chlorate dissolves in water to form a weak acid.

Explain why a weak acid has a higher pH than a strong acid of the same concentration.

Hydrogen chloride is produced in the reaction between methane and chlorine.

Figure 6 represents the equation for the reaction.

Table 4 shows the bond energies.

Calculate the overall energy change for the reaction.

Nitric acid (HNO₃) is a strong acid.

What is meant by a ‘strong acid’?

Nitric acid is used as a dilute aqueous solution.

What is meant by ‘dilute aqueous solution’?

10 cm³ of a nitric acid solution has a pH of 1

Water is added to the nitric acid solution to change the pH of the nitric acid solution to pH 3

How does the hydrogen ion concentration change?

Tick () one box.

Write the ionic equation for the reaction between an acid and an alkali.

The equation shows the reaction between magnesium carbonate and nitric acid.

What is the ratio of the number of moles of magnesium carbonate to the number of moles of nitric acid in the reaction?

Tick () one box.

A student mixed some magnesium carbonate with excess nitric acid.

The student then added two drops of universal indicator to the solution.

What colour was the solution after the addition of universal indicator?

Tick () one box.

A student investigated the temperature change when different masses of

magnesium carbonate were reacted with excess nitric acid.

Figure 6 shows the apparatus.

This is the method used.

1. Pour 50 cm³ of nitric acid into a polystyrene cup.

2. Measure the temperature of the solution.

3. Add 0.50 g of magnesium carbonate.

4. Stir the mixture.

5. Measure the temperature.

6. Repeat steps 1 to 5 with different masses of magnesium carbonate.

Give two improvements to the method to produce more accurate results.

Do not refer to improvements to the apparatus in your answer.

This question is about hydrogen chloride and hydrochloric acid.

Complete the dot and cross diagram to represent the bonding in hydrogen chloride on Figure 7. Use dots (o) and crosses (x) to represent electrons. You should show only the electrons in the outer shells.

Hydrogen chloride dissolves in water to produce hydrochloric acid. Hydrochloric acid is a strong acid. What is meant by the term strong acid?

Describe how magnesium can be used to distinguish between a strong acid and a weak acid of the same concentration.

The concentration of hydrochloric acid is increased by a factor of 100 What is the change in pH?

Ethene and hydrogen chloride react to produce chloroethane. The displayed formulae equation for the reaction is:

The reaction is exothermic. In the reaction the energy released forming new bonds is 56 kJ/mol greater than the energy needed to break existing bonds. Table 1 shows some bond energies.

Calculate the bond energy X.

This question is about acids, alkalis and bases. A student reacted zinc oxide powder with hydrochloric acid to produce zinc chloride solution.

Complete the equation for the reaction by writing the state symbols.

Give one way that the student could speed up the reaction between zinc oxide powder and hydrochloric acid.

Hydrochloric acid was the limiting reactant.

How could the student know when all the hydrochloric acid has reacted?

How could the student obtain zinc chloride solution from the reaction mixture when all the hydrochloric acid has reacted?

Describe how zinc chloride crystals are produced from zinc chloride solution.

Sulfuric acid and sodium hydroxide react to produce sodium sulfate.

Sulfuric acid is gradually added to sodium hydroxide solution. The pH of the mixture changes as the sulfuric acid is added until in excess. Suggest the pH at:

• the start before sulfuric acid is added

• the end when sulfuric acid is in excess.

Complete the symbol equation for the preparation of sodium sulfate. You should balance the equation.

A solution of hydrochloric acid had a hydrogen ion concentration of 1.0 mol/dm³ Water was added to the hydrochloric acid until the pH increased by 1 What was the hydrogen ion concentration of the hydrochloric acid after water had been added? Tick (✓) one box.

A scientist does two tests on four white solids. The solids are labelled A, B, C and D Test 1 Adds the sample of the solid to distilled water and stirs. Test 2 Measures the pH of the solution after Test 1 Table 2 shows the results.

These four solids are:

• magnesium oxide

• phosphorus oxide

• silicon dioxide

• sodium oxide.

Table 3 shows the solubility of these four solids in water.

Identify the solids A, B, C and D. Explain your answers.

10 cm³ of solution B is added to a beaker. Distilled water is added to the beaker until the final volume in the beaker is 1000 cm³ The pH of the solution is measured before and after distilled water is added. Table 4 shows the results.

Calculate the value of X.