The pH scale and neutralisation

This question is about acids and alkalis.

Universal indicator is used to measure the pH of solutions.

Figure 16 shows the colours of universal indicator at different pH values.

A student added universal indicator to nitric acid in a beaker.

The student added drops of potassium hydroxide solution to the nitric acid until pH 7 was reached.

The student could not be sure that the pH of the mixture was 7

Give one reason why.

Use Figure 16.

Name a piece of equipment that could be used to give a more accurate measurement of pH.

Name the type of reaction when potassium hydroxide solution reacts with nitric acid.

The formula of nitric acid is HNO₃

Calculate the relative formula mass (M_r) of nitric acid.

Relative atomic masses (A_r): H = 1 N = 14 O = 16

Potassium hydroxide is an alkali.

Which ion do all alkalis contain?

Tick () one box.

H⁺ K⁺ O²⁻ OH⁻

The concentration of the solution of potassium hydroxide was 5.6 g/dm³.

Calculate the mass of potassium hydroxide in 5 cm³ of the solution.

1 dm³ = 1000 cm³

This question is about acids and alkalis.

Universal indicator is used to measure the pH of solutions.

Figure 3 shows the colours of universal indicator at different pH values.

A student added universal indicator to nitric acid in a beaker.

The student added drops of potassium hydroxide solution to the nitric acid until pH 7 was reached.

The student could not be sure that the pH of the mixture was 7

Give one reason why.

Use Figure 3.

Name a piece of equipment that could be used to give a more accurate measurement of pH.

Name the type of reaction when potassium hydroxide solution reacts with nitric acid.

The formula of nitric acid is HNO₃

Calculate the relative formula mass (M_r) of nitric acid.

Relative atomic masses (A_r): H = 1 N = 14 O = 16

Potassium hydroxide is an alkali.

Which ion do all alkalis contain?

Tick () one box.

H⁺ K⁺ O²⁻ OH⁻

The concentration of the solution of potassium hydroxide was 5.6 g/dm³.

Calculate the mass of potassium hydroxide in 5 cm³ of the solution.

1 dm³ = 1000 cm³

Excess hydrochloric acid in the stomach can cause pain. The excess hydrochloric acid can be neutralised by a calcium carbonate tablet.

A student investigated how the pH changed when a calcium carbonate tablet was added to hydrochloric acid.

This is the method used.

1. Add 10 cm³ of hydrochloric acid to a beaker.

2. Measure the pH of the hydrochloric acid using an indicator.

3. Add a calcium carbonate tablet to the hydrochloric acid.

4. Time for 3 minutes.

5. Measure the pH of the mixture using an indicator.

Which two of the following pieces of equipment are needed in this method?

Tick (✓) two boxes.

Measuring cylinder

Newtonmeter

Ruler

Stop clock

Thermometer

Name an indicator used to measure pH.

Name a piece of equipment that gives a more accurate pH value than an indicator.

The word equation for the reaction is:

calcium carbonate + hydrochloric acid calcium chloride + water + carbon dioxide

Why is fizzing seen during the reaction?

Give one safety precaution the student should have taken.

What is the pH of a neutral solution?

Tick (✓) one box.

1 4 7 10

A student reacted hydrochloric acid with excess calcium carbonate.

A solution of calcium chloride was produced.

Figure 5 shows the method used to produce calcium chloride crystals from the reaction mixture.

Describe the method shown in Figure 5 to produce calcium chloride crystals from the reaction mixture.

Include the equipment used.

This question is about acids and salts.

Nitric acid is a strong acid.

A solution of nitric acid can be dilute.

Explain how nitric acid can be both strong and dilute.

The pH value of a solution of nitric acid increases by 1.

How does the hydrogen ion concentration of the solution change?

Tick (✓) one box.

Decreases by a factor of 10

Decreases by a factor of 100

Increases by a factor of 10

Increases by a factor of 100

Question 8 continues in the next page

A student reacted nitric acid with excess calcium carbonate.

The word equation for the reaction is:

calcium carbonate + nitric acid calcium nitrate + water + carbon dioxide

This is the method used.

1. Measure 100 cm³ of nitric acid into a beaker.

2. Add calcium carbonate powder to the nitric acid.

3. Stir the mixture.

4. Repeat steps 2 and 3 until the calcium carbonate is in excess.

5. Filter the mixture.

Describe the additional steps that should be included in the method to determine the mass of calcium carbonate that reacted.

The formula of nitric acid is HNO₃

Which expression gives the percentage (%) by mass of oxygen in HNO₃?

Relative atomic mass (A_r): O = 16

Relative formula mass (M_r): HNO₃ = 63

Tick (✓) one box.

What is the formula of calcium nitrate?

Use the periodic table.

Tick (✓) one box.

CaNO₃

Ca(NO₃)₂

Ca₂NO₃

Ca₂(NO₃)₃

Question 8 continues in the next page

Magnesium chloride is a salt.

Calculate the number of magnesium ions in 47.5 g of magnesium chloride (MgCl₂).

Relative atomic masses (A_r): Mg = 24 Cl = 35.5

Avogadro constant = 6.02 × 10²³ per mole

This question is about acids and alkalis.

Which ion is produced by all acids in aqueous solution?

Tick (✓) one box.

Cl⁻ H⁺ Na⁺ OH⁻

The pH scale is a measure of the acidity or alkalinity of a solution.

What is used to measure the pH of a solution?

Tick (✓) one box.

Iodine solution

Limewater

Universal indicator

Give one safety precaution used when measuring the pH of an acid.

Sodium hydroxide solution reacts with sulfuric acid to produce a salt and one other product.

Which salt is produced when sodium hydroxide solution reacts with sulfuric acid?

Tick (✓) one box.

Sodium chloride

Sodium nitrate

Sodium sulfate

What is the other product when sodium hydroxide solution reacts with sulfuric acid?

Tick (✓) one box.

Oxygen

Sodium

Water

Draw one line from each solution to the pH of that solution.

What is the type of reaction when sodium hydroxide solution reacts with sulfuric acid?

Tick (✓) one box.

Combustion

Decomposition

Neutralisation

This question is about acids and alkalis.

Magnesium reacts with acids to produce a salt and hydrogen.

The ionic equation for the reaction is:

In a redox reaction, both oxidation and reduction occur.

Explain why this reaction is described as a redox reaction.

What happens to the pH of an acid when the hydrogen ion concentration decreases by a factor of ten?

Tick (✓) one box.

The pH decreases by 1.

The pH decreases by 10.

The pH increases by 1.

The pH increases by 10.

Write the ionic equation that represents the neutralisation reaction between an acid and an alkali in aqueous solution.

You should include state symbols.

A teacher demonstrates the reaction of potassium with water.

Give two observations seen when potassium reacts with water.

Potassium reacts with water to form a solution with a pH of 13.

Explain why the solution has a pH of 13.

You should refer to ions in your answer.

Figure 12 shows four models representing the same volume of:

a strong acid at two different concentrations

a weak acid at two different concentrations.

Which model represents the weak acid with the higher concentration?

Tick (✓) one box.

W X Y Z

Justify your answer.

Give two limitations of using the models in Figure 12 to represent acids.

One use of carbon dioxide is in fizzy drinks.

In fizzy drinks carbon dioxide gas dissolves in water to form an aqueous solution of

The equation for the reaction is:

Complete the equation by writing the state symbol for carbonic acid (H₂CO₃).

Choose the answer from the box.

Which ion causes carbonic acid to be acidic?

Tick (✓) one box.

Describe how to test the pH of carbonic acid.

Give the result of the test.

Ammonia gas is produced from nitrogen gas and hydrogen gas in a reversible reaction.

The word equation is:

nitrogen + hydrogen ammonia

Figure 12 represents an ammonia molecule.

What is the formula of ammonia?

When does a reversible reaction reach dynamic equilibrium?

Tick (✓) one box.

Which condition is needed for the reversible reaction between nitrogen and hydrogen to be at dynamic equilibrium?

Tick (✓) one box.

How can the direction of a reversible reaction be changed?

Iron is used as a catalyst in the industrial production of ammonia.

Why is a catalyst used?

150 000 million kg of ammonia is produced each year.

85% of the ammonia produced each year is used to manufacture fertilisers.

Calculate the mass of ammonia used each year to manufacture fertilisers.

Catalase is an enzyme.

What type of molecule is an enzyme?

Hydrogen peroxide decomposes in the presence of catalase.

This is the equation for the reaction:

Describe how the student could test for the gas produced.

A student investigated the effect of pH on the activity of catalase.

Describe how the student could use an indicator to measure the pH of a solution.

Table 6 shows the results.

What is the optimum pH for catalase in this reaction?

Use Table 6.

How could the student find a more accurate value for the optimum pH?

Tick (✓) one box.

Explain the result for catalase at pH 3.0

Catalase is an enzyme.

What type of molecule is an enzyme?

Hydrogen peroxide decomposes in the presence of catalase.

This is the equation for the reaction:

Describe how the student could test for the gas produced.

A student investigated the effect of pH on the activity of catalase.

Describe how the student could use an indicator to measure the pH of a solution.

Table 1 shows the results.

What is the optimum pH for catalase in this reaction?

Use Table 1.

How could the student find a more accurate value for the optimum pH?

Tick (✓) one box.

Explain the result for catalase at pH 3.0

A teacher demonstrated the temperature change when hydrochloric acid is added to sodium hydroxide.

This is the method used.

1. Add 25.0 cm³ of sodium hydroxide solution to a polystyrene cup.

2. Measure the temperature of the sodium hydroxide solution.

3. Add 25.0 cm³ of hydrochloric acid to the sodium hydroxide solution.

4. Stir the solution.

5. Measure the maximum temperature of the solution.

Draw one line from each measurement to the most suitable piece of equipment to use to make the measurement.

The teacher did the experiment four times.

Table 1 shows the teacher’s results.

Calculate the mean maximum temperature rise.

Do not use the anomalous result in your calculation.

How could the accuracy of the experiment be improved?

Tick one box.

The reaction between hydrochloric acid and sodium hydroxide is a neutralisation reaction.

The reaction produces a salt and one other product.

Complete the word equation for the reaction.

Universal indicator is used to measure the pH of solutions.

Hydrochloric acid is pH 1

Sodium hydroxide is pH 13

Draw one line from the pH to the colour of universal indicator in a solution with that pH.

A teacher demonstrated the temperature change when hydrochloric acid is added to sodium hydroxide solution.

This is the method used.

1. Measure 25 cm³ of sodium hydroxide solution using a measuring cylinder.

2. Add the sodium hydroxide solution to a polystyrene cup.

3. Record the temperature of the sodium hydroxide solution.

4. Add 5 cm³ of hydrochloric acid from a burette to the sodium hydroxide solution.

5. Stir the solution.

6. Record the temperature of the solution.

7. Repeat steps 4–6 until 50 cm³ of hydrochloric acid in total is added.

Table 1 shows some of the teacher’s results.

Figure 4 shows the results when 30 cm³ to 50 cm³ of hydrochloric acid was added to sodium hydroxide solution.

A line of best fit has been drawn through these results.

Complete Figure 4.

You should:

• plot the data from Table 1 on Figure 4

• draw a line of best fit through these results

• continue both lines of best fit until the lines meet.

Estimate the maximum temperature reached in the reaction.

Use Figure 4.

The teacher used a temperature sensor to measure the temperature of the reaction mixture.

What is the resolution of the temperature sensor?

Tick one box.

Suggest two ways of improving the accuracy of the results.

The pH of the solution changes as hydrochloric acid is gradually added to sodium hydroxide solution, until hydrochloric acid is in excess.

Describe how the pH of the solution changes.

Give reasons for these changes.

You should refer to the pH value of the solution at different stages in the procedure.

In a different demonstration the teacher used a 25 cm³ solution containing 1.4 g of sodium hydroxide.

Calculate the concentration of the sodium hydroxide solution in g/dm³