The pH scale & neutralisation

A student investigates the reaction of magnesium carbonate and dilute sulfuric acid.

The student wants to measure the pH of the dilute sulfuric acid.

Suggest the pH of dilute sulfuric acid.

Name an indicator that the student could use to measure the pH of dilute sulfuric acid.

State the colour of the indicator after it has been added to the dilute sulfuric acid.

Name of indicator........

Name a piece of equipment the student could use to measure the pH more accurately.

When magnesium carbonate reacts with dilute sulfuric acid, it forms a salt, water and carbon dioxide.

What is the name of the salt?

The student adds an excess of magnesium carbonate to dilute sulfuric acid until no more of it reacts.

magnesium carbonate(s) + sulfuric acid(aq) salt(aq) + water(l) + carbon dioxide(g)

Magnesium carbonate is a white powder that is insoluble in water.

A colourless solution of the salt is formed.

Describe two observations the student would see as the reaction is happening.

The student separates the salt from the solution formed at the end of the reaction.

Step 1: They remove the excess magnesium carbonate.

Step 2: They remove the water from the salt solution.

State the names of the separation techniques used in Step 1 and Step 2.

The student measures the mass of the salt obtained when different masses of magnesium carbonate are added to the same volume of dilute sulfuric acid.

The table shows their results.

Describe the relationship between the mass of magnesium carbonate and the mass of the salt.

A student thinks that when 6.0 g of magnesium carbonate has been added it is in excess.

Explain why the student is correct.

A student investigates the reaction of magnesium carbonate and dilute sulfuric acid.

The student wants to measure the pH of the dilute sulfuric acid.

Suggest the pH of dilute sulfuric acid.

Name an indicator that the student could use to measure the pH of dilute sulfuric acid.

State the colour of the indicator after it has been added to the dilute sulfuric acid.

Name of indicator........

Name a piece of equipment the student could use to measure the pH more accurately.

When magnesium carbonate reacts with dilute sulfuric acid, it forms a salt, water and carbon dioxide.

What is the name of the salt?

The student adds an excess of magnesium carbonate to dilute sulfuric acid until no more of it reacts.

magnesium carbonate(s) + sulfuric acid(aq) salt(aq) + water(l) + carbon dioxide(g)

Magnesium carbonate is a white powder that is insoluble in water.

A colourless solution of the salt is formed.

Describe two observations the student would see as the reaction is happening.

The student separates the salt from the solution formed at the end of the reaction.

Step 1: They remove the excess magnesium carbonate.

Step 2: They remove the water from the salt solution.

State the names of the separation techniques used in Step 1 and Step 2.

The student measures the mass of the salt obtained when different masses of magnesium carbonate are added to the same volume of dilute sulfuric acid.

The table shows their results.

Describe the relationship between the mass of magnesium carbonate and the mass of the salt.

A student thinks that when 6.0 g of magnesium carbonate has been added it is in excess.

Explain why the student is correct.

The table shows the colours of an indicator at different pH values.

Which colour is this indicator in a neutral solution?

A Green

B Orange

C Pink

D Purple

Nitrogen is a gas found in the Earth’s atmosphere.

The table shows the percentages of different gases found in the Earth’s atmosphere.

Calculate the percentage of nitrogen in the Earth’s atmosphere.

Nitrogen reacts with hydrogen to form ammonia.

The word equation for the reaction is:

Describe how the word equation shows that the reaction is reversible.

The word equation for the forward reaction is:

Write the word equation for the backward reaction.

This table shows the percentage of ammonia produced in the reaction at different pressures.

Plot the data from the table on the graph. The first two points are already plotted.

Draw the curve of best fit.

Oxides of nitrogen released from cars cause acid rain.

Oxides of nitrogen responsible for acid rain are given the formula NO_x.

What is the value of x in nitrogen dioxide?

Normal rain water is slightly acidic.

Describe a test and its result to show that acid rain is more acidic than normal rain water.

Test........

Result........

Acid rain is a dilute solution of a weak acid.

What is the pH of acid rain?

A 1–2

B 4–5

C 8–9

D 13–14

Zinc, Zn, reacts with sulfuric acid, H₂SO₄, to form the salt, ZnSO₄, and hydrogen.

Write the balanced symbol equation for the reaction of zinc with sulfuric acid.

Name the salt, ZnSO₄, made from zinc and sulfuric acid.

To make sure all the sulfuric acid reacts, an excess of zinc is used.

Describe how universal indicator could be used to show that all the sulfuric acid has reacted.

Calculate the relative formula mass of ZnSO₄.

Relative atomic mass (A_r): O = 16.0 S = 32.1 Zn = 65.4

Relative formula mass of ZnSO₄ =........

The percentage mass of an element in a compound can be calculated using the formula

Calculate the percentage mass of zinc in ZnSO₄.

Give your answer to 1 decimal place.

The reaction between zinc and sulfuric acid is exothermic.

Explain what is meant by an exothermic reaction.

The diagram shows the reaction profile for the reaction.

Label the activation energy on the diagram.

Explain the term activation energy.

The table shows the temperature changes in four reactions.

The reaction between zinc and sulfuric acid is slightly exothermic.

Which shows the reaction between zinc and dilute sulfuric acid?

Give a reason for your answer.

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

Hydrochloric acid, HC l (aq), is an example of a strong acid.

The graph shows the pH of a dilute hydrochloric acid solution at different concentrations.

Concentration of dilute hydrochloric acid solution (mol/dm³)

Write the formula of the ion that gives the dilute hydrochloric acid solution the pH shown on the graph.

The pH of the dilute hydrochloric acid solution can be measured using either universal indicator or a pH meter.

Explain which method would be better to use for measuring the pH shown on the graph.

Describe how the pH changes with the concentration of dilute hydrochloric acid solution on the graph.

As the concentration of the dilute hydrochloric acid solution increases by a factor of ten, the pH of the solution decreases by one.

Use data from the graph to show that this statement is true.

Calculate the mass of hydrochloric acid, HCl, in 100 cm³ of solution that gives a pH 1.5. (e)

Use data from the graph.

Give your answer to 2 significant figures.

Relative molecular mass (M_r): HCl = 36.5

The table shows the colours of universal indicator in solutions of different pH.

A sample of water has a pH of 7. A small amount of dilute hydrochloric acid is added to the water.

Which colour does universal indicator turn in this solution?

A Blue

B Green

C Orange

D Purple

A solution has a pH of 3.

The solution is diluted with water by a factor of 1000.

What is the pH of the solution after dilution?

A 2

B 4

C 5

D 6

Calcium is a metal found in Group 2 of the Periodic Table.

Draw the arrangement of electrons in an atom of calcium.

Calcium is a metal which can conduct electricity.

Describe the structure and bonding in a metal and explain why metals can conduct electricity.

You can include a diagram in your answer.

Calcium reacts with water to form a solution of calcium hydroxide, Ca(OH)₂, and hydrogen.

Write the balanced symbol equation for the reaction of calcium with water.

Include state symbols in your equation.

A solution of calcium hydroxide is also called limewater.

Name the gas limewater is used as a test for.

Calculate the number of moles in 1.88 g of calcium hydroxide.

Give your answer to 2 significant figures.

Relative atomic mass (A_r): H = 1.0 O = 16.0 Ca = 40.1

Use your answer to part (d)(i) to calculate the concentration of calcium hydroxide in the solution formed.

Give your answer in mol / dm³.

Concentration of solution =........ mol / dm³

A student adds an excess of dilute hydrochloric acid, HC l, to a solution of calcium hydroxide, Ca(OH)₂.

Write the balanced ionic equation for the reaction of dilute hydrochloric acid and a solution of calcium hydroxide.

Describe and explain how the pH of the solution of calcium hydroxide changes as the dilute hydrochloric acid is added until it is in excess.

A student investigates how the pH of dilute hydrochloric acid changes as sodium hydroxide solution is added to it.

Fig. 13.1 shows the equipment the student uses.

The student:

• Adds 10 cm³ dilute hydrochloric acid to X.

• Adds 0.5 cm³ of the sodium hydroxide solution to the dilute hydrochloric acid.

• Swirls the mixture and measures its pH with a pH probe.

• Repeats adding 0.5 cm³ of the sodium hydroxide solution each time until 10 cm³ of the sodium hydroxide solution has been added.

What is the name of the piece of equipment labelled X ?

The student plots a graph of some of their results.

Look at the table. It shows the rest of the student’s results.

Plot the results on the graph and draw a line of best fit.

Volume of sodium hydroxide solution (cm³)

The dilute hydrochloric acid is exactly neutralised when the pH of the mixture is 7.

Use the graph to work out the volume of sodium hydroxide solution needed to exactly neutralise the dilute hydrochloric acid.

A solution has a hydrogen ion concentration of 1 × 10^–6 mol / dm³. The solution has a pH of 6. 9

What is the hydrogen ion concentration of a solution with a pH of 3?

1 × 10^–9 mol / dm³ A

1 × 10^–6 mol / dm³ B

1 × 10^–3 mol / dm³ C

1 × 10^–1 mol / dm³ D

Phosphoric acid, H₃PO₄, is a strong acid.

A student investigates how the pH of a solution of dilute phosphoric acid changes when a solution of calcium hydroxide is slowly added to it from a burette.

The student then calculates the concentration of hydrogen ions as the pH changes.

Table 16.1 shows the results of her experiment.

Explain why phosphoric acid is described as a strong acid.

Explain why the solution of phosphoric acid used is described as dilute.

Complete the balanced symbol equation for the reaction between phosphoric acid and calcium hydroxide.

A student tests three solutions A, B and C. He wants to identify which solution is acidic.

The student adds a metal carbonate to each solution.

Table 13.1 shows his results.

Which solution, A, B or C, is acidic?

Tick (✓) one box.

Suggest a pH value for the acidic solution.

Write down two other tests the student could use to identify that the solution is acidic.

The student adds the acidic solution to a solution of sodium hydroxide. A neutralisation reaction takes place.

He records the pH of the mixture.

Table 13.2 shows his results.

Describe the relationship between the volume of acidic solution added and the pH of the mixture.

Sodium hydroxide is an alkali.

Which ion do solutions of alkalis contain?

H⁺ Na⁺ OH^– SO₄^2–

In a different neutralisation reaction sulfuric acid, H₂SO₄, reacts with sodium hydroxide, NaOH.

Complete the balanced symbol equation for this reaction.

The student measures how the pH of the solution changes as the acid is added.

Look at the graph of her results.

What volume of acid is needed to neutralise the alkali?

The mixture becomes less alkaline as the acid is added.

Describe how the pH of the mixture changes as the acid is added.

Explain why the mixture becomes less alkaline as the acid is added.

Use ideas about hydrogen ions and pH in your answer.