Strong & weak acids

This question is about alkalis and acids.

What is the formula of the ion that all alkalis contain when in solution?

A student planned a titration experiment to determine the concentration of a sodium hydroxide solution.

This is the student’s plan.

1. Measure 25.0 cm³ of sulfuric acid of known concentration using a pipette.

2. Add the sulfuric acid to a conical flask.

3. Add 3 drops of universal indicator to the conical flask.

4. Place the conical flask on a white tile.

5. Fill a burette with sodium hydroxide solution to the 0.00 cm³ mark.

6. Add sodium hydroxide solution to the conical flask and swirl the flask.

7. Stop adding sodium hydroxide solution when there is a colour change.

8. Record the volume of sodium hydroxide solution used.

9. Repeat steps 1 to 8 until consistent results are obtained.

Suggest two improvements to the plan.

Give one reason for each improvement.

Figure 9 shows the burette after one titration.

What is the reading on the burette?

In a different titration, 25.0 cm³ of 0.216 mol/dm³ sulfuric acid needed 11.25 cm³ of sodium hydroxide solution for neutralisation.

The equation for the reaction is:

Calculate the concentration of the sodium hydroxide solution.

Table 4 gives information about solutions of two acids.

Which is a correct statement about the solutions of HC l and HCN in Table 4 ?

Tick () one box.

In Table 4, the solution of HC l has a lower pH than the solution of HCN.

Explain why.

Use the data in Table 4.

This question is about acids and their reactions.

Acids can be either weak or strong.

What is meant by ‘a weak acid’?

Explain what happens to the pH of an acid as the acid is diluted with water.

A student does a titration to find the volume of acid needed to neutralise an alkali.

The student fills a burette with the acid.

Give three more steps the student must do before adding the acid to the alkali from the burette.

You should name any equipment used.

The student titrated a solution containing 0.0045 moles of sodium hydroxide with 0.15 mol/dm³ hydrochloric acid.

The equation for the reaction is:

Calculate the volume of hydrochloric acid in cm³ needed in the titration.

A calcium atom is larger than a magnesium atom.

Explain why calcium reacts more vigorously than magnesium with hydrochloric acid of the same concentration.

This question is about acids and alkalis.

Ethanoic acid is a weak acid. What is meant by ‘weak acid’? Answer in terms of ionisation.

The concentration of an acid can be measured in mol/dm³. Which combination of changes increases the concentration of an acid? Tick (✓) one box.

The concentration of an acid can be determined by titration. An indicator is added to an alkali in a flask.

Name an indicator that can be used in this titration. Give the colour change of the indicator when acid from a burette is added to the alkali in the flask.

Sodium carbonate dissolves in water to produce an alkaline solution. Give the formula of the ion that makes a solution alkaline.

A student does a titration using sodium carbonate solution and nitric acid. The equation for the reaction is:

25.0 cm³ of 0.124 mol/dm³ sodium carbonate solution is neutralised by

Calculate the concentration of the nitric acid. Give your answer to 3 significant figures. You should calculate:

• the number of moles of sodium carbonate in 25.0 cm³ of the solution

• the number of moles of nitric acid in 23.6 cm³ of the nitric acid

• the concentration of the nitric acid in mol/dm³.

When hydrochloric acid dissolves in water, hydrogen ions (H⁺) and chloride ions (Cl⁻) are produced.

A solution of hydrochloric acid with pH 4.5 has a concentration of H⁺ ions of

What is the concentration of H⁺ ions in a solution of hydrochloric acid with pH 2.5?

Which element has atoms that have the same electronic structure as the chloride ion? Use the periodic table.

This question is about acids and alkalis.

Explain why the pH of an acid depends on:

• the strength of the acid

• the concentration of the acid.

A student titrated 25.00 cm³ of hydrochloric acid with 0.100 mol/dm³ barium hydroxide solution. Table 2 shows the results.

The student calculated the volume of barium hydroxide solution to be used in the

Explain why the student used a volume of 23.50 cm³ of barium hydroxide solution in the titration calculation.

25.00 cm³ of the hydrochloric acid reacted with 23.50 cm³ of the 0.100 mol/dm³ barium hydroxide solution. The equation for the reaction is:

Calculate the concentration of the hydrochloric acid in mol/dm³.

Another student titrated sulfuric acid with barium hydroxide solution. The equation for the reaction is:

The student measured the electrical conductivity of the mixture during the titration. The better a conductor, the higher the electrical conductivity value. Figure 10 shows the results.

Explain why the electrical conductivity of the mixture was zero when the sulfuric acid had just been neutralised. Use the equation for the reaction. Refer to ions in your answer.

The student then added a further 10 cm³ of barium hydroxide solution. The electrical conductivity of the mixture increased. Give one reason why.

This question is about acids. Hydrogen chloride and ethanoic acid both dissolve in water. All hydrogen chloride molecules ionise in water. Approximately 1% of ethanoic acid molecules ionise in water.

A solution is made by dissolving 1 g of hydrogen chloride in 1 dm³ of water. Which is the correct description of this solution? Tick (✓) one box.

Which solution would have the lowest pH? Tick (✓) one box.

A student investigated the concentration of a solution of sodium hydroxide by titration with a 0.0480 mol/dm³ ethanedioic acid solution. This is the method used.

1. Measure 25.0 cm³ of the sodium hydroxide solution into a conical flask using a 25.0 cm³ pipette.

2. Add two drops of indicator to the sodium hydroxide solution.

3. Fill a burette with the 0.0480 mol/dm³ ethanedioic acid solution to the 0.00 cm³ mark.

4. Add the ethanedioic acid solution to the sodium hydroxide solution until the indicator changes colour.

5. Read the burette to find the volume of the ethanedioic acid solution used.

Suggest two improvements to the method that would increase the accuracy of the result.

Ethanedioic acid is a solid at room temperature. Calculate the mass of ethanedioic acid (H₂C₂O₄) needed to make 250 cm³ of a solution with concentration 0.0480 mol/dm³ Relative formula mass (M_r): H₂C₂O₄ = 90

The student found that 25.0 cm³ of the sodium hydroxide solution was neutralised by 15.00 cm³ of the 0.0480 mol/dm³ ethanedioic acid solution. The equation for the reaction is:

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

This question is about acids and alkalis.

Dilute hydrochloric acid is a strong acid. Explain why an acid can be described as both strong and dilute.

A 1.0 10^–3 mol/dm³ solution of hydrochloric acid has a pH of 3.0 What is the pH of a 1.0 10^–5 mol/dm³ solution of hydrochloric acid?

A student titrated 25.0 cm³ portions of dilute sulfuric acid with a 0.105 mol/dm³ sodium hydroxide solution.

Table 4 shows the student’s results.

The equation for the reaction is:

Calculate the concentration of the sulfuric acid in mol/dm³ Use only the student’s concordant results. Concordant results are those within 0.10 cm³ of each other.

Explain why the student should use a pipette to measure the dilute sulfuric acid and a burette to measure the sodium hydroxide solution.

Calculate the mass of sodium hydroxide in 30.0 cm³ of a 0.105 mol/dm³ solution. Relative formula mass (M_r): NaOH = 40