Concentration of solutions

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

A student electrolysed copper sulfate solution using inert electrodes.

Figure 8 shows the apparatus used.

Copper was produced at the negative electrode.

Oxygen was produced at the positive electrode.

Copper sulfate solution contains copper ions and hydrogen ions.

Why is copper produced instead of hydrogen during the electrolysis of copper sulfate solution?

Tick (✓) one box.

Copper is less reactive than hydrogen.

Copper has the same reactivity as hydrogen.

Copper is more reactive than hydrogen.

The student measured how the mass of copper produced varied with time.

Table 1 shows the results.

What conclusion can be made about how the mass of copper produced varied with time?

Use Table 1.

Predict the time taken to produce 0.20 g of copper.

Use Table 1.

0.5 dm³ of a solution of copper sulfate contains 3.2 g of copper sulfate.

Calculate the concentration of the solution of copper sulfate.

Use the equation:

Choose the unit from the box.

Copper sulfate has the formula CuSO₄

Calculate the percentage (%) by mass of copper in CuSO₄

Give your answer to 3 significant figures.

Relative atomic mass (A_r): Cu = 63.5

Relative formula mass (M_r): CuSO₄ = 159.5

This question is about electrolysis.

Figure 9 shows the electrolysis of molten potassium chloride using inert electrodes.

Why must potassium chloride be molten during the electrolysis?

Why are inert electrodes used in electrolysis?

A gas is released during the electrolysis of molten potassium chloride.

Describe the test to identify the gas released.

Give the result if the gas is present.

Potassium is produced at the negative electrode.

Write the half equation for the reaction at the negative electrode during the electrolysis of molten potassium chloride.

What type of reaction occurs at the negative electrode?

An aqueous solution of potassium chloride was electrolysed.

Hydrogen gas was produced at the negative electrode.

Explain why hydrogen gas is produced during the electrolysis of an aqueous solution of potassium chloride.

50 cm³ of potassium chloride solution contains 0.030 moles of potassium chloride.

Calculate the concentration of the potassium chloride solution in g/dm³.

Relative formula mass (M_r) of potassium chloride = 74.5

Concentration = g/dm³ _________________

This question is about chemical quantities.

0.40 dm³ of a solution contains 48.4 g of solute.

Calculate the concentration of the solution.

Give the unit.

Calculate the number of carbon dioxide molecules in 3.00 moles of carbon dioxide.

The Avogadro constant = 6.02 × 10²³ per mole.

Give your answer to 3 significant figures.

Metal M forms a metal oxide with the formula M₂O₃

The relative formula mass of the metal oxide is 152.

Determine the identity of metal M.

Relative atomic mass (A_r): O = 16

This question is about solutions.

What is meant by a ‘solute’?

Sugar solution X and sugar solution Y have different concentrations.

A student investigated which solution had the higher concentration.

The student evaporated sugar solution at a temperature of 40 °C until only sugar remained.

Figure 13 shows the equipment used.

Plan a method to show if sugar solution X or sugar solution Y has the higher concentration.

Figure 14 shows the balance.

The resolution is the smallest change in the quantity being measured that a measuring instrument can show.

What is the resolution of the balance?

Tick (✓) one box.

0.01 g
0.10 g
1.00 g 10

This question is about the reactions of metals.

A student investigated the temperature change when a metal was added to 25 cm³ of dilute sulfuric acid.

The student repeated the investigation with different metals.

The student kept all other variables constant.

Table 1 shows the results.

Figure 6 shows an incomplete bar chart for the data in Table 1.

Complete Figure 6.

You should:

• write the correct scale on the y-axis

• plot the bar for magnesium.

Another student investigated displacement reactions of metals.

The student added magnesium, nickel and zinc to different metal sulfate solutions and recorded when a reaction occurred.

Predict which metals will react with each metal sulfate solution.

Complete Table 2.

You should:

• use a tick (✓) to show where a reaction will occur

• use a cross (×) to show where no reaction will occur.

Table 1 is repeated here to help you.

The student dissolved 0.0025 moles of nickel sulfate in water to make 5 cm³ of nickel sulfate solution.

Calculate the concentration of the nickel sulfate solution in g/dm³

Relative formula mass (M_r) of nickel sulfate = 155

This question is about copper sulfate.

The formula of copper sulfate is CuSO₄

Table 5 shows information about the atoms in copper sulfate.

Complete Table 5.

Copper oxide and sulfuric acid react to produce copper sulfate and water.

Complete the word equation for this reaction.

What type of substance is copper oxide?

Tick (✓) one box.

A student planned to make blue copper sulfate crystals.

This is the method the student used.

1. Add 25 cm³ of dilute sulfuric acid to a conical flask.

2. Gently warm the dilute sulfuric acid.

3. Add 2 g of black copper oxide to the dilute sulfuric acid.

4. Stir the mixture.

5. Evaporate some of the water from the mixture using an electric heater.

6. Leave the mixture to cool.

Not all the copper oxide reacted. The student did not remove the excess copper oxide.

What would the product look like after step 6?

Tick (✓) one box.

The student should have filtered the mixture after step 4.

Draw a diagram of the apparatus the student could use.

You should label:

• the pieces of equipment used

• where the excess copper oxide collects.

What equipment should the student use to measure:

• 2 g of copper oxide

• 25 cm³ of dilute sulfuric acid?

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

1 g of copper sulfate is dissolved in water to make 25 cm³ of copper sulfate solution.

Calculate the concentration of the copper sulfate solution in g/dm³

A student planned to make copper sulfate crystals from excess copper oxide and dilute sulfuric acid.

The equation for the reaction is:

Why is it necessary to add excess copper oxide?

This is the method used.

1. Add 25 cm³ of dilute sulfuric acid to a conical flask.

2. Gently warm the dilute sulfuric acid.

3. Add excess copper oxide to the dilute sulfuric acid.

4. Stir the mixture.

5. Heat to evaporate all the water from the mixture.

Suggest two improvements to the method.

Explain why each improvement is needed.

The student used:

• 2 g of copper oxide (in excess)

• 25 cm³ of a solution of dilute sulfuric acid with a concentration of 49 g/dm³

Determine by how many moles the copper oxide (CuO) was in excess.

Relative atomic masses (A_r): Cu = 63.5 O = 16

Relative formula mass (M_r) of sulfuric acid = 98

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