Concentration of solutions

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 energy changes of reactions.

Zinc reacts with copper sulfate solution.

The word equation for the reaction is:

zinc + copper sulfate → zinc sulfate + copper

What type of reaction is the reaction between zinc and copper sulfate solution?

Tick () one box.

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

Give your answer to 3 significant figures.

Relative atomic mass (A_r): Cu = 63.5

Relative formula mass (M_r): CuSO₄ = 159.5

A student investigated the energy change in the reaction between zinc and copper sulfate solution.

This is the method used.

1. Measure 25 cm³ of copper sulfate solution into a polystyrene cup.

2. Weigh 0.20 g of zinc powder.

3. Add the zinc powder to the copper sulfate solution.

4. Measure the highest temperature reached by the mixture.

5. Repeat steps 1 to 4 using different masses of zinc powder.

Control variables are used to make an investigation a fair test.

Which is a control variable in the investigation?

Tick () one box.

Figure 6 shows the results.

What is the minimum mass of zinc powder needed to react with all the copper sulfate solution?

Use Figure 6.

What is the maximum temperature change in the reaction between zinc powder and 25 cm³ of copper sulfate solution?

Use Figure 6.

25 cm³ of copper sulfate solution contained 6.75 g of copper sulfate.

Calculate the concentration of the solution in g/dm³.

You should:

calculate the volume of the solution in dm³ (1000 cm³ = 1 dm³)

use the equation:

Another student investigated the energy change of the reaction between sodium hydrogencarbonate and hydrochloric acid.

This is the method used.

1. Measure 25 cm³ of hydrochloric acid.

2. Weigh 1.0 g of sodium hydrogencarbonate.

3. Add the sample of sodium hydrogencarbonate to the hydrochloric acid.

4. Measure the lowest temperature reached by the mixture.

5. Repeat steps 1 to 4 using different masses of sodium hydrogencarbonate.

Figure 7 shows the results.

Draw two straight lines of best fit on Figure 7.

The lines should cross.

Which statement describes the energy change in the reaction shown in Figure 7 ?

Tick () one box.

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.

Acids and alkalis are substances that produce ions in aqueous solution. Draw one line from each substance to the ion always produced by that substance in aqueous solution.

Ion always produced in

What type of aqueous solution has a pH of 11? Tick (✓) one box.

A student determined the reacting volumes of hydrochloric acid and sodium hydroxide solution by titration. This is the method used.

1. Measure 25.0 cm³ of the sodium hydroxide solution.

2. Add the sodium hydroxide solution to a conical flask.

3. Add 3 drops of indicator to the sodium hydroxide solution.

4. Add the hydrochloric acid drop by drop until the indicator changes colour.

5. Record the volume of the hydrochloric acid added.

6. Repeat steps 1 to 5 three more times.

Which piece of equipment should be used to measure 25.0 cm³ of the sodium hydroxide solution in step 1? Tick (✓) one box.

Which piece of equipment should be used to add the hydrochloric acid drop by drop in step 4? Tick (✓) one box.

Table 1 shows the results.

Which is the anomalous result in Table 1 ?

Suggest one reason for the anomalous result in Table 1.

The student used a solution of sodium hydroxide of concentration 4.00 g/dm³. Calculate the mass of sodium hydroxide in 25.0 cm³ of this solution.

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 citric acid (C₆H₈O₇). Citric acid is a solid. A student investigated the temperature change during the reaction between citric acid and sodium hydrogencarbonate solution. This is the method used.

1. Pour 25 cm³ of sodium hydrogencarbonate solution into a polystyrene cup.

2. Measure the temperature of the sodium hydrogencarbonate solution.

3. Add 0.20 g of citric acid to the polystyrene cup.

4. Stir the solution.

5. Measure the temperature of the solution.

6. Repeat steps 3 to 5 until a total of 2.00 g of citric acid has been added.

The student plotted the results on a graph. Figure 6 shows the student’s graph.

Figure 6 shows an anomalous point when 0.60 g of citric acid was added. This was caused by the student making an error. The student correctly:

• measured the mass of the citric acid

• read the thermometer

• plotted the point.

Suggest one reason for the anomalous point.

Explain the shape of the graph in terms of the energy transfers taking place. You should use data from Figure 6 in your answer.

A second student repeated the investigation using a metal container instead of the polystyrene cup. The container and the cup were the same size and shape. Sketch a line on Figure 6 to show the second student’s results until 1.00 g of citric acid had been added. The starting temperature of the solution was the same. Explain your answer.

The student used a solution of citric acid to determine the concentration of a solution of sodium hydroxide by titration.

The student made 250 cm³ of a solution of citric acid of concentration 0.0500 mol/dm³ Calculate the mass of citric acid (C₆H₈O₇) required. Relative atomic masses (A_r): H = 1 C = 12 O = 16

This is part of the method the student used for the titration.

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

2. Add a few drops of indicator to the flask.

3. Fill a burette with citric acid solution.

Describe how the student would complete the titration.

Give two reasons why a burette is used for the citric acid solution.

13.3 cm³ of 0.0500 mol/dm³ citric acid solution was needed to neutralise 25.0 cm³ of sodium hydroxide solution. The equation for the reaction is:

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

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A student investigated the temperature change in the reaction between dilute sulfuric acid and potassium hydroxide solution. This is the method used.

1. Measure 25.0 cm³ potassium hydroxide solution into a polystyrene cup.

2. Record the temperature of the solution.

3. Add 2.0 cm³ dilute sulfuric acid.

4. Stir the solution.

5. Record the temperature of the solution.

6. Repeat steps 3 to 5 until a total of 20.0 cm³ dilute sulfuric acid has been added.

Suggest why the student used a polystyrene cup rather than a glass beaker for the reaction.

Table 6 shows some of the student’s results.

Figure 11 shows some of the data from the investigation.

Complete Figure 11:

• plot the data from Table 6

• draw a line of best fit through these points

• extend the lines of best fit until they cross.

Determine the volume of dilute sulfuric acid needed to react completely with 25.0 cm³ of the potassium hydroxide solution. Use Figure 11.

Determine the overall temperature change when the reaction is complete. Use Figure 11.

The student repeated the investigation. The student used solutions that had different concentrations from the first investigation. The student found that 15.5 cm³ of 0.500 mol/dm³ dilute sulfuric acid completely reacted with 25.0 cm³ of potassium hydroxide solution. The equation for the reaction is:

Calculate the concentration of the potassium hydroxide solution in mol/dm³ and in

Relative atomic masses (A_r): H = 1 O = 16 K = 39

This question is about elements in Group 1.

A teacher burns sodium in oxygen.

What is the name of this type of reaction?

Tick one box.

The teacher dissolves the product of the reaction in water and adds universal indicator.

The universal indicator turns purple.

What is the pH value of the solution?

Tick one box.

The solution contains a substance with the formula NaOH

Give the name of the substance.

All alkalis contain the same ion.

What is the formula of this ion?

Tick one box.

A solution of NaOH had a concentration of 40 g/dm³

What mass of NaOH would there be in 250 cm³ of the solution?

The melting points of the elements in Group 1 show a trend.

Table 6 shows the atomic numbers and melting points of the Group 1 elements.

Plot the data from Table 6 on Figure 11.

Predict the melting point, X, of rubidium, atomic number 37

Use Figure 11.

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