Chemical measurements & uncertainty

A student investigated the reaction of magnesium with oxygen.

Figure 6 shows the apparatus.

This is the method used.

1. Measure the mass of an empty crucible.

2. Add 0.10 g of magnesium to the crucible.

3. Heat the crucible and contents for 5 minutes.

4. Allow to cool and measure the mass of the crucible and contents.

5. Repeat steps 1 to 4 using different masses of magnesium.

Complete the word equation for the reaction.

magnesium + oxygen →

Complete the sentence.

Choose the answer from the box.

Table 3 shows the measurements for one of the experiments.

Calculate the mass of magnesium in the crucible before heating.

Why does the reaction result in an increase in the mass of the contents of the crucible?

Tick () one box.

The student determined the mass of the contents of the crucible after heating each mass of magnesium.

Figure 7 shows the results.

Draw a ring around the anomalous result in Figure 7.

The student did the experiment using 0.60 g of magnesium four times.

Table 4 shows the results.

Calculate mean value X.

The student used a Bunsen burner instead of a water bath to heat the crucible.

Why did the student use a Bunsen burner?

Tick () one box.

A different student did the investigation.

The student heated the crucible for 1 minute instead of for 5 minutes.

The student obtained different results.

Suggest one reason why the student obtained different results.

A student investigated the temperature change when different masses of zinc were added to copper sulfate solution.

Figure 5 shows the apparatus.

This is the method used.

1. Pour 50 cm³ of copper sulfate solution into a polystyrene cup.

2. Measure the starting temperature of the copper sulfate solution.

3. Add 1.0 g of zinc.

4. Stir the mixture.

5. Measure the highest temperature reached.

6. Repeat steps 1 to 5 two more times.

7. Repeat steps 1 to 6 with different masses of zinc.

The student varied the mass of zinc.

What type of variable is the mass of zinc?

Tick () one box.

The word equation for the reaction is:

zinc + copper sulfate → salt A + copper

What is the name of salt A ?

The temperature of the solution increases when zinc reacts with copper sulfate solution.

Give two other observations that can be made when zinc reacts with copper sulfate solution.

Figure 6 shows the highest temperature reached in one experiment.

Complete Table 3.

Use Figure 6.

A teacher repeated the investigation using a digital thermometer.

Table 4 shows the results.

Calculate value B in Table 4.

The range of the results is the minimum value of temperature increase to the maximum value of temperature increase.

What is the range of temperature increase for the experiment with 2.0 g of zinc?

One of the results for 3.0 g of zinc is anomalous.

Which result is anomalous?

Suggest one reason why this result is anomalous.

This question is about electrolysis. Figure 14 shows the apparatus used to investigate the electrolysis of potassium sulfate solution.

Potassium sulfate contains K⁺ and SO₄^2– ions. What is the formula of potassium sulfate? Tick (✓) one box.

What are the volumes of gases collected in the electrolysis experiment? Use Figure 14.

A student made the following hypothesis: ‘The volumes of gases collected in this electrolysis experiment are in the same ratio as hydrogen atoms to oxygen atoms in a water molecule.’ Explain how the volumes of gases collected in the experiment in Figure 14 support the student’s hypothesis. Use your answer to Question 06.2

The experiment is repeated 4 times. The volumes of oxygen collected in the 4 experiments are:

The mean volume of oxygen collected in the 4 experiments is 9 cm³ The measure of uncertainty is the range of a set of measurements about the mean.

What is the measure of uncertainty in the 4 experiments?

Tick (✓) one box.

Calculate the mass of potassium sulfate needed to make 1.0 dm³ of solution.

This question is about electrolysis. Figure 2 shows the apparatus used to investigate the electrolysis of potassium sulfate solution.

Potassium sulfate contains K⁺ and SO₄^2– ions. What is the formula of potassium sulfate? Tick (✓) one box.

What are the volumes of gases collected in the electrolysis experiment? Use Figure 2.

A student made the following hypothesis: ‘The volumes of gases collected in this electrolysis experiment are in the same ratio as hydrogen atoms to oxygen atoms in a water molecule.’ Explain how the volumes of gases collected in the experiment in Figure 2 support the student’s hypothesis. Use your answer to Question 02.2

The experiment is repeated 4 times. The volumes of oxygen collected in the 4 experiments are:

The mean volume of oxygen collected in the 4 experiments is 9 cm³ The measure of uncertainty is the range of a set of measurements about the mean.

What is the measure of uncertainty in the 4 experiments? Tick (✓) one box.

Calculate the mass of potassium sulfate needed to make 1.0 dm³ of solution.

A student investigated the change in temperature when different masses of zinc were added to copper sulfate solution. This is the method used.

1. Measure the volume of copper sulfate solution using a measuring cylinder.

2. Pour the copper sulfate solution into a metal container.

3. Add 2 g of zinc.

4. Measure the temperature of the solution.

5. Repeat steps 1 to 4 with different masses of zinc.

Figure 7 shows the apparatus.

Give three improvements to the investigation to make the results more accurate.

Figure 8 shows part of the measuring cylinder.

What is the volume of copper sulfate solution in Figure 8 ?

When zinc was added to copper sulfate solution the temperature increased. Figure 9 shows the reaction profile.

What type of reaction is shown in Figure 9 ? Tick (✓) one box.

Figure 10 shows the results.

Determine the gradient of the line in Figure 10. Use the equation:

Suggest why the student should not use more than 10 g of zinc. Use Figure 10. You should extend the graph line.

This question is about oxygen and compounds of oxygen.

What is the state symbol of oxygen at room temperature?

Figure 4 shows the percentage by mass of the elements calcium, carbon and oxygen in calcium carbonate.

What is the percentage by mass of calcium in calcium carbonate?

At high temperature, sodium nitrate decomposes into sodium nitrite and oxygen. A student heats three samples of sodium nitrate. The mass of each sample was 4.50 g The mass of solid after heating was recorded. Table 2 shows the mass of solid after heating in each experiment.

Calculate the mean mass of solid after heating. Give your answer to 3 significant figures.

Table 3 shows the electronic structure of hydrogen and oxygen.

Figure 5 shows part of a dot and cross diagram of a molecule of water (H₂O). Complete the dot and cross diagram. You should show only the electrons in the outer energy levels.

Oxygen and sulfur are examples of simple molecules.

Complete the sentence. Choose the answer from the box.

Figure 6 shows the relative sizes of an oxygen molecule and a sulfur molecule.

How does the boiling point of sulfur compare with the boiling point of oxygen? Complete the sentences.

than the intermolecular forces in oxygen.

This question is about electrolysis. A student investigates the mass of copper produced during electrolysis of copper chloride solution. Figure 12 shows the apparatus.

Which gas is produced at the positive electrode (anode)? Tick one box.

Copper is produced at the negative electrode (cathode). What does this tell you about the reactivity of copper? Tick one box.

Table 4 shows the student’s results.

Determine the mean mass of copper produced after 3 minutes.

Calculate the mass X of copper produced in Experiment 2 after 5 minutes. Use Table 4 on page 19

The copper chloride solution used in the investigation contained 300 grams per dm³ of solid CuCl₂ dissolved in 1 dm³ of water. The students used 50 cm³ of copper chloride solution in each experiment. Calculate the mass of solid copper chloride used in each experiment.

This question is about electrolysis. A student investigates the mass of copper produced during electrolysis of copper chloride solution. Figure 1 shows the apparatus.

Which gas is produced at the positive electrode (anode)? Tick one box.

02

Copper is produced at the negative electrode (cathode). What does this tell you about the reactivity of copper? Tick one box.

Table 1 shows the student’s results.

Determine the mean mass of copper produced after 3 minutes.

Calculate the mass X of copper produced in Experiment 2 after 5 minutes. Use Table 1 on page 3

The copper chloride solution used in the investigation contained 300 grams per dm³ of solid CuCl₂ dissolved in 1 dm³ of water. The student used 50 cm³ of copper chloride solution in each experiment. Calculate the mass of solid copper chloride used in each experiment.