Oxidation and reduction in terms of electrons

A student investigated the energy change of 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. Measure the temperature of the copper sulfate solution.

3. Add 0.20 g of zinc powder to the copper sulfate solution.

4. Stir the reaction mixture.

5. Record the highest temperature reached.

6. Repeat steps 1 to 5 with different masses of zinc powder.

Figure 3 shows the results.

Draw two lines of best fit on Figure 3.

The lines should cross.

Explain the results shown in Figure 3.

Do not refer to anomalous points.

Use data from Figure 3.

Explain why using a polystyrene cup gives more accurate results than using a glass beaker.

Complete the ionic equation for the reaction between zinc and copper sulfate solution.

Include state symbols.

A different student repeated steps 1 to 5 of the method four times using 0.50 g of zinc powder.

Table 2 shows the results.

Calculate the mean highest temperature reached.

Include the uncertainty in your answer.

The results show random errors.

The student did not make any measuring errors.

Suggest one reason for the random errors in this experiment.

This question is about displacement reactions.

Iron is extracted from iron oxide by a displacement reaction with carbon. The equation for the reaction is:

Which substance in the equation is reduced? Give one reason for your answer. Answer in terms of oxygen.

Which expression shows how to calculate the mass of carbon needed to produce 1 mole of iron from iron oxide? Relative atomic mass (A_r): C = 12 Tick (✓) one box.

A student investigated displacement reactions of four different metals represented by A, B, C and D. A, B, C and D are not the actual chemical symbols for the metals. The student:

• added each metal to aqueous solutions of the metal nitrates

• observed whether a reaction took place.

Table 6 shows information about three of the reaction mixtures.

The ionic equation for Reaction 1 is:

Why is this a redox reaction?

Tick () one box.

Which of the four metals has the greatest tendency to form positive ions? Use Table 6. Tick (✓) one box.

The nitrate ion has the formula NO₃^– Which of the four metals could be aluminium? Explain your answer. Use Table 6.

Metal X is extracted from an oxide of metal X by reaction with hydrogen. The equation for the reaction is:

The percentage atom economy for obtaining metal X by this method is 77.3%. Calculate the relative atomic mass (A_r) of metal X. Relative atomic masses (A_r): H = 1 O = 16

This question is about zinc and compounds of zinc. A student produces pure crystals of zinc chloride by reacting zinc oxide with hydrochloric acid. The equation for the reaction is:

The student adds zinc oxide to hydrochloric acid until the zinc oxide is in excess. Give one observation that the student could make to show that the zinc oxide is in excess.

Why is excess zinc oxide used rather than excess hydrochloric acid?

Name one other compound that the student could add to hydrochloric acid to produce zinc chloride.

Describe how the student should obtain crystals of zinc chloride from a solution of zinc chloride.

Zinc chloride is also produced in a displacement reaction between zinc and copper chloride solution. The equation for the reaction is:

Complete the ionic equation for this reaction.

Why is zinc described as being oxidised in this reaction?

Zinc and copper can be used with another substance to produce electricity. Complete Figure 7 to show how zinc, copper and another substance can be used to light a lamp. Label:

• zinc

• copper

• the other substance used.

The symbol represents the lamp.

This question is about Group 1 elements.

Give two observations you could make when a small piece of potassium is added to water.

Complete the equation for the reaction of potassium with water. You should balance the equation.

Explain why the reactivity of elements changes going down Group 1.

Sodium reacts with oxygen to produce the ionic compound sodium oxide. Oxygen is a Group 6 element.

Draw a dot and cross diagram to show what happens when atoms of sodium and oxygen react to produce sodium oxide. Diagram

Why is oxygen described as being reduced in the reaction between sodium and oxygen?

Explain why sodium oxide has a high melting point.

This question is about displacement reactions.

The displacement reaction between aluminium and iron oxide has a high activation energy. What is meant by ‘activation energy’?

A mixture contains 1.00 kg of aluminium and 3.00 kg of iron oxide. The equation for the reaction is:

Show that aluminium is the limiting reactant. Relative atomic masses (A_r): O = 16 Al = 27 Fe = 56

Magnesium displaces zinc from zinc sulfate solution.

Complete the ionic equation for the reaction. You should include state symbols.

Explain why the reaction between magnesium atoms and zinc ions is both oxidation and reduction.

Titanium is a transition metal. Titanium is extracted from titanium dioxide in a two stage industrial process. Stage 1 TiO₂ + 2 C + 2 Cl₂ TiCl₄ + 2 CO Stage 2 TiCl₄ + 4 Na Ti + 4 NaCl

Suggest one hazard associated with Stage 1.

Water must be kept away from the reaction in Stage 2. Give one reason why it would be hazardous if water came into contact with sodium.

Suggest why the reaction in Stage 2 is carried out in an atmosphere of argon and not in air.

Titanium chloride is a liquid at room temperature. Explain why you would not expect titanium chloride to be a liquid at room temperature.

In Stage 2, sodium displaces titanium from titanium chloride.

Sodium atoms are oxidised to sodium ions in this reaction. Why is this an oxidation reaction?

Complete the half equation for the oxidation reaction.

In Stage 2, 40 kg of titanium chloride was added to 20 kg of sodium. The equation for the reaction is:

Relative atomic masses (A_r): Na = 23 Cl = 35.5 Ti = 48 Explain why titanium chloride is the limiting reactant. You must show your working.

For a Stage 2 reaction the percentage yield was 92.3% The theoretical maximum mass of titanium produced in this batch was 13.5 kg. Calculate the actual mass of titanium produced.