Half equations at electrodes

This question is about metals.

Iron is extracted from iron oxide by reduction with carbon.

Why can iron be extracted by reduction with carbon?

Answer in terms of reactivity.

Aluminium is extracted by the electrolysis of aluminium oxide.

Figure 4 shows the apparatus used to extract aluminium.

Explain why a mixture of aluminium oxide and cryolite is used as the electrolyte instead of only aluminium oxide.

Oxygen gas is produced at the positive electrode.

Write a balanced half equation for the production of oxygen at the positive electrode.

Chromium is extracted by reacting chromium oxide with aluminium.

The equation for the reaction is:

Which substance in the equation is reduced?

Table 3 shows the relative cost of extracting equal masses of aluminium, chromium and iron.

Give one reason for the difference in the cost of extracting aluminium and iron.

Use Table 3.

Give one reason for the difference in the cost of extracting aluminium and chromium

Use Table 3.

Metals are mixed together to form alloys.

Explain why alloys are harder than pure metals.

In the Earth most metals are found as compounds.

Name one metal that is found in the Earth as the metal itself.

Figure 9 shows a reactivity series.

Suggest the most economical method for extracting metal Z from an oxide of metal Z

Figure 10 shows the electrolysis cell used to extract aluminium from aluminium oxide.

Name substance X shown in Figure 10.

Explain what happens to the positive carbon electrodes during the extraction of aluminium from aluminium oxide.

The formula of aluminium oxide is Al₂O₃

Write a half equation for the reaction at the negative electrode in Figure 10.

During electrolysis ions are discharged at the electrodes to produce elements. A student investigates the electrolysis of sodium chloride.

Sodium chloride solution conducts electricity. Complete the sentence.

Figure 5 shows the apparatus for the electrolysis of sodium chloride solution.

Suggest an element that could be used to make the inert electrodes.

Complete the half equation for the production of chlorine (Cl₂) at the positive electrode.

Sodium chloride solution has a pH of 7 During the electrolysis of sodium chloride solution:

• hydrogen gas is produced at the negative electrode

• the pH of the solution increases.

Explain why.

This question is about the electrolysis of aqueous solutions.

Hydrogen gas and chlorine gas are produced when sodium chloride solution is electrolysed.

Hydrogen ions (H⁺) are attracted to the negative electrode. The half equation for the reaction at the negative electrode is:

What type of reaction happens at the negative electrode? Give the reason for your answer.

Chloride ions are attracted to the positive electrode. Complete the half equation for the production of chlorine gas (Cl₂).

Hydrogen gas and oxygen gas are produced when sodium sulfate solution is electrolysed. Explain how oxygen gas is produced in the electrolysis of sodium sulfate solution.

This question is about electrolysis.

Some metals are extracted from molten compounds using electrolysis. Why is electrolysis used to extract some metals?

Aluminium is produced by electrolysis of a molten mixture. What two substances does the molten mixture contain?

Copper and chlorine are produced when molten copper chloride is electrolysed. Complete the half equation for the reaction at each electrode.

Half equation at negative electrode

Half equation at positive electrode

Figure 4 shows the apparatus a student used to electrolyse copper chloride solution.

The student:

• measured the mass of copper deposited on the negative electrode after 60 minutes

• compared the mass deposited with the expected value.

Suggest two reasons why the mass deposited was different from the expected value.

Figure 5 shows the expected mass of copper produced each minute.

Determine the expected mass of copper after 24 hours. Use Figure 5.

Silver nitrate solution is electrolysed. Figure 6 shows the change in mass of the negative electrode over 10 hours.

Determine the mass of the negative electrode at the start of the experiment. Use Figure 6.

Calculate the gradient of the line in Figure 6. Give the unit.