Question 1:
Table 1.11 shows electrodes, electrolytes and observations at the anode for three electrolytic cells.
(a) Name the anions present in copper(II) chloride, CuCl2 solution.
(b) State the name of the gases released at the anode in electrolytic cells I and II.
Explain your answers.
(c)(i) Write the half equation for the reaction that occurs at the anode of electrolytic cell III.
(c)(ii) Explain how the product at the anode in electrolytic cell III is formed.
(d) State the type of reaction that occurs at the anode.
(e) If the experiment of electrolytic cell I is repeated using molten copper(II) chloride, CuCl2, predict the observation at the anode.
Answer:
(a) Chloride ions and hydroxide ions
(b)
Electrolytic cell I
– Oxygen gas.
– Hydroxide ions are discharged because the E0 value of OH− ion is less positive compared to the E0 value of Cl− ion
– Four OH− ions lose four electrons to form one oxygen molecule and two water molecules.
Electrolytic cell II
– Chlorine gas- Cl− ions are discharged because the concentration of Cl− ions are higher than OH− ions.
– Two chloride ions lose two electrons to form one chlorine molecule.
(c)(i) Cu → Cu2+ + 2e−
(c)(ii)
– Copper is the active electrode.
– Copper atoms ionise to form Cu2+ ions at the anode.
(d) Oxidation reaction.
(e) Greenish yellow gas is released
Table 1.11 shows electrodes, electrolytes and observations at the anode for three electrolytic cells.
(a) Name the anions present in copper(II) chloride, CuCl2 solution.
(b) State the name of the gases released at the anode in electrolytic cells I and II.
Explain your answers.
(c)(i) Write the half equation for the reaction that occurs at the anode of electrolytic cell III.
(c)(ii) Explain how the product at the anode in electrolytic cell III is formed.
(d) State the type of reaction that occurs at the anode.
(e) If the experiment of electrolytic cell I is repeated using molten copper(II) chloride, CuCl2, predict the observation at the anode.
Answer:
(a) Chloride ions and hydroxide ions
(b)
Electrolytic cell I
– Oxygen gas.
– Hydroxide ions are discharged because the E0 value of OH− ion is less positive compared to the E0 value of Cl− ion
– Four OH− ions lose four electrons to form one oxygen molecule and two water molecules.
Electrolytic cell II
– Chlorine gas- Cl− ions are discharged because the concentration of Cl− ions are higher than OH− ions.
– Two chloride ions lose two electrons to form one chlorine molecule.
(c)(i) Cu → Cu2+ + 2e−
(c)(ii)
– Copper is the active electrode.
– Copper atoms ionise to form Cu2+ ions at the anode.
(d) Oxidation reaction.
(e) Greenish yellow gas is released
Question 2:
Salim uses the apparatus shown in Figure 1.35 to electroplate an iron key with silver, Ag metal.
(a) What is the purpose of electroplating the iron key with silver, Ag?
(b) After 30 minutes Salim found out that the iron key has not been electroplated with silver, Ag.
(i) Suggest a suitable electrolyte X.
(ii) What should Salim do with the silver plate, Ag and iron key so that it can be electroplated with silver, Ag?
Answer:
(a) Iron key looks more attractive / resistant to corrosion.
(b)(i) Silver nitrate solution.
(b)(ii) Connect the iron key to the negative terminal of the batteries and connect the silver plate to the positive terminal of the batteries.
Salim uses the apparatus shown in Figure 1.35 to electroplate an iron key with silver, Ag metal.
(a) What is the purpose of electroplating the iron key with silver, Ag?
(b) After 30 minutes Salim found out that the iron key has not been electroplated with silver, Ag.
(i) Suggest a suitable electrolyte X.
(ii) What should Salim do with the silver plate, Ag and iron key so that it can be electroplated with silver, Ag?
Answer:
(a) Iron key looks more attractive / resistant to corrosion.
(b)(i) Silver nitrate solution.
(b)(ii) Connect the iron key to the negative terminal of the batteries and connect the silver plate to the positive terminal of the batteries.
Question 3:
You are required to conduct an experiment to purify nickel, Ni by electrolysis.
(a) Draw a labelled set-up of apparatus to be used in this experiment.
(b) State the observations at the anode and cathode.
(c) Write the half equation for the reaction that occurs at the anode.
Answer:
(a)
(b)
Anode: Impure nickel metal becomes thinner.
Cathode: Pure nickel metal becomes thicker.
(c) Ni → Ni2+ + 2e−
You are required to conduct an experiment to purify nickel, Ni by electrolysis.
(a) Draw a labelled set-up of apparatus to be used in this experiment.
(b) State the observations at the anode and cathode.
(c) Write the half equation for the reaction that occurs at the anode.
Answer:
(a)
(b)
Anode: Impure nickel metal becomes thinner.
Cathode: Pure nickel metal becomes thicker.
(c) Ni → Ni2+ + 2e−