(a)(i) Define the term standard electrode potential.
(ii) State three factors that affect the discharge of ions during electrolysis.
(iii) State two functions of a salt bridge in an electrochemical cell.
(b) Describe briefly what happens when a solution of copper (II) tetraoxosulphate (VI) is electrolyzed using copper electrodes.
c) Calculate the mass of copper deposited at the cathode when a current of 0.2A is passed through a solution of copper (II) tetraoxosulphate (VI) for 35 minutes using copper electrodes. [H = 1.00, O = 16.0, S = 32.0, Cu = 64.0, IF = 96,500C]
(d)(i) State three characteristics of a catalyst.
ii) Name one manufacturing process in which each of the following metals is used as catalyst: I. iron; II. nickel; Ill. platinum.
c-NA
(a)(i) The standard electrode potential of an element is the potential difference developed when the element is in contact with a solution of its ions of concentration \(1\ \text{mol dm}^{-3}\) at 298 K and 1 atmosphere, measured relative to the standard hydrogen electrode (which is taken as zero).
(a)(ii) Three factors affecting the discharge of ions during electrolysis: the position of the ion in the electrochemical series (relative ease of discharge), the concentration of the ion in solution, and the nature of the electrode used.
(a)(iii) Two functions of a salt bridge: it completes the electrical circuit by allowing ions to flow between the two half-cells, and it maintains electrical neutrality in the half-cells (preventing charge build-up).
(b) Electrolysis of \(CuSO_4\) with copper electrodes
Copper is deposited at the cathode: \(Cu^{2+} + 2e^- \to Cu\). At the anode the copper electrode itself dissolves: \(Cu \to Cu^{2+} + 2e^-\). Copper is therefore transferred from anode to cathode, the anode loses mass while the cathode gains mass, and the blue colour of the solution stays constant because the \(Cu^{2+}\) concentration is unchanged (this is the basis of electro-refining).
(c) Mass of copper deposited
\[Q = It = 0.2 \times (35 \times 60) = 420\ \text{C}\]
From \(Cu^{2+} + 2e^- \to Cu\), \(2 \times 96500\ \text{C}\) deposits 64 g of copper.
\[\text{mass} = \frac{420}{2 \times 96500} \times 64 = 0.139\ \text{g}\]
About 0.14 g of copper is deposited.
(d)(i) Three characteristics of a catalyst: it is chemically unchanged in mass and composition at the end of the reaction; it is needed only in a small amount; and it is specific in its action (a given catalyst works for a particular reaction).
(d)(ii) Manufacturing processes using the metals as catalysts:
- I. Iron: the Haber process (manufacture of ammonia).
- II. Nickel: the hydrogenation of vegetable oils (manufacture of margarine).
- III. Platinum: the Ostwald process (catalytic oxidation of ammonia in the manufacture of nitric acid); it is also used in the Contact process.
(a)(i) The standard electrode potential of an element is the potential difference developed when the element is in contact with a solution of its ions of concentration \(1\ \text{mol dm}^{-3}\) at 298 K and 1 atmosphere, measured relative to the standard hydrogen electrode (which is taken as zero).
(a)(ii) Three factors affecting the discharge of ions during electrolysis: the position of the ion in the electrochemical series (relative ease of discharge), the concentration of the ion in solution, and the nature of the electrode used.
(a)(iii) Two functions of a salt bridge: it completes the electrical circuit by allowing ions to flow between the two half-cells, and it maintains electrical neutrality in the half-cells (preventing charge build-up).
(b) Electrolysis of \(CuSO_4\) with copper electrodes
Copper is deposited at the cathode: \(Cu^{2+} + 2e^- \to Cu\). At the anode the copper electrode itself dissolves: \(Cu \to Cu^{2+} + 2e^-\). Copper is therefore transferred from anode to cathode, the anode loses mass while the cathode gains mass, and the blue colour of the solution stays constant because the \(Cu^{2+}\) concentration is unchanged (this is the basis of electro-refining).
(c) Mass of copper deposited
\[Q = It = 0.2 \times (35 \times 60) = 420\ \text{C}\]
From \(Cu^{2+} + 2e^- \to Cu\), \(2 \times 96500\ \text{C}\) deposits 64 g of copper.
\[\text{mass} = \frac{420}{2 \times 96500} \times 64 = 0.139\ \text{g}\]
About 0.14 g of copper is deposited.
(d)(i) Three characteristics of a catalyst: it is chemically unchanged in mass and composition at the end of the reaction; it is needed only in a small amount; and it is specific in its action (a given catalyst works for a particular reaction).
(d)(ii) Manufacturing processes using the metals as catalysts:
- I. Iron: the Haber process (manufacture of ammonia).
- II. Nickel: the hydrogenation of vegetable oils (manufacture of margarine).
- III. Platinum: the Ostwald process (catalytic oxidation of ammonia in the manufacture of nitric acid); it is also used in the Contact process.
