(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
Explanation
(a)(i) Define the term standard electrode potential: It is the measure of the tendency of an element to form ions in solution relative-to the tendency of hydrogen atoms to form ions in solution at standard condition/ the potential difference that exists between an electrode and the hydrogen electrode under standard conditions (of I moldm\(^{-3}\) concentration at 298k and 1 atm).
(ii) State three factors that affect the discharge of ions during electrolysis: (1) Position of ions in the electrochemical series/standard electrode potential value. (2) Nature or reactivity of electrode used. (3) (relative) concentration of ions.
(iii) State two functions of a salt. bridge in an electrochemical cell: (1) Allows electrical contact between two solutions/complete the electric circuit (2) Maintains electrical neutrality in each half cell/allows ions flow in and out of salt bridge.
(b)(i) Describe briefly what happens when a solution of copper(II) tetraoxosulpahte(VI) is electrolysed using copper electrodes:
CuSO\(_4\) \(\rightleftharpoons\) Cu\(^{2+}\) + SO\(_4^{2-}\); Cu\(^{2+}\) discharged/Cu metal deposited/Cu cathode increases in mass.
H\(_2\)O \(\rightleftharpoons\) H\(+\) + OH\(-\) Copper anode dissolves/ionizes/decreases in size to give Cu\(^{2+}\) ions.
Solution remains blue/concentration of Cu\(^{2+}\) ions is constant.
(c) Calculate the mass of copper(II)tetraoxosulphate(V1) for 35 minutes using copper electrodes:. [H=1, O=16, S=32, Cu=64, IF=96,500]
Cu\(^{2+}\) + 2e ---> Cu
Q = It = 0.2 x 35 x 60 = 420C
2F = 2e = 1mole \(\frac{Cu}{2}\) x 96500C = 64g
420C = \(\frac{420}{ 2 x 96500}\) x 64gCu
= 0.14gCu.
(d)(i) State three characteristics of catalyst: (1) Remains unchanged in chemical nature and mass. (2) Does not affect the types of product formed. (3) Alters (increase or decrease) the rate of chemical reaction. (4) They are reactions specific. (5) Cannot initiate a reaction that is not feasible. (6) Has no effect on the equilibrium of a reversible reaction. (7) Required in small quantity.
(ii) Name one manufacturing process in which each of the following metals is used as a catalyst:
I. Iron – used in Haber process.
II. Nickel – hydrogenation of vegetable oil/alkenes.
III. Platinum – used in preparation of hydrogen iodido from hydrogen and iodine/contact process for H\(_2\)SO\(_4\) production/manufacture of HNO\(_3\) used in Hydrogenation.