How is electrolysis used in the industry?<\/a><\/li>\n<\/ul>\nElectrolysis of other concentrated aqueous solutions:<\/strong><\/p>\n(a) Electrolysis of concentrated lead(II) nitrate\u00a0solution<\/strong><\/p>\n\n- Concentrated lead(II) nitrate, Pb(NO3<\/sub>)2<\/sub> solution consists of Pb2+<\/sup>, H+<\/sup>, NO3<\/sub>–<\/sup> and OH–<\/sup> ions that move freely.<\/li>\n
- The Pb2+<\/sup> ions and H+<\/sup> ions move to the cathode, while the NO3<\/sub>–<\/sup> ions and OH–<\/sup> ions move to the anode.<\/li>\n
- At the cathode:<\/strong> The Pb2+<\/sup> ions are selectively discharged because of their higher concentration in the electrolyte.
\nPb2+<\/sup>(aq) + 2e–<\/sup>\u00a0\u2192\u00a0Pb(s)<\/li>\n- At the anode<\/strong>: The OH–<\/sup>\u00a0ions are selectively discharged because their position in the electrochemical series is lower than the NO3<\/sub>–<\/sup> ions. Here, the concentration factor is unimportant.
\n4OH–<\/sup>(aq) \u2192 O2<\/sub>(g) + 2H2<\/sub>O(l) + 4e–<\/sup><\/li>\n<\/ul>\n(b) Electrolysis of concentrated potassium\u00a0iodide solution<\/strong><\/p>\n\n- Concentrated potassium iodide, KI solution consists of K+<\/sup>, H+<\/sup>, I–<\/sup> and OH–<\/sup> ions that move freely.<\/li>\n
- The K+<\/sup> ions and H+<\/sup> ions move to the cathode, while the I–<\/sup> ions and OH–<\/sup> ions move to the anode.<\/li>\n
- At the cathode:<\/strong> The H+<\/sup> ions are selectively discharged because their position in the electrochemical series is lower than the K+<\/sup> ions. Here, the concentration factor is unimportant.
\n2H+<\/sup>(aq) + 2e–<\/sup> \u2192 H2<\/sub>(g)<\/li>\n- At the anode:<\/strong> The I–<\/sup> ions are selectively discharged because of their higher concentration in the electrolyte.
\n2I–<\/sup>(aq) \u2192\u00a0I2<\/sub>(aq) + 2e–<\/sup><\/li>\n<\/ul>\n Electrolysis of other aqueous solutions using active electrodes:<\/strong><\/p>\n(a) Electrolysis of silver nitrate, AgNO3<\/sub> solution using silver electrodes<\/strong><\/p>\n\n- Silver nitrate solution consists of Ag+<\/sup> ions, H+<\/sup> ions, NO3<\/sub> ions and OH–<\/sup> ions.<\/li>\n
- At the cathode:<\/strong> The Ag+<\/sup> ions and H+<\/sup> ions move to the cathode. The Ag+<\/sup> ion is lower than the H+<\/sup>\u00a0ion in the electrochemical series. Hence, the Ag+<\/sup> ions are selectively discharged to form silver atoms. Silver metal is deposited on the cathode.
\nAg+<\/sup>(aq) + e–<\/sup>\u00a0\u2192 Ag(s)<\/li>\n- At the anode:<\/strong> The NO–<\/sup> ions and OH–<\/sup> ions move to the anode. However, these ions are not discharged. Instead, the silver electrode dissolves to form Ag+<\/sup> ions.
\nAg(s) \u2192 Ag+<\/sup>(aq) + e–<\/sup><\/li>\n- Consequently, the concentration of the silver nitrate solution remains unchanged.<\/li>\n<\/ul>\n
(b) Electrolysis of saturated sodium chloride, NaCl solution using graphite as the anode and mercury as the cathode<\/strong><\/p>\n\n- Saturated sodium chloride solution consists of Na+<\/sup> ions, H+<\/sup> ions, Cl–<\/sup> ions and OH–<\/sup> ions.<\/li>\n
- At the cathode:<\/strong> The Na+<\/sup> ions and H+<\/sup>\u00a0ions move to the mercury cathode. The Na+<\/sup> ions are selectively discharged to form sodium metal. The sodium formed then combines with mercury to form sodium amalgam.
\nNa+<\/sup>(aq) + e–<\/sup>\u00a0\u2192 Na(l)
\nNa(l) + Hg(l) \u2192 Na\/Hg(l) \u00a0 (Amalgam)
\nEven though Na+<\/sup> ion is higher than H+<\/sup>\u00a0ion in the electrochemical series, the Na+<\/sup> ions are selectively discharged because of the effect of the mercury electrode.<\/li>\n- At the anode:<\/strong> The Cl–<\/sup> ions and OH–<\/sup> ions move to the graphite anode. The Cl–<\/sup>\u00a0ions are selectively discharged because of their higher concentration in the electrolyte. Hence, chlorine gas is formed.
\n2Cl–<\/sup>(aq) \u2192\u00a0Cl2<\/sub>(g) + 2e–<\/sup><\/li>\n<\/ul>\nElectrolysis of Copper(II) Sulphate Solution\u00a0Experiment 1<\/strong><\/h2>\nAim:<\/strong> To investigate the electrolysis of copper(II) sulphate solution and dilute sulphuric acid.
\nMaterials:<\/strong> 0.1 mol dm-3<\/sup> copper(II) sulphate solution, 0.1 mol dm-3<\/sup> sulphuric acid and wooden splint.
\nApparatus:<\/strong> Batteries, carbon electrodes, electrolytic cell, connecting wires with crocodile clips, ammeter, test tubes and switch.
\nProcedure:<\/strong><\/p>\nA. Electrolysis of copper(II) sulphate solution<\/strong><\/p>\n\n- An electrolytic cell is filled with 0.1 mol dm-3<\/sup> copper(II) sulphate, CuSO4<\/sub> solution until it is half full.<\/li>\n
- The apparatus is set up as shown in Figure. The test tube must be full of the copper(II) sulphate solution at the beginning of the activity.
\n<\/li>\n - The switch is turned on to allow electricity to pass through the electrolyte for 15 minutes.<\/li>\n
- The observations at the anode, cathode and electrolyte are recorded.<\/li>\n
- The gas gathered at the anode is tested using a glowing wooden splint.<\/li>\n<\/ol>\n
B. Electrolysis of dilute sulphuric acid<\/strong><\/p>\n\n- An electrolytic cell is filled with dilute sulphuric acid, H2<\/sub>SO4<\/sub> until it is half full.<\/li>\n
- The apparatus is set up as shown in Figure. The test tubes must be full of dilute sulphuric acid at the beginning of the activity.
\n<\/li>\n - The switch is turned on to allow electricity to pass through the electrolyte for 15 minutes.<\/li>\n
- The observations at the anode, cathode and electrolyte are recorded.<\/li>\n
- The gas gathered at the cathode is tested using a lighted wooden splint.<\/li>\n
- The gas gathered at the anode is tested using a glowing wooden splint.<\/li>\n<\/ol>\n
Observations:<\/strong><\/p>\n\n\n\nElectrolyte<\/strong><\/td>\nObservation<\/strong><\/td>\n<\/tr>\n\nCathode<\/strong><\/td>\nAnode<\/strong><\/td>\nChange in solution<\/strong><\/td>\n<\/tr>\n\nCopper(II) sulphate solution<\/td>\n | A brown solid is deposited on the cathode.<\/td>\n | Gas bubbles are released. A colourless gas which relights a glowing wooden splint is produced.<\/td>\n | The intensity of the blue colour of the electrolyte decreases.<\/td>\n<\/tr>\n | \nDilute sulphuric acid<\/td>\n | Gas bubbles are released. A colourless gas is produced which gives a ‘pop’ sound when tested with a lighted wooden splint.<\/td>\n | Gas bubbles are released. A colourless gas which relights a glowing wooden splint is produced.<\/td>\n | The colourless solution remains unchanged.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n The ammeter needle is deflected.<\/p>\n Discussion:<\/strong><\/p>\n\n- The aqueous solution of copper(II) sulphate consists of copper(II) ions, Cu2+<\/sup>, sulphate ions, SO4<\/sub>2-<\/sup>, hydrogen ions, H+<\/sup> and hydroxide ions, OH–<\/sup> that move freely.\n
\n- During the electrolysis, the Cu2+<\/sup> ions and H+<\/sup> ions move to the cathode. The Cu2+<\/sup> ions are selectively discharged whereby each Cu2+<\/sup> ion accepts two electrons to form copper metal.
\nCu2+<\/sup>(aq) + 2e–<\/sup> \u2192\u00a0Cu(s)<\/li>\n- The SO4<\/sub>2-<\/sup>\u00a0ions and OH–<\/sup> ions move to the anode. The OH–<\/sup> ions are selectively discharged by donating electrons to form oxygen and water.
\n4OH–<\/sup>(aq) \u2192 O2<\/sub>(g) + 2H2<\/sub>O(I) + 4e–<\/sup><\/li>\n- The intensity of the blue colour of the electrolyte decreases as the concentration of blue Cu2+<\/sup> ions decreases when more copper is deposited on the cathode.<\/li>\n
- The electrolyte becomes more acidic because of the H+<\/sup> ions and SO4<\/sub>2-<\/sup> ions left.<\/li>\n<\/ul>\n<\/li>\n
- Dilute sulphuric acid consists of hydrogen ions, H+<\/sup>, sulphate ions, SO4<\/sub>
| | | | | |