{"id":2919,"date":"2023-10-03T16:27:17","date_gmt":"2023-10-03T16:27:17","guid":{"rendered":"http:\/\/localhost\/ecole9ja\/?p=2919"},"modified":"2023-10-03T16:31:25","modified_gmt":"2023-10-03T16:31:25","slug":"week-6-ss2-first-term-chemistry-notes","status":"publish","type":"post","link":"https:\/\/ecolebooks.com\/nigeria\/posts\/week-6-ss2-first-term-chemistry-notes\/","title":{"rendered":"Week 6 &#8211; SS2 First Term Chemistry Notes"},"content":{"rendered":"<p><strong>WEEK    6<br \/>\n<\/strong> Electrolysis <strong><br \/>\n\t\t\t\t<\/strong><img decoding=\"async\" src=\"https:\/\/ecolebooks.com\/nigeria\/wp-content\/uploads\/9jalessonsimages\/100323_1627_Week6SS2Fi1.jpg\" alt=\"\"\/><br \/>\n\t\tWhen an electric current is passed through an electrolyte solution, the ions of the electrolyte undergo chemical changes at the respective electrodes. The chemical reaction carried out by passing electricity is called electrolysis.<br \/>\nit is important that we familiarize ourselves with different terms that we are going to use to explain different phenomena. It is crucial that the definitions and meanings of these terms be understood at the outset in order that concepts defined in this chapter are easily and clearly apprehended. These terms are given hereunder:<\/p>\n<ul>\n<li><strong>Electrolysis<\/strong>: decomposition of a compound in solution or molten state by passing electricity through it.\n<\/li>\n<li><strong>Conductor<\/strong>: a solid substance that allows electricity to pass through it. All metals are included in this class.\n<\/li>\n<li><strong>Non-conductor or insulator<\/strong>: a solid substance that does not allow electricity to flow through it. All non-metals fall in this class.\n<\/li>\n<li><strong>Electrolyte<\/strong>: a substance which, when dissolved or molten, conducts electricity and is decomposed by it.\n<\/li>\n<li><strong>Non-electrolyte<\/strong>: a compound which cannot conduct electricity, be it in molten or solution state.\n<\/li>\n<li><strong>Electrode<\/strong>: a graphite or metal pole (rod) or plate through which the electric current enters or leaves the electrolyte.\n<\/li>\n<li><strong>Cathode<\/strong>: a negative electrode which leads electrons into the electrolyte.\n<\/li>\n<li><strong>Anode<\/strong>: a positive electrode which leads electrons out of the electrolyte.\n<\/li>\n<li><strong>Ion<\/strong>: a positively or negatively charged atom or radical (group of atoms).\n<\/li>\n<li><strong>Cation<\/strong>: a positive ion which moves to the cathode during electrolysis.\n<\/li>\n<li><strong>Anion<\/strong>: a negative ion which moves to the anode during electrolysis.\n<\/li>\n<\/ul>\n<p><strong>The electrolytic cell (voltameter) <\/strong><br \/>\n\tThe apparatus in which electrolysis is carried out is called electrolytic cell. A battery supplies the direct current. Graphite electrodes carry the current into and out of the liquid electrolyte. Graphite is chosen because it is quite unreactive (inert). It will not react with the electrolyte or with products of electrolysis. Electrons flow from the <em>negative terminal<\/em> (cathode) of the battery around the circuit and back to the <em>positive terminal<\/em> (anode). In the electrolyte it is the <em>ions<\/em> that move to carry the current.<br \/>\n<img decoding=\"async\" src=\"https:\/\/ecolebooks.com\/nigeria\/wp-content\/uploads\/9jalessonsimages\/100323_1627_Week6SS2Fi2.jpg\" alt=\"\"\/><br \/>\n\t6.2. THE MECHANISM OF ELECTROLYSIS<br \/>\nThe conductivity of ionic compounds is explained by the fact that ions move in a particular direction in an electric field. This can be shown in experiments with coloured salts. For example, copper (II) chromate (VI) (CuCrO<sub>4<\/sub>) dissolves in water to give a <strong>green<\/strong> solution. This solution is placed in a U-tube. A colourless solution of dilute hydrochloric acid (HCl) is then layered on top of the salt solution in each arm. Graphite rods are fitted as shown in figure 13.3. These rods (electrodes) carry the current into and out of the solution.<br \/>\nAfter passing the current for a short time, the solution around the cathode becomes <strong>blue<\/strong>. Around the anode, the solution becomes <strong>yellow<\/strong>. These colours are produced by the movement (migration) of the ions in the salt. The positive copper ions (Cu<sup>2+<\/sup>) are blue in solution. They are attracted to the cathode (negative electrode). The negative chromate ions (CrO<sub>4<\/sub><sup>2-<\/sup>) are yellow in solution. They are attracted to the anode (the positive electrode). The use of coloured ions in solution has shown the direction that positive and negative ions move in an electric field. Always positive ions (cations) move to the cathode and negative ions (anions) move to the anode.<br \/>\n<img decoding=\"async\" src=\"https:\/\/ecolebooks.com\/nigeria\/wp-content\/uploads\/9jalessonsimages\/100323_1627_Week6SS2Fi3.jpg\" alt=\"\"\/><br \/>\n\t<strong><em>\u00a0 The movement of ions in solution<\/em><\/strong><br \/>\n\t\u00a0<br \/>\n\u00a0PREFERENTIAL (SELECTIVE) DISCHARGE OF IONS<br \/>\nWhen a salt such as sodium chloride is dissolved in water, its ions are set free to move. So the solution can be electrolysed. Since the salts, alkalis and acids are dissolved in water, most of the solutions are aqueous. There is then a complication in electrolysis of such substances in aqueous form. This is because the water used to dissolve them also do ionize partially (it is a weak electrolyte)<br \/>\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 H<sub>2<\/sub>O\u21d4 H<sup>+<\/sup> + OH<sup>&#8211;<\/sup><br \/>\n\tThen at each electrode, we get more than one ion for discharge, but only one is supposed to be discharged. Take an example of electrolysis of copper (II) sulphate solution using platinum electrodes. By ionic theory, the solution ionizes thus:<br \/>\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0CuSO<sub>4 (aq)<\/sub> \u2192 Cu<sup>2+ <\/sup><sub>(aq)<\/sub> + SO<sub>4<\/sub><sup>2-<\/sup><sub>(aq)<\/sub> (strong electrolyte)<br \/>\n\u00a0\u00a0\u00a0\u00a0\u00a0<br \/>\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 H<sub>2<\/sub>O\u21d4 H<sup>+<\/sup> + OH<sup>&#8211;<\/sup>\u00a0\u00a0\u00a0\u00a0 (weak electrolyte)<br \/>\nDuring electrolysis, Cu<sup>2+ <\/sup>and H<sup>+ <\/sup>ions move to the cathode while SO<sub>4<\/sub><sup>2-<\/sup>and OH<sup>&#8211;<\/sup> ions move to the anode.<br \/>\n\u00a0<br \/>\n\u00a0<\/p>\n<div>\n<table>\n<tbody>\n<tr>\n<td>Cathode<\/td>\n<td>Anode<\/td>\n<\/tr>\n<tr>\n<td>Cu<sup>2+<\/sup><\/td>\n<td>SO<sub>4<\/sub><sup>2-<\/sup><\/td>\n<\/tr>\n<tr>\n<td>H<sup>+<\/sup><\/td>\n<td>OH<sup>&#8211;<\/sup><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>\u00a0<br \/>\n\u00a0In situations like this, the order of discharge of the ions at the electrode will depend on:<\/p>\n<ol>\n<li>the position of the metal ion or radical in the electrochemical series;\n<\/li>\n<li>the concentration or nature of the ions (or electrolyte) to be discharged; and\n<\/li>\n<li>the nature of the electrodes used.\n<\/li>\n<\/ol>\n<p>\u00a0<br \/>\n\u00a0<\/p>\n<ol>\n<li><strong>The position of ion or radical in the electrochemical series<\/strong>\n\t\t<\/li>\n<\/ol>\n<p>\u00a0<br \/>\n\u00a0<\/p>\n<div>\n<table>\n<tbody>\n<tr>\n<td><strong><em>Cations<\/em><\/strong><\/td>\n<td>\u00a0\u00a0<\/td>\n<td><strong><em>Anions<\/em><\/strong><br \/>\n\t\t\t\t\t\t\u00a0\u00a0<\/td>\n<td>\u00a0\u00a0<\/td>\n<\/tr>\n<tr>\n<td>\u00a0K<sup>+<\/sup><\/td>\n<td>ease of discharge<br \/>\nincreases<\/td>\n<td>SO<sub>4<\/sub><sup>2-<\/sup><\/td>\n<td>ease of discharge increases<\/td>\n<\/tr>\n<tr>\n<td>Ca<sup>2+<\/sup><\/td>\n<td>NO<sub>3<\/sub><sup>&#8211;<\/sup><\/td>\n<\/tr>\n<tr>\n<td>Na<sup>+<\/sup><\/td>\n<td>Cl<sup>&#8211;<\/sup><\/td>\n<\/tr>\n<tr>\n<td>Mg<sup>2+<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<td>Br<sup>&#8211;<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<\/tr>\n<tr>\n<td>Al<sup>3+<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<td>I<sup>&#8211;<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<\/tr>\n<tr>\n<td>Zn<sup>2+<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0 OH<sup>&#8211;<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<\/tr>\n<tr>\n<td>Fe<sup>2+<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0\u00a0<\/td>\n<\/tr>\n<tr>\n<td>Pb<sup>2+<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0\u00a0<\/td>\n<\/tr>\n<tr>\n<td>H<sup>+<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0\u00a0<\/td>\n<\/tr>\n<tr>\n<td>\u00a0 Cu<sup>2+<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0\u00a0<\/td>\n<\/tr>\n<tr>\n<td>\u00a0Ag<sup>+<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0\u00a0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The arrangement of ions above is the same as that of the electrochemical series. If all other factors are constant, any ion will be discharged from solution in preference to those above it. For example, in sodium hydroxide solution, containing H<sup>+<\/sup> (from water) and Na<sup>+ <\/sup>(from the salt), H<sup>+<\/sup> discharges in preference to Na<sup>+<\/sup>.<br \/>\nIn copper sulphate solution, containing \u00a0OH<sup>&#8211;<\/sup> (from water) and \u00a0SO<sub>4<\/sub><sup>2-<\/sup> as negative ions, \u00a0OH<sup>&#8211;<\/sup> is discharged in preference to \u00a0SO<sub>4<\/sub><sup>2-<\/sup>.<\/p>\n<div>\n<table>\n<tbody>\n<tr>\n<td>\u00a0<br \/>\n\u00a0Cathode<\/td>\n<td>\u00a0<br \/>\n\u00a0\u00a0\u00a0<\/td>\n<td>\u00a0<br \/>\n\u00a0\u00a0 Anode<\/td>\n<\/tr>\n<tr>\n<td>Cu<sup>2+<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0 SO<sub>4<\/sub><sup>2-<\/sup><\/td>\n<\/tr>\n<tr>\n<td>H<sup>+<\/sup><\/td>\n<td>\u00a0\u00a0<\/td>\n<td>\u00a0 OH<sup>&#8211;<\/sup><\/td>\n<\/tr>\n<tr>\n<td>Cu<sup>2+\u00a0 <\/sup>+ 2e<sup>&#8211; <\/sup>\u2192 Cu<sub>(s)<\/sub><br \/>\n\t\t\t\t\t\t<em>copper is discharged (loses its charge)<\/em><\/td>\n<td>\u00a0<br \/>\n\u00a0\u00a0\u00a0<\/td>\n<td>4OH<sup>&#8211;<\/sup>\u21922H<sub>2<\/sub>O<sub>(l)<\/sub>+O<sub>2(g)<\/sub>+4e<sup>&#8211; <\/sup>\u00a0\u00a0\u00a0\u00a0<br \/>\n<em>hydroxyl ion is discharged<\/em><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>\u00a0<br \/>\n\u00a0In other words, we can say that the reaction that occurs at the <strong><em>cathode<\/em><\/strong> is <em>reduction<\/em> (electron gain) and that which occurs at the <strong><em>anode<\/em><\/strong> is <em>oxidation<\/em> (electron loss).<br \/>\n\u00a0<br \/>\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <em>Result<\/em><\/p>\n<ul>\n<li>At cathode, copper is deposited\n<\/li>\n<li>At anode, oxygen is given out (liberated)\n<\/li>\n<li>The solution at the end of electrolysis is colourless and acidic because in the electrolyte there are left \u00a0H<sup>+<\/sup> and \u00a0SO<sub>4<\/sub><sup>2-<\/sup> ions, which remain moving freely in the solution as ionic sulphuric acid.\n<\/li>\n<\/ul>\n<p>\u00a0<br \/>\n\u00a0<strong>2. The concentration or nature of electrolyte<\/strong><br \/>\n\tTake an example of electrolysis of sodium chloride using platinum electrodes when in:<\/p>\n<ol>\n<li>aqueous solution;\n<\/li>\n<li>concentrated aqueous solution; or\n<\/li>\n<li>fused or molten state.\n<\/li>\n<\/ol>\n<p>\u00a0<br \/>\n\u00a0<\/p>\n<ol>\n<li><strong><em>aqueous solution<\/em><\/strong>\n\t\t<\/li>\n<\/ol>\n<p>NaCl \u2192 Na<sup>+ <\/sup>+ Cl<sup>&#8211;<\/sup><br \/>\n\tH<sub>2<\/sub>O\u21d4H<sup>+<\/sup> + OH<sup>&#8211;<\/sup><br \/>\n\t\u00a0\u00a0\u00a0 During electrolysis:<\/p>\n<div>\n<table>\n<tbody>\n<tr>\n<td>Cathode<\/td>\n<td>Anode<\/td>\n<\/tr>\n<tr>\n<td>\u00a0Na<sup>+<\/sup>\u00a0and \u00a0\u00a0H<sup>+<\/sup><\/td>\n<td>Cl<sup>&#8211;<\/sup>\u00a0\u00a0and \u00a0OH<sup>&#8211;<\/sup><\/td>\n<\/tr>\n<tr>\n<td>\u00a0H<sup>+<\/sup> \u00a0ions are discharged in preference to \u00a0Na<sup>+<\/sup> ions:<br \/>\n\u00a0\u00a0 2H<sup>+\u00a0 <\/sup>+ 2e<sup>&#8211; <\/sup>\u2192 H<sub>2(g)<\/sub><br \/>\n\t\t\t\t\t\t\u00a0\u00a0<\/td>\n<td>OH<sup>&#8211;<\/sup>\u00a0ions are discharged in preference to Cl<sup>&#8211;<\/sup>\u00a0ions:<br \/>\n4OH<sup>&#8211;<\/sup>\u21922H<sub>2<\/sub>O<sub>(l) <\/sub>+O<sub>2(g)<\/sub>+4e<sup>&#8211; <\/sup>\u00a0\u00a0\u00a0\u00a0<br \/>\n\u00a0\u00a0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>\u00a0<br \/>\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <em>Result<\/em><\/p>\n<ul>\n<li>At cathode, hydrogen is given out\n<\/li>\n<li>At anode, oxygen is out\n<\/li>\n<li>The concentration of the solution remains constant since all \u00a0Na<sup>+<\/sup> and \u00a0Cl<sup>&#8211;<\/sup> ions remain undisturbed in the solution. This means that the \u00a0Na<sup>+<\/sup> and \u00a0Cl<sup>&#8211;<\/sup> ions that are left in the solution are equivalent to sodium chloride solution.\n<\/li>\n<\/ul>\n<p>\u00a0<strong><em>i. Concentrated aqueous solution<\/em><\/strong><br \/>\n\t\u00a0\u00a0\u00a0\u00a0 NaCl \u2192 Na<sup>+ <\/sup>+ Cl<sup>&#8211;<\/sup><br \/>\n\t\u00a0\u00a0\u00a0\u00a0 H<sub>2<\/sub>O\u21d4H<sup>+<\/sup> + OH<sup>&#8211;<\/sup><\/p>\n<div>\n<table>\n<tbody>\n<tr>\n<td>Cathode <\/td>\n<td>Anode <\/td>\n<\/tr>\n<tr>\n<td>\u00a0Na<sup>+<\/sup>and \u00a0H<sup>+<\/sup><br \/>\n\t\t\t\t\t\t\u00a0<br \/>\n\u00a0\u00a0H<sup>+<\/sup> ions are discharged in preference to \u00a0Na<sup>+<\/sup>\u00a0 ions since \u00a0Na<sup>+<\/sup> and \u00a0H<sup>+<\/sup> are very far from each other in e. c.s<br \/>\n2H<sup>+\u00a0 <\/sup>+ 2e<sup>&#8211; <\/sup>\u2192 H<sub>2(g)<\/sub><\/td>\n<td>\u00a0Cl<sup>&#8211;<\/sup>\u00a0and \u00a0OH<sup>&#8211;<\/sup>\u00a0<br \/>\n\u00a0<br \/>\n\u00a0Cl<sup>&#8211;<\/sup>\u00a0ions are discharged in preference to \u00a0OH<sup>&#8211;<\/sup> ions since Cl<sup>&#8211;<\/sup> and \u00a0OH<sup>&#8211;<\/sup> ions are very close to each other in the e. c. s\u00a0 (and because there are more \u00a0Cl<sup>&#8211;<\/sup> ions in the solution)<br \/>\n2Cl<sup>&#8211; <\/sup>\u2192 Cl<sub>2(g)<\/sub> + 2e<sup>&#8211;<\/sup><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<br \/>\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <em>Result<\/em><\/p>\n<ul>\n<li>At cathode \u00a0H<sub>2(g)<\/sub> is given off\n<\/li>\n<li>At anode Cl<sub>2(g)<\/sub> is given off\n<\/li>\n<li>The solution becomes progressively more alkaline as the electrolysis goes on because \u00a0Na<sup>+<\/sup> and \u00a0OH<sup>&#8211;<\/sup>\u00a0\u00a0ions remain in solution as caustic soda (sodium hydroxide) solution. This is the main method used in the manufacture of sodium hydroxide in industry.\n<\/li>\n<\/ul>\n<p>\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0Na<sup>+<\/sup><sub>(aq) <\/sub>+ OH<sup>&#8211;<\/sup><sub>(aq)<\/sub> \u2192 NaOH<sub>(aq)<\/sub><\/p>\n<ol>\n<li>\u00a0<strong><em>Fused or molten sodium chloride<\/em><\/strong>\n\t\t<\/li>\n<\/ol>\n<p>NaCl \u2192 Na<sup>+ \u00a0<\/sup>+ Cl<sup>&#8211;<\/sup><br \/>\n\t\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 During electrolysis:<\/p>\n<div>\n<table>\n<tbody>\n<tr>\n<td>Cathode<\/td>\n<td>Anode<\/td>\n<\/tr>\n<tr>\n<td>Na<sup>+<\/sup> + e<sup>&#8211;<\/sup> \u2192 Na<sub>(l)<\/sub><br \/>\n\t\t\t\t\t\t\u00a0\u00a0<\/td>\n<td>2Cl<sup>&#8211;<\/sup> \u2192 Cl<sub>2(g)<\/sub> + 2e<sup>&#8211;<\/sup><br \/>\n\t\t\t\t\t\t\u00a0\u00a0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <em>Result<\/em><\/p>\n<ul>\n<li>At cathode sodium is liberated (deposited)\n<\/li>\n<li>At anode chlorine is given off\n<\/li>\n<\/ul>\n<p>\u00a0<br \/>\n\u00a0<strong>3. The nature of electrodes (inert vs active electrodes)<\/strong><br \/>\n\t<strong>Example 1<\/strong><\/p>\n<ol>\n<li>If dilute sulphuric acid \u00a0(H<sub>2<\/sub>SO<sub>4<\/sub>) is electrolysed using platinum electrodes:\n<\/li>\n<\/ol>\n<p>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 H<sub>2<\/sub>SO<sub>4<\/sub> \u2192 2H<sup>+<\/sup> + SO<sub>4<\/sub><sup>2-<\/sup><br \/>\n\t\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 H<sub>2<\/sub>O\u21d4H<sup>+<\/sup> + OH<sup>&#8211;<\/sup><\/p>\n<div>\n<table>\n<tbody>\n<tr>\n<td>Cathode<\/td>\n<td>\u00a0\u00a0\u00a0\u00a0\u00a0 Anode<\/td>\n<\/tr>\n<tr>\n<td>2H<sup>+\u00a0 <\/sup>+ 2e<sup>&#8211; <\/sup>\u2192 H<sub>2(g)<\/sub><\/td>\n<td>\u00a0\u00a0\u00a0\u00a0\u00a0 SO<sub>4<\/sub><sup>2-<\/sup> and OH<sup>&#8211;<\/sup><br \/>\n\t\t\t\t\t\t\u00a0\u00a0\u00a0\u00a0\u00a0 4OH<sup>&#8211;<\/sup>\u21922H<sub>2<\/sub>O<sub>(l)<\/sub>+O<sub>2(g)<\/sub>+4e<sup>&#8211;<\/sup><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <em>Result<\/em><\/p>\n<ul>\n<li>At cathode \u00a0H<sub>2(g)<\/sub> is given out\n<\/li>\n<li>\u00a0At anode \u00a0O<sub>2(g)<\/sub>\u00a0 \u00a0is given out\n<\/li>\n<li>The solution becomes acidic at the end of electrolysis because of the acidic ions (SO<sub>4<\/sub><sup>2-<\/sup>) left in the finala solution.\n<\/li>\n<\/ul>\n<ol>\n<li>If dilute sulphuric acid is electrolysed using graphite electrodes:\n<\/li>\n<\/ol>\n<p>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 H<sub>2<\/sub>SO<sub>4<\/sub> \u2192 2H<sup>+<\/sup> + SO<sub>4<\/sub><sup>2-<\/sup><br \/>\n\t\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 H<sub>2<\/sub>O\u21d4H<sup>+<\/sup> + OH<sup>&#8211;<\/sup><\/p>\n<div>\n<table>\n<tbody>\n<tr>\n<td>Cathode <\/td>\n<td>Anode<\/td>\n<\/tr>\n<tr>\n<td>2H<sup>+\u00a0 <\/sup>+ 2e<sup>&#8211; <\/sup>\u2192 H<sub>2(g)<\/sub><br \/>\n\t\t\t\t\t\t\u00a0\u00a0<\/td>\n<td>SO<sub>4<\/sub><sup>2-<\/sup> and OH<sup>&#8211; <\/sup><br \/>\n\t\t\t\t\t\t\u00a0\u00a0<\/td>\n<\/tr>\n<tr>\n<td>\u00a0\u00a0<\/td>\n<td>4OH<sup>&#8211;<\/sup>\u21922H<sub>2<\/sub>O<sub>(l) <\/sub>+ O<sub>2(g) <\/sub>+ 4e<sup>&#8211;<\/sup><\/td>\n<\/tr>\n<tr>\n<td>\u00a0\u00a0<\/td>\n<td><img decoding=\"async\" src=\"https:\/\/ecolebooks.com\/nigeria\/wp-content\/uploads\/9jalessonsimages\/100323_1627_Week6SS2Fi4.png\" alt=\"\"\/><\/td>\n<\/tr>\n<tr>\n<td>\u00a0<br \/>\n\u00a0\u00a0\u00a0<\/td>\n<td>C + O<sub>2<\/sub> \u2192 CO<sub>2(g)<\/sub><br \/>\n\t\t\t\t\t\t\u00a0\u00a0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>\u00a0<br \/>\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <em>Result <\/em><\/p>\n<ul>\n<li>At cathode, \u00a0H<sub>2(g)<\/sub> is given out\n<\/li>\n<li>At anode, a mixture of O<sub>2<\/sub>, CO and CO<sub>2<\/sub> gases are formed\n<\/li>\n<\/ul>\n<p><strong>Example 2<\/strong><br \/>\n\tElectrolysis of copper (II) sulphate using:<\/p>\n<ol>\n<li>platinum electrodes\n<\/li>\n<li>copper electrodes\n<\/li>\n<\/ol>\n<p>\u00a0<br \/>\n\u00a0<\/p>\n<ol>\n<li><strong><em>With platinum electrodes<\/em><\/strong>\n\t\t<\/li>\n<\/ol>\n<p>CuSO<sub>4<\/sub> \u2192 Cu<sup>2+<\/sup> + SO<sub>4<\/sub><sup>2-<\/sup><br \/>\n\t\u00a0\u00a0\u00a0\u00a0 H<sub>2<\/sub>O\u21d4H<sup>+<\/sup> + OH<sup>&#8211;<\/sup><\/p>\n<div>\n<table>\n<tbody>\n<tr>\n<td>Cathode <\/td>\n<td>Anode<\/td>\n<\/tr>\n<tr>\n<td>H<sup>+<\/sup> and Cu<sup>2+<\/sup><\/td>\n<td>SO<sub>4<\/sub><sup>2-<\/sup> and OH<sup>&#8211; <\/sup><\/td>\n<\/tr>\n<tr>\n<td>Cu<sup>2+<\/sup> + 2e<sup>&#8211;<\/sup> \u2192 Cu<sub>(s)<\/sub><br \/>\n\t\t\t\t\t\t\u00a0\u00a0<\/td>\n<td>4OH<sup>&#8211;<\/sup>\u21922H<sub>2<\/sub>O<sub>(l) <\/sub>+ O<sub>2(g) <\/sub>+ 4e-<br \/>\n\u00a0\u00a0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <em>Result <\/em><\/p>\n<ul>\n<li>At cathode copper is deposited\n<\/li>\n<li>At anode oxygen is given out\n<\/li>\n<li>The solution turns colourless and acidic to litmus due to \u00a0SO<sub>4<\/sub><sup>2-<\/sup> and H<sup>&#8211; <\/sup>\u00a0ions remaining in the solution, both of which are acidic in nature and are equivalent to acqueous sulphuric acid.\n<\/li>\n<\/ul>\n<p>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 2H<sup>+<\/sup> + SO<sub>4<\/sub><sup>2-<\/sup> \u2192 H<sub>2<\/sub>SO<sub>4<\/sub><\/p>\n<ol>\n<li><strong><em>With copper electrodes<\/em><\/strong>\n\t\t<\/li>\n<\/ol>\n<p>CuSO<sub>4<\/sub> \u2192 Cu<sup>2+<\/sup> + SO<sub>4<\/sub><sup>2-<\/sup><br \/>\n\t\u00a0\u00a0\u00a0 H<sub>2<\/sub>O\u21d4H<sup>+<\/sup> + OH<sup>&#8211;<\/sup><\/p>\n<div>\n<table>\n<tbody>\n<tr>\n<td>Cathode<\/td>\n<td>Anode<\/td>\n<\/tr>\n<tr>\n<td>H<sup>+<\/sup> and Cu<sup>2+<\/sup><\/td>\n<td>\n<ol>\n<li>\u00a0SO<sub>4<\/sub><sup>2-<\/sup><\/li>\n<\/ol>\n<\/td>\n<\/tr>\n<tr>\n<td>Cu<sup>2+<\/sup> + 2e<sup>&#8211;<\/sup> \u2192 Cu<sub>(s)<\/sub><\/td>\n<td>\n<ol>\n<li>\u00a0OH<sup>&#8211;<\/sup><\/li>\n<\/ol>\n<\/td>\n<\/tr>\n<tr>\n<td>\u00a0\u00a0<\/td>\n<td>\n<ol>\n<li>\u00a0Cu \u2192 Cu<sup>2+<\/sup> + 2e<sup>&#8211;<\/sup><\/li>\n<\/ol>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>\u00a0<br \/>\n\u00a0The \u00a0SO<sub>4<\/sub><sup>2-<\/sup> \u00a0and \u00a0OH<sup>&#8211;<\/sup>\u00a0ions move to the anode and there are possibilities of one of these being discharged. However, these ions are not discharged but remain in solution. Instead, copper atoms of the anode lose electrons and go into solution as copper ions.<br \/>\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Cu \u2192 Cu<sup>2+<\/sup> + 2e<sup>&#8211;<\/sup><br \/>\n\t\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <em>Result<\/em><\/p>\n<ul>\n<li>At cathode copper is deposited\n<\/li>\n<li>At anode copper dissolves (ionizes)\n<\/li>\n<li>\n<div>The concentration of the solution remains constant since for every one mole of \u00a0Cu<sup>2+<\/sup> discharged, there is one mole of \u00a0Cu \u00a0dissolved or ionized into one mole of\u00a0Cu<sup>2+<\/sup> ions. This method is applied in the purification of impure copper where the impure copper is made the anode, pure copper the cathode, and copper sulphate solution the electrolyte.\n<\/div>\n<p><strong>EVALUATION\u00a0\u00a0\u00a0\u00a0<br \/>\n<\/strong>1.Define Electrolysis<br \/>\nIi Define the following terms\n<\/li>\n<\/ul>\n<p>I.anode  ii. cathode  ii i. anoins  iv. cations v.ion  vi. electrode<br \/>\nii State 3 factors that affect the preferential discharge of ions.\u00a0\u00a0\u00a0\u00a0<\/p>\n","protected":false},"excerpt":{"rendered":"<p>WEEK 6 Electrolysis When an electric current is passed through an electrolyte solution, the ions&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1,235],"tags":[],"class_list":["post-2919","post","type-post","status-publish","format-standard","hentry","category-posts","category-first-term-ss2-chemistry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/posts\/2919","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/comments?post=2919"}],"version-history":[{"count":1,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/posts\/2919\/revisions"}],"predecessor-version":[{"id":2920,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/posts\/2919\/revisions\/2920"}],"wp:attachment":[{"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/media?parent=2919"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/categories?post=2919"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/tags?post=2919"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}