G10 worksheet for Electrloysis

1 By the end of the topic, students should be able to: Explain why molten ionic compounds conduct electricity but solid ionic compounds do not. State in which direction-Anions and cations move during elecytrolysis-Electrons move in the wires joined to the electrodes in electrolysis. State the ions present , name the products and give the electrodes reactions in the electrolysis of-Molten sodium chloride using inert aqueous sodium chloride, using inert sulphuric acid using inert copper(II) sulphate using carbon electrodes-Aqueous copper (II) sulphate using copper electrode Predict the likely products of the electrolysis of a molten compoundor of an aqueous worksheet for Electrloysis Explain what happen in refining copper. Describe electroplating ( copper plating) Describe the extraction of aluminium by tick in the box if you can do the Electrolytes are ionic compounds that conduct electricity.

2 The electrolyte can be either a molten ionic compound or an aqueous solution of an ionic compound. Electrolytes conduct electricity because they contain positive and negative ons that can move freely throughout the liquid. Solid ionic compounds do not conduct electricity. Why?_____ When an electric current flows through an electrolyte, the compound is decomposed in a chemical reaction. This is called USED IN ELECTROLYSIS2 The diagram below shows the flow of electrons to and from the battery in an electrolytic OF MOLTEN IONIC COMPOUNDS When a molten ionic compound is electrolysed,-the positive cations go to the _____and are discharge by _____ electrons to become _____. -the negative anions go to the _____ and are discharge by _____ electrons to become neutral ionic compound is decomposed into its _____. Example 1: Electrolysis of molten potassium )What ions are present?

3 _____b)Which one will move towards the cathode? )Which one will move towards the anode? )Write the anode half equation. _____3e)Write the cathode half equation. _____f)Write the overall redox reaction. _____Electrolysis of molten sodium chloridea)What ions are present? _____b)Which one will move towards the cathode? )Which one will move towards the anode? )Write the anode half equation. _____e)Write the cathode half equation. _____f)Write the overall redox reaction. _____ Why is it important to keep on heating the crucible throughout the electrolysis?_____ When these ions react this is called discharging the ions . Why?_____ Please proceed to do exercise from: 4 worksheet 1 ELECTROLYSIS OF AQUEOUS SOLUTIONS There are 2 major differences here. The temperature is room temperature and there is water in the reaction.

4 A small number of water molecules ioniseH2O(l) H+(aq) + OH-(aq) So all aqueous solutions have small concentration of H+ and OH- ions. In electrolysis, when more than one type of cation or anion is present in a solution, only ONE cation and one anion are preferentially discharged. This is called selective discharge of ions. How do you decide which ion is discharged? It depends on three factors-The position of the metal (producing the cation) in the reactivity relative ease of discharge of an concentration of the anion in the electrolyte. The ease of discharge of cations and anions is shown of dilute sodium chloride solution5 In dilute NaCl (aq) what cations are present? _____- what anions are present? _____Using the reactivity series of metal and the relative ease of discharge of anion:-Which cation is reduced? _____-Which anion is oxidised? _____-Write the anode half equation.

5 _____-Write the cathode half equation. _____- Write the overall redox reaction. _____ Please proceed to do exercise from: worksheet 2 ELECTROLYSIS WITH REACTIVE ELECTRODES Electrodes can be inert. These do not react, they are just conductors of electricity to transfer electrons. platinum and graphite (carbon) Other electrodes can be reactive and be oxidized and are made from most of the other metals. These electrodes are oxidised before Please proceed to do exercise from: worksheet 3 SUMMARY7 INDUSTRIAL APPLICATION OF ELECTROLYSIS1)Electroplating8 Electroplating is coatingan object with a metal by electrolysis. The object is the cathode. The metal to be plated is the anode. The electrolyte is a solution of the metal ions to be plated. During electroplating, metal from the anode dissolves in the electrolyte as metal ions. These ions go to the cathode where they are discharged onto the objectas a layer of metal.

6 An example of electroplating copper is shown in the diagram for useChromiumTinSilver2)Purifying (Refining) of metals Similar to plating but the impure metal is the anode so it is oxidised and then reduced to a pure metal. This electrolysis is used to refine copper (see diagram)9-Write the anode half equation. _____-Write the cathode half equation. _____- Write the overall redox reaction. _____3) Extraction of metals from their ores Metals can be extracted from their ores by electrolysis. Electricity is expensive, so electrolysis is only used to extract very reactive metals such as sodium, calcium and aluminium. These metals, high up in the reactivity series, cannot be extracted by other methods. Pure Al2O3 is extracted from bauxite. Al2O3 has a very high melting point (>2000 C) so it is added to molten cryolite (Na3 AlF6) which dissolves the Al2O3 at about 950 C.

7 The mixture is now electrolysed using carbon electrodes. Why is it an advantage to use a lower melting point to extract Al?_____10 Recycling of Aluminium Aluminium is recycled because it saves the cost of extracting new metal from aluminium ore. About 90% of the cost of aluminium is due to the expenses of CELLS A simple electric cell consists of two different metals in an electrolyte. An example is shown in the diagram. The metals are zinc and copper, and the electrolyte is aqueous sodium chloride. The more reactive metal (higher up in the reactivity series) is the negative electrode. It becomes negative because the electrode dissolves in the electrolyte leaving electrons on the electrode:Zn Zn2+ + 2e- Electrons go from the negative electrode through the wire to the positive The less reactive metal (lower down in the reactivity series) is the positive electrode. It becomes positive because positive ions in the electrolyte take electrons from the electrode and are discharged.

8 For example, if the electrolyte is NaCl (aq), hydrogen ions from the solution are discharged:2H+ + 2e- H2 The further apart in the reactivity series the two metals are, the bigger is the voltage. So a magnesium + copper cell has a bigger voltage than a zinc + copper OF ELECTRIC CELLS Electric cells are also known as batteries. Batteries are used in small flashlights and cars becausea)They can be carried about without attached electrical )They can be used outdoors where there is no mains electricity available. Please proceed to do exercise from: Chemistry Insights, Pg 354, Questions, Question 1-2 worksheet 412 worksheet 113 Prepared by Kartini IshakWORKSHEET 2 Electrolysis of Concentrated Aqueous Sodium Chloride In dilute NaCl (aq) what cations are present? _____- what anions are present? _____Using the reactivity series of metal and the relative ease of discharge of anion:-Which cation is reduced?

9 _____-Which anion is oxidised? _____-Write the anode half equation. _____-Write the cathode half equation. _____- Write the overall redox reaction. _____Electrolysis of Dilute Sulphuric Acid In dilute H2SO4 (aq) what cations are present? _____- what anions are present? _____Using the reactivity series of metal and the relative ease of discharge of anion:-Which cation is reduced? _____-Which anion is oxidised? _____-Write the anode half equation. _____-Write the cathode half equation. _____- Write the overall redox reaction. _____Electrolysis of Aqueous Copper (II) Sulphate14 Prepared by Kartini Ishak In dilute CuSO4 (aq) what cations are present? _____- what anions are present? _____Using the reactivity series of metal and the relative ease of discharge of anion:-Which cation is reduced? _____-Which anion is oxidised? _____-Write the anode half equation.

10 _____-Write the cathode half equation. _____- Write the overall redox reaction. _____WORKSHEET 315 worksheet 4 16y9 revision 18y9 revision