Beatty 17.5 ELECTROCHEM (W5) Review 2023 Answers4E1

1 Beatty Secondary School Science Department (Chemistry Unit) Chemistry 6092 Name: ___________________________________ ( ) Date: _______________ Class: 4E___ TOPIC: ELECTROCHEMISTRY (WORKSHEET 5) – REVIEW Multiple-Choice Questions 1 Element X is extracted by the electrolysis of a molten compound of elements X and Y. The electrode reactions are as shown. What could be the identity of the compound? positive electrode: 2Y2− → Y2 + 4e− negative electrode: X2+ + 2e− → X A aluminium oxide B magnesium oxide C calcium chloride D potassium chloride ( B ) 2 A metal can be obtained by the electrolysis of its molten chloride. The table shows properties of the metal and its chloride. substance melting point / °C boiling point / °C density / gcm−3 metal 328 1750 11 metal chloride 534 950 4.5 In which state will the metal be formed in electrolysis? A as a solid below the molten chloride B as a liquid below the molten chloride C as a solid on the surface of the molten chloride D as a liquid on the surface of the molten chloride ( B ) 3 Which of the following involves the largest number of electrons for complete discharge during electrolysis? A 4 mol of Al3+ ions B 6 mol of Cu2+ ions C 5 mol of OH− ions D 7 mol of O2− ions ( D ) 4 Dilute sulfuric acid was electrolysed using inert electrodes. What volumes (at r.t.p) of hydrogen and oxygen were formed by the passage of 1 mole of electrons? volume of hydrogen / dm3 volume of oxygen / dm3 A 24 12 B 12 6 C 6 12 D 12 24 ( B )

2 5 Processes 1, 2 and 3 each involve the movement of charged particles. Which process(es) involve(s) the movement of ions? A process 1 only B process 2 only C process 1 and 2 D process 2 and 3 ( D ) 6 Aluminium is obtained by electrolysis of molten aluminium oxide. Which statement about the electrolysis is correct? A Aluminium ions are oxidised to aluminium at the negative electrode. B Aluminium ions are oxidised to aluminium at the positive electrode. C Aluminium ions are reduced to aluminium at the negative electrode. D Aluminium ions are reduced to aluminium at the positive electrode. ( C ) 7 What happens to the ions that move to the negative electrode during electrolysis of molten potassium iodide? A Ions are reduced. B Ions form molecules. C Ions increase in charge. D Ions release electrons. ( A ) 8 In the electrolysis of molten sodium chloride, 46 g of sodium is formed at the cathode. How many moles of chlorine gas are formed at the anode? A 0.5 mol B 1.0 mol C 2.0 mol D 4.0 mol ( B )

3 9 The following three different solutions were electrolysed using inert electrodes. 1 aqueous sodium chloride 2 concentrated hydrochloric acid 3 dilute sulfuric acid Which solution(s) produce(s) hydrogen at the cathode? A 1 only B 1 and 2 only C 1, 2 and 3 D 2 only ( C ) 10 In the purification of copper, a sample of copper contain ing metal impurities that are below it in the reactivity series. The loss in mass of the positive electrod e was 50 g and the gain in mass of the negative electrode was 45 g. What was the percentage purity of this sample of copper? A 10.0% B 11.1% C 90.0% D 95.0% ( C ) 11 Electrical energy is produced by a simple cell as a result of A formation of covalent bonds between atoms. B formation of negative ions from atoms. C positive and negative ions coming together. D transfer of electrons from a more reactive to a less reactive element. ( D ) 12 The diagram shows a cell. What statement about the cell is correct? A Electrons pass from magnesium to the silver electrode through the electrolyte. B The cell shows that silver is more reactive than magnesium. C The magnesium electrode loses electrons. D The silver electrode is oxidised. ( C ) 13 Which statement(s) about simple cells is/are correct? 1 A greater voltage is produced using magnesium and silver than using magnesium and copper. 2 The electrolyte is an aqueous solution containing positive and negative ions. 3 The more reactive metal will release electrons. A 1, 2 and 3 B 1 and 3 only C 1 only D 2 and 3 only ( A )

4 Structured Questions 14 The table gives the colours of six salts. salt colour copper(II) sulfate, CuSO4 blue copper(II) nitrate, Cu(NO3)2 blue potassium chromate, K2CrO4 yellow sodium chromate, Na2CrO4 yellow sodium nitrate, NaNO3 colourless potassium nitrate, KNO3 colourless (a) Write down the names of the three elements combined in potassium chromate. potassium, chromium and oxygen (b) Suggest the colour of: sodium ions: colourless copper(II) ions: blue chromate ions: yellow copper(II) chromate solution: green (c) The apparatus shown in the diagram below was set up. (d) After some time , a yellow band moves through the gel towards the anode and a blue band towards the cathode. Explain these observations. The positively charged copper(II) ions will migrate t o the negative electrode while the negatively charged chromate ions ions will migrate to the positive electrode . Since copper(II) ions give a blue colouration, the blue band can be seen migrating t owards the anode . As chromate ions give a y ellow colouration, the yellow band can be seen migrating towards the cathode.

5 15 Both d ilute aqueous potassium chloride and molten potassium chloride can be electrolysed. Describe two differences between the products of the electrolysis of dilute a queous potassium chloride and the electrolysis of molten potassium chloride. At the negative electrode , hydrogen gas will be liberated from the electrolysis of aqueous pota ssium chlori de, whereas mol ten potassium will be deposited from the electrolysis of molten potassium chloride. At the positive electrode, oxygen gas and water will be formed from the electrolysis of aqueous pota ssium chloride, whereas chlorine gas will be liberated from the electrolysis of molten potassium chloride. 16 The table shows information about the electrolysis of some substances. Complete the table by filling in the missing information. substance electrodes used product of reaction at positive electrode product of reaction at negative electrode concentrated aqueous copper(II) chloride carbon chlorine copper metal dilute aqueous copper(II) chloride copper copper(II) ions copper metal molten sodium chloride platinum chlorine sodium 17 The diagram shows a cell for purifying copper. (a) Describe what you would observe during this electrolysis and write the equations for the reactions at the electrodes. The a node will dissolve and decreases in mass and solid impurities can be observed sinking to bottom of the beaker. Equation: Cu (s) → Cu2+ (aq) + 2e− The cathode increases in mass with the reddish-brown copper deposit forming at the electrode. Equation: Cu2+ (aq) + 2e−→ Cu (s)

6 (b) Describe how the apparatus shown can be modified in order to electroplate an iron object, such as knife or nickel. The pu re copper electrode can be placed at the positive terminal / made the anode, while the iron object can be p laced at the negat ive terminal / made the cathode. 18 A student sets up two different experiments for electroplating an object with silver. (a) Write equations, with state symbols, to show the reactions that happen at the anode and cathode during each experiment. Experiment 1: Anode: 4OH−(aq) → 2H2O(l) + O2(g) + 4e− Cathode: Ag+(aq) + e− → Ag(s) Experiment 2: Anode: Ag(s) → Ag+(aq) + e− Cathode: Ag+(aq) + e− → Ag(s) (b) At the beginning of each experiment the stu dent removes a sample of the electrolyte, aqueous silver nitrate, and puts it in a test-tube. The student then add