The electrolysis of sodium chloride solution produces useful substances. covalent ionic non-metallic

Transcription

1 1 The electrolysis of sodium chloride solution produces useful substances. (a) (i) Choose a word from the box to complete the sentence. covalent ionic non-metallic Electrolysis takes place when electricity passes through... compounds when they are molten or in solution. (ii) Choose a word from the box to complete the sentence. alkenes elements salts During electrolysis the compound is broken down to form... (b) The table of ions on the Data Sheet may help you to answer this question. The diagram shows an apparatus used for the electrolysis of sodium chloride solution. Reproduced with the permission of Nelson Thornes Ltd from PATRICK FULLICK et al, ISBN First published in 2006 Page 1 of 23

2 Identify the products A, B and C on the diagram using substances from the box. chlorine gas hydrogen gas oxygen gas sodium hydroxide solution sodium metal (i) A is... (ii) B is... (iii) C is... (Total 5 marks) 2 The electrolysis of sodium chloride solution is an industrial process. (a) Why do chloride ions move to the positive electrode? Page 2 of 23

3 (b) Sodium chloride solution contains two types of positive ions, sodium ions (Na + ) and hydrogen ions (H + ). Tick ( ) the reason why hydrogen is produced at the negative electrode and not sodium. Reason Tick ( ) Hydrogen is a gas. Hydrogen is less reactive than sodium. Hydrogen is a non-metal. Hydrogen ions travel faster than sodium ions. (c) Solution X is alkaline. Which ion makes solution X alkaline? (d) Electrolysis of sodium chloride solution produces hydrogen and chlorine. The hydrogen and chlorine can be used to make hydrogen chloride. (i) The diagrams show how the outer electrons are arranged in atoms of hydrogen and chlorine. Complete the diagram to show how the electrons are arranged in a molecule of hydrogen chloride (HCl). Page 3 of 23

4 (ii) Name the type of bond between the hydrogen and the chlorine atoms in a molecule of hydrogen chloride.... (iii) Some hydrogen chloride was bubbled into water. This made a solution with a ph of 1. Which ion gave the solution a ph of 1?... (Total 6 marks) 3 The table below shows information about three metals. Metal Mainly found as % of metal in Earth s crust Relative cost of 1 kg Aluminium Aluminium oxide, Al 2 O Gold Gold Iron Iron(III) oxide, Fe 2 O (a) Suggest why gold is a very expensive metal. Iron is extracted from iron oxide by reduction with carbon. Aluminium cannot be extracted by reduction with carbon. (b) (i) What is the name of the process used to extract aluminium from aluminium oxide? (ii) Why is it more expensive to extract aluminium than iron? Page 4 of 23

5 (c) Complete and balance the symbol equation for the reaction to produce iron from iron(iii) oxide CO 2 (2) (Total 5 marks) 4 This question is about potassium. (a) Humphrey Davy was a professor of chemistry. In 1807 Davy did an electrolysis experiment to produce potassium. (i) Davy first tried to electrolyse a solid potassium salt to produce potassium. Explain why this electrolysis did not work. (2) (ii) Humphrey Davy was the first person to produce potassium. Humphrey Davy s experiment to produce this new element was quickly accepted by other scientists. Suggest why. Page 5 of 23

6 (b) A student dissolved some potassium chloride in water. The student tried to electrolyse the potassium chloride solution to produce potassium. The apparatus the student used is shown in the diagram. The student expected to see potassium metal at the negative electrode, but instead saw bubbles of a gas. Name the gas produced at the negative electrode. Explain why this gas was produced at the negative electrode and why potassium was not produced. The reactivity series of metals on the Chemistry Data Sheet may help you to answer this question. (3) (c) The student tried to electrolyse molten potassium chloride to produce potassium. (i) Potassium metal was produced at the negative electrode. Describe how potassium atoms are formed from potassium ions. (2) Page 6 of 23

7 (ii) Complete and balance the equation for the reaction at the positive electrode....cl Cl (iii) Complete the diagram to show the electronic structure of a chloride ion (Cl ). (Total 10 marks) 5 The electrolysis of sodium chloride solution is an industrial process. The diagram shows the apparatus used in a school experiment. (a) One of the products of the electrolysis of sodium chloride solution is hydrogen. (i) Why do hydrogen ions move to the negative electrode? (ii) How does a hydrogen ion change into a hydrogen atom? Page 7 of 23

8 (b) Hydrogen is used to make ammonia (NH 3 ). Complete the diagram to show the bonding in ammonia. Use dots ( ) and crosses (x) to show electrons. Show only outer shell electrons. (2) (c) The table shows the ions in sodium chloride solution. Positive ions hydrogen sodium Negative ions chloride hydroxide In industry, some of the waste from the electrolysis of sodium chloride solution is alkaline and has to be neutralised. (i) Which ion makes the waste alkaline? (ii) This waste must be neutralised. Write the ionic equation for the neutralisation reaction. Page 8 of 23

9 (d) In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. The electrolysis of sodium chloride solution also produces chlorine and sodium hydroxide. In industry, the electrolysis of sodium chloride solution can be done in several types of electrolysis cell. Some information about two different types of electrolysis cell is given below. Mercury cell Membrane cell Cost of construction Expensive Relatively cheap Additional substances used Mercury, which is recycled. Mercury is toxic so any traces of mercury must be removed from the waste Membrane, which is made of a polymer. The membrane must be replaced every 3 years. Amount of electricity used for each tonne of chlorine produced in kwh Quality of chlorine produced Quality of sodium hydroxide solution produced Pure 50% concentration. Steam is used to concentrate the sodium hydroxide solution produced. Needs to be liquefied and distilled to make it pure. 30% concentration. Steam is used to concentrate the sodium hydroxide solution produced. Page 9 of 23

10 Use the information and your knowledge and understanding to compare the environmental and economic advantages and disadvantages of these two types of electrolysis cell. (6) (Total 12 marks) Page 10 of 23

11 6 The diagrams represent the electronic structure of a magnesium atom and a chlorine atom. Magnesium reacts with chlorine to make the ionic compound called magnesium chloride. This contains magnesium ions, Mg 2+, and chloride ions, Cl - (a) (i) Which structure, A, B or C, represents a magnesium ion? The magnesium ion is Structure (ii) Which structure, D, E or F, represents a chloride ion? The chloride ion is Structure Page 11 of 23

12 (b) Magnesium metal can be extracted from sea water. Sea water contains magnesium chloride, MgCl 2 (i) Calcium hydroxide, Ca(OH) 2, is added to the sea water. Magnesium hydroxide, Mg(OH) 2, is produced as a solid. This is the equation for the reaction: MgCl 2 (aq) + Ca(OH) 2 (aq) Mg(OH) 2 (s) + CaCl 2 (aq) Draw a ring around the correct answer to complete each sentence. soluble Magnesium hydroxide forms as a solid because it is insoluble in water. dissolved precipitation. This type of reaction is called neutralisation. thermal decomposition. (2) (ii) How is the solid magnesium hydroxide separated from the solution? (iii) An acid is then added to the solid magnesium hydroxide to make magnesium chloride. Draw a ring around the name of this acid. nitric acid hydrochloric acid sulfuric acid Page 12 of 23

13 (c) Electrolysis is used to extract magnesium metal from magnesium chloride. (i) What must be done to solid magnesium chloride to allow it to conduct electricity? (ii) Why do the magnesium ions move to the negative electrode? (iii) Name the product formed at the positive electrode. (Total 9 marks) Page 13 of 23

14 7 This question is about the electrolysis of two compounds. Figure 1 shows the electrolysis of molten lead bromide. Figure 1 (a) The electrolyte contains lead ions (Pb 2+ ) and bromide ions (Br ). Complete the sentences. Use words from the box. atoms bromide bromine ions lead molecules oxygen At the positive electrode the gas produced is... At the negative electrode lead... gain electrons and.... (3) Page 14 of 23

15 (b) A student measured the volumes of each gas produced during the electrolysis of water. The table below shows the student s results. Time in minutes Volume of gas produced in cm 3 Hydrogen Oxygen The student plotted a graph of the results for oxygen. Figure 2 shows the graph. The student did not put a scale on the y axis. On the graph in Figure 2: complete the scale for the y axis plot the results for hydrogen include a line of best fit. Figure 2 Page 15 of 23

16 (3) (c) Use the graph to calculate the mean volume of oxygen produced per second. Mean volume of oxygen produced =... cm 3 / s (3) (Total 9 marks) Page 16 of 23

17 8 Some students investigated reactions to produce magnesium. (a) The students used electrolysis to produce magnesium from magnesium chloride, as shown in the figure below. (i) Magnesium chloride contains magnesium ions and chloride ions. Why does solid magnesium chloride not conduct electricity? (ii) One of the products of the electrolysis of molten magnesium chloride is magnesium. Name the other product. (iii) Why do magnesium ions (Mg 2+ ) move to the negative electrode? (iv) At the negative electrode, the magnesium ions (Mg 2+ ) gain electrons to become magnesium atoms. How many electrons does each magnesium ion gain?... Page 17 of 23

18 (b) The students did the experiment four times and weighed the magnesium produced. The table below shows their results. Experiment Mass of magnesium produced in grams (i) There is an anomalous result. Suggest one possible reason for the anomalous result. (ii) Calculate the mean mass of magnesium produced, taking account of the anomalous result. Mean mass =... g (2) Page 18 of 23

19 (c) The formula of magnesium chloride is MgCl 2 The relative formula mass of magnesium chloride is 95. The relative atomic mass of magnesium is 24. (i) Use the equation to calculate the percentage mass of magnesium in magnesium chloride. Percentage mass of magnesium = 100% Percentage mass of magnesium in magnesium chloride =... % (2) (ii) Draw a ring around the relative mass of chlorine in MgCl (d) Magnesium is also produced from the reaction of magnesium oxide with silicon. (i) The equation for the reaction is: 2 MgO(s) + Si(s) SiO 2 (s) + 2 Mg(s) What is the meaning of this symbol? Draw a ring around the correct answer. neutralisation reaction precipitation reaction reversible reaction (ii) The forward reaction is endothermic. Draw a ring around the correct answer to complete the sentence. In an endothermic reaction the temperature of the surroundings decreases. increases. stays the same. (Total 12 marks) Page 19 of 23

20 9 The figure below shows an apparatus to produce elements from a solution of an ionic compound. (a) What is the name of the process in the figure? Tick one box. Combustion Crystallisation Distillation Electrolysis Page 20 of 23

21 (b) The table below shows the products formed from three experiments using different compounds and the apparatus shown in the figure above. Compound State Product at cathode Product at anode Copper chloride Molten Copper Chlorine Copper chloride Aqueous solution Copper Chlorine Potassium bromide Molten Potassium Bromine Use the table above to name the products formed at each electrode if using an aqueous solution of potassium bromide. At cathode... At anode... (2) (c) Explain why copper is formed at the cathode during the electrolysis of its salts. (2) (Total 5 marks) 10 Copper can be produced from copper(ii) sulfate solution by two different methods. Method 1 Electrolysis (a) To produce copper by electrolysis a student has inert electrodes, a d.c. power supply, a switch and electrical wires for the external circuit. Draw and label the apparatus set up to produce copper from copper(ii) sulfate solution by electrolysis. (2) Page 21 of 23

22 (b) Suggest why the colour of the copper(ii) sulfate solution fades during the electrolysis. (3) (c) Explain how copper is produced from copper(ii) sulfate solution by electrolysis. (4) Page 22 of 23

23 Method 2 Displacement (d) The chemical equation for the displacement of copper using iron is: CuSO 4 + Fe Cu + FeSO 4 Calculate the minimum mass of iron needed to displace all of the copper from 50 cm 3 of copper(ii) sulfate solution. The concentration of the copper(ii) sulfate solution is 80 g CuSO 4 per dm 3. Relative atomic masses (A r ): O = 16; S = 32; Fe = 56; Cu = 63.5 Give your answer to 2 significant figures. Mass of iron =... g (4) (Total 13 marks) Page 23 of 23