Answer ALL questions

Transcription

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2 Answer ALL questions 01. Most experiments involving electrolysis use inert electrodes, which do not take part in the reactions. However, in some experiments the electrodes do take part in the reactions. A student investigates the electrolysis of copper(ii) sulfate solution using copper electrodes which do take part in the reaction. She uses this apparatus. She uses this method. weigh two clean strips of copper use one strip as the positive electrode and the other as the negative electrode after electrolysis wash the strips of copper with ethanol (a liquid that boils at 78 C) dry the strips of copper and reweigh themthe ionic half-equations for the reactions at the electrodes are Positive electrode Negative electrode Cu(s) 2e Cu2+(aq) Cu2+(aq) + 2e Cu(s) (a) Suggest why the copper strips would dry more quickly when washed with ethanol rather than with water. (b) The student's results are shown in the table. The table shows that the decrease in mass of the positive electrode was 0.32 g. (i) Calculate the increase in mass, in grams, of the negative electrode. Increase in mass =...g 1

3 (ii) The ionic half-equations show that the increase in mass of the negative electrode should be the same as the decrease in mass of the positive electrode. Suggest two reasons why the increase in mass of the negative electrode in the student's experiment was less than expected (c) Another student investigated the effect of changing the electrical charge, in faradays, passed during the electrolysis. He wanted to find how this affected the increase in mass of the negative electrode. One faraday is the electrical charge of one mole of electrons. His results are shown in the table. 2

4 (i) On the grid, plot a graph of increase in mass against electrical charge. Draw a straight line of best fit. Start your line at the origin (0,0). (3) (ii) Draw a circle around the anomalous result. (iii) Suggest why the straight line should go through the origin. (iv) Explain why the graph shows that the increase in mass is directly proportional to the electrical charge passed. 3

5 (v) Use your graph to estimate the increase in mass, in grams, of the copper electrode that would be produced by passing an electrical charge of 0.55 faradays. Increase in mass =...g (Total for Question = 12 marks) 02. A student does some experiments to find the heat energy released when natural gas burns. She uses this apparatus. (a) The diagram shows the thermometer readings in one of her experiments. 4

6 Use these readings to complete the table, entering all values to the nearest 0.1 C. (3) (b) The student repeats the experiment three times. The table shows her results. (i) Calculate the amount, in moles, at room temperature and pressure, of methane burned in experiment 1. Assume that natural gas contains only methane. (The volume of 1 mol of a gas at room temperature and pressure is cm 3 ) amount =... mol (ii) The quantity of heat energy released in experiment 1 is J. Calculate the molar enthalpy change, in kj/mol, for the combustion of methane. molar enthalpy change =... kj/mol 5

7 (iii) The temperature rise in experiment 2 is 41.2 C. Calculate the heat energy change in experiment 2 using the expression heat energy change = volume of water 4.2 temperature change (in J) (in cm 3 ) (in C) heat energy change =... J (iv) The student uses the results from experiment 3 to calculate the molar enthalpy change, in kj/mol, for the combustion of methane. She compares her value with the value in a data book. Which is the best explanation for the large difference between these two values? A natural gas contains other gases that release heat energy when burned B C not all of the heat energy is transferred to the water some of the water evaporates during the experiment D the student measures the gas by volume instead of by mass (c) The student uses a table of average bond energies to calculate another value for the molar enthalpy of combustion of methane. The equation for the combustion can be shown using displayed formulae. 6

8 (i) Use values from the table to calculate the energy taken in when the bonds in the reactants are broken. energy taken in =... kj (ii) Use values from the table to calculate the energy given out when the bonds in the products are formed. energy given out =... kj (iii) Use your answers to (i) and (ii) to calculate the molar enthalpy change for the combustion of methane. molar enthalpy change =... kj/mol 03. Diamond and graphite are two naturally-occurring forms of carbon. The diagrams below show the arrangement of the carbon atoms in diamond and in graphite. The black dots ( ) represent carbon atoms. (Total for question = 15 marks) 7

9 (a) Name the type of structure in diamond and explain, in terms of its bonding, why diamond has a high melting point. (4) (b) Explain, in terms of its structure, why graphite can act as a lubricant. (c) The structure of graphite has one feature in common with that of metals. This feature allows graphite to conduct electricity. Suggest what this feature is and why it allows graphite to conduct electricity. (d) In 1985, a new form of carbon was discovered. It was called buckminsterfullerene after the architect Buckminster Fuller, who designed buildings with complex geometric shapes. Buckminsterfullerene (C 60) has a simple molecular structure containing 60 carbon atoms per molecule. It looks a little bit like a football. 8

10 Suggest why buckminsterfullerene has a much lower melting point than diamond. 04. There are two important ways to manufacture ethanol. Reaction 1 C 2H 4 + H 2O C 2H 5OH Reaction 1 C 6H 12O 6 2C 2H 5OH + 2CO 2 (Total for question = 10 marks) (a) (i) Identify one raw material that could be used as the source of C 6H 12O 6 (ii) Reaction 2 uses a catalyst called zymase, which is present in yeast. Identify the catalyst used in reaction 1. (iii) In both reactions it is important to control the temperature. State why the temperature in reaction 2 is kept below 35 C. 9

11 (b) A manufacturing company plans to build a factory to produce ethanol on a large scale. The factory will be near an oilfield. The ethanol will be used as a solvent for perfume. Suggest why the company should use reaction 1 rather than reaction 2. (3) (c) In the future, it may be necessary to convert the ethanol (produced by reaction 2) into ethene. Write the equation for this reaction and state the type of reaction that occurs. Equation Type of reaction (Total for Question = 8 marks) 10

12 05. Sulfuric acid can be manufactured from sulfur in a four stage process. stage 1 stage 2 stage 3 stage 4 sulfur is burned in air to form sulfur dioxide S + O 2 SO 2 the sulfur dioxide is reacted with more oxygen to form sulfur trioxide SO 2 + ½ O 2 SO 3 the sulfur trioxide is absorbed in concentrated sulfuric acid to make oleum SO3 + H 2SO 4 H 2S 2O 7 the oleum is carefully diluted with water to form sulfuric acid (a) Write a chemical equation for the formation of sulfuric acid from oleum.... (b) A mass of 80 tonnes of sulfur is reacted with oxygen in stage 1. Calculate the maximum mass, in tonnes, of sulfur trioxide that can be produced in stage 2. [1 tonne = g] (3) maximum mass =... tonnes (c) Calculate the minimum volume at rtp, in cubic decimetres (dm 3 ), of oxygen required to completely react with 64 tonnes of sulfur dioxide. [1 mol of oxygen at rtp has a volume of 24 dm 3 ] volume of oxygen =... dm 3 (Total for question = 6 marks) 11

13 06. Many chemical reactions occur in the atmosphere. (a) The pie chart shows the relative amounts of some gases in air. (i) Label the pie chart with the name of the gas that makes up most of the air. (ii) What type of bonds exist in the gas mentioned in part (i)? (iii) What is the approximate percentage of oxygen in air? Place a cross ( ) in one box (iv) Use words from the box to complete the sentences about some of the other gases in air. Each word may be used once, more than once or not at all. One of the gases in air is argon. It is called a noble gas because it is very.... The percentage of... vapour in air varies with the weather. 12

14 (b) Rain water is naturally slightly acidic because carbon dioxide dissolves in it. The word equation for the reaction that occurs is: carbon dioxide + water carbonic acid Acid rain is more acidic because pollutant gases in the atmosphere also dissolve in water. (i) Identify the acid formed when sulfur dioxide reacts with water. (ii) Identify another pollutant gas that forms acid rain. (iii) State two problems caused by acid rain (Total for Question = 9 marks) (Total for paper = 60 marks) 13