Q1. Methane and oxygen react together to produce carbon dioxide and water.

Transcription

1 Chemistry C3 Higher Questions Part 2 Q1. Methane and oxygen react together to produce carbon dioxide and water. The methane gas will not burn in oxygen until a flame is applied, but once lit it continues to burn. (a) Explain why energy must be supplied to start the reaction but it continues by itself once started. (4) (b) Sketch an energy level diagram for the reaction and indicate on the diagram the nett energy released. Page 1

2 (3) (Total 7 marks) Q2. The diagram shows some of the elements in Groups I and 7 of the Periodic Table. (a) The elements in Group 1 have similar chemical properties. Describe one chemical reaction which shows that lithium, sodium and potassium react in the same sort of way. You should say what you would react them with and what substances would be produced. Page 2

3 What you would react them with Substances produced (3) (b) All the elements in Group 7 react with hydrogen. Fluorine reacts in the dark, explosively, at very low temperatures. Chlorine reacts explosively in sunlight, at room temperature. Bromine, in light, only reacts if heated to about 200 C. Suggest the conditions needed for hydrogen and iodine to react. Give reasons for your answer. (c) Hydrogen and chlorine react to produce hydrogen chloride. Balance the symbol equation for the reaction. H 2 + Cl 2 HCl (d) Use your understanding of atomic structure to explain the trend in reactivity in the Group 7 elements. (Total 8 marks) Page 3

4 Q3. The symbol equation shows the decomposition of water. 2H 2O 2H 2 + O 2 An energy level diagram for this reaction is shown below. Explain the significance of x, y and z on the energy level diagram in terms of energy transfers that occur in the reaction. You should make specific reference to the bonds broken and formed and to the nett energy transfer (energy transferred to or from the surroundings) (Total 6 marks) Page 4

5 Q4. Ammonia is manufactured from nitrogen and hydrogen in the Haber Process. The diagram shows some details of the manufacturing process. (a) Nitrogen is obtained from the air. From where is the hydrogen obtained? (b) What happens to the unreacted nitrogen and hydrogen? (c) Ammonium nitrate is made from ammonia. Farmers spread nitrates on to soil to make crops grow better. The nitrates may get into people s bodies even if they do not eat the crops. Explain how this can happen. Page 5

6 (d) The equation for the Haber Process is this: N 2 + 3H 2 2NH 3 At equilibrium, nitrogen, hydrogen and ammonia are present in the reactor. (i) What is meant by equilibrium? (ii) Explain, as fully as you can, why: the yield of ammonia decreases with increase in temperature, despite this fact, a comparatively high temperature of 4500C is used for the industrial process, iron powder is added to the reactor. (4) (Total 9 marks) Q5. These are the electronic structures of the atoms of three different elements element A element B element C Page 6

7 (a) Identify elements A and B. Element A is... Element B is... (b) (i) Why is element C more reactive than element A? (ii) Why is element B unreactive? (Total 6 marks) Q6. The idea of a periodic table of the elements was started by John Newlands about 140 years ago. He wrote down the elements he knew about in order, starting with the lightest atoms. Then he arranged them into seven groups, like this: Page 7

8 (a) Write down three differences between the groups in Newlands periodic table and the groups in the modern periodic table (up to the element Ca, which is calcium). (3) (b) Suggest one reason why this part of Newlands table was different from the modern one. (c) Dimitri Mendeléev later developed the periodic table of the elements. He arranged the elements according to their properties and their relative atomic masses. The diagram shows where Mendeléev put tellurium (Te) and iodine (I) in his table because of their properties. (The diagram uses present day symbols and the atomic numbers of the elements have been added to Mendeléev s table.) Page 8

9 (i) What is wrong with this arrangement of tellurium and iodine in terms of their relative atomic masses? (ii) Explain why this is not a problem in the modern periodic table. (Total 7 marks) Q7. The electronic structures of five elements, V, W, X, Y and Z are shown below. Page 9

10 (a) (i) Write the letters of the two elements which belong to the same group in the Periodic Table... (ii) To which group do they belong?... (b) Write the letters of two elements that are gases... (c) Lithium, sodium and potassium are the first three elements in Group 1 of the Periodic Table. (i) Lithium reacts with cold water to produce lithium hydroxide and hydrogen. Describe how the reaction between sodium and water is (A) similar and (B) different to that between lithium and water. (A) Similar... (B) Different... (3) (ii) Potassium is much more reactive than lithium. Explain this in terms of their electronic structures (3) Page 10

11 (Total 9 marks) Q8. You will find the information on the Data Sheet helpful when answering this question. This equation shows the reaction between ethene and oxygen. C 2H 4 + 3O 2 2CO 2 + 2H 2O The structural formulae in the equation below show the bonds in each molecule involved. Use the three stages shown at (a), (b) and (c) below to calculate the nett energy transfer when the formula mass (1 mole) of ethene reacts with oxygen. (a) Write down the bonds broken and the bonds formed during the reaction. (Some have already been done for you.) (b) Calculate the total energy changes involved in breaking and in forming all of these Page 11

12 bonds. (Some have already been done for you.) (4) (c) Describe, as fully as you can, what the figures in (b) tell you about the overall reaction. (Total 8 marks) Q9. Ammonia is manufactured from nitrogen and hydrogen. The reaction is shown in the equation below. The diagram shows some details of the manufacturing process. Page 12

13 The graph shows the percentage of reacting gases converted into ammonia at different temperatures and pressures. At room temperature and pressure, the reaction is very slow and only a small percentage of the reacting gases is converted to ammonia. Use the information on the diagram and graph to: (a) describe the conditions used in the manufacture of ammonia to increase the rate Page 13

14 of reaction. (4) (b) describe and explain the conditions used in the manufacture of ammonia to increase the yield. (7) (Total 11 marks) Page 14

15 Q10. The symbol equation shows the reaction between methane and oxygen. CH 4 + 2O 2 CO 2 + 2H 2O methane oxygen carbon dioxide water The structural formulae in the equation below show the bonds in each molecule involved. In the three stages shown at (i), (ii) and (iii) below, calculate the net energy transfer when the formula mass (1 mole) of methane reacts with oxygen. (i) Write down the bonds broken and the bonds formed during the reaction. Bonds broken Bonds formed number type number type (4) (ii) Calculate the total energy changes involved in breaking and in forming each of these bonds. Total energy change in breaking bonds Total energy change in forming bonds (4) Page 15

16 (iii) Describe, as fully as you can, what the above figures in (ii) tell you about the overall reaction. (Total 10 marks) Q11. The table shows the properties of four elements from Group VII of the Periodic Table. (a) Complete the spaces in the table. (4) (b) Comment briefly on the trend in melting points for these four elements. Page 16

17 (c) Explain, in as much detail as you can: (i) why the reactions of these elements with hydrogen are similar. (ii) why their reactivity with hydrogen decreases from fluorine to iodine. (4) (Total 9 marks) Q12. The symbol equation below shows the reaction when methane burns in oxygen. CH 4 + 2O 2 CO 2 + 2H 2O An energy level diagram for this reaction is shown below. Page 17

18 (a) Which chemical bonds are broken and which are formed during this reaction? (4) (b) Explain the significance of x, y and z on the energy level diagram in terms of the energy transfers which occur when these chemical bonds are broken and formed. (5) (Total 9 marks) Page 18

19 Q13. Ammonia is manufactured in the Haber Process, from nitrogen and hydrogen. (a) Balance this symbol equation for the process. (b) The graph below shows the percentage of reacting gases converted into ammonia, at different temperatures and pressures. (i) What does the graph suggest about the temperature and pressure needed to convert the maximum percentage of reacting gases into ammonia? (ii) Suggest reasons why the manufacture of ammonia in the Haber Process is usually carried out at about 400 C and 200 atmospheres pressure. Page 19

20 (Total 6 marks) Q14. (a) Ammonia is manufactured from nitrogen and hydrogen. The equation for the reaction between them is: N 2(g) + 3H 2(g) 2NH 3(g) (i) What is the source of the nitrogen? (ii) Why does increasing the pressure increase the chance of molecules of hydrogen reacting with molecules of nitrogen? (iii) The percentage yield of ammonia is the percentage, by mass, of the nitrogen and hydrogen which has been converted to ammonia. Calculate the mass, in tonnes, of ammonia which can be produced from 90 tonnes of hydrogen when the percentage yield is 50%. The relative atomic masses are: H 1; N 14. Show clearly how you get to your answer. Mass =... tonnes Page 20

21 (b) The percentage yield of ammonia depends on the temperature and pressure inside the reaction vessel. The set of graphs show this. (i) MPa is the symbol for which unit? (ii) What is the percentage yield of ammonia produced at a temperature of 450 C and a pressure of 20 MPa? (iii) Suggest what changes the chemical engineers should make to both the temperature and the pressure to increase the percentage yield of ammonia. Temperature... Page 21

22 Pressure... (iv) How can the rate of ammonia production be increased without changing the temperature or pressure or the mass of hydrogen and nitrogen? (c) About four-fifths of ammonia production is used to produce fertilisers. One of them is known as NPK. It is made in the following way. Some ammonia is converted to nitric acid which is then mixed with phosphoric acid. The mixture is neutralised with more ammonia and the solution is partly evaporated. Potassium chloride is added to form granules. The granules are coated to make the fertiliser free-flowing. Complete the flow-chart for the production of NPK by writing in the names of the correct chemicals in the six boxes. (Total 10 marks) Page 22

23 Q15. (a) The diagram shows the electronic structure of a particular element. In a similar way, show the electronic structure of another element from the same group in the periodic table and name the element you select. Name of element selected... (4) (b) The element lithium gives a moderate reaction with cold water, releasing hydrogen and forming a solution of lithium hydroxide. Describe how sodium is similar to and how it is different from lithium in its chemical reaction with cold water. Explain any similarity or difference in terms of their atomic structure. Similarity.... Reason Difference.... Reason Page 23

24 ... (5) (Total 9 marks) Q16. The balanced equation for the combustion of ethane is shown using structural formulae. (a) Complete the table to show the number of bonds broken and made when two molecules of ethane react with seven molecules of oxygen. Type of bond C C C H O O C O H O Number of bonds broken Number of bonds made (b) The combustion of ethane is a strongly exothermic process. Draw a labelled energy level diagram showing the endothermic and exothermic parts of the overall reaction. Indicate the activation energy on the diagram. (4) (c) Explain, in terms of particles and the activation energy of a reaction, how a catalyst is able to increase the rate of reaction. Page 24

25 (Total 8 marks) Q17. (a) In industry ammonia is produced from nitrogen and hydrogen. The equation for the reaction is: (i) What does the symbol (g) represent? (ii) What does the symbol represent? (iii) Nitrogen is used for the industrial production of ammonia. From what raw material does this nitrogen come? (iv) Hydrogen is used for the industrial production of ammonia. It is obtained from the reaction between methane and steam. The equation for this reaction is: CH 4 + H 2O 3H 2 + CO Explain how you can tell that this equation is balanced. Page 25

26 (b) Ammonia is used to make ammonium salts which can be used as fertilisers. (i) Complete the names in the following sentence. One example is ammonium... which is made by reacting ammonia with... acid. (ii) All ammonium salts are soluble in water. Why is this a useful property of a fertiliser? (c) Ammonia is a covalent, chemical compound. (i) Complete the following sentence to describe a chemical compound. In a chemical compound, two or more... (ii) What is a covalent bond? (Total 10 marks) Page 26

27 Q18. (a) The table shows how Group 7 elements react with hydrogen. Element Reaction with hydrogen Fluorine Chlorine Description Explosive reaction in dim light Explosive reaction in sunlight Product Hydrogen fluoride Hydrogen chloride Bromine Reacts if heated Hydrogen bromide Iodine Reacts if heated strongly Hydrogen iodine (i) Explain why all the Group 7 elements react in a similar way with hydrogen. (ii) Explain the difference in the rates of the reaction of fluorine with hydrogen, and of iodine with hydrogen. (b) Explain why Group 0 elements are monatomic. Page 27

28 (Total 6 marks) Q19. The table gives some properties of the element silicon. Melting point 1410 ºC Relative atomic mass 28 Conductivity Compounds Conducts electricity Forms compounds with covalent bonds Position in periodic table Group 4 Reaction with water Density Unreactive Relatively low (a) Give two ways in which silicon is similar to the alkali metals (b) Give two ways in which the properties of silicon are different from those of the alkali metals (Total 4 marks) Page 28

29 Q20. John Newland produced a periodic table in The first 21 elements in his table are shown in the diagram. Column H Li Be B C N O F Na Mg Al Si P S Cl K Ca Cr Ti Mn Fe Use the periodic table on the Data Sheet to help you to answer these questions. (a) In which two columns of Newland s periodic table do all the elements have similar properties? (b) The modern periodic table is arranged in a different order to Newland s table. (i) What order is used in the modern periodic table? (ii) Argon has a higher relative atomic mass than potassium. Explain why. (iii) Describe the changes in the number of electrons in the atoms of elements in the period which begins with potassium and ends with krypton. Page 29

30 (Total 5 marks) Q21. The table shows how Group 7 elements react with hydrogen. Reaction with hydrogen Element Description Product Fluorine Chlorine Explosive reaction in dim light Explosive reaction in sunlight Hydrogen fluoride Hydrogen chloride Bromine Reacts if heated Hydrogen bromide Iodine Reacts if heated strongly Hydrogen iodine Explain the difference in the rates of the reaction of fluorine with hydrogen and of iodine with hydrogen (Total 2 marks) Q22. In the Haber process, nitrogen and hydrogen react to make ammonia. N 2(g) + 3H 2(g) nitrogen + hydrogen 2NH 3 (g) ammonia Page 30

31 % ammonia present at equilibrium Pressure in atmospheres Temperature in ºC The actual conditions used in the Haber process are usually 450 C and 200 atmospheres. (a) What effect does increasing the pressure have on the percentage of ammonia made? Use the balanced symbol equation to explain why. (b) A lower temperature of 100 C gives high percentages of ammonia at most pressures. Why is this temperature not used in the Haber process? Page 31

32 (c) Describe and explain the effect of an increase in the temperature on the reaction between nitrogen and hydrogen in the Haber process. (3) (Total 6 marks) Q23. Hydrogen chloride is made by reacting hydrogen with chlorine. H 2(g) + Cl 2(g) 2HCl(g) Bond Bond energy in kj H H 436 Cl Cl 242 H Cl 431 Is the reaction between hydrogen and chlorine exothermic or endothermic? Use the bond energies to explain your answer Page 32

33 (Total 3 marks) Q24. Use the Periodic Table of Elements on the Data Sheet to help you to answer this question. Francium (Fr) is a very rare element. It is estimated that there is only 25 g of francium in the Earth s crust. Francium is radioactive and has a half-life of only a few minutes. Mendeleev predicted the existence of francium in the 1870s but the element was not discovered until (a) Explain why Mendeleev was able to predict the existence of francium in the 1870s. (b) Suggest why there is not much experimental evidence for the properties of francium. (c) (i) If you could react francium with water, how would the reaction compare with that of sodium with water? Page 33

34 (ii) Explain the reason for your answer. (Total 6 marks) Q25. Ethanol is used as a fuel. (a) Balance the symbol equation for the combustion reaction. C 2H 5OH + O 2 CO 2 + H 2O (b) The energy level diagram represents the combustion of ethanol. Describe what must happen to the molecules of ethanol and oxygen to allow them to react Page 34

35 (3) (c) We can use bond energies to calculate the energy change for the reaction between hydrogen and oxygen. 2H 2 + O 2 2H 2O Bond Bond energy in kj H H 436 O H 464 O = O 498 (i) Calculate the total bond energy of the reactants Total bond energy of reactants =... kj (ii) Is the reaction between hydrogen and oxygen exothermic or endothermic? Use bond energies to explain your answer Page 35

36 (Total 8 marks) Q26. Beryllium and calcium are metals in Group 2 of the periodic table. The diagrams show their electronic structures. (a) Why do beryllium and calcium have similar chemical properties? (b) Calcium is more reactive than beryllium. Suggest an explanation for this in terms of the electronic structure of the two elements. Page 36

37 (Total 3 marks) Q27. In sea water the bromine is present as bromide ions (Br ). The equation below shows how chlorine can be used to displace bromine from sea water. Cl 2(g) + 2Br (aq) Br 2(g) + 2Cl (aq) Explain, as fully as you can, why chlorine can displace bromine from sea water. To obtain full marks your answer should refer to electronic structure (Total 3 marks) Q28. (a) What is the name given to the block of elements in the middle of the Periodic Table which includes vanadium? Page 37

38 (b) Some of the properties of vanadium are shown in this list. It has a high melting point. It is a solid at room temperature. It is a conductor of electricity. It is a good conductor of heat. It forms coloured compounds. If forms crystalline compounds. It forms compounds that are catalysts. Select two properties, from the list above, which are not typical of a Group 1 metal (Total 3 marks) Q29. The Haber process is used to make ammonia NH 3. The table shows the percentage yield of ammonia at different temperatures and pressures. PRESSURE (ATMOSPHERES) PERCENTAGE (%) YIELD OF AMMONIA AT 350 C PERCENTAGE (%) YIELD OF AMMONIA AT 500 C Page 38

39 (a) (i) Use the data in the table to draw two graphs on the grid below. Draw one graph for a temperature of 350 C and the second graph for a temperature of 500 C. Label each graph with its temperature. (4) (ii) Use your graphs to find the conditions needed to give a yield of 30% ammonia.... C and... atmospheres (iii) On the grid sketch the graph you would expect for a temperature of 450 C. (b) (i) This equation represents the reaction in which ammonia is formed. N 2(g) + 3H 2(g) 2NH 3(g) + heat What does the symbol in this equation tell you about the reaction? Page 39

40 (ii) Use your graphs and your knowledge of the Haber process to explain why a temperature of 450 C and a pressure of 200 atmospheres are used in industry. (5) (c) (i) Ammonium nitrate is one type of artificial fertiliser. Calculate the relative formula mass of ammonium nitrate NH 4NO 3. (Relative atomic masses: H = 1, N = 14, O = 16.) (ii) Use your answer to part (c)(i) to help you calculate the percentage by mass of nitrogen present in ammonium nitrate NH 4NO 3. (Total 15 marks) Q30. At room temperature, hydrogen peroxide decomposes very slowly to form water and oxygen. The decomposition is speeded up when a catalyst is added. (a) The following equation represents the decomposition of hydrogen peroxide. The structural formulae of the chemicals involved are shown. Page 40

41 Use the following information about bond energies to answer this part of the question. BOND BOND ENERGY (kj) O = O 498 O O 146 H O 464 (i) Calculate the energy needed to break all the bonds in the reactants kj (ii) Calculate the energy released when new bonds are formed in the products kj (iii) Calculate the energy change for this reaction..... kj Page 41

42 (iv) Is the reaction exothermic or endothermic?. Explain why... (b) (i) What is meant by activation energy?.. (ii) The energy level diagram for the decomposition of hydrogen peroxide into water and oxygen is shown below. Which energy change, A, B, C or D, is the activation energy?... (iii) Explain, in terms of energy, how a catalyst makes hydrogen peroxide decompose more quickly.... (Total 9 marks) Page 42

43 Q31. One definition of an element is: A substance that cannot be broken down into simpler substances by chemical methods The table below shows some of the substances which Antoine Lavoisier thought were elements. He divided the substances into four groups. He published these groups in The modern names of some of the substances are given in brackets. ACID-MAKING ELEMENTS GAS-LIKE ELEMENTS METALLIC ELEMENTS EARTHY ELEMENTS sulphur light cobalt mercury lime (calcium oxide) phosphorus charcoal (carbon) caloric (heat) oxygen azote (nitrogen) hydrogen copper gold iron lead nickel platina (platinum) silver tin magnesia (magnesium oxide) barytes (barium sulphate) argilla (aluminium oxide) silex (silicon dioxide) magnese tungsten zinc Dmitri Mendeleev devised a Periodic Table of the elements in A modern version of this table is shown on the Data Sheet. Give two ways in which Mendeleev s table is more useful than Lavoisier s Page 43

44 (Total 2 marks) Q32. The flow chart below shows the main stages in the production of ammonium nitrate. (a) (i) Name the two raw materials shown in the flow chart as A and B. Raw material A... Raw material B... Page 44

45 (ii) What is the purpose of the iron in the reactor?.. (b) (i) Balance the equation which represents the reaction which produces ammonia in the Haber process. N H 2... NH 3 and heat (ii) The table shows how temperature and pressure affect the amount of ammonia produced in this reaction. TEMPERATURE ( C) PRESSURE (ATM) PERCENTAGE OF NITROGEN AND HYDROGEN CONVERTED TO AMMONIA (%) Explain, as fully as you can, why a temperature of about 450 C and a pressure of about 200 atmospheres are normally used in the industrial process Page 45

46 ... (6) (Total 10 marks) Q33. Sodium and potassium are both in Group 1 of the Periodic Table. (a) Explain, by reference to their electronic structures, why both elements are placed in Group (b) Use the Data Sheet to help you to answer this question. The diagrams below represent the electronic structures of some atoms and ions. Which one of the structures, A - F (i) represents a sodium atom,... (ii) represents a potassium ion?... Page 46

47 (c) Sodium and potassium both react with cold water. (i) The word equation represents the reaction of sodium with water. sodium + water sodium hydroxide + hydrogen Complete and balance the symbol equation for this reaction NaOH +... (ii) How does the reactivity of potassium with water differ from that of sodium with water?. Explain this difference in reactivity by reference to the electronic structures of the potassium and sodium atoms (4) (Total 9 marks) Q34. X is an element with the following properties: melts at 220 C and boils at 188 C; does not conduct electricity at room temperature; forms molecular compounds with non-metals; forms ionic salts with metals in which its ion has a 1 charge. Page 47

48 (a) Would you expect X to be a solid, a liquid or a gas at 20 C? (b) Predict the formula of the product formed when X reacts with aluminium. (The aluminium ion is Al 3+ and the X ion is X.) Select your answer from the list below. AlX AlX 2 AlX 3 Al 3X Al 2X 3 Predicted formula... (c) To which Group of the Periodic Table does the element X belong? (Total 3 marks) Q35. X is an element with the following properties: melts at 220 C and boils at 188 C; does not conduct electricity at room temperature; forms molecular compounds with non-metals; forms ionic salts with metals in which its ion has a 1 charge. (a) Would you expect X to be a solid, a liquid or a gas at 20 C? Page 48

49 (b) Predict the formula of the product formed when X reacts with aluminium. (The aluminium ion is Al 3+ and the X ion is X.) Select your answer from the list below. AlX AlX 2 AlX 3 Al 3X Al 2X 3 Predicted formula... (c) To which Group of the Periodic Table does the element X belong? (Total 3 marks) Page 49