Fuhua 2018 Prelim P2

2 Section A Answer all the questions in the spaces provided. A1 Table A1.1 shows the most common oxidation states of some elements A, B, C, D and E. element most common oxidation states A +1 B +2 C -1 D -2 E +4 Table A1.1 Use the letter(s) to answer the following questions. (a) Which element has a giant molecular structure? [1] (b) Which elements consist of molecules? [1] (c) Which elements conduct electricity in both solid and liquid states? [1] (d) What are the chemical formulae of the oxides of B and C? formula of oxide of B formula of oxide of C [2] (e) No element from Group 0 appear in the table. Use the information in the table to explain why this is true. [2]

3 (f) Draw the dot and cross diagram to show the bonding in the compound formed between the following elements. Show only the outer electrons. (i) B and C [1] (ii) D and E [2] [Total: 10] A2 Graph A2.1 shows the percentage yield of ammonia in the equilibrium mixture under different temperature and pressure conditions. Graph A2.1 temperature / °C yield of ammonia / % 400 atm 200 atm 100 atm 50 atm 25 atm

4 (a) In an industrial Haber process, the operating conditions are at a temperature of 450°C and a pressure of 200 atm. With reference to the graph, state the percentage yield of ammonia under such operating conditions. [1] (b) In industrial Haber process, the yield of ammonia is never 100%. Suggest a reason why. [1] (c) It has been stated that, ‘the use of 450°C is a compromise between the equilibrium yield of ammonia and the rate of reaction’. Explain this statement. [2] (d) The ammonia is separated as a liquid from the unreacted gases. Apart from cost, suggest two other reasons why the unreacted gases are recycled. [2] (e) Calculate the mass, in tonnes, of ammonia which can be produced from 90 tonnes of hydrogen when the percentage yield is 50%. [1 tonne = 1000 kg] [3] [Total: 9]

5 A3 Table A3 .1 shows some data about the names, structural formulae and enthalpy change of combustion of aldehydes. name of aldehydes structural formula boiling point / °C enthalpy change of combustion (kJ/mol) methanal HCHO -19.0 -571 ethanal CH3CHO 20.2 -1170 48.8 -1820 butanal CH3CH2CH2CHO 74.8 -2480 Table A3.1 (a) Use two pieces of evidence in the table to explain why aldehydes are a homologous series. [2] (b) Give the name and structural formula of the third member of this homologous series. name structural formula [2] (c) Calculate the enthalpy change of combustion when 1 g of methanal burns. Show your working. [2]

6 (d) The enthalpy change of combustion in kJ/mol increases from methana l to butanal. Explain why. [2] (e) Butanone is an isomer of butanal. butanal butanone The enthalpy change of combustion of butanone is same as that for butanal . Suggest why the enthalpy of combustion for the two isomers are the same. [2] [Total: 10] A4 Jane carried out a series of experiments according to the following procedure: • She added excess magnesium powder in 25 cm 3 of various aqueous salt solutions with the same concentration. • She calculated the maximum temperature rise in each experiment. She tabulated the results obtained as shown in Table A4.1 below. experiment solution maximum temperature rise / °C 1 copper(II) sulfate 42 2 lead(II) nitrate 32 3 sulfuric acid 38 4 zinc sulfate 14 5 calcium chloride 0 6 sodium nitrate 0 Table A4.1

7 (a) State the type of energy change that occurred in experiment 1 to 4. Explain your answer. [2] (b) (i) How does the temperature rise relate to the difference in reactivity of magnesium and the metal? [1] (ii) Predict the temperature rise when she added excess magnesium powder to 25 cm3 of iron(II) sulfate of the same concentration. Explain your reasoning. temperature rise °C reason [2] (iii) Write an ionic equation for the reaction in (b)(ii). [1] (c) Explain why there is no rise in temperature for experiment 5 and 6. [2] (d) Predict the temperature rise when she added excess magnesium powder to to 25 cm3 of hydrochloric acid of the same concentration. Explain your reasoning. temperature rise °C reason [3] [Total: 11]

8 A5 Two steel corrosion prevention methods are anodic protection and cathodic protection. Anodic protection involves the coating of steel with a less reactive metal such as tin while cathodic protection attaches blocks of a more reactive metal such as zinc on certain parts of a steel body. (a) State the role of steel as the anode or cathode in either of the protection methods used steel anodic protection cathodic protection [1] (b) Cathodic protection is used in underground steel pipes and ships hulls. Explain how cathodic protection stops the steel from rusting. [2] (c) (i) Anodic protection is generally applied to steel storage tanks used to store very corrosive liquids such as sulfuric acid. Suggest how anodic protection stops such steel tanks from rusting. [1] (ii) Suggest why cathodic protection is not suitable as a rust prevention method for these storage tanks. [1] (iii) If the copper coating is scratched, it would bring about faster than expected corrosion of the steel tank. Explain why. [1] [Total: 6]

9 A6 Table A6.1 shows the names and formulae of some salts and the names of some other compounds used to make them. Complete the table by filling in the missing information. name of salt formula of salt names of compounds used to make salt silver nitrate AgNO3 ___________________ and ___________________ potassium ethanoate CH3COOK potassium hydroxide and ___________________ ammonium sulfate sulfuric acid and ___________________ zinc carbonate ZnCO3 ___________________ and ___________________ Table A6.1 [Total: 4]

10 Section B: Free Response Questions [30 marks] Answer all three questions in this section. The last question is in the form of an either/or and only one of the alternatives should be attempted. B7 The First Periodic Table In 1869, a Russian chemist, Dmitri Mendeleev, was the first scientist to devise a Periodic Table as shown in Fig. B7.1. He arranged the elements known at the time in order of relative atomic mass. He realised that by arranging the elements in this order, certain types of element occurred regularly, for example a reactive non- metal was directly followed by a very reactive light metal, then a less reactive light metal. Fig. B7.1 atomic number Graph B7.2 atomic radius/nm

11 In the modern Periodic Table, the properties of the elements are a funct ion of their atomic numbers. Graph B7.2 gives a series of curves when the atomic radii of elements in successive periods are plotted against the atomic numbers. The radius of an atom is determined mainly by two f actors. One factor is the attraction between the positively charged nucleus and the electrons. Th