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Centre Number Candidate Number Candidate Name International General Certificate of Secondary Education UNIVERSITYOF CAMBRIDGELOCALEXAMINATIONS SYNDICATE 0620/3 CHEMISTRY PAPER 3 27 MAY 1999 Thursday Afternoon 1 hour 15 minutes Candidates answer on the question paper. Additional materials: Mathematical tables. TIME 1 hour 15 minutes INSTRUCTIONS TO CANDIDATES Write your name, Centre number and candidate number in the spaces at the top of this page. Answer all questions. Write your answers in the spaces provided on the question paper. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. Mathematical tables are available. You may use a calculator. A copy of the Periodic Table is printed on page 12. FOR EXAMINER'S USE 1 2 3 4 5 TOTAL This question paper consists of 12 printed pages. 88 (8M) OF91694/3 @ UCLE8 1999 [Turn over 2 1 Lead has been used on roofs since about 5000 BC. It is suited to this use because it is both malleable and resistant to corrosion. Lead rapidly becomes coated with a layer of basic lead(II) carbonate that protects it from further corrosion. (a) (i) Describe the structure of a typical metal such as lead. ,............................................................................................. [2] (ii) How does the structure of a metal explain why it is malleable? ...... ...... , [2] (b) Suggest an explanation why exposure to atmospheric pollution changes basic lead(II) carbonate into lead(II) sulphate. ... ..., ., .............. ... ..... """"""""""""""""""""""""""" [3] (c) Basic lead(II) carbonate has a formula of the type xPbCO3.yPb(OH)2' where x and y are whole numbers. Basic lead(II) carbonate was heated in the apparatus shown below. basic lead carbonate t HEAT sodium hydroxide, carbon dioxide reacts here ice (i) liquid collects here How could you show that the liquid collected contained water? [2] 3 (ii) How could you show that the carbonate gave off carbon dioxide on heating? [2] (iii) Explain why sodium hydroxide reacts with the non-metal oxide carbon dioxide. ................................................................................................................................... [2] ; (d) Use the following information to calculate x and yand to write the formula for the basic lead(II) carbonate. PbCO3 PbO + CO2 Pb(OH)2 PbO + H2O The basic lead(II) carbonate when heated gave 1.056 g of carbon dioxide and 0.216 g of water. The mass of one mole of CO2 = g [1] Number of moles of CO2 formed - ............ [1] The mass of one mole of H2O = 18g Number of moles of H2O formed - Therefore x = ........................ [1] and y = ............ The formula for the basic carbonate is ..... ........ .... ....... [1] 4 2 In both Europe and the USA, scientists are investigating the use of hydrogen as a fuel for aeroplanes and cars. It is more efficient and produces less pollution than the existing petroleum-based fuels. (a) (i) Name the fuel obtained from petroleum that is used for jet aircraft. [1] (ii) Name two pollutants formed by the combustion of petroleum fuels and then explain why the combustion of hydrogen would produce less pollution. , . ................................................................................................................................... , , ............................................................ [3] (b) Describe a method of manufacturing hydrogen. raw material ,........................................ brief description of process............................................................................................. .......................................................................................................................................... """"""""""""'" [2] (c) Hydrogen could be transported in heavy cylinders as a gas under pressure or as a liquid at low temperatures. (i) The pressure exerted by a gas is caused by the molecules of the gas colliding with the walls of the container. Why would the pressure inside a cylinder increase if the temperature was increased? .......... [2] (ii) Explain what happens to the molecules in gaseous hydrogen as it changes into a liquid at -253 aG. . ...... [3] 5 (d) An alternative method of 'transporting' hydrogen is to change it into methanol. This liquid is easily transported and can be decomposed to re-form hydrogen. Methanol can be made by the following reaction. CO(g) + 2H2(g) ~ CH30H(g) the forward reaction is exothermic The gases are passed over a catalyst at 300 °C. On cooling, the methanol becomes a liquid. (i) The reaction is carried out at high pressure. What effect would this have on the position of equilibrium? " (ii) .[1 ] Explain why an increase in pressure would increase the rate of the reaction. ,........................................................ [2] , (iii) What would be the effect of decreasing the temperature on the concentration of methanol at equilibrium? Give a reasoned explanation for your answer. ,........................................................................... ,......... .[2] 6 3 (a) The alcohols form a homologous series. Their names, formulae and heats of combustion are given below. The heat of combustion is the quantity of heat energy given out when one mole of the alcohol is burned in an excess of oxygen. name formula mass of one mole / g heat of combustion / kJ per mole -720 methanol CHsOH 32 ethanol CHsCH20H 46 -1370 propanol CHsCH2CH20H 60 -2020 butanol (i) Complete the last line in the table by writing the formula for butanol, calculating the mass of one mole and by predicting the heat of combustion. [3] (ii) It is possible to predict physical properties of the members of a homologous series. Describe two other characteristics of a homologous series. ....................................................................................... [2] (iii) The alcohol CHsCH(OH)CHs is a structural isomer of the propanol in the table. Explain the term structural isomer. . [2] (b) Give a diagram to show the arrangement of the valency electrons in one molecule of the covalent compound methanol. Use x to represent an electron from a carbon atom. Use 0 to represent an electron from a hydrogen atom. Use @to represent an electron from an oxygen atom. [3] (c) Ethanol can be made from starch. Starch is a complex carbohydrate with a structure of the type shown. -0-0-0-0-0-0- 7 This can be broken down by enzymes to simple sugars with formulae of the type shown. H0 (i) D- 0H What other method changes starch into simple sugars? [2] (ii) Give a brief description of how sugars are changed into ethanol. ...... """""" ............ ... ... .[3] (d) Some alcohols are easily oxidised. mineral wool soaked in propanol copper(II) oxide t HEAT cold water chemical formed by oxidation of propanol ------- The chemical formed has a pH of 2. Give the name and structural formula of the chemical formed. name """"""""" .[1] structural formula [1] 8 4 Sulphur production in the USA is about ten million tonnes per year. 90% of this sulphur is used to make sulphuric acid. (a) Sulphur dioxide is made by burning sulphur in air. Most of it is used in the Contact Process. Give one other use of this gas. [1] (b) Bacteria can oxidise the sulphur in coal to sulphuric acid. Water draining off coal tips contains sulphate ions and hydrogen ions. (i) Describe how you could show the presence of sulphate ions in the water. ................................................................................................................................... [2] (ii) Without using an indicator, how could you show that the water from the coal tips is acidic? """"""""""""""""""""""""""" ,........ [2] , (c) In the Contact Process, sulphur dioxide is made by spraying molten sulphur into air. (i) Suggest why the molten sulphur is used in the form of a spray. ... (ii) , .[1] Describe how sulphur dioxide is changed into sulphur trioxide. ...................................................................................................... .................................................................................................... [3] , (iii) Complete the equations for the formation of sulphuric acid from sulphur trioxide. + -. H2S207 + -. S03 H2S207 "...H2SO4 [2] 9 (d) Over 50% of the sulphuric acid is used to make fertilisers such as the nitrogen-based fertiliser ammonium sulphate. (i) Give one other use of sulphuric acid. [1] """""""""""""""""""""""""""" (ii) Nitrogen is one of the three elements essential for plant growth that is added to soil in fertilisers. Name the other two. and (iii) [2] The base ammonia is neutralised by sulphuric acid to form ammonium sulphate. Define the term base. ..................... .[2] 10 5 You will need to use the Periodic Table of the Elements to answer this question. (a) A radioactive isotope of the element iodine, 1251, is used to treat cancer. How many electrons and how many neutrons are there in one atom of this isotope of iodine? number of electrons [1] " number of neutrons [1] (b) Given below are the formulae of the oxides of some of the elements. They are given in the same order as in the Periodic Table. MgO CaO SiO2 AI203 P203 SrO (i) Use the electronic structures of the elements to explain why oxides of elements in the same group have the same type of formula. .. . ,... (ii) [2] Use the electronic structures of the elements to explain why oxides of elements in the same period have different formulae. . ... , , ..,.. , ............. ....... .[1] 11 (iii) Complete the table that shows the reaction, if any, of the oxides with acid and alkali. Indicate a reaction with "R" and no reaction with "NR". oxide type of oxide magnesium oxide basic aluminium oxide amphoteric silicon(IV) oxide acidic reaction with acid reaction with alkali [3] (c) (i) Predict the formula for: the strontium ion, """"""""""""""""""""""",""""""'""""""""""""""""""""" the phosphide ion. (ii) """"""""""""'[2] Write the formula for strontium phosphide [1] (d) The reactivity of elements in the same group varies in a predictable way. (i) Name a metal that reacts more violently with cold water than does potassium. [1] (ii) Complete the word equation. potassium + water --. + ........................................ """"""""""""""""""'" [2]