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GCE JUN 2006 : (AS 1) General Chemistry

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Centre Number 71 Candidate Number ADVANCED SUBSIDIARY (AS) General Certificate of Education 2006 Chemistry assessing Module 1: General Chemistry ASC11 Assessment Unit AS 1 [ASC11] WEDNESDAY 7 JUNE, MORNING TIME 1 hour 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all sixteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all six questions in Section B. Write your answers in the spaces provided in this question paper. 1 20.1.06BP 2 2.3.06EA INFORMATION FOR CANDIDATES The total mark for this paper is 100. Quality of written communication will be assessed in question 14(d)(iii). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided. For Examiner s use only Question Number Section A 1 10 Section B 11 12 13 14 15 16 Total Marks ASC1S6 2092 Marks Section A For each of the questions only one of the lettered responses (A D) is correct. Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 20 cm3 of 0.3 mol dm 3 potassium hydroxide solution is exactly neutralised by A B C D 2 Which one of the following electron configurations has two unpaired electrons? A B C D 3 10 cm3 of 0.3 mol dm 3 sulphuric acid 10 cm3 of 0.6 mol dm 3 sulphuric acid 20 cm3 of 0.3 mol dm 3 sulphuric acid 20 cm3 of 0.6 mol dm 3 sulphuric acid 1s2 2s1 1s2 2s2 2p3 1s2 2s2 2p4 1s2 2s2 2p6 3s2 3p5 Which one of the following shows the trend in electronegativity values of the elements in the Periodic Table? Down a group A decrease decrease B decrease increase C increase decrease D increase increase 1 20.1.06BP 10.2.05BP 22 10.3.05BP 2.3.06EA 3 8.4.05EA Across a period ASC1S6 2092 2 [Turn over 4 Which one of the following sodium compounds produces a gas when treated with dilute sulphuric acid? A B C D 5 If the price of one tonne (1000 kg) of sulphur is 160, what is the cost (to the nearest pound) of the sulphur needed to make one tonne of sulphuric acid (H2SO4)? A B C D 6 52 98 160 490 A positively charged particle with the electron configuration 2.8 is A B C D 7 sodium carbonate sodium chloride sodium fluoride sodium iodide an aluminium ion. a fluoride ion. an oxide ion. a potassium ion. The orbitals of a nitrogen atom may be represented as shown. 1s 2s 2p Which one of the following diagrams represents the arrangement of electrons in the ground state of the nitrogen atom? 1 20.1.06BP 2 2.3.06EA A B C D ASC1S6 2092 3 [Turn over 8 Which one of the following chloro-compounds is non-polar? A B C D 9 HCl CCl4 CH3Cl CHCl3 Which one of the following contains a coordinate bond? A B C D N2 NH3 NH 2 NH+ 4 10 The enthalpy of neutralisation when an acid reacts with an alkali is, by definition, the number of kilojoules released by the formation of one mole of water. the formation of one mole of salt. the neutralisation of one mole of acid. the neutralisation of one mole of alkali. 1 20.1.06BP 2 2.3.06EA A B C D ASC1S6 2092 4 [Turn over Section B Examiner Only Marks Remark Answer all six questions in the spaces provided. 11 There are three accepted intermolecular forces i.e. van der Waals forces (attractions between induced dipoles) permanent dipole attractions hydrogen bonding Complete the following table. = present = not present liquid van der Waals permanent dipole hydrogen bonding water ammonia xenon hydrogen chloride 1 20.1.06BP 2 2.3.06EA [3] ASC1S6 2092 5 [Turn over 12 Rocket fuels need to supply a large amount of energy, yet have a low mass i.e. a high power to weight ratio. Examiner Only Marks Remark One potential reaction is that of fluorine with diborane (a boron hydride). HH H B B H HH diborane B2H6(g) + 6F2(g) 6HF(g) + 2BF3(g) (a) Calculate the enthalpy change when one mole of diborane reacts completely with fluorine given the following bond enthalpies. kJ mol 1 158 389 293 566 627 Bond F F B H B B H F B F __________________________________________________________ __________________________________________________________ _______________________________________________________ [3] (b) The bond enthalpy of hydrogen fluoride is 566 kJ mol 1 whereas that of hydrogen iodide is 299 kJ mol 1. State what would be observed when hydrogen fluoride and hydrogen iodide are heated. __________________________________________________________ __________________________________________________________ 1 20.1.06BP 2 2.3.06EA _______________________________________________________ [2] ASC1S6 2092 6 [Turn over (c) Calculate the total volume of gas produced at 20 C and one atmosphere pressure by the complete reaction of 7 g of diborane with fluorine. Examiner Only Marks Remark __________________________________________________________ __________________________________________________________ _______________________________________________________ [3] (d) State and explain the shape of the boron trifluoride molecule. __________________________________________________________ __________________________________________________________ 1 20.1.06BP 2 2.3.06EA _______________________________________________________ [2] ASC1S6 2092 7 [Turn over 13 Calcium fluoride, CaF2, occurs naturally as fluorite or fluorspar. Impurities give a blue variety known as Blue John. Fluorspar is the major source of hydrogen fluoride and fluorine. It can be prepared in the laboratory by precipitation or direct combination of the elements. Examiner Only Marks Remark (a) What is the colour of pure calcium fluoride? _______________________________________________________ [1] (b) Explain the formation of calcium fluoride from calcium and fluorine atoms using dot and cross diagrams showing outer electrons only. [3] (c) Write an equation for the precipitation of calcium fluoride by mixing solutions of calcium chloride and sodium fluoride. _______________________________________________________ [1] (d) Calcium fluoride reacts with concentrated sulphuric acid to form hydrogen fluoride and calcium sulphate. Write an equation for the reaction. 1 20.1.06BP 2 2.3.06EA _______________________________________________________ [2] ASC1S6 2092 8 [Turn over (e) Calcium fluoride is sparingly soluble in water; 0.0025 g dissolves in 100 cm3 of water at 18 C. Examiner Only Marks Remark Calculate the concentration of fluoride ions in moles per litre using the following headings: (i) relative formula mass of calcium fluoride ____________________________________________________ [1] (ii) number of moles of calcium fluoride in 0.0025 g ____________________________________________________ [1] (iii) number of moles of fluoride ion in 0.0025 g of calcium fluoride ____________________________________________________ [1] (iv) number of moles of fluoride ion in 100 cm3 of water ____________________________________________________ [1] (v) number of moles of fluoride ion per litre of water ____________________________________________________ [1] (f) The natural presence of fluoride ions in domestic water supplies is regarded as beneficial by some, but the deliberate addition of fluoride ions is controversial. (i) State a benefit of fluoride ions in drinking water. ____________________________________________________ [1] (ii) Explain why some people object to the addition of fluoride ions to drinking water. 2 2.3.06EA ______________________________________________________ 1 20.1.06BP ____________________________________________________ [1] ASC1S6 2092 9 [Turn over 14 All naturally occurring sodium atoms are represented by the symbol 23Na. 11 However, radioactive isotopes of sodium may be prepared. Examiner Only Marks Remark (a) (i) State the number of electrons, protons and neutrons in an atom of 23Na. 11 ______________________________________________________ ____________________________________________________ [2] (ii) Explain why 23Na and 24Na are regarded as isotopes. 11 11 ______________________________________________________ ____________________________________________________ [2] (b) A sample of sodium from a nuclear reactor contains 2.00% of 24Na 11 and 98.00% of 23Na by mass. Calculate the relative atomic mass of the 11 sodium in the sample to two decimal places. __________________________________________________________ __________________________________________________________ __________________________________________________________ 1 20.1.06BP 2 2.3.06EA _______________________________________________________ [3] ASC1S6 2092 10 [Turn over (c) A major use of sodium metal is in sodium street lamps. The lamp contains mercury vapour which conducts electricity at high voltages. Sodium within the lamp vaporises and the electrical energy causes yellow (orange) light to be given out. Examiner Only Marks Remark (i) Explain, in terms of energy levels, how the yellow light is generated. ______________________________________________________ ______________________________________________________ ____________________________________________________ [3] (ii) When the light from the sodium lamp is analysed the spectrum shows two bright yellow lines at wavelengths of 589 nm and 589.6 nm. (1 nm = 1 10 9 m) 589 589.6 Using the equations E = hv and c = v , calculate the energy change (in joules) associated with the line at 589 nm. ______________________________________________________ ______________________________________________________ ______________________________________________________ 1 20.1.06BP 2 2.3.06EA ____________________________________________________ [3] ASC1S6 2092 11 [Turn over (d) If larger amounts of energy are supplied to sodium vapour (gas) it ionises. Examiner Only Marks Remark (i) Using state symbols, write the equation which represents the first ionisation energy of sodium. ____________________________________________________ [1] (ii) The value of the first ionisation energy for sodium is 500 kJ mol 1. The second ionisation energy has a value of 4513 kJ mol 1. Explain why this is a much higher value. ______________________________________________________ ______________________________________________________ ____________________________________________________ [2] (iii) The first ionisation energies of the alkali metals are shown in the graph below. Li 500 first ionisation energy 400 kJ mol 1 Na K Rb Cs 300 Explain why lithium has a higher first ionisation energy than sodium. ______________________________________________________ 2 2.3.06EA ______________________________________________________ ______________________________________________________ 1 20.1.06BP ____________________________________________________ [2] Quality of written communication ASC1S6 2092 [2] 12 [Turn over BLANK PAGE 1 20.1.06BP 2 19.2.06PEG (Questions continue overleaf) ASC1S6 2092 13 [Turn over 15 Oxalic acid (ethanedioic acid) is a weak dicarboxylic acid. It is similar to acetic acid (ethanoic acid) which is a monocarboxylic acid. COOH Examiner Only Marks Remark CH3COOH COOH oxalic acid acetic acid (a) Suggest the meaning of the term dicarboxylic acid. __________________________________________________________ _______________________________________________________ [2] (b) Both of these acids react with alkalis. Write the equation for the reaction of oxalic acid with excess sodium hydroxide. _______________________________________________________ [2] (c) Weak acids such as oxalic acid can be titrated with strong alkalis using phenolphthalein as indicator. State the colour of phenolphthalein in alkaline and acidic solution. alkali __________________________________________________ [1] acid ___________________________________________________ [1] (d) When oxalic acid reacts with a small amount of phosphorus pentachloride, a mixture of gases is produced: COOH PCl5 + COOH CO2 + CO + 2HCl + POCl3 2 2.3.06EA __________________________________________________________ 1 20.1.06BP How could you show, using a named silver salt, that hydrogen chloride was a product? _______________________________________________________ [3] __________________________________________________________ ASC1S6 2092 14 [Turn over (e) Oxalic acid reacts with excess phosphorus pentachloride to give oxalyl chloride which has the following percentage composition by mass. element 18.9 chlorine 55.9 oxygen Remark % composition carbon Examiner Only Marks 25.2 (i) Calculate the empirical formula of oxalyl chloride. ______________________________________________________ ______________________________________________________ ______________________________________________________ ____________________________________________________ [3] (ii) Explain why the empirical formula could not be the molecular formula. ______________________________________________________ 1 20.1.06BP 2 2.3.06EA ____________________________________________________ [1] ASC1S6 2092 15 [Turn over 16 In the laboratory, ammonia can be prepared by heating a mixture of ammonium chloride and calcium hydroxide, as shown in the diagram below. Examiner Only Marks Remark test tube ammonium chloride + calcium hydroxide ceramic wool heat calcium oxide The equation for the reaction is: 2NH4Cl + Ca(OH)2 2NH3 + CaCl2 + 2H2O (a) The ammonia gas is collected upwards. Calculate the relative molecular masses of ammonia, oxygen and nitrogen and use them to explain why ammonia is collected in this way. ammonia __________________________ oxygen __________________________ nitrogen __________________________ explanation ________________________________________________ _______________________________________________________ [3] (b) Calculate the volume of ammonia produced, at 20 C and one atmosphere pressure, if 1.07 g of ammonium chloride are heated with excess calcium hydroxide. __________________________________________________________ __________________________________________________________ 1 20.1.06BP 2 2.3.06EA _______________________________________________________ [3] ASC1S6 2092 16 [Turn over (c) Ammonia gas is alkaline. Examiner Only Marks Remark (i) Describe the effect of ammonia on moist Universal Indicator paper. ____________________________________________________ [1] (ii) Gases are normally dried using concentrated sulphuric acid. Explain why this drying agent would be unsuitable in the case of ammonia. ______________________________________________________ ____________________________________________________ [2] (iii) Ammonia may be detected using concentrated hydrochloric acid. Write the equation for the reaction and describe what is seen. ______________________________________________________ ____________________________________________________ [2] (d) Ammonia can act as a reducing agent. When passed over heated copper(II) oxide the following reaction occurs: 2NH3 + 3CuO 3Cu + N2 + 3H2O Deduce the oxidation numbers of nitrogen and copper in the reactants and products and use them to explain the redox change. __________________________________________________________ __________________________________________________________ 1 20.1.06BP 2 2.3.06EA _______________________________________________________ [3] ASC1S6 2092 17 [Turn over (e) The shape of the ammonia molecule is explained using electron pair repulsion theory. Examiner Only Marks Remark (i) Draw the dot and cross diagram for ammonia showing only the outer electrons. [2] (ii) Draw and name the shape of the ammonia molecule. name __________________________ [2] (iii) Explain why the bond angle in ammonia is not 109 . ______________________________________________________ ____________________________________________________ [2] 1 20.1.06BP 2 2.3.06EA THIS IS THE END OF THE QUESTION PAPER ASC1S6 2092 18 [Turn over 1 20.1.06BP 2 19.2.06PEG S 1/06 5000 302507(145) [Turn over 1 20.1.06BP 10.2.05BP 22 10.3.05BP 2.3.06EA 3 8.4.05EA

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Additional Info : Gce Chemistry June 2006 Assessment Unit AS 1Module 1: General Chemistry
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