Chemistry Assessment Unit AS 1

Transcription

1 Centre Number 71 Candidate Number ADVANCED SUBSIDIARY (AS) General Certificate of Education January 2008 Chemistry Assessment Unit AS 1 assessing Module 1: General Chemistry ASC11 [ASC11] THURSDAY 17 JANUARY, 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. INFORMATION FOR CANDIDATES The total mark for this paper is 100. Quality of written communication will be assessed in question 13(a)(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. ASC1W For Examiner s use only Question Number Section A 1 10 Section B Total

2 Section A For each of the following 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 Which one of the following solids consists of molecular covalent crystals? A B C D Diamond Graphite Quartz Rhombic sulphur 2 Which one of the following compounds does not exhibit hydrogen bonding? A Ammonia, NH 3 B Ethanol, C 2 H 5 OH C Methane, CH 4 D Water, H 2 O 3 Which one of the following graphs represents the change in melting point across the third period from sodium to argon? A melting point B melting point atomic number atomic number C melting point D melting point atomic number atomic number ASC1W [Turn over

3 4 The hydrogen spectrum is best described as a series of A equally spaced lines. B lines becoming closer together as the frequency increases. C lines becoming closer together as the wavelength increases. D lines becoming closer together and then further apart. 5 Magnesium has three isotopes as shown below. Relative atomic mass Percentage abundance (%) A B C D In an experiment g of lead oxide were reduced to form g of lead. What is the empirical formula of the lead oxide? A PbO B Pb 3 O 2 C Pb 3 O 4 D Pb 4 O 3 7 Which one of the following ions has the smallest radius? A F B Mg 2+ C Na + D O 2 ASC1W [Turn over

4 8 The electronegativity values for carbon, fluorine, nitrogen and oxygen are given below. Which one of these values is most likely to be that of nitrogen? A 2.5 B 3.0 C 3.5 D Which one of the following is responsible for the open structure of ice? A Covalent bonds B Dipole dipole attractions C Hydrogen bonds D Van der Waals forces 10 Phenol is converted to trichlorophenol (TCP) according to the equation below. C 6 H 5 OH + 3Cl 2 C 6 H 2 Cl 3 OH + 3HCl If 50.0 g of phenol produced 97.6 g of TCP, what is the percentage yield of the TCP? A 47.6% B 49.4% C 51.2% D 92.9% ASC1W [Turn over

5 Section B Answer all six questions in this section. 11 Metal salts are used to produce colours in fireworks. (a) Complete the table below to give the flame colour of each of the metal chlorides listed. Metal chloride Barium chloride Strontium chloride Flame colour [2] (b) Using a diagram, explain how the flame colours of the metal chlorides originate. [3] ASC1W [Turn over

6 12 Beryllium chloride, BeCl 2, and ammonia, NH 3, are covalent compounds. (a) State the octet rule and explain whether beryllium chloride obeys the rule. [2] (b) The ammonium ion, NH + 4, contains a coordinate bond. (i) Explain what is meant by a coordinate bond. [1] (ii) Draw a dot and cross diagram, using outer electrons only, to show the bonding in an ammonium ion. [2] ASC1W [Turn over

7 13 A dilute solution of hydrogen peroxide can be used as an antiseptic mouthwash. The concentration of the hydrogen peroxide solution can be measured by reaction with excess acidified potassium iodide solution. H 2 O 2 + 2H + + 2I 2H 2 O + I 2 The liberated iodine is then estimated by titration with standard sodium thiosulphate solution. (a) (i) Name the indicator used in this titration. [1] (ii) Explain what is meant by the term standard solution. [1] (iii) Describe, giving experimental detail, how you would carry out the titration. Assume all the apparatus is clean and dry. [4] Quality of written communication [2] ASC1W [Turn over

8 (b) 25.0 cm 3 of the mouthwash was diluted to 250 cm 3. A 25.0 cm 3 portion of the diluted mouthwash required 22.5 cm 3 of 0.1 M sodium thiosulphate for a complete reaction. (i) Write an equation for the reaction between sodium thiosulphate, Na 2 S 2 O 3, and iodine I 2. [2] (ii) Calculate the concentration of the hydrogen peroxide in the mouthwash in g dm 3 using the following headings: Number of moles of sodium thiosulphate used. Number of moles of iodine, I 2, liberated in 25.0 cm 3 of diluted mouthwash solution. Number of moles of H 2 O 2 present in 25.0 cm 3 of diluted mouthwash solution. Number of moles of H 2 O 2 in 25.0 cm 3 of undiluted mouthwash. Mass of H 2 O 2 in 25.0 cm 3 of undiluted mouthwash. Concentration of H 2 O 2 in undiluted mouthwash in g dm 3. [4] ASC1W [Turn over

9 14 Kerosene is a mixture of hydrocarbons. When it is mixed with hydrogen peroxide it can be used as a rocket fuel. (a) The kerosene burns in oxygen released by the hydrogen peroxide. (i) One component of kerosene is dodecane, C 12 H 26. Write an equation for the complete combustion of dodecane. (ii) Draw an enthalpy level diagram for the combustion of dodecane using the axes below, labelling the y-axis. Extent of reaction [2] (iii) Explain, in terms of enthalpy, why the combustion of dodecane is exothermic. ASC1W [Turn over

10 (b) The enthalpy of combustion of hydrocarbons can be calculated using Hess s Law. (i) Explain what is meant by the term standard enthalpy of combustion. (ii) State Hess s Law. (iii) One of the constituents of petrol is octane, C 8 H 18. Use the information below to calculate the enthalpy of combustion of octane. C 8 H 18 (l) O 2 (g) 8CO 2 (g) + 9H 2 O(l) C(s) + O 2 (g) CO 2 (g) ΔH = kj mol 1 8C(s) + 9H 2 (g) C 8 H 18 (l) ΔH = kj mol 1 H 2 (g) O 2 (g) H 2 O(l) ΔH = kj mol 1 Enthalpy of combustion kj mol 1 [3] ASC1W [Turn over

11 (c) The enthalpy of combustion can also be calculated using bond enthalpy values. (i) Explain what is meant by the term bond enthalpy. [1] (ii) Use the bond enthalpy values below to calculate the total bond enthalpy for the products and the overall enthalpy change for the combustion of 1 mole of octane given that the total of the bond enthalpies of the reactants is kj. Bond Bond enthalpy C = O 750 kj mol 1 H O 463 kj mol 1 Total bond enthalpy of products Enthalpy change for the combustion of octane [2] (iii) Explain the difference in the value of the enthalpy of combustion from Hess s Law with that obtained using bond enthalpies. ASC1W [Turn over

12 15 Sodium and fluorine are reactive elements which combine directly to form the ionic salt, sodium fluoride. (a) Sodium has the typical properties of a metal. (i) Draw a diagram to show the bonding in sodium metal. [2] (ii) Explain why sodium is malleable. [1] conducts electricity. (b) (i) Write an equation, including state symbols, for the formation of sodium fluoride from sodium and fluorine. (ii) Draw dot and cross diagrams, using outer electrons only, to show the formation of sodium fluoride from sodium and fluorine atoms. [3] ASC1W [Turn over

13 (iii) Suggest why fluoride is added to some toothpastes. [1] (iv) Explain why some people object to the fluoridation of drinking water. [1] (c) The graph below represents the first ionisation energies of elements from sodium to argon. first ionisation energy atomic number (i) Explain the general rise in the first ionisation energy across the period. (ii) Explain the decrease in the first ionisation energy from numbers 12 to 13 and from 15 to to to 16 ASC1W [Turn over

14 (iii) Complete the graph of the successive ionisation energies of sodium. log ionisation energy number of electron removed [2] ASC1W [Turn over

15 16 The halogens fluorine, chlorine, bromine, iodine and astatine form Group VII of the Periodic Table. (a) Fluorine is the most electronegative element. Explain what is meant by the term electronegative element. [1] (b) The halogens react with hydrogen to form hydrogen halides. (i) Write an equation for the reaction between fluorine and hydrogen. [1] (ii) Show the polarity of the hydrogen fluorine bond on the diagram below. H F [1] (iii) State and explain the trend in the thermal stability of the hydrogen halides. (iv) The hydrogen halides dissolve in water to form acidic solutions. List the hydrogen halides in order of increasing acidic strength. Weakest acid: Strongest acid: [1] ASC1W [Turn over

16 (c) The sodium salts of these acids are colourless ionic solids. (i) How could you distinguish between solid samples of sodium chloride and sodium bromide using aqueous silver nitrate and dilute ammonia solution? [4] (ii) Write the equation for the reaction of sodium bromide with concentrated sulphuric acid. (iii) Give two observations when concentrated sulphuric acid is added to solid sodium iodide. ASC1W [Turn over

17 (d) Chlorine reacts with cold dilute sodium hydroxide according to the equation: Cl 2 + 2NaOH NaCl + NaOCl + H 2 O (i) State the oxidation number of chlorine in each of the following species. Cl 2 NaCl NaOCl [3] (ii) Explain, using the oxidation numbers, why this is described as a redox reaction. (iii) What name is given to this type of redox reaction? [1] THIS IS THE END OF THE QUESTION PAPER ASC1W

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