TPJC H2 Chem 2012 Prelim P1 QP

2 TPJC_2012_9647_P1 Section A For each question, there are four possible answers, A, B, C, and D. Choose the one you consider to be correct. 1. Which molecule has six bonding electrons? A C2H4 C H2S B CO2 D NCl3 2. Which of the following ions has the smallest ionic radius? A F − C Na + B Mg 2+ D Al 3+ 3. Consider the following half-equations. Fe 2+ → Fe 3+ + e C2O4 2– → 2CO2 + 2e What volume of 0.01 mol dm-3 K2Cr2O7 is required to oxidise 20 cm3 of an acidified solution of 0.01 mol dm-3 FeC2O4? A 10 cm3 C 30 cm3 B 20 cm3 D 40 cm3

3 TPJC_2012_9647_P1 4. Which one of the following graphs below shows the correct plot of pV against p for a fixed mass of ideal gas at two temperatures, T1 and T2, in which T1 > T2? 5. A student used the apparatus below to determine the enthalpy change of combustion of propan-1-ol. The following results were obtained: mass of propan-1-ol burnt = 0.60 g mass of water heated = 200 g initial temperature of water = 21.00C Given that the enthalpy change of combustion propan-1-ol is −2021 kJ mol−1 and the heat capacity of water is 4.17 J K−1 g−1, what would be the final temperature of the water? A 24.2 oC C 29.1 oC B 45.2 oC D 48.4 oC

4 TPJC_2012_9647_P1 6. The radius and charge of each of six ions are shown below: The ionic solids AX, BY and CZ are of the same lattice type. What is the correct order of their lattice energies placing the one with the highest numerical value first? A CZ > AX > BY C CZ > BY > AX B AX > CZ > BY D AX > BY > CZ 7. The table below shows the standard thermodynamic values for the synthesis of hydrogen chloride: H2 (g) + Cl2 (g) → 2HCl (g). ∆Hɵ -184.6 kJ mol-1 ∆Sɵ +0.02 kJ K-1 mol-1 From the data, what is the value of ∆Gɵ? A +178.6 kJ mol-1 C -185.1 kJ mol-1 B -178.6 kJ mol-1 D -190.6 kJ mol-1 8. How would the magnitude of the following vary down Group II? (i) the standard electrode potential of M 2+ (aq)/ M(s) electrode, Eo , (ii) the lattice energy of the oxide, ∆Ho latt, (iii) the standard enthalpy change of hydration of M 2+ (g), ∆Ho hyd.

5 TPJC_2012_9647_P1 9. The mechanism for a certain reaction is given below: 2A C (fast) C + B  D (slow) D + B  A2B2 (fast) What conclusion can be drawn from the above mechanism? A The rate equation is rate = k[C][B]. B The units of the rate constant, k, is mol-2 dm6 s-1. C The reaction is first order with respect to D. D The overall equation is 2A + 2B + C + D  A2B2. 10. The diagrams P, Q, R and S show how a change in conditions affects the Maxwell- Boltzmann distribution of molecular energies for gas G. In each case, the original distribution is shown by a solid line and the distribution after a change has been made is shown by a dashed line. Which one of the following statements is correct? A the change shown in diagram Q occurs when a catalyst is used. B the change shown in diagram R occurs when the temperature is increased. C the change shown in diagram P occurs when the temperature is decreased. D the change shown in diagram S occurs when the pressure of G is decreased at constant temperature

6 TPJC_2012_9647_P1 11. Using a colorimeter, the following reaction is studied by finding the time taken for a coloured reactant, A, to decolourise. The reaction is catalysed by Y. Y A + B  C + D The following results are obtained. Experiment Volume of A added / cm3 Volume of B added / cm3 Volume of Y added / cm3 Volume of H2O added / cm3 Time taken / s 1 10 20 10 10 20 2 10 10 10 20 40 3 10 20 5 15 40 4 5 20 10 15 20 What is the rate equation for the reaction? A rate = k[B][Y] C rate = k[B] B rate = k[A][Y] D rate = k[A][B][Y] 12. CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O The above reaction can be said to have reached dynamic equilibrium when A the equilibrium constant K is equal to 1. B the reaction between the acid and the alcohol has stopped. C the concentrations of the products equal those of the reactants. D the rate of production of ethyl ethanoate equals its rate of hydrolysis. 13. The pH change during a titration when a monobasic acid is added dropwise to 20.0 cm3 of NaOH is shown below. Which statement about the titration is correct? 4 Volume of acid added/cm3 10 20 30 40 pH 7 10 12

7 TPJC_2012_9647_P1 A Both an acidic and basic buffer can be formed at different points during this titration. B Both phenolphthalein and methyl orange can be used as an indicator for this titration. C Ethanoic acid is used in this titration and it has a pKa value of less than 4. D Benzoic acid is used in this titration and it has a similar concentration as NaOH. 14. What is the pH of an aqueous solution containing 0.1 mol dm-3 sodium benzoate and 0.01 mol dm-3 benzoic acid? [Ka (benzoic acid) = 6 x 10-5 mol dm-3] A 3.22 C 4.78 B 4.22 D 5.22 15. Public swimming pools are often chlorinated to kill bacteria. As an alternative to chlorination, silver ions can be used in a concentration of not more than 10 -6 mol dm -3 and not less than 10 -7 mol dm -3 of silver ions. Which of the following compounds would, in saturated solution, provide the necessary concentration of silver ion? compound solubility product A AgBr 5 x 10 -13 mol 2 dm -6 B AgCl 2 x 10 -10 mol 2 dm -6 C AgIO3 2 x 10 -8 mol 2 dm -6 D Ag2CO3 5 x 10 -12 mol 3 dm -9 16. The use of the Data Booklet is relevant to this question. Studies have shown that the corrosion of copper hulls of sea-going ships could be prevented by placing strips of ‘sacrificial metals’ on the hulls. Which metal is least likely to dissolve when attached to the copper hull of a sea-going ship? A iron C tin B magnesium D zinc

8 TPJC_2012_9647_P1 17. During electrolysis under suitable conditions, 0.785 g of chromium is deposited on the cathode when 4370 C of electricity is passed into a chromium-containing electrolyte. Which of the following could have been the electrolyte? A CrCl2 C K2CrO3 B CrCl3 D K2Cr2O7 18 “Group II metals have higher melting points than the Group I metals.“ A student suggested four possible reasons to explain the above statement. Which of these is most likely to be correct? A There is larger overlap of valence electrons between Group II metal atoms than Group I metal atoms. B Two valence electrons are available from each Group II metal atom for bonding the atom into the metallic lattice. C Group II metals have higher total ionization energies than Group I metals during formation of ions with octet electronic configuration. D Group II metal atoms have larger atomic radius than Group I metal atoms. 19. Which statement is true about the chemistry of sodium bromide? A It is a much weaker reducing agent than sodium chloride. B It reacts with iron(III) chloride solution to form a pale green solution. C It liberates a red-brown gas on warming with concentrated sulphuric acid. D It is formed together with sodium bromate(I) when bromine is bubbled into hot concentrated sodium hydroxide. 20. The standard enthalpy changes of formation of HCl and HI are –92 kJ mol-1 and +26 kJ mol-1 respectively. Which statement is most important in explaining this difference? A The bond energy of HI is smaller than the bond energy of HCl. B The bond energy of I2 is smaller than the bond energy of Cl2. C Chlorine is more electronegative than iodine. D The activation energy for the H2 / Cl2 reaction is much less than that for the H2 / I2 reaction.

9 TPJC_2012_9647_P1 21. The highest oxide s of the elements sodium to sulfu r are separately added to water. Which of the following diagrams best represents the pH of the solution produced? 22. Transition metal