ACJC H2 CHEM P1 Prelim

2 Section A For each question, there are four possible answers, A, B, C and D. Choose the one you consider to be correct. 1 The hardness present in a water sample due to dissolved calcium ions can be determined by using ion-exchange column as shown in the diagram. Ca2+ + 2H+-resin → Ca2+-resin + 2H+ A 50 cm 3 sample of a solution containing calcium sulfate was passed through the ion- exchange resin. The calcium ions in the sample were quantitatively exchanged by hydrogen ions. The sample collected in the flask required 25 cm 3 of 1.0 × 10 -2 mol dm-3 potassium hydroxide for complete neutralisation. What was the concentration of the calcium sulfate in the original sample? A 2.5 × 10 -3 mol dm-3 B 5.0 × 10-3 mol dm-3 C 2.0 × 10-2 mol dm-3 D 4.0 × 10-2 mol dm-3 Hard water Ion-exchange resin Treated water 2 A tube filled with 50 cm 3 of methane and 150 cm 3 of oxygen at room temperature was inverted over a vessel containing KOH (aq) as shown in the diagram. The hydrocarbon was ignited for the following reaction to take place. CH 4 + 2O2 → CO2 + 2H2O When the setup is cooled to room temperature, at which level will the liquid be? A. 50 cm3 B. 100 cm3 C. 150 cm3 D. 200 cm3 ACJC 2011 9647/01/Aug/2011 [Turn over

3 3 The successive ionisation energies (IE) of two elements, A and B, are given below: IE/ kJ mol-1 1 st 2 nd 3 rd 4 th 5 th 6 th 7 th 8 th A 550 1065 4138 5500 6910 8760 10230 11800 B 1140 2103 3470 4560 5760 8550 9940 18600 What is the likely formula of the compound that is formed when A reacts with B? A AB2 B AB C A2B D A2B3 4 The value of pV is plotted against p at the same temperature for four gases, where p is the pressure and V is the volume of the gas. Which of the following represent the possible identities of Gases 1 to 4? Gas 1 Gas 2 Gas 3 Gas 4 A Ne CH 3F HF H2O B Ne HF CH3F H 2O C H2O Ne CH3F HF D H2O HF CH3F Ne Gas 1 Gas 4 Gas 2 Gas 3 pV p 5 In which of the following sequences are the molecules quoted in order of decreasing boiling points? A Ti, K, Ca B I2, HF, HCl C SCl2, AlCl3, MgCl2 D CCl4, CH4, CH2Cl2 ACJC 2011 9647/01/Aug/2011 Preliminary Examination

4 6 When two liquids are mixed, heat may be evolved if the intermolecular bonds formed are stronger than those broken, even if there is no chemical reaction occurring. Which of the following pair of liquids, when mixed, will give out heat? A CHCl 3 and C5H12 B CCl4 and (CH3)2CO C CCl4 and CH3CH2OH D CH2Cl2 and (CH3)2CO 7 The following graph shows the first ionisation energies of eight consecutive elements J to R, which have atomic numbers between 3 to 20 in the Periodic Table. M R Q P N J K L Atomic Number 1st Ionisation Energy/ kJ mol-1 Which one of the following statements about the elements is false? A Oxides of Q react with dilute H2SO4(aq). B Ions of M are able to act as homogeneous catalysts. C The ionic radius of J is larger than the ionic radius of K. D N forms a chloride which reacts with water to give a neutral solution. ACJC 2011 9647/01/Aug/2011 [Turn over

5 8 Reverse osmosis is a method of obtaining pure water from seawater or polluted water, which is now being used in Singapore and other countries. This process works by applying a constant pressure to a sample of impure water next to a semi-permeable membrane. The semi-permeable membrane only allows small molecules such as water to pass through, but retains all other molecules and ions. Hence, what are the correct signs for ΔS and ΔG for the reverse osmosis process? ΔS ΔG A Positive Positive B Positive Negative C Negative Positive D Negative Negative Impure water under pressure Impure water Pure water Semi-permeable membrane 9 When 1.200 g of propan-1,2,3-triol was burnt, it was found that 100 g of water was heated from 25 oC to 67 oC. This process was found to have an efficiency of 80%. What is the enthalpy change of combustion of propan-1,2,3-triol in kJ mol -1? A -1080 B -1350 C -1680 D -2420 ACJC 2011 9647/01/Aug/2011 Preliminary Examination

6 10 The reaction between potassium manganate(VII) and ethanedioic acid is an example of auto-catalytic reactions, in which one of the products catalyses the reaction. 2MnO 4 -(aq) + 5H2C2O4(aq) + 6H3O+(aq) → 2Mn2+(aq) + 10CO2(g) + 14 H2O(l) Which graph correctly represents the kinetics of this reaction? A B C D Rate Time Rate Time Rate Time Rate Time 11 An imine can be prepared by reacting benzaldehyde with ammonia in methanol: CHO NH3 H2O NH ++ Which of the following statements about the above reaction sequence is correct? A The value of Kc will increase upon the addition of ammonia. B The backward reaction is favoured by the addition of benzaldehyde. C The forward reaction is favoured by the addition of dilute aqueous sulfuric acid. D The preparation of imine proceeds via nucleophilic addition mechanism, followed by elimination mechanism. ACJC 2011 9647/01/Aug/2011 [Turn over

7 12 The following graph shows the change in pH when 30.0 cm 3 of 1.0 mol dm -3 solution of aqueous NH3 is titrated against 1.0 mol dm-3 solution of dilute aqueous H2SO4. Given that K b of NH3 is 1.8 x 10-5 mol dm-3, what is the pH of the solution at point Z? A 8.86 B 9.26 C 9.79 D 11.6 pH Volume of acid added / cm3 7.50 Z 15.00 13 The solubility products of barium carbonate (BaCO 3) and barium molybdate (BaMoO 4) are 2.58 x 10-9 mol2 dm-6 and 3.54 x 10-8 mol2 dm-6 at 25 °C respectively. Which of the following statements is false? A Barium molybdate has a higher solubility than barium carbonate. B Addition of nitric acid will increase the solubility of barium carbonate. C Addition of potassium molybdate to a solution containing barium molybdate will decrease the solubility product of barium molybdate. D When barium nitrate is added to a solution containing equal concentrations of carbonate and molybdate ions, barium carbonate is precipitated first. ACJC 2011 9647/01/Aug/2011 Preliminary Examination

8 14 The equations for three reactions are given below: Cl2(g) + H2S(g) → 2HCl(g) + S(s) SO2(g) + 2H2S(g) → 2H2O(l) + 3S(s) Cl2(g) + 2H2O(l) + SO2(g) → 2HCl(aq) + H2SO4(aq) Which is the correct order of strength of the three reacting gases as oxidising agents? Strongest Weakest A Chlorine Sulfur dioxide Hydrogen sulfide B Chlorine Hydrogen sulfide Sulfur dioxide C Hydrogen sulfide Sulfur dioxide Chlorine D Sulfur dioxide Hydrogen sulfide Chlorine 15 The use of the Data Booklet is relevant to this question. A cell is set up by connecting a Pb 2+/Pb half-cell and an acidified MnO4 −/Mn2+ half-cell. Which of the following is a correct description of the effect on the e.m.f (potential difference) of the cell when the corresponding change is made? Change Effect on e.m.f of cell A Addition of NH 3 (aq) into oxidation half-cell Increases B Addition of H2SO4 (aq) into reduction half-cell Decreases C Addition of NaOH (aq) into reduction half-cell Increases D Replace lead with an alloy of lead and zinc Remains the same [Mn2+(aq)] = [H+(aq)] = [MnO4 −(aq)] = 1.0 mol dm-3 voltmeter lead [Pb2+(aq)] = 1.0 mol dm-3 salt bridge platinum V ACJC 2011 9647/01/Aug/2011 [Turn over

9 16 The diagram shows t