2019 VJC H2 Chem Prelim P1 QP and Ans

2 VJC PRELIM 9729/01/19 2019 VJC H2 Chem Prelim P1 For each question there are four possible answers, A, B, C, and D. Choose the one you consider to be correct. 1 Use of the Data Booklet is relevant to this question. Which of the following statements are incorrect? 1 Both isotopes of Ti22 56 and Ti22 58 have more neutrons than electrons. 2 The first ionisation energy increases continuously from sodium to phosphorus as the number of protons increases but number of inner quantum shells remains the same. 3 The second ionisation energy of chromium is lower than the second ionisation energy of manganese as manganese has one more proton than chromium. A 1, 2 and 3 C 2 only B 2 and 3 only D 3 only 2 In which of the following pairs does the first substance have a higher melting point than the second substance? first substance second substance A CH3CH2OCH3 CH3CH2NHCH3 B CH3CH2CH2CH2OH CH3CHClCH2CH2OH C RbCl KCl D H2NCH2COCO2H H2NCH2CH2CO2H

3 VJC PRELIM 9729/01/19 [Turn Over 3 The dye ‘alizarin’ sticks fast to cotton when a ‘mordant’ containing aluminium ion is used. Under alkaline conditions, the aluminium ions become bonded to the hydroxyl groups of cotton. The dye ‘alizarin’ can then bond with the aluminium ions, giving the structure below which dyes cotton red. OO O OH Al3+ O OHH Which statement is correct? A The formula for ‘alizarin’ ion is C14H9O4–. B There are 12 carbon atoms in the ‘alizarin’ ion that are sp2 hybridised. C In the absence of a mordant, alizarin can bind to cotton via hydrogen bonding. D There is a decrease in the bond angles about the oxygen atoms of the cotton hydroxyl groups upon binding to aluminium ions. 4 Two vessels W and X are connected by a closed valve. Vessel X contains three times the volume of W. W contains argon gas at 20 C at a pressure of 1.00 × 105 Pa while X has been evacuated. In an experiment, the valve is opened and the temperature of the whole system is raised to T oC. The final pressure in the system decreases by 6.82 x 104 Pa. What is the final temperature in the system? A 99.7 oC C 526 oC B 373 oC D 799 oC ‘alizarin’ ion W X

4 VJC PRELIM 9729/01/19 5 The graph below shows the variation in the s tandard enthalpy change of vapo risation, ΔHovap, for eight consecutive elements in the Periodic Table, all with atomic number, 10 Z 20. Which one of the following statements is incorrect? A Effervescence of hydrogen gas is observed when sodium is added to the solution containing chloride of element P. B Element U is the most electronegative element among all the eight elements. C When a mixture of the oxides of element R and element W is dissolved in water, the solution is approximately neutral. D The oxide of element Q has a lower melting point than the oxide of element T. 6 Given a sample of strontium carbonate that was mixed with strontium nitrate, two separate experiments using the same mass of the solid mixture were conducted. Experiment 1: Excess dilute hydrochloric acid was added to the sample and volume of gas evolved was found to be 75 cm3. Experiment 2: The sample was heated strongly to constant mass and the volume of gas evolved was found to be 200 cm3. All volumes were measured at the same temperature and pressure. What is the mole ratio of strontium nitrate to strontium carbonate in the sample? A 2 : 3 C 5 : 6 B 5 : 3 D 9 : 5   P Q R T U V W X ΔH o vap / kJ mol –1 atomic number, Z

5 VJC PRELIM 9729/01/19 [Turn Over 7 When H2SO4 is used to make an aqueous solution, the solution is found to contain H 2SO4 molecules, H+ ions, HSO4– ions and SO42– ions. Which one of the following statements best describes the system? A The solution contains equal number of moles of H+ ions and HSO4– ions. B The solution contains equal number of moles of HSO4– ions and SO42– ions. C The number of moles of H2SO4 dissociated is equal to the sum of the number of moles of H+ ions and HSO4– ions. D The number of moles of H2SO4 dissociated is equal to the sum of the number of moles of HSO4– ions and SO42– ions. 8 A 10 cm 3 sample of the hydrocarbon C 3H8 is burned in excess oxygen and the product gases are collected as follows. The increase in mass of the collecting vessels P and Q are MP and MQ respectively and the volume of the residual gas is VR. Which one of the following statements is incorrect? A The ratio 𝑉R 10 is equal to 5. B The ratio 𝑀𝐐 𝑀𝐏 is equal to 1.8. C The volume of residual gas, VR, only contains excess O2. D The increase in mass in vessel P, MP, is smaller than the increase in vessel Q, MQ. product gases, H2O + CO2 + excess of O2 anhydrous calcium chloride soda lime (a mixture of calcium oxide and sodium hydroxide) Q P residual gas

6 VJC PRELIM 9729/01/19 9 Which one of the following pairs contains identical enthalpy change values? A first ionisation energy of oxygen –1 x first electron affinity of oxygen B standard enthalpy change of combustion of C(graphite) standard enthalpy change of formation of CO2(g) C standard enthalpy change of neutralization between H2SO4(aq) and NaOH(aq) standard enthalpy change of neutralization between H2SO4(aq) and NH3(aq) D bond energy of F2(g) standard enthalpy change of atomisation of F2(g) 10 The table below gives the enthalpy change s and entropy changes for the dissolution of sodium chloride and magnesium chloride. ∆Hosol, kJ mol–1 ∆Sosol, J mol–1 K–1 I NaCl(s) + (aq)  Na+(aq) + Cl–(aq) +3.87 +43.0 II MgCl2(s) + (aq)  Mg2+(aq) + 2Cl–(aq) –155 –97.1 Which one of the following statements can be supported by the information given? A Reaction II is more spontaneous than reaction I at higher temperatures. B The hydration energy of Mg2+ is more exothermic than the hydration energy of Na+. C The system becomes more disordered when there is gre ater number of product particles. D The lattice energy of MgCl2 is more exothermic than the sum of the hydration energies of its ions. 11 When 10 g of calcium carbonate was added to 100 cm3 of 0.10 mol dm–3 hydrochloric acid, the volume of CO2 produced was recorded as follows: time / s 0 50 75 100 125 150 175 200 225 250 total volume of CO2 given off / cm3 0 60 78 90 99 105 108 114 120 120 Which one of the following statements cannot be deduced from these results? A The rate constant is around 0.02 s–1. B The rate of the reaction decreases with time C The half-life of the reaction is around 50 seconds. D The reaction is first order with respect to hydrochloric acid.

7 VJC PRELIM 9729/01/19 [Turn Over 12 In the upper atmosphere, nitrogen oxides participate in the decomposition of ozone, O3, via the following elementary steps: reaction I : O3  O2 + O reaction II : O + NO2  O2 + NO reaction III : O3 + NO  O2 + NO2 Which of the following statements can be deduced from the information given? 1 The overall equation for the decomposition of ozone is 2O3  3O2. 2 Reaction II must take place before reaction III can occur. 3 Both NO and NO2 can behave as a catalyst for the decomposition of ozone. A 1, 2 and 3 C 1 and 3 only B 1 and 2