ACJC H2 CHEM P1 Questions Prelim

© ACJC 2015 9647/01/Prelim/15 [Turn over 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 Pure silicon required for microchips can be manufactured by heating silicon tetrachloride with zinc. 1.27 g of pure silicon could be obtained by heating 8.50 g of impure silicon tetrachloride with an excess of zinc. What is the percentage of impurity by mass in the sample of silicon tetrachloride? A 9.56 % B 14.9 % C 85.1 % D 90.4 % 2 Two elements M and N have the following properties:  M and N form ionic compounds K2M and K2N respectively.  Element N forms NF6 molecules whereas M is not able to do so. Which pair of electronic configurations of M and N is correct? M N A [He]2s22p2 [Ne]3s23p2 B [He]2s22p2 [Ne]3s23p4 C [He]2s22p4 [Ne]3s23p2 D [He]2s22p4 [Ne]3s23p4 3 In which of the following pairs does the first species have a larger bond angle than the second? A SO2, PI3 B SO3 2-, SO4 2- C H2S, NH3 D H2O, H3O+

© ACJC 2015 9647/01/Prelim/15 [Turn over 3 4 Which of the following statements is correct? A BCl3 and BrCl3 have the same molecular shape. B Cyclohexene and propanone are non–polar liquids. C LiAlH4 and NaBF4 contain dative covalent bonds. D XeF4 and H2C=C=CH2 are planar molecules. 5 In which of the following pairs does the first substance have a higher melting point than the second? First substance Second substance A CH3CH2OCH3 CH3CH2NHCH3 B CH3(CH2)4CH3 (CH3)2CHCH(CH3)2 C RbCl KCl D C O OH OH C O OH OH 6 Which of the following correctly shows the arrangement of the ions in decreasing order of ionic radius? A F– > O2– > N3– B Ca2+ > K+ > Cl- C S2– > Mg2+ > Na+ D Se2- > Br- > Ga3+

© ACJC 2015 9647/01/Prelim/15 [Turn over 4 7 Which graph correctly describes the behaviour of fixed masses of the ideal gases L and M where the number of moles of L is greater than number of moles of M? A B C D 8 A student dissolved 10.5 g of sodium fluoride in 250 g of water. The following data is obtained: Lattice energy of NaF −918 kJ mol-1 Enthalpy change of hydration of F- −457 kJ mol-1 Enthalpy change of hydration of Na+ −390 kJ mol-1 Given that the specific heat capacity of water is 4.2 J g-1 K-1, what would be the final temperature of the solution, if the initial temperature of water is 30 oC? A 6.5 °C B 13.1 oC C 16.9 oC D 46.9 oC

© ACJC 2015 9647/01/Prelim/15 [Turn over 5 9 Passing steam over hot coal produces combustible mixture of gases. H2O(g) + C(s) H2(g) + CO(g) ΔH = +131 kJ mol-1 In a certain mixture, the equilibrium partial pressures of steam and hydrogen gas are 90 kPa and 183 kPa respectively. What will be the new equilibrium partial pressure of hydrogen gas if the new equilibrium partial pressure of steam is increased to 150 kPa? A 100 kPa B 123 kPa C 236 kPa D 372 kPa 10 Paracetamol (pKa = 9.5) is a widely used over-the-counter pain reliever and fever reducer. Its solubility in water is 12.78 mg cm-3 at 25 oC. (Mr of Paracetamol = 151.0) What is its pH in water at 25 oC? A 0.0846 B 1.07 C 5.29 D 9.50 11 The yellow pigment used for road markings is lead(II) chromate, PbCrO4. Concentrated lead(II) nitrate is added dropwise to 0.010 mol dm -3 potassium chromate(IV). What is the concentration of lead(II) ions when the first trace of precipitate appears? (Ksp of PbCrO4 = 1.69 x 10-14 mol2 dm-6) A 1.69 x 10-14 mol dm-3 B 1.69 x 10-12 mol dm-3 C 1.30 x 10-9 mol dm-3 D 1.30 x 10-7 mol dm-3

© ACJC 2015 9647/01/Prelim/15 [Turn over 6 12 In an experiment, 20 cm3 of a 0.1 mol dm-3 solution of a metallic salt reacted exactly with 50 cm3 of 0.1 mol dm-3 potassium peroxodisulfate solution. The half-equation for reduction of peroxodisulfate ion is S2O8 2-(aq) + 2e‾ → 2SO4 2-(aq) If the original oxidation number of the metal in the salt was +2, what would be the new oxidation number of the metal? A +1 B +3 C +5 D +7 13 A tiny magnesium electrode which creates an electrical cell with inhaled oxygen could be used in the construction of heart “pacemakers”. From the relevant half-cells: Mg2+ + 2 e Mg Eo = -2.38 V ½ O2 + 2H+ + 2e H2O Eo = +1.23 V the cell e.m.f. would be 3.61 V under standard conditions. However, in the body a potential of 3.25 V is more usual. Which of the following gives the best explanation for this lower e.m.f.? A the small size of the magnesium electrode B the low concentration of Mg2+ ions surrounding the magnesium electrode C the high resistance of the body fluids surrounding the electrodes D the pH of between 7 and 8 of the body fluid surrounding the electrodes 14 Which of the following statements about but-1-ene, CH3CH2CH=CH2 is correct? A It exhibits geometric isomerism. B It gives a ketone and carbon dioxide on strong oxidation. C It gives a chiral compound upon reacting with hydrogen bromide. D It reacts with cold dilute potassium manganate(VII) to form butane-2,3-diol.

© ACJC 2015 9647/01/Prelim/15 [Turn over 7 15 Methylcyclohexane was reacted with limited chlorine in the presence of uv light. Assuming that only mono -chlorination takes place and the reaction occurs at the same rate at all carbon atoms, what is the ratio of the products obtained below? A 1 : 3 : 4 : 4 : 2 B 1 : 3 : 2 : 2 : 2 C 1 : 1 : 4 : 4 : 2 D 1 : 3 : 4 : 2 : 1 16 -Candinene can be found in juniper berries. Compound Y is the minor product formed when -Candinene is reacted with HCl. How many stereoisomers does Y have? A 32 B 64 C 128 D 256

© ACJC 2015 9647/01/Prelim/15 [Turn over 8 17 The equation below represents the reaction between benzene and fuming sulfuric acid (a mixture of sulfur trioxide and sulfuric acid). C6H6 + SO3 C6H5SO3H What is the role of sulfuric acid? A a dehydrating agent B to generate the electrophile C an oxidising agent D a nucleophilic reagent 18 When (chloromethyl)benzene, C 6H5CH2Cl, is treated in succession with two reagents O and P, it gives phenylethanoic acid, C6H5CH2COOH. Which of the following is a possible combination for reagents O and P? O P A NaOH (aq) K2Cr2O7 (aq) B Cl2 (aq) NaOH (aq) C NaCN (in aqueous ethanol) dilute H2SO4 D NaCN with trace of NaOH dilute HCl 19 Which of the following reagent gives similar results for both butanone and butanal? A an aqueous solution containing [Ag(NH3)2]+ B acidified aqueous potassium dichromate(VI) C iodine and aqueous sodium hydroxide D 2,4-dinitrophenylhydrazine H2SO4

© ACJC 2015 9647/01/Prelim/15 [Turn over 9 20 Different hydroxy compounds P, Q and R react with HCl differently. Relative Ease of Reaction: P > Q > R Which of the following is the correct set of identities of compounds P to R? P Q R A B C D

© ACJC 2015 9647/01/Prelim/15 [Turn over 10 21 Compound P can be converted to R in two steps. What are Q and R? Q R A B C D

© ACJC 2015 9647/01/Prelim/15 [Turn over 11 22 Which reagent could be used to separate a mixture of phenylamine and methylbenzene? A dilute aqueous sodium hydrogencarbonate B dilute aqueous sodium hydroxide C dilute hydrochloric acid D sodium 23 Nylon is the