SRJC_H2_CHEM_P1 ANS

1 SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 2 CHEMISTRY 9746/01 Prelim Examination Vetting Copy MCQ Solutions Mole concept (Dilution calculation, back titration) 1 3.920 g of an oxide of formula MO was completely dissolved in 30.0 cm 3 of 2.00 mol dm -3 sulphuric acid. The resulting solution was made up to 100 cm 3. 25.0 cm 3 of this solution was neutralised by 27.5 cm 3 of 0.100 mol dm-3 sodium hydroxide. What is the relative atomic mass of M? A 47.9 B 54.9 C 55.9 D 101.0 Solution: C Amount of NaOH = 327.5 0.1 2.75 101000   mol Amount of unreacted H2SO4 in 25.0 cm3 of solution = 1.375 x 10─3 mol. Amount of unreacted H2SO4 in 100 cm3 of solution = 33100 1.375 10 5.5 1025.0    mol. Initial amount of H2SO4 = 30.0 2.0 0.061000 mol Therefore, the amount of H2SO4 that reacts with MO = 0.06 – 5.5x10-3= 0.0545 mol Given that 1 mol of H 2SO4 reacts with 1 mol of MO ( M has an oxidation state of +2), therefore, no of moles of MO in 3.920g of MO = 0.0545 mol Given no. of moles of MO = mass of MO/ molar mass of MO 0.0545 = 3.920/(molar mass of M + 16.0) Molar mass of M = (3.920/0.0545) – 16.0 = 55.9 g/mol

2 REDOX (Use of half equation to deduce mole of reactants) 2 A commercial production of iodine involves the reduction of a solut ion of iodate(V) ions, IO3 , with the theoretical quantity of hydrogen sulphite ions, HSO 3  in acidic condition. The hydrogen sulphite ions are oxidised to sulphate ions, SO 4 2 while the iodate( V) ions are reduced to iodine, I2. Given H2O(l) + HSO3 ─(aq) → SO4 2─(aq) + 3H+(aq) + 2e─ How many moles of hydrogen sulphite ions are needed to r educe one mole of iodate(V) ions? A 0.4 B 1 C 2.5 D 5 Solution: C Reduction: IO3െ is reduced to I2. Reduction half-equation: 2IO3െ(aq) + 12H+(aq) + 10eെ → I2(aq) + 6H2O(l) Oxidation: HSO3 ─ is oxidised to SO4 2─ Oxidation half-equation: H2O(l) + HSO3 ─(aq) → SO4 2─(aq) + 3H+(aq) + 2e─ ( x 5) Overall equation: 2IO3െ(aq) + 5HSO3 ─(aq) → I2(aq) + H2O(l) + 5SO4 2─(aq) + 3H+(aq) Atomic Structure (deduce no of protons, electrons and neutrons in atoms or ions) 3 One of the isotopes of carbon is carbon-14. Carbon-14 is radioactive and is used in carbon dating by archaeologists. Which one of the following species is isotonic and isoelectronic with respect to an atom of carbon-14? A 13C B 14N+ C 16O2+

3 D 17F+ Solution: C Number of protons in Carbon-14= 6p Number of neutrons in Carbon-14 = 14 – 6 = 8n Number of electrons = 6e Gas La w (Interpretation of graph) A 13C 6p 7e 7n B 14N+ 7p 6e 7n C 16O2+ 8p 6e 8n D 17F+ 9p 8e 8n 4 Which o