2019 TJC H2 Chem Prelim P1 ANS

1 2019 TJC JC2 H2 Chemistry Prelim MCQ Worked Solutions Question 1 Answer: C Particle Neutron Nucleon Proton Electron U 16 33 17 17 V͞ 18 35 17 18 S2͞ 16 32 16 18 T2+ 17 34 17 15 Q3͞ 16 31 15 18 Question 2 Answer: C CH4 + 2O2 CO2 + 2H2O x 0.95x CH4 + 3/2 O2 CO + 2H2O 0.05x If combustion is complete, x dm3 CH4 will require 2x dm3 O2. Combustion of 1 mol CH4 to form CO, requires 3/2 mol O2 ie ½ mol O2 less than complete combustion. To obtain 0.05x mol CO will need 0.05x/2 mol less O2. Amt of O2 needed for incomplete combustion = 2x – 0.05x/2 Or Volume of methane burnt = y dm3 5% of methane is burnt to give CO and the remaining 95% is burnt to give CO2 Vol of methane burnt to give CO = 0.05y Vol of methane burnt to give CO2 = (1-0.05)y CH4 + 2O2  CO2 + 2H2O Volume used (1-0.05)y 2(1-0.05)y CH4 + 3/2O2  CO + 2H2O Volume used 0.05y 3/2(0.05y) Vol of O2 used = 2(1-0.05)y + 3/2(0.05y) = 2y – 2(0.05)y + 3/2(0.05y) = 2y – ½ (0.05y) Question 3 Answer: D Na : [Ne]3s1 (1 unpaired electron) P3͞ : [Ar] (0 unpaired electron) V : [Ar]3d34s2 (3 unpaired electron) Mn2+: [Ar]3d5 (5 unpaired electron) Question 4 Answer: B  1 2 3 4 5 6 7 8 9 10 C C D B A C C B B A 11 12 13 14 15 16 17 18 19 20 C D A D D A A B D C 21 22 23 24 25 26 27 28 29 30 B D B A C B D B A C 1 1

2 Question 5 Answer: A ICl2͞ : 2BP + 3 LP, shape linear, Bond angle 1800, non-polar CO2 : 2 BP, shape linear, Bond angle 1800 , non-polar BCl3 : 3 BP shape trigonal planar, Bond angle 1200 , non-polar ClO2͞ : 2 BP + 2 LP, shape bent, Bond angle <109.50 , polar HCN : 2 BP, shape linear, Bond angle 1800, polar XeF4 : 4 BP + 2 LP, shape square planar, Bond angle 900, non-polar Question 6 Answer: C I Both diamond and silicon have giant molecular structures. The atomic radius of C is smaller than Si. C-C bond length is shorter than Si-Si bond. Diamond has a higher mp than silicon as more energy is needed to break the stronger C-C bonds. II H2O is able to form more hydrogen bonds on average compared to NH3 as it has 2 lone pair of electrons on O. III SiCl4 has a simple molecular structure and Al2O3 has a giant ionic structure. The id-id attractions between SiCl4 molecules is weaker than the strong ionic bonds in Al2O3. IV Both Br2 and ICl have similar Mr. The id-id attractions between Br2 molecules is weaker than the pd-pd attractions between ICl molecules. Question 7 Answer: C 1 Structure of dimer Al2Cl6 Shape of AlCl3 = Trigonal planar hence bond angle is 120o. Shape of Al2Cl6 = Tetrahedral about each Al atom hence bond angle is not 120o. 2 Using ideal gas equati