2019 ASRJC Prelim H2 Chem P1 ANS

ASRJC JC2 PRELIMS 2019 9729/01/H2 1 ANDERSON SERANGOON JUNIOR COLLEGE H2 Chemistry 9729 2019 JC2 Prelim Exam Paper 1 Worked Solutions 1 Answer: C 68Ge has 32 protons and 36 neutrons. When ‘a proton changes into a neutron’, 68X contains 31 protons and 37 neutrons. X is gallium (Ga) which is in Group 13, i.e. has 3 valence electrons, only 1 of which is in the outer p orbitals. Ga: [Ar] 3d10 4s2 4p1 2 Answer: C X: The biggest jump in IE is between 4 th to 5 th electron hence, X has 4 valence electrons and belongs to Group 14. Y: The biggest jump in IE is between 6 th to 7 th electron hence , X has 6 valence electrons and belongs to Group 16. Possible covalent compounds formed are CO2, CS2 and SiO2. 3 Answer: C Notice that N1 and N3 only have two covalent bonds with carbon atoms. To fulfil octet, they need to gain one electron each from the central Mg atom to form N–. Hence, N1 and N3 are involved in ionic bonding. N2 and N 4 have three covalent bonds with carbon at oms. They have one lone pair each, which interacts with the central Mg2+ ion via co–ordinate bonding. 4 Answer: D Dipole moments cancel out. B: Dipole moment is smaller than that in D since S is less electronegative than O. C: Dipole moment is smaller than that in D as the net dipole moment of C–F bonds reduces the dipole moment of C=O bond

ASRJC JC2 PRELIMS 2019 9729/01/H2 2 D: 5 Answer: C V nRT mV RTM mM RTV M RT p p p p     p is directly proportional to . The graph should be a straight line that passes through the origin. Hence, A is wrong pV = nRT p is directly proportional to T / K. The graph should be a straight line that passes through the origin. Hence, B is wrong. V is also directly proportional to T / K. Hence, C is correct pV = nRT 1 V p nRT : 1 p  V at constant T. The graph should be a straight line that passes through the origin. Hence, D is wrong. 6 Answer: B The solution is one which is able to maintain the pH at about 5, hence it is an acidic buffer. Only the mixture in option B can form an acidic buffer.

ASRJC JC2 PRELIMS 2019 9729/01/H2 3 7 Answer: C H2O H+ + OH Kw = [H+][OH] Since the stoichiometric coefficients of H + and OH ions are equal in the above equation, [H +] = [OH–] at all temperatures. Hence, water is a neutral liquid at all temperatures. Option B is wrong. When temperature of water increases, Kw also increases. This shows that the position of equilibrium has shifted to the right , i.e. the forward reaction is favoured, and more H + and OH  ions are produced. Since the endothermic reaction is favoured when temperature increases, the dissociation of water (forward reaction) is an endothermic reaction. Option D is wrong. The value of Kw does not provide any information about hydrogen bonding between water molecules. Option A is wrong. 8 Answer: C A: Volatility of halogens (X2) decreases: F2 > Cl2