RI 2022 Prelim P1 (Ans)

1 © Raffles Institution 2022 9729/01/S/22 2022 RI H2 Chemistry Prelim Paper 1 – Suggested Solutions Question 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Answer C C A A A B B B D B A A D D C MCQ worked solutions Q1 (Ans: C) Option A is incorrect. (NH4)2Fe(SO4)2 has 5 ions per formula unit  total number of ions = 5  2  6.02  1023 K2Cr2O7 has 3 ions per formula unit  total number of ions = 3  4  6.02  1023 Option B is incorrect. Number of NO2 molecules = 46 14 + (16  2)  6.02  1023 Number of N2 molecules = 14 14  2  6.02  1023 Option C is correct. Number of electrons in 1 mol of N2 = (7 + 7)  6.02  1023 Number of electrons in 1 mol of CO = (6 + 8)  6.02  1023 Option D is incorrect. Let Vm be the molar volume of gas. At the same temperature and pressure, number of atoms in 5 dm3 of O2 = 5 Vm  2  6.02  1023 number of atoms in 10 dm3 of Ar = 10 Vm  6.02  1023 Q2 (Ans: C) Let a be the fraction of 63Cu and (1 – a) be the fraction of 65Cu in naturally occurring copper. From the Data Booklet, the relative atomic mass of Cu is 63.5. 63.5 = 63a + 65(1 – a)  a = 0.75 Hence, in the sample of bronze, % composition of Cu63 % composition of Cu65 = d 88 – d = 0.75 0.25 d = 66 Question 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Answer C D B A B D C C D C D B B A D

2 © Raffles Institution 2022 9729/01/S/22 Q3 (Ans: A) 30Si4+ 31P3− 32S2− Number of electrons 10 18 18 Number of neutrons 16 16 16 Number of protons 14 15 16 Statement 1 is correct. The ions have the same number of neutrons. Statement 2 is incorrect. As the ions have different number of electrons, their electronic configurations are different. Statement 3 is incorrect. The ionic radii increase in the order 30Si4+ < 32S2− < 31P3−. The valence electrons of 30Si4+ are found in the n=2 shell while the valence electrons of 31P3– and 32S2− are found in the n=3 shell. Hence the ionic radius of 30Si4+ is smaller than that of 31P3– and 32S2−. Since 31P3− and 32S2− are isoelectronic with the same electronic configuration, their valence electrons experience the same shielding effect. However, nuclear charge of 31P3− is smaller than that of 32S2−. Hence, the effective nuclear charge of 31P3− is smaller than that of 32S2−, and therefore 31P3− has a larger ionic radius than 32S2−. Q4 (Ans: A) Angle of deflection  charge mass ions 7Li2− 15O2+ 15N4− 11C3+ charge mass 0.286 0.133 0.267 0.273 Q (11C3+) should be a cation as it is attracted to the negatively charged plate, and its charge/mass ratio should be between that of the two anions P (7Li2−) and R (15N4−). Q5 (Ans: A) Indium is a Group 13 element with 3 valence electrons. Hence, there should be a large jump between the third and fourth IE as the fourth electron is removed from an inner electronic shell. Hence, option A is correct.

3 © Raffles Institution 2022 9729/01/S/22 Q6 (Ans: B