VJC 2021 Prelim H2P1 Ans [FInal]

1 Victoria Junior College 2021 H2 Chemistry Prelim Exam 9729/1 Suggested Answers 1 A 2 B 3 A 4 A 5 B 6 D 7 C 8 D 9 C 10 B 11 B 12 D 13 C 14 D 15 A 16 C 17 B 18 D 19 A 20 D 21 B 22 D 23 B 24 C 25 D 26 C 27 C 28 A 29 A 30 C 1 A (1, 2 and 3) Option 1: Incorrect X2+ has 53 electrons, X atom has 55 electrons (protons), X is Cs while Xe has 54 electrons (or protons). Hence, the atom of X is not isoelectronic with the atom of Xe. Option 2: Incorrect Both XF and RbF have giant ionic structure. Since LE α |q+q–/(r+ + r–)|, as size of X+ is bigger than Rb+, hence XF has a less exothermic LE and ionic bond strength in XF is weaker. Hence, XF has a lower melting point than RbF. Option 3: Incorrect Since Fr is below Cs, Fr should have a lower first IE as first IE decreases down the group. Option 4: Correct Since angle of deflection α (charge / mass) ion Na+ X2+ charge / mass 1/23 = 0.0435 2/133 = 0.0150 Hence, X2+ has a smaller angle of deflection. 2 B Option A: Correct Ethanol, C2H5OH, which has a highly electron–deficient H atom (d+) that is covalently bonded to a highly electronegative O, can be attracted to the lone pair of a highly electronegative atom (d–), which is O in caffeine through hydrogen bonding. Option B: Incorrect Caffeine does not have a planar structure since there are 3 bond pair of electrons and 1 lone pair around each N atom having three single bonds around it, it is trigonal pyramidal about each of these N atoms. Option C: Correct Each double bond is made up of 1 sigma and 1 pi bonds while each single bond is made up of only 1 sigma bond. Option D: Correct There are 5 carbon atoms having 3 bond pair of electrons around each of them, implying that they are sp2 hybridised. 3 A Option A: Correct CH3CO2–NH4+ has a giant ionic structure. More energy is required to break the stronger electrostatic forces of attraction between oppositely charged ions. CH3CH2NH2 has a simple molecular structure with weaker hydrogen bonds between molecules. Hence, CH3CO2–NH4+ has a higher bp. Option B: Incorrect SiO2 has a giant molecular structure while SiCl4 a simple molecular structure. More energy is required to break the stronger and extensive covalent bonds between atoms in SiO2 than the id-id interactions between non-polar SiCl4 molecules. Hence SiO2 has a higher bp. Option C: Incorrect Both PH3 and SiCl3H exist as simple molecules. SiCl3H has a larger electron number, hence its electron cloud is more polarisable resulting in stronger id-id interactions between SiCl3H molecules. Thus SiCl3H has a higher bp. Option D: Incorrect Both Ni(OH)2 and NiSO4 exist as giant ionic structures. Since SO42– has a higher charge than OH– and LE α |q+q–/(r++r–)|, LE of NiSO4 is more exothermic and more energy is required to break the stronger ionic bonds in NiSO4. Hence, NiSO4 has a higher bp. 4 A When the vessel is dented, pV = nRT n = pV/RT = (52.8 x 103 x 38.5 x 10–6) / [8.31 x (27 +273)] = 8.15 x 10–4 mol Amount of gas remained unc