2024 Prelims VJC H2 Chem P1 (Ans)

1 VICTORIA JUNIOR COLLEGE 2024 JC2 H2 CHEMISTRY PRELIM EXAM PAPER 1 ANSWERS 1 A 7 C 13 B 19 A 25 D 2 B 8 A 14 A 20 B 26 A 3 B 9 C 15 C 21 D 27 D 4 D 10 D 16 D 22 C 28 D 5 C 11 A 17 D 23 A 29 D 6 B 12 B 18 B 24 C 30 C 1 A Since there are 4 valence electrons in the Group 14 elements, the electronic configuration of the valence shell at its ground state should be ns2np2. This corresponds to the electrons with four highest energy. 2 B Element X has the highest 6th ionisation energy, it means that the sixth electron removed from X is from its next inner shell. Hence, X has five valence electrons and X is in Group 15. As W, X, Y and Z are four consecutive elements in the Periodic Table, W is in group 14. Hence, the formula of the fluoride of W is WF4. 3 B (1 and 2 only) Option 1: Correct Lone pair electrons on oxygen in CH3OCH3 is donated to the vacant orbital of boron in BF3 to form the dative bond. Option 2: Correct The bond angle around B changes from 120 ° in BF3 (3 bond pairs, trigonal planar) to 109.5 ° in J (4 bond pairs, tetrahedral). Option 3: Incorrect In CH3OCCH3, there are 2 bond pairs 2 lone pairs around O (bent). In Q, there are 3 b ond pairs and 1 lone pair around O (trigonal pyramidal). 4 D Option A: correct statement Since O is more electronegative than N, the H2O molecule has a greater dipole moment than the NH 3 molecule, which results in stronger permanent dipole- permanent dipole (pd-pd) interactions between H 2O molecules. Hence, more energy is required to overcome the stronger pd-pd between H2O molecules. Option B: correct statement Since O is more electronegative than N, th e hydrogen bonds formed between H2O molecules are stronger than that between NH3 molecules. More energy is required to overcome the stronger hydrogen bonding between H 2O molecules. Option C: correct statement The extent of hydrogen bonds is greater for H 2O (2 hydrogen bonds per molecule) than NH3 (1 hydrogen bond per molecule). Hence, more energy is required to overcome the more extensive hydrogen bonds between H2O molecules. Option D: Incorrect statement Energy is required to overcome the intermolecular force of attractions (hydrogen bonds) between H2O molecules and that between NH3 molecules. Hence, the strength of O–H bonds in water and N –H bonds in NH 3 does not affect the boiling points of H2O and NH3. 5 C pV = nRT Since V is the same for both gases, V R = nT p = constant nATA pA = nD2TD2 pD2 where D2 is deuterium gas, 2H2 Since, n = m Mr , mA pAMrA TA = mD2 pD2Mr D2 TD2 18.0 2 × pD2 × MrA (40 + 273) = 0.6 pB× 2.0 × 2 (20 + 273) MrA = 64.1 6 B Ion of V is positively charged as its ionic radius is smaller than its atomic radius. Hence, V could be Na, Mg, Al or Si as these elements form cations with 10 electrons. Ion of Z is negatively charged as its ionic radius is bigger than its atomic radius. Hence, Z could be P, S or C l as these