2024 H1 Chem Prelim P1 Ans_VJC

1 VICTORIA JUNIOR COLLEGE 2024 JC2 H1 CHEMISTRY PRELIMINARY EXAMINATION PAPER 1 ANSWERS 1 A 7 A 13 D 19 A 25 D 2 B 8 C 14 A 20 B 26 C 3 C 9 D 15 C 21 A 27 C 4 B 10 A 16 C 22 B 28 A 5 D 11 C 17 D 23 C 29 B 6 C 12 B 18 D 24 A 30 D 1 A particle electronic configuration A C– 1s22s22p3 B N2– 1s22s22p5 C F+ 1s22s22p4 D Ne 1s22s22p6 Hence, C– has a half-filled set of p orbitals. 2 B Element X has the highest 6 th 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 1 5. 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 C (1 and 3 only) Option 1: Correct A dative bond is formed when the lone pair on O in CH3OCH3 is donated to the vacant orbital of B in BF3. Option 2: Incorrect The bond angle around B changes from 120° in BF3 (3 bond pairs, trigonal planar), to 109.5° in Q (4 bond pairs, tetrahedral). Option 3: Correct In CH3OCH3, there are 2 b ond pairs and 2 lone pairs around O (bent). In Q, there are 3 bond pairs and 1 lone pair around O (trigonal pyramidal). 4 B Option A: Incorrect NH3: Trigonal pyramidal All dipole moments are not cancelled out, so the molecule is polar. CCl4: Tetrahedral All dipole moments are cancelled out, so molecule is non-polar. Option B: Correct CO and HF: linear Since electronegativity difference is greater between H and F than between C and O, so HF is more polar than CO. Option C: Incorrect H2O and H2S: bent. Since O is more electronegative than S, so H2O is more polar than H2S since O-H bond is more polar than S-H bond. Option D: Incorrect CO2: linear; BF3: trigonal planar Dipole moments in these two molecules cancel out and so these molecules are non-polar. 5 D (CH3)2CHOH and CH 3CH2CH2OH form hydrogen bonds between molecules. However, CH3CH2CH2OH, with its straight-chain structure, has greater surface area for molecular interaction, leading to greater extent and stronger instantaneous dipole –induced dipole interactions than (CH3)2CHOH, which is a branched molecule having smaller area for molecular interaction. Hence, more energy is required to overcome the stronger id-id interactions between CH3CH2CH2OH and CH 3CH2CH2OH has a higher boiling point than (CH3)2CHOH. There are only weaker permanent dipole -permanent dipole interactions between CH 3CH2CHO molecules, hence, CH3CH2CHO has the lowest boing point among three molecules. 6 C (2 and 3 only) Bronsted-Lowry base is a proton acceptor. Option 1: Incorrect NH3 donated a lone pair to CH 3Cl to form CH 3NH2. There is no transfer of proton in this reaction. Option 2: Correct HNO3 accepted a proton to form H2NO3+ Option 3: Correct H2O accepted a proton to form H3O+ 7 A Since Kw increases when temperature increases, the dissociation of water is endothe