2022 TMJC H2 Chem Prelim P1 (Ans)

2022 H2 Chem Prelim P1 (Ans) Tampines Meridian Junior College 2022 JC2 Preliminary Examination H2 Chemistry 1 In which species are the numbers of protons, neutrons and electrons all different? A F− 9 19 B Na+ 11 23 C P15 31 D S2− 16 32 Answer: B F− 9 19 9 protons, 10 neutrons, 10 electrons Na+ 11 23 11 protons, 12 neutrons, 10 electrons (all different) P15 31 15 protons, 16 neutrons, 15 electrons S2− 16 32 16 protons, 16 neutrons, 18 electrons 2 Beams of charged particles are deflected by an electric field. When a beam of protons passes through an electric field of constant strength, the angle of deflection is +12 . In another experiment under identical conditions, particle Y is deflected by an angle of – 4 . What could be the composition of particle Y? protons neutrons electrons 1 1 2 2 2 3 3 5 3 4 5 1 A 1, 2 and 3 B 1 and 2 C 1 only D 3 only Answer: B Magnitude of angle deflected  charge/mass charge/mass for 1H+ = 1  deflected by 12 o for 1 unit of charge/mass To be deflected through angle of – 4 o (i.e. opposite side of protons), particle Y should be negatively-charged, with charge/mass = – 1/3 Option 1: charge/mass = – 1/3 ✓ Option 2: charge/mass = – 2/6 = – 1/3 ✓ Option 3: charge/mass = + 3/9 = + 1/3 

2 2022 H2 Chem Prelim P1 (Ans) Tampines Meridian Junior College 2022 JC2 Preliminary Examination H2 Chemistry 3 Use of the Data Booklet is relevant to this question. In which pair of compounds does the first molecule have a smaller bond angle than the second molecule? A BF3, NH3 B H2O, H2S C BeCl2, SCl2 D XeF4, SiCl4 Answer: D A: BF3 (trigonal planar; bond angle 120o) > NH3 (trigonal pyramidal; bond angle 107o) B: Both H2O and H2S have bent shape. As O is more electronegative than S, bond pairs of electrons are nearer to the central O atom. There is greater repulsion between bond pairs in H2O and thus bond angle of H2O > bond angle of H2S. C: BeCl2: 2 bond pairs and 0 lone pairs around Be atom  180o SnCl2: 2 bond pairs and 1 lone pairs round Sn atom  118o D: XeF4 (square planar; bond angle ~90 o) < SiCl4 (tetrahedral; bond angle 109.5 o) 4 To produce decaffeinated coffee, pure liquid CO2 is sometimes used to extract caffeine from coffee beans. It was discovered that the solubility of caffeine greatly increased when a mixture of ethanol and liquid CO2 was used. Which interaction best explains why caffeine is more soluble in the ethanol -CO2 mixture as compared to liquid CO2? A instantaneous dipole - induced dipole interactions B permanent dipole - permanent dipole interactions C hydrogen bonding D dative covalent bond

3 Tampines Meridian Junior College 2022 JC2 Preliminary Examination H2 Chemistry [Turn over Answer: C Ethanol can form hydrogen bond to both caffeine and CO2, allowing greater solubility. 5 Which graph does not share the same genera