NJC 2022 A Level Chem Solution

H2 Chemistry TYS 2022 suggested answers Paper 1 Answer Key 1 C 11 D 21 A 2 C 12 C 22 B 3 D 13 B 23 B 4 C 14 B 24 B 5 A 15 C 25 D 6 B 16 C 26 D 7 A 17 A 27 A 8 B 18 C 28 A 9 B 19 B 29 D 10 D 20 30 D 2022 A level Paper 1 suggested answers 1 Ans: C NaF is an ionic compound with strong ionic bonds between Na+ and F− ions. Largest amount of energy is required to overcome strong ionic bond and it has the highest boiling point. CH3CH2CH3, CH3CH2NH2 and CH3CH2OH are covalent compounds with simple molecular structure. CH3CH2CH3 is non-polar with instantaneous dipole-induced dipole (id-id) interaction between its molecules while CH3CH2NH2 and CH3CH2OH are polar with id-id and hydrogen bonding (H-bond) between molecules. Least amount of energy is required to overcome the id-id in CH3CH2CH3 and it has the lowest boiling point. As O is more electronegative than N, the dipole of O−H bond is greater than N−H bond. More energy is required to overcome the stronger H -bond between CH3CH2OH molecules as compared to CH3CH2NH2. Hence boiling point of CH3CH2OH is greater than CH3CH2NH2. 2 Ans: C Electronegativity decreases down the Group. Cl is more electronegative than Br. Statement A is incorrect. Statement B is correct but it does not help to explain the polarity of the bond. Outer shell electrons in Br experience greater shielding effect due to greater number of INNER shell electrons than Cl. Down the Group, the increase in shielding effect and increase in distance of outer shell electron from the nucleus outweighs the increase in nuclear charge. Nuclear attraction towards outer shell electrons decreases down the Group and hence Br is less electronegative than Cl, leading to a polar covalent bond between Br and Cl. Statement C is correct and explain the polarity. Statement D is incorrect, the repulsion between electrons in outer shell is negligible. E.g. repulsion between 4s and 4p electrons. 3 Ans: D pKa = −lgKa, hence Ka = 10−pKa. Data suggests that thioacetic acid has a larger Ka value and dissociates into H+ more readily than ethanoic acid. Statements 1&2 are incorrect. If the solutions are of the same concentration, thioacetic acid (larger Ka) will give a higher [H+]. We can use this information to deduce that the S−H bond is broken more readily than O−H bond. Bond energy values in Data Booklet also support this (O−H 460 kJ mol−1 vs S−H 347 kJ mol−1) Statement 3 is correct.

4 Ans: C pV = nRT (Note: p in Pa, V in m3, T in K) total mol of gas, n = pV RT = 3.55 ´ 107 ´ 5 ´ 10-3 8.31 ´ (20+273) = 72.9 mol Since the gas contains equal amount of O2 and N2O, amount of N2O = 36.45 mol Mass of N2O used = 36.45  (14.0  2 + 16.0) = 1604 g  1.60 kg 5 Ans: A Solution of AlCl3 is pH 3 due to significant cation hydrolysis, dissociated H+ can react with Na2CO3 to give effervescence of CO2(g). Solution of MgCl2 is pH 6.5 due to slight cation hydrolysis, it is