EJC 2021 GCE A-Level H1 Chemistry Paper 1 Suggested Solution

Eunoia Junior College 8873 H1 Chemistry 2021 Paper 1 Suggested Solution 1 Atom Q has 70 n + p and 10 more n than p. Thus there are 40 n and 30 p  Q is 30Zn. Atom R has 70 n + p and 2 fewer n than Q. Thus there are 38 n and 32 p  R is 32Ge.  A 2 Small jump between 4 th and 5 th I.E. and large jump between 6th and 7th I.E.  ns2 np4 configuration  Group 16  C 3 A : B : C : D ✓:  D 4 Since N is in Group 15 with 5 valence electrons, N gains 3 electrons to give the monatomic nitride anion, N3–, with an octet. For electrical neutrality, the formula of the solid is (Zy+)3(N3–)y. If the solid is ZN 3, y = 9 which is not possible since Z9+ does not exist. If the solid is Z 3N, y = 1 which is possible for Z+ cations.  B 5 Cyanogen is 1 ✓: There are two  bonds about each C, hence a linear molecule. 2 ✓: There are 4  bonds and 3  bonds. 3 : There are only two lone pairs of electrons, one on each N atom.  B 6 Boiling point of Br 2 is higher than that of CH3CH2Br  stronger IMF in Br2 The Br –C bond in Br –CH2CH3 is polar, while the Br–Br bond in Br2 is non-polar  id-id and pd-pd in CH3CH2Br, and id-id in Br2 [statement 1] Br2 (Mr = 159.8) has a larger and more polarisable electron cloud [statement 4] compared to CH3CH2Br ( Mr = 108.9)  stronger id-id in Br2  B 7 1 ✓: When pressure is increased, the gas particles are forced closer together and the strength of IMF increases. If the IMF becomes sufficiently strong such that the potential energy overcomes the kinetic energy at room temperature, the gas will liquefy. 2 : At high pressure, the gas particles are forced closer together and the strength of IMF becomes significant. When the potential energy overcomes the kinetic energy, the gas will liquify. 3 ✓: At low temperature, the kinetic energy of the gas particles is lower. If the kinetic energy becomes sufficiently low, such that the potential energy due to the IMF becomes more significant, the gas will liquify.  B 8 The weaker bond is more reactive as it would takes less energy to break the bond, leading to a decrease in the activation energy. A more polar bond is more reactive as the partial charges will be sites of reactivity, attracting species of the opposite charge, again lowering the activation energy.  D 9 A : HCl(aq) is an Arrhenius acid as it produces H+(aq) in solution. But CuO is not an Arrhenius base as it is insoluble and does not produce OH–(aq). B : The reaction does not take place in aqueous medium, hence does not involve Arrhenius acid and base. C : HCl(aq) is an Arrhenius acid as it produces H +(aq) in solution. But CaCO3 is not an Arrhenius base as it is insoluble and does not produce OH–(aq). D ✓: HCl(aq) is an Arrhenius acid as it produces H +(aq) in solution, and KOH(aq) is an Arrhenius base as it produces OH–(aq) in solution.  D 10 ( ) ( ) ( )2H O H aq OH aq+− +l