EJC 2020 GCE A Level 8873 H1 Chemistry Paper 1 Suggested Solution

Eunoia Junior College 8873 H1 Chemistry 2020 Paper 1 Suggested Solution 1 Isotopes have the same number of protons, but different number of neutrons  A or C Since the two particles have different charges, the difference between the number of protons and electrons must be different.  C 2 Examine the number of p, n and e 58 3 28Ni  60 2 28Ni  62 2 28Ni  64 3 28Ni  p 28 28 28 28 n 30 32 34 36 e 25 26 26 25 m 9.712×1026 1.005×1025 1.038×1025 1.072×1025  C 3 A : The 3d subshell can hold a maximum of 10 electrons. The shell with principal quantum number 3 can hold a maximum of 2 (3s) + 6 (3p) + 10 (3d) = 18 electrons. B : According to Aufbau principle, electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. C : The order of filling the orbitals is 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s … … D : In atoms of transition elements, the electronic configuration is [Ar] 3dn 4s2 or [Ar] 3d5 4s1 (Cr), with n = 1–9  B 4 Within the same principal quantum shell n, the energy of the orbitals is in the order: ns < np < nd < nf and there are 1 s orbital, 3 p orbitals, 5 d orbitals and 7 f orbitals in each principal quantum shell.  A 5 Gaseous HC l has a simple molecular structure with a polar covalent bond between H and the electronegative atom Cl, i.e. uneven sharing of a pair of electrons between the two nuclei, with a resultant partial plus charge on the H and a partial minus charge on the Cl.  C 6  C 7  A 8 By definition, bond energy is the energy needed to break one mole of the gaseous bond. Covalent bond length:  A 9 Arrhenius acid produces H+(aq), while Arrhenius base produces OH–(aq).  D 10 For an indicator to show the end-point of a titration, the working pH range of the indicator must lie within the region of rapid pH change during the titration.  A 11 Blood contains the H2CO3/HCO3– buffer. To maintain the pH of blood, the conjugate base HCO 3– must remove H 3O+ from the lactic acid produced during exercise: HCO3– + H3O+  H2CO3 + H2O  C 12 A : Since both I and Xe does not conduct electricity and have rather low boiling points, both I and Xe exists as simple molecules. B : Te is only a semi-conductor (like Si), so it is a metalloid with a giant covalent structure. C : Period 3 only contains 3 metal lic elements, Na, Mg and Al, while there are at least 5 metallic elements (high electrical conductivity and high boiling point) in Period 5. D : Rubidium in Group 1 is a metal despite having a melting point below 1000 K.  C 13 1 : Electronegativity of the halogen decreases down the group, all are more electronegative than H. Hence the difference in electronegativity decreases down the group. 2 : Down the group, the atomic (covalent) radius increases, hence the bond length is longer, with the bonding pair of electrons getti