RI 2018 A-Level H2 Chem Solution

This document is copyrighted, please do not reproduce it without permission © Raffles Institution 2018 A-Level H2 Chemistry Paper 1 Suggested Solutions 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 D D D B C D C C C B C D A A A 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 A B A C D C A B D A B B C D D Q1 (D) Particle Direction of deflection Angle of deflection proton (positively charged) towards the negatively charged plate x° ( x° < y°) electron (negatively charged) towards the positively charged plate y° Since angl e of deflection ∝ � charge mass �, and a proton is heavier than an electron, the angle of deflection for proton is smaller, i.e. x° < y°. Q2 (D) The high charge density of Al3+ causes the distortion of the electron cloud of C l– to such an extent that electron sharing becomes predominant. Hence AlCl3 and A l2Cl6 are predominantly covalent compounds i.e. they exist as discrete molecules. Al2Cl6 is formed from the dimerisation of A lCl3, in which one C l atom of each AlCl3 donates a pair of electrons to the vacant, low -lying orbital of the A l atom in the neighbouring A lCl3 to form a dative covalent/coordinate bond (represented by ' →' from the Cl donor atom to the Al acceptor atom). Q3 (D ) Since the electronegativity of C, Se and C l are all different, all three molecules contain polar covalent bonds. Molecule no. of lp & bp Shape Bond dipoles cancel? Polar? CSe2 2 bp linear yes × SeCl2 2 bp 2 lp bent no √ CCl4 4 bp tetrahedral yes × Q4 (B ) Cs+, I− and Xe are isoelectronic species (i.e. with same total number of electrons) ⇒ their outermost e− experience the same shielding effect. However, nuclear charge of Cs+ > Xe > I−. ∴E lectrostatic attraction between the nucleus and the outermost e− of Cs+ > Xe > I−. ∴ E nergy required to remove the outermost e − decreases in the order: ∆H1 > ∆H3 > ∆H2 Q5 (C ) A Incorrect. (A mole of substance is the amount of that substance which contains as many elementary entities as there are carbon atoms in 12 g of carbon-12.) Since 1 mole of compound (e.g. CO 2) contains more than 1 mole of atoms (e.g. 1 mole of C and 2 moles of O atoms), it will not contain the same number of atoms as there are atoms in 12 g of carbon-12. B Incorrect. Relative isotopic mass = mass of 1 atom of the isotope 1 12 × mass of 1 atom of carbon-12 C Correct. Relative atomic mass = (weighted) average mass of 1 atom of the element 1 12 × mass of 1 atom of carbon-12 D Incorrect. Relative molecular mass = (weighted) average mass of 1 molecule of the substance 1 12 × mass of 1 atom of carbon-12 Q6 (D ) Atomic radius decreases across a period and increases down a group. Group Period 1 13 17 4 K Br 5 Rb In ∴ Rb has the largest atomic radius

This document is copyrighted, please do not reproduce it without permission © Raffles Institution Q7 (C ) At sea le