CIE A Level Chemistry (9701) Solved Past Paper May/June 2019 P22
1b ) Le Chatelier’s Principle is iif any factors affecting equilibrium has been changed, equilibrium shifts to the side which opposes that change. If temperature gets increased, equilibrium would shift to the side which decreases temperature i.e endothermic reaction.
2 ci) Bronsted-Lowry acid states that acid is a proton donor and Bronsted-Lowry base theory states that base is a proton acceptor.
2 cii) Conjugate acid is found on the right of the equation and is the one which will lose a Hydrogen atom and form product on the left. Conjugate base is the one which gains Hydrogen atom. In this question, H3O+ is a conjugate acid because it loses H+ and forms H2O while Cl-is a conjugate base because it gains H+ to form HCl.
3 ai) NaCl and MgCl2 dissolve in water and keeping pH constant while Al2Cl6, SiCl4 and PCl5 hydrolyze into water giving off HCl fumes
4d) Free radical substitution reaction for Methane is as follows:
- Initiation——–> Cl2=Cl* + Cl*
- Propagation—–> CH4 + Cl*= HCl + CH3*
CH3* + Cl2= Cl* + CH3Cl
(This continues until no more radicals form)
- Termination——> Cl* + Cl*=Cl2
CH3* + CH3*= C2H6
5 aii) To form ester from a carboxylic acid and an alcohol, concentrated H2SO4 is to be used + heat under reflux. If the process reverses then heat+ dilute H2SO4 along with H+ or OH- can be used depending upon the products forming. If an acid and alcohol are desired then H+ can be used or if a salt and alcohol are desired then OH- can be used.