past paper questions

Question 1

describe the stages in a catalytic converter that result in the decrease of emissions of gases.

Answer 1

• CO/NO molecules are adsorbed on the surface of the catalytic converter
• bonds are weakened resulting in a chemical reaction between CO and NO
• CO2/N2 are desorbed from the catalytic surface

Question 2

why do successive ionisation energies increase

Answer 2

because the same number of protons is attracting a decreasing number of electrons

Question 3

enthalpy change?

Answer 3

bonds broken - bond formed

Question 4

what conditions are required for the reaction between chlorine and sodium hydroxide

Answer 4

hot alkali

Question 5

give two reasons why Ssystem is expected to be positive

Answer 5

• there is an increase in the number of moles
• there is a change of state - gas produced from solid

Question 6

why is the wooden block lifted by the flask

Answer 6

• because the reaction is endothermic
• this freezes the water so block attaches to the flask

Question 7

why is the proton only from the carboxylic acid and not the methyl group dpnated to a water molecule

Answer 7

• the loss of a hydrogen from the O−H group is made possible by the delocalisation of charge of/stabilisation on the carboxylate ion

Question 8

give a reason why the ammonium cannot act as a ligand

Answer 8

ammonium ions do not have a lone pair of electrons for bonding

Question 9

explain why there is a significant difference in the lattice energy values for magnesium iodide

Answer 9

• magnesium ion is small and highly charged
• iodide ion has a large ionic radius
• iodide ion is polarised by the magneisum ion
• bonding in magnesium ion has partial covalent character

Question 10

Explain why the melting temperature of silicon(IV) oxide is much higher than that of iodine,
even though the bonding in both is covalent.

3m

Answer 10

• silicon = giant covalent
• strong covalent bonds between layers
• require a lot of energy to be broken
• iodine only has weak london forces that must be broken

Question 11

Explain why both water and carbon dioxide molecules have polar bonds but only water is a polar molecule

4 marks

Answer 11

• oxygen is more electronegative than hydrogen and carbon
• results in polar bond with oxygen being negative and both C and H positive
• CO2 is symmetrical so dipoles cancel out
• lone pair of electrons on ocygen mean dipoles dont cance

Question 12

State, in terms of electrons, why iodine is classified as an oxidising agent in this reaction.

1m

Answer 12

iodine gains electrons