past paper notes

Question 1

Describe the trend in the reactivity of the halogens Cl 2, Br2 and I2 as oxidising agents.
Explain this trend using values of Eo
(X2 /X–) from the Data Booklet. /2

Answer 1

Cl2 is a good oxidising agent and I2 is a poor oxidising agent as compared to Cl2. oxidising power of halogens decreases down the groups

as the E value for X2/X- decreases down the group

Question 2

Kpc for hydrophobic compounds is larger

Question 3

Suggest the sign of the entropy changes, ΔSo
, for each of the two types of polymerisation.
Explain your answers.

Answer 3

1) ΔSo
for addition polymerisation:
-Will be negative as many gas molecules are combining to form a large molecule

2) ΔSo
for condensation polymerisation:
- positive as water forms

Question 4

enthalpy change, ΔHo
formula

Answer 4

bonds broken - bonds formed

Question 5

State one natural and one man-made occurrence of oxides of nitrogen. /1

Answer 5

natural: lighting

man made: burning of fossil fuels

Question 6

Explain why the solubility of the Group 2 hydroxides, M(OH)2, increases down the group./3

Answer 6

delta H and delta hyd becomes less exothermic down the group

delta latt decreases more than delta hyd

delta sol becomes more exothermic

Question 7

The sulfates of Group 2 elements become less soluble down the group.
Explain this trend./3

Answer 7

H latt and H hyd gets more exo down the group

H hyd decreases by a larger value

H sol gets less exothermic

Question 8

Explain why most copper(II) salts are coloured. /4

Answer 8

d orbitals split into two levels by repulsion of approaching ligands

light absorbed

and complementary colour seen

electron promoted

Question 9

Suggest why copper(I) salts are usually white

Answer 9

all orbitals in Cu are full

Question 10

Explain the origin of the colour in transition element complexes. /4

Answer 10

d subshell splits into two sets of d orbitals of different energy

wavelength of light absorbed

electron promoted

complementary colour seen

Question 11

The two complex ions [Fe(CN)6]
4– and [Fe(CN)5NO]2– are different colours.

Explain why the colours of the two complex ions are different. /2

Answer 11

Different energy gap

different wavelength of light absorbed

Question 12

State and explain the trend in the thermal stability of the Group 2 carbonates down the
group. /3

Answer 12

increases down the group

as the ionic radii increases so less force of attraction between nucleus and valence electron

less distortion of CO3 2- anion

Question 13

lattice energy gets less exo across the period

lattice energy gets more exo down the group

Question 14

Write two equations to show how a solution containing gallic acid, C7H6O5, and gallate
ions, C7H5O5–
, acts as a buffer.

Answer 14

C7H6O5 + OH- —–C7H5O5- + H+

H+ + OH- H2O

C7H6O5- + H+ —- C7H6O5

Question 15

d orbital energy levels in octahedral
and in tetrahedral complexes from degenerate d orbitals

Answer 15

in an octahedral complex:
two orbitals in higher energy
level
and three orbitals in lower energy
level

in a tetrahedral complex:
three orbitals in higher energy level
and two orbitals in lower energy level

Question 16

Describe the action of cisplatin as an anticancer drug. /2

Answer 16

binds to DNA

which prevents DNA Replication

Question 17

Suggest why carboplatin does not show cis-trans isomerism. /1

Answer 17

atoms in a bidentate can only bond 90degree not 180 degree

Question 18

Kpc of non polar molecules is lower

Question 19

Describe the trend in the first electron affinity of the Group 16 elements S to Te.
Explain your answer. /2

Answer 19

electron affinity gets less exo down the group as the ionic radii increases

Question 20

Explain why transition elements have variable oxidation states /1

Answer 20

the d and s subshells are closer in energy

Question 21

Explain why transition elements can form complex ions. /1

Answer 21

incomplete d subshell orbital present that accept a lone pair

Question 22

The first electron affinity of an atom is usually an exothermic process, whereas the second
electron affinity is an endothermic process.
Suggest why.

Answer 22

energy required to overcome the repulsion between electron and anion

Question 23

describe the mode of action of a heterogenous catalyst in a reaction? /3

Answer 23

adsorption of reactants to the surface of the catalyst

bonds in the reactants weaken (lowering the activation energy)

reaction occurs and the products are desorbed

Question 24

A salt bridge is used in an electrochemical cell.
State the function of the salt bridge. Explain your answer. /1

Answer 24

ions move to maintain charge balance