Alevel questions

Question 1

Explain what is meant by enthalpy change of solution

Answer 1

For 1 mole of a compound to dissolve

Question 2

How to determine the maximum temperature in K for feasibility

Answer 2

Delta H / Delta S

Question 3

How to plot a graph with rate and concentration

Answer 3

Rate on y axis and concentration on x axis

Question 4

What happens to kp when temperature increases in exothermic reaction and to pressure and catalyst

Answer 4

• Temperature increases so Kp decreases
• Kp stays the same in pressure
• ratio of products to reactants remains the same and so there is no change in Kp

Question 5

What is the equation using ln A

Answer 5

ln A = ln k + Ea / RT

Question 6

What is meant by the term rate determining step

Answer 6

The slowest step

Question 7

How to determine whether the acid is strong or weak with ka and pea values

Answer 7

Higher Ka value and lower pKa = stronger acid

Question 8

State and explain the relative difference in the Ka value of a strong acid compared with that of a weak acid.

Answer 8

Strong acid will have a higher Ka value compared to weak acid.
This is because strong acid dissociate fully in water.
Weak acid only partially dissociate in water

Question 9

Describe how the student could calibrate the pH meter before use

Answer 9

Place the bulb of the pH meter into distilled water and allow the reading to settle.
Adjust the reading on the pH meter so that it reads 7.0
Rinse the probe with distilled water between each reading

Question 10

State the meaning of the term bronstead Lowry base

Answer 10

Proton acceptor

Question 11

Propanoic acid has Ka 1.34 * 10^-5
Hydrofluoric acid has Ka 5.6 * 10^-4

Explain why using Ka to calculate the pH of solution of hydrofluoric acid would give a less accurate result than the same calculation for propanoic acid

Answer 11

Hydrofluoric acid has a larger Ka value than propanoic acid and so is a stronger acid.
Hydrofluoric acid dissociates more in solution than propanoic acid
The difference between undissociated and equilibrium becomes larger and the assumption that undissociated = equilibrium becomes less accurate.

Question 12

Why is graphite soft

Answer 12

It has layers which can slide
There are weak London forces between the layers

Question 13

Explain what is meant by the term salt

Answer 13

When the H+ in an acid is replaced by a metal ion

Question 14

What does (V) represent in chloric (V) acid?

Answer 14

Oxidation number of chlorine

Question 15

State the charge carriers that transfer current
through wire
through solution in electrochemical cells

Answer 15

Wire - electrons
Solution - ions

Question 16

Fuel cells are a type of electrochemical cell being developed as a source of energy.
1. State one important difference between a fuel cell and a conventional electrochemical cell.
2. Write the equation for the overall reaction that takes place in a hydrogen fuel cell.
3. State two ways that hydrogen might be stored as a fuel for cars
4. Suggest why some people consider that the use of hydrogen as a fuel consumes more energy than fossil fuels.

Answer 16

1. Fuel cell converts energy from reaction of a fuel with oxygen into a electrical energy
2. 2H2 + O2 –> 2H2O
3. Hydrogen can be stored at low temperature, in liquid form. Hydrogen can be absorbed within solid
4. Energy is needed to make the hydrogen fuel cell

Question 17

Suggest another process that might be used in the future to obtain hydrogen gas of the Haber process

Answer 17

Electrolysis of water

Question 18

What is meant by the term ligand?

Answer 18

A molecule or ion that donates a pair of electrons to a central metal ion to form a coordinate bond