A level paper 1 mistakes

Question 1

Iron ions form a pale green solution, but zinc ions form a colourless solution.
Explain why zinc ions are colourless.

Answer 1

Zinc ions have a full 3d sub-shell
So electrons cannot move between 3d orbitals

Question 2

Why is the value for enthalpy of neutralisation less for ethanoic acid than HCl or nitric acid?

Answer 2

Some energy is required to break O-H bonds to release H+ ions so the value is less

Question 3

What is a reason why a solid is not included in a Kp expression?

Answer 3

The partial pressure of the solid is constant

Question 4

What is more soluble, potassium hydroxide or barium hydroxide?

Answer 4

Potassium hydroxide

Question 5

Is sodium thiosulfate a strong or weak base?

Answer 5

Weak base

Question 6

What indicator can be used when sodium thiosulfate is a base in a titration?
And what will be the colour change?

Answer 6

Starch

Blue/black to colourless

Question 7

Enthalpy change of neutralisation values:
Ethanoic acid = -55.2 KJmol-1
Hydrochloric acid = -57.1 KJmol-1

Explain this difference.

Answer 7

Ethanoic acid is a weak acid and so only partially ionises.
So some energy is used to fully ionise.

Question 8

Explain why magnesium carbonate decomposes much more readily on heating than barium carbonate.

Answer 8

the magnesium ion/cation is smaller (than the
barium ion/cation) (1)
which polarises the (large) carbonate (ion)/anion (1)
and weakens the carbon-oxygen bond (C-O/C=O) bonds (1)

Question 9

Explain why the first electron affinity becomes less negative from chlorine to iodine.

Answer 9

From chlorine to iodine, atomic radius increases.
In iodine, the electron being added experiences more shielding from the nucleus.
So therefore less attractive force.
The shielding outweighs the increase in nuclear charge.

Question 10

Explain why ethane-1,2-diol is soluble in water.

Answer 10

Hydrogen bonds form with water.
The bonds will be a similar strength to each other.