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)