2021 paper 1 PPE

Question 1

Compare the electrical conductivities of solid and aqueous barium chloride. (2)

Answer 1

• barium chloride doens’t conduct when solid because the ions are immobile
• can conduct when in an aqueous solution because ions are mobile

Question 2

Describe the use of aqueous barium chloride in qualitative analysis. (2)

Answer 2

• test for sulfate
• white precipitate forms

Question 3

Why do Br2 and I2 not exist in the gaseous state under standard conditions. (1)

Answer 3

• induced d.p-d.p forces b/w molecules

Question 4

Explain how electrical conductivity occurs in Mercury(II) Bromide and mercury, in solid and molten states. (5)

Answer 4

• mercury bromide conducts when molten but not solid

^ bcs ions are mobile in molten HgBr2
^ but fixed in a lattice in solid HgBr2

• Mercury conducts in both solid & molten states
  ^ bcs delocalised electrons can move in both

Question 5

Explain why iodine is less reactive than bromine. (3)

Answer 5

• iodine has a larger atomic radius
• iodine has less nuclear attraction
• iodine has greater shielding