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1.15 Halogen displacement reactions

6 exam questions worth 13 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.

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1
Multiple choice [1 mark]

Which mixture would react?

Choose one answer.

Correct Not quite: the answer is Chlorine water and potassium iodide solution

Mark scheme

C

Model answer

C: chlorine is more reactive than iodine, so it displaces iodine from potassium iodide.

2
Short answer [2 marks]

Chlorine water is added to colourless potassium bromide solution.

Describe what you would see and name the coloured product.

Mark scheme

  • solution turns orange / yellow-orange (1)
  • bromine (1)

Model answer

The colourless solution turns orange because bromine is formed.

Your mark
3
Short answer [2 marks]

Write a balanced symbol equation for the reaction between bromine and potassium iodide.

Mark scheme

  • correct formulae: Br2, KI, KBr, I2 (1)
  • balanced: Br2 + 2KI → 2KBr + I2 (1)

Model answer

Br2 + 2KI → 2KBr + I2

Your mark
4
Extended response [3 marks]

Explain why bromine does not react with potassium chloride solution.

Mark scheme

  • bromine is less reactive than chlorine (1)
  • bromine atoms are larger / outer shell further from nucleus, so attract electrons less strongly (1)
  • so bromine cannot gain electrons from chloride ions / cannot displace chlorine (1)

Model answer

Bromine is less reactive than chlorine. Its outer shell is further from the nucleus, so it attracts electrons less strongly than chlorine does, and cannot take electrons from chloride ions to displace chlorine.

Your mark
5
Short answer [3 marks]

Higher tier.

The ionic equation for the reaction of chlorine with iodide ions is:

Cl2 + 2\mathrm{I^-} → 2\mathrm{Cl^-} + I2

Identify which substance is oxidised and which is reduced. Explain your answer in terms of electrons.

Mark scheme

  • iodide ions are oxidised (1)
  • because they lose electrons (1)
  • chlorine is reduced because it gains electrons (1)

Model answer

Iodide ions are oxidised because they lose electrons to form iodine. Chlorine is reduced because it gains electrons to form chloride ions.

Your mark
6
Required practical [2 marks]

A student mixes halogen solutions with potassium halide solutions.

Give one safety precaution and explain why it is needed.

Mark scheme

  • use a fume cupboard / good ventilation, OR wear eye protection, OR avoid skin contact (1)
  • because halogens are toxic / harmful / irritant (1)

Model answer

Work in a fume cupboard, because halogens such as chlorine are toxic.

Your mark
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