The Halogens
6 marks · NormalState the physical state and color of chlorine at room temperature.
Describe what you would observe when chlorine gas is bubbled through a solution of potassium iodide.
Write a balanced chemical equation for the reaction in part b.
Explain why this reaction happens in terms of the reactivity of the halogens.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) A green gas
(b) The solution turns brown as iodine is formed.
(c) 2KI(aq) + Cl2(g) \rightarrow 2KCl(aq) + I2(aq)
(d) Chlorine is more reactive than iodine, so it displaces iodine from potassium iodide.
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Marking points
B1 (a) · 1 mark · States both the correct physical state (gas) and color (green) for chlorine at room temperature.
B1 (b) · 1 mark · Observation that a brown solution forms (accept orange/brown or brown color).
B1 (b) · 1 mark · States that iodine is formed or released.
M1 (c) · 1 mark · Correct reactants and products identified in word or symbol equation.
A1 (c) · 1 mark · Correct balanced chemical equation: 2KI(aq) + Cl2(g) → 2KCl(aq) + I2(aq).
B1 (d) · 1 mark · States or explains that chlorine is more reactive than iodine, so it displaces iodine.
Worked solution
a) Chlorine at room temperature is a green gas.
b) When chlorine gas is bubbled through potassium iodide solution, the solution turns brown as iodine is formed.
c) The equation above shows chlorine displacing iodine from potassium iodide.
d) This happens because chlorine is more reactive than iodine, so chlorine displaces iodine from the compound.