Reactions of metals with water

3 marks · Easy

Potassium reacts vigorously when added to a trough of cold water.

(a)

Describe two observations you would make during this reaction.

[2 marks]

(b)

Name the gas produced in this reaction.

[1 mark]

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.

Show answer

(a) — · must show Fizzing, Lilac flame, Potassium moves on surface, Melts into a ball, Hissing sound

(b) Hydrogen · must show Hydrogen

Common mistakes: Omitting flame or explosion; naming oxygen as the gas produced.

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · States one correct observation: e.g. 'The potassium moves rapidly across the surface' or 'bubbles of gas are produced.'

B2 (a) · 1 mark · States a different valid observation: e.g. 'A lilac flame is seen' or 'the potassium melts into a ball.'

B1 (b) · 1 mark · Names the gas produced as hydrogen.

Worked solution

a) Two possible observations:

- The potassium moves quickly on the surface of the water.

- A lilac-coloured flame appears.

b) The gas produced is hydrogen.