Acid–alkali indicators

2 marks · Normal

You are given a colourless solution that could be either hydrochloric acid or sodium hydroxide solution. Describe how you would use universal indicator to help identify which solution is which.

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Also accept: Universal indicator red = acid, blue = alkali

Common mistakes: Not linking the colour to the specific chemical

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Marking points

M1 · 1 mark · States to add universal indicator to the solution

A1 · 1 mark · States acid (HCl) gives red/orange; alkali (NaOH) gives blue/purple colour

Worked solution

Add universal indicator to the solution. If it turns red, the solution is hydrochloric acid; if it turns blue or purple, the solution is sodium hydroxide.