Acid–alkali indicators
3 marks · EasyA student uses universal indicator solution to test three unknown liquids. The results are recorded in Table 2.
| Liquid | Colour observed |
|---|---|
| A | orange |
| B | green |
| C | purple |
State the likely pH of liquid B, based on the observed colour.
Suggest the type of solution for liquid C (strong acid, weak acid, neutral, weak alkali, strong alkali).
Describe how the universal indicator is used to obtain this information from the liquids.
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) 7
(b) Strong alkali
(c) Add universal indicator to the liquid and compare the resulting colour to a pH chart to estimate the pH type.
Common mistakes: Purple meaning acid
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Marking points
B1 (a) · 1 mark · States pH 7 for green colour (neutral).
B2 (b) · 1 mark · Identifies strong alkali for purple colour.
M1 (c) · 1 mark · Describes adding universal indicator and comparing to chart.
Worked solution
a. Green with universal indicator suggests pH 7, which is neutral. b. Purple with universal indicator suggests a strong alkali (pH 11–14). c. Universal indicator is added to the liquid. The colour that forms is compared to a pH colour chart to find the pH value and thus the type of solution.