Fig. 1 shows a student testing three colourless solutions with universal indicator in a spotting tile. The student adds two drops of each solution to separa...
Question 1 Report
Fig. 1 shows a student testing three colourless solutions with universal indicator in a spotting tile. The student adds two drops of each solution to separate wells, then adds indicator. Solution P turns red, Q turns green and R turns purple. The student thinks P contains hydrochloric acid and R is an alkali. The same dropper is rinsed with distilled water between tests.
(a) Give the pH range that could apply to solution P. [2]
(b) Use the colours to describe which solution is neutral and which is alkaline. [2]
(c) Give one reason why the dropper is rinsed before it is used with the next solution. [2]
Answer Details
(a) Universal indicator turning red shows that solution P is acidic, so it can have any pH below 7, for example pH 1 to 6. [2]
(b) Solution Q is neutral because universal indicator is green at pH 7. Solution R is alkaline, or a base, because it turns purple. [2]
(c) Rinsing the dropper prevents contamination of the next solution with the previous one. This ensures that the indicator colour and pH result remain valid. [2]
Exam reminder: On the universal indicator scale, green means neutral, colours below green towards red show acidity, and colours towards blue or purple show alkalinity.
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