The diagram shows a swimming-pool controller adding a small amount of acid to pool water. The controller keeps the pH within a safe range so that chlorine d...
Question 1 Report
The diagram shows a swimming-pool controller adding a small amount of acid to pool water. The controller keeps the pH within a safe range so that chlorine disinfectant works well without irritating swimmers' eyes.
(a) Name the pH of a neutral solution at room temperature. [1]
(b) Use the term alkaline to describe pool water with pH 8.2. [1]
(c) Explain why adding acid decreases the pH of the pool water. [2]
The diagram shows a student using red cabbage indicator to compare household liquids. Cabbage indicator is purple before it is mixed with a solution. The student is investigating lemon juice, washing-up liquid and distilled water.
(a) Name the type of substance that turns cabbage indicator red or pink. [1]
(b) Describe the expected indicator colour in distilled water. [1]
(c) Explain why washing-up liquid is likely to have a pH above 7. [2]
(d) Use the term alkali to describe a soluble base. [1]
Answer Details
pH, acids, and alkalis
For pool water: (a) A neutral solution at room temperature has pH 7. [1] (b) Pool water of pH 8.2 is alkaline. [1] (c) Acid adds hydrogen ions to the water. This increases hydrogen-ion concentration, so pH falls. [2]
For cabbage indicator: (a) An acid turns cabbage indicator red or pink. [1] (b) Distilled water is neutral, so the indicator remains purple. [1] (c) Washing-up liquid is likely to be alkaline, or a base. Alkaline solutions have pH values greater than 7. [2] (d) An alkali is a base that dissolves in water. [1]
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