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Correct swimming pool maintenance requires regular monitoring of the pH level of the water - HSC - SSCE Chemistry - Question 23 - 2006 - Paper 1
Question 23
Correct swimming pool maintenance requires regular monitoring of the pH level of the water. (a) Select the best indicator from the graph to check that the pH of swi... show full transcript
Worked Solution & Example Answer:Correct swimming pool maintenance requires regular monitoring of the pH level of the water - HSC - SSCE Chemistry - Question 23 - 2006 - Paper 1
Step 1
Select the best indicator from the graph to check that the pH of swimming pool water lies within the correct range of 7.0 – 7.6. Justify your choice.
Answer
The best indicator to check the pH of swimming pool water, which needs to remain between 7.0 and 7.6, is Bromothymol blue. This indicator changes color from yellow at pH 6.0 to blue at pH 7.6. In the range of 7.0 to 7.6, Bromothymol blue will be greenish-yellow to green, which provides a clear indication that the pH is within the acceptable range.
Step 2
Step 3
Explain how the addition of sodium hypochlorite will affect the pH of the water in the pool.
Answer
The addition of sodium hypochlorite (NaOCl) introduces hypochlorite ions (OCl⁻) into the pool water, which can react with water to produce hypochlorous acid (HOCl) and hydroxide ions (OH⁻). The reaction is as follows:
The production of hydroxide ions will increase the pH of the water, making it more basic.