1. pH at which it changes colour
Indicators
Different indicators change colour at different pHs. This means that not all indicators are suitable for distinguishing between solutions with different pHs.
Indicator name
pH at which it changes colour
Colour at lower pH
Colour at higher pH
Methyl yellow
3.5
Red
Yellow
Bromocresol green
4.7
Blue
Bromothymol blue
7.0
Phenolphthalein
9.3
Colourless
Use the information above to work out the colour of the indicator at a particular pH:
phenolphthalein at pH 11
bromocresol green at pH 3
Use the information to work out the best indicator to use to distinguish between:
A solution with a pH of 4.0 and one with a pH of 5.0.
A solution with a pH of 6.0 and one with a pH of 9.
Would you be able to use phenolphthalein to distinguish between a solution with a pH of 11.0, and one with a pH of 12.0? Explain your answer.

2. pH at which it changes colour
Indicators
Answers
Indicator name
pH at which it changes colour
Colour at lower pH
Colour at higher pH
Methyl yellow
3.5
Red
Yellow
Bromocresol green
4.7
Blue
Bromothymol blue
7.0
Phenolphthalein
9.3
Colourless
Use the information above to work out the colour of the indicator at a particular pH:
phenolphthalein at pH 11 Red
bromocresol green at pH 3 Yellow
Use the information to work out the best indicator to use to distinguish between:
A solution with a pH of 4.0 and one with a pH of 5.0. Bromocresol green
A solution with a pH of 6.0 and one with a pH of 9. Bromothymol blue
Would you be able to use phenolphthalein to distinguish between a solution with a pH of 11.0, and one with a pH of 12.0? Explain your answer.
No, the indicator would be red in both solutions.