2:28 describe the use of litmus, phenolphthalein and methyl orange to distinguish between acidic and alkaline solutions

Indicators are substances which change colour in response to a change in pH (acid or alkali).

Indicator	Colour in acidic solution [H⁺]	Colour in alkaline solution [OH^-]
Litmus	Red	Blue
Methyl orange	Red	Yellow
Phenolphthalein	Colourless	Pink

Methyl orange is orange in a neutral solution

Past paper questions on spec point:

Spec	Q'stion	Ans	MS
2:28	Jan '12 (2), Q 5 b	Answer	MkS
2:28	Jan '14 (1), Q 8 c iii	Answer	MkS
2:28	Jan '15 (1), Q 11 a ii	Answer	MkS
2:28	Jan '16 (2), Q 5 b iii	Answer	MkS
2:28	Jan '17 (1), Q 5 b iv	Answer	MkS
2:28	Jan '17 (1), Q 5 b v	Answer	MkS
2:28	Jan '17 (1), Q 7 b	Answer	MkS
2:28	Jan '17 (2), Q 4 a	Answer	MkS
2:28	Jan '18 (1), Q 7 c ii	Answer	MkS
2:28	Jan '18 (2), Q 1 b	Answer	MkS
2:28	Jan '18 (2), Q 1 c	Answer	MkS
2:28	May '10 (2), Q 6 a iii	Answer	MkS
2:28	May '14 (1), Q 15 b ii	Answer	MkS
2:28	May '15 (1), Q 3 c i	Answer	MkS
2:28	May '15 (1), Q 3 c ii	Answer	MkS
2:28	May '15 (1), Q 8 b	Answer	MkS
2:28	May '15 (1), Q 8 c	Answer	MkS
2:28	May '15 (1R), Q 4 b iii	Answer	MkS
2:28	May '15 (2R), Q 4 a iii	Answer	MkS
2:28	May '16 (2), Q 6 c	Answer	MkS
2:28	May '16 (2R), Q 5 c i	Answer	MkS
2:28	May '17 (1R), Q 14 b ii	Answer	MkS