Acid–alkali indicators
4 marks · NormalState the colour of each indicator in an acidic solution.
| Indicator | Colour in Acidic Solution |
|---|---|
| Litmus | |
| Methyl orange | |
| Phenolphthalein | |
| Universal indicator |
State the colour of phenolphthalein in an alkaline solution.
Name an indicator which is purple in a neutral solution.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) — · must show Litmus: red, Methyl orange: red, Phenolphthalein: colourless, Universal indicator: red
(b) pink · must show pink
(c) litmus · must show litmus
Also accept: Accept 'colourless' for phenolphthalein in acid
Common mistakes: Mixing up colours of indicators
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct colour of litmus, methyl orange, and universal indicator in acidic solution (any two correct for the mark).
B2 (a) · 1 mark · Correct colour of phenolphthalein in acid.
B3 (b) · 1 mark · Phenolphthalein in alkali: pink.
B4 (c) · 1 mark · Litmus is purple in a neutral solution.
Worked solution
| Indicator | Colour in Acidic Solution |
|---|---|
| Litmus | red |
| Methyl orange | red |
| Phenolphthalein | colourless |
| Universal indicator | red |
Phenolphthalein in alkaline solution: pink.
Litmus is purple in a neutral solution.