pH and indicators
3 marks · Easy| Solution | Litmus (colour) | Methyl orange (colour) | Phenolphthalein (colour) |
|---|---|---|---|
| A | red | red | colourless |
| B | blue | yellow | pink |
| C | blue | yellow | colourless |
Use the table to answer the following questions about solutions A, B, and C.
Which solution is acidic?
Which solution is alkaline?
Which indicator could you use to distinguish solutions B and C? State the colour it would show for each.
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) A
(b) B
(c) Phenolphthalein; pink in B, colourless in C
Common mistakes: confusing indicator colours
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Identifies A as acidic (from indicators)
B1 (b) · 1 mark · Identifies B as alkaline
B1 (c) · 1 mark · States phenolphthalein as indicator; gives correct colour for both B (pink) and C (colourless)
Worked solution
a. A is acidic: litmus = red, methyl orange = red, phenolphthalein = colourless (these are acidic colours).
b. B is alkaline: litmus = blue, methyl orange = yellow, phenolphthalein = pink (alkali colours).
c. Use phenolphthalein: it is pink in B (alkaline) and colourless in C (neutral or not strongly alkaline).