Chemistry · May / June 2025 · Paper 12 · Question 20

The diagram shows the change in pH as a strong alkali is added to a weak acid. [graph: pH vs volume of strong alkali / cm³] 40 cm³ of a strong alkali is added to a weak acid and a sample of the solution is tested separately with methyl orange and thymolphthalein. Which row is correct?

1. Amethyl orange test: red; thymolphthalein test: colourless
2. Bmethyl orange test: yellow; thymolphthalein test: colourless
3. Cmethyl orange test: red; thymolphthalein test: blue
4. Dmethyl orange test: yellow; thymolphthalein test: blue

As printed in the paper