Chemistry · May / June 2023 · Paper 11 · Question 16

Universal indicator contains several dyes. The reversible reaction of one dye, IndOH, is shown. IndOH(aq) + H⁺(aq) ⇌ Ind⁺(aq) + H₂O(l) colour X colour Y A few drops of universal indicator solution are added to 50 cm³ of water. A few drops of dilute hydrochloric acid are added to the solution. Which row describes what happens when the acid is added?

1. ApH decreases; colour of solution shifts towards colour X
2. BpH decreases; colour of solution shifts towards colour Y
3. CpH increases; colour of solution shifts towards colour X
4. DpH increases; colour of solution shifts towards colour Y

As printed in the paper