O-LevelChemistryAcids, Bases & Salts5070/11 · May/June 2023 · Q161 Mark
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?
ApH: decreases, colour of solution shifts towards: colour X
BpH: decreases, colour of solution shifts towards: colour Y
CpH: increases, colour of solution shifts towards: colour X
DpH: increases, colour of solution shifts towards: colour Y
✓ Correct answer
B: pH: decreases, colour of solution shifts towards: colour Y
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