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Rates, equilibrium and pH

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Question 21

The equilibrium equation for an indicator, HIn\text{HIn}HIn, is shown below:

HIn(aq)⇌In−(aq)+H+(aq) \text{HIn(aq)} \rightleftharpoons \text{In}^-\text{(aq)} + \text{H}^+\text{(aq)} HIn(aq)⇌In−(aq)+H+(aq)
  • Colour of HIn(aq)\text{Colour of HIn(aq)}Colour of HIn(aq): Yellow
  • Colour of In−(aq)\text{Colour of In}^-\text{(aq)}Colour of In−(aq): Blue

A student adds a few drops of this indicator to a beaker containing 25.0 cm3 of 0.10 mol dm-3 aqueous sodium hydroxide, causing the solution to turn blue. An excess of 0.10 mol dm-3 hydrochloric acid is then slowly added to the beaker with continuous stirring.

Which statement describes the colour change of this solution during the addition of the acid?

The colour changes from blue to yellow.

The colour changes from blue to green and then to yellow.

The colour changes from yellow to green and then to blue.

The colour remains blue throughout the titration.

Rates, equilibrium and pH Questions

  1. A Level
  2. /Chemistry
  3. /Rates, equilibrium and pH