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Rates, equilibrium and pH

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Question 18

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 few drops of this indicator are added to a solution of 0.10 mol dm-3 sodium hydroxide, causing the solution to turn blue. An excess of 1.0 mol dm-3 hydrochloric acid is then slowly added dropwise with stirring until the acid is in excess.

Which statement describes the colour changes observed in the solution?

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

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

The colour changes from blue directly to yellow.

The colour stays blue.

Rates, equilibrium and pH Questions

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