Question

For a series of indicators, the colours and pH range over which colour change takes place are as follows

Indicator	Colour change over pH range
U	Yellow to blue pH 0.0 to 1.6
V	Red to yellow pH 2.8 to 4.1
W	Red to yellow pH 4.2 to 5.8
X	Yellow to blue pH 6.0 to 7.7
Y	Colourless to red pH 8.2 to 10.0

Which of the following statements is correct?

• A. Indicator V could be used to find the equivalence point for 0.01 M acetic acid and 0.1 M ammonium hydroxide (ammonia solution) titration
• B. Indicator Y coIud be used to distinguish between 0.1 M HCI and 0.001 M NaOH solutions in water
• C. Indicator X could be used to distinguish between solution of ammonium chloride and sodium acetate
• D. Indicator W could be suitable for use in determining the concentration of acetic acid in vinegar by base titration

Answer 1

Answer: (C)

Indicator X could be used to distinguish between solution of ammonium chloride and sodium acetate

From titration curve, it can be seen that

Indicator X could be used to distinguish between solution of ammonium chloride (weak base + strong acid). So X will act as an indicator here & will show color change.

In the case of sodium acetate (weak acid + strong base), X can not be used as an indicator because it will not show color change in that range.