For a series of indicators, the colour 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 followinfg statements is correct ?

Options

A. Indicator `V` could be used to find the equivalence point for `0.01M` acetic and `0.1M` ammonium hydroxide (ammonia solution) titration.
B. Indicator `Y` could be used to distinguish between `0.1M HCI` and `0.01M 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

C

Explanation

a. For the titration of `W_(A)` and `W_(B)`, there is no sharp change in the `pH` value near the end point.
`(pH` varies between `6.0` and `8.0)`
So indicator `V` can not be used. But indicator `X` can be used.
`CH_(3)COOH+NH_(4)OH rArr pH = 7`
b. `{:(0.01MNaOHhArr,pH=13),(0.001MNaOhhArr,pH=11):}]`
`Y` cannot be used. Choose an indicator which has different colour for `pH = 13` and `11`.
c. `X` can be used since it will given different colout in both the solutions. `NH_(4)CI ` (Salt of `S_(A)//S_(A) pH lt7)` and `CH_(3)COONa` (salt of `W_(A)//S_(B) pH gt 7)`.
d. `Y` will be suitable indicator not `W`.
`CH_(3)COOH + Base rArr pH gt 7`.