An alkali is titrated against an acid with methyl orange as indicator, which of the following is a correct combination ?
| Base | Acid | End point | |
|---|---|---|---|
| (1) | Strong | Strong | Pink to colourless |
| (2) | Weak | Strong | Colourless to pink |
| (3) | Strong | Strong | Pinkish red to yellow |
| (4) | Weak | Strong | Yellow to pinkish red |
- (A)Strong base, Strong acid, Pink to colourless
- (B)Weak base, Strong acid, Colourless to pink
- (C)Strong base, Strong acid, Pinkish red to yellow
- (D)Weak base, Strong acid, Yellow to pinkish red✓ Correct
Answer: (D)
Solution
Methyl orange changes colour over roughly pH to , showing yellow in the less acidic region and turning pinkish-red once the solution becomes distinctly acidic, so it suits a titration that ends on the acid side, as a weak base against a strong acid does. Such a titration starts basic and yellow and reaches its end point when the solution just turns acidic and pinkish-red, so the correct combination is a weak base and a strong acid with the colour change from yellow to pinkish-red.
JEE Main · 2018 · 08 Apr 2018 · Offline · Single correct option