Some Basic Concepts of Chemistry 2 Question 10
10. An alkali is titrated against an acid with methyl orange as indicator, which of the following is a correct combination?
(2018 Main)
| Base | Acid | End point | |
|---|---|---|---|
| (a) | Weak | Strong | Colourless to pink |
| (b) | Strong | Strong | Pinkish red to yellow |
| (c) | Weak | Strong | Yellow to pinkish red |
| (d) | Strong | Strong | Pink to colourless |
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Solution:
- Methyl orange show Pinkish colour towards more acidic medium and yellow orange colour towards basic or less acidic media. Its working $\mathrm{pH}$ range is
Weak base have the $\mathrm{pH}$ range greater than 7 . When methyl orange is added to this weak base solution it shows yellow orange colour.
Now when this solution is titrated against strong acid the $\mathrm{pH}$ move towards more acidic range and reaches to end point near 3.9 where yellow orange colour of methyl orange changes to Pinkish red resulting to similar change in colour of solution as well.
