Chemical and Ionic Equilibrium - Result Question 28-1
28. The best indicator for detection of end point in titration of a weak acid and a strong base is phenolphthalein
$(1985,1 M)$
(a) methyl orange ( pH 3 to 4 )
(b) methyl red (pH 4.4 to 6.2)
(c) bromothymol blue (pH 6 to 7.5)
(d) phenolphthalein ($8$ to $10.6$ )
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Answer:
Correct Answer: 28. (a, c)
Solution:
- When a weak acid $(\mathrm{H} X)$ is titrated against a strong base $NaOH$ , basic salt $(\mathrm{Na} X)$ is present at the end point which makes end point slightly basic with pH around $8$ . Hence, phenolphthalein, that changes its colour in this pH range, would be the best choice of indicator to detect the end point.
BETA
