Question

The variation of pH during the titration of 0.5 N Na2CO3 against 0.5 N HCl is shown in the following graph:The following table indicates the colour and pH range of different indicators:Based on the given graph and table, which of the following statements are correct?a. The first point of inflection can be detected by cresolphthalein.b. The complete neutralisation can be detected by bromothymol blue.c. The second point of inflection can be detected by bromocresol red.d. The volume of HCl required for the first point of inflection is half of the volume of HCl required for the second point of inflection.

• A. (A) a, b and d
• B. (B) a, c and d
• C. (C) a, b and c
• D. (D) b, c and d

Answer 1

Answer: (C)

(C) a, b and c

Answer 2

Explanation:
The first end point is observed in the pH range of 10 to 7.9 and can be detected using cresolpthalein, which shows a colour change (in this case, red to colourless) in the pH range of 8.2 to 9.8.Since, bromothymol shows the colour change in the pH range of 6.0 to 7.6, the end point will also be the equivalence point.The second point of inflection is observed in the pH range of 6.1 to 4.0 and can be detected with bromocresol red, which shows a colour change in the pH range of 4.2 to 6.3.Hence, statements a, b and c are correct.