The ionization constant of benzoic acid is 6.46 x 10^–5 and Kc for silver benzoate is 2.5 x 10^–13. How many times silver benzoate is more soluble in a buffer of pH = 3.19 as compared to its solubility in pure water ?

(1) 3.317

(2) 9.5

(3) 1000

(4) 7.5

30 ml of 0.06 M solution of the protonated form of an anion acid methionine (H₂A⁺) is treated with 0.09 M NaOH. Calculate pH after addition of 20 ml of base. pKa₁, = 2.28 and pKa₂ = 9.2.

1. 5.5

2. 5.74

3. 9.5

4. None

A certain acid–base indicator is red in acid solution and blue in basic solution 75% of the indicator is presentin the solution in its blue form at pH = 5. Calculate the pH at which the indicator shows 90% red form?

(1) 3.56

(2) 5.47

(3) 2.5

(4) 7.4

Ionisation constant of HA (weak acid) and BOH (weak base) are 3.0 x 10^–7 each at 298K. The percent degree of hydrolysis of BA at the dilution of 10L is :

1. 25

2. 50

3. 75

4. 40

Calculate the molar solubility of zinc tetrathiocyanato–N–mercurate (II) if its K_sp = 2.2 x 10^–7.

(1) 0.00380

(2) 0.000469

(3) 0.0095

(4) 0.0183

An acid–base indicator which is a weak acid has a pK_a value = 5.45. At what cocentration ratio of sodiumacetate to acetic acid would the indicator show a colour half–way between those of its acid and conjugate base forms? pK_a of acetic acid = 4.75. [log 2 = 0.3]

(1) 4 : 1

(2) 7 : 1

(3) 5 : 1

(4) 2 : 1

The indicator constant of phenolphthalein is approximately 10^–10. A solution is prepared by adding 100.01c.c. of 0.01 N sodium hydroxide to 100.00 c.c. of 0.01N hydrochloric acid. If a few drops of phenolphthalein are now added, what fraction of the indicator is converted to its coloured form?

(1) $\frac{2}{3}$

(2) $\frac{3}{4}$

(3) $\frac{1}{2}$

(4) $\frac{9}{11}$

A certain mixture of HCl and CH₃ – COOH is 0.1 M in each of the acids. 20 ml of this solution is titrated against 0.1M NaOH. By how many units does the pH change from the start to the stage when the HCl is almost completely neutralised? K_a for acetic acid = 1.8 x 10^–6.

(1) 2.03

(2) 0.775

(3) 2.325

(4) 3.172

A buffer solution is made by mixing a weak acid HA (K_a = 10^–6) with its salt NaA in equal amounts. What should be the amount of acid or salt that should be added to make 90 ml of buffer solution of buffer capacity. 0.1 ?

(1) 10 milli moles

(2) 22 milli moles

(3) 9 milli moles

(4) 11 milli moles

A sample of water has a hardness expressed as 80 ppm of Ca²⁺. This sample is passed through an ion exchange column and the Ca²⁺ is replaced by H⁺. What is the pH of the water after it has been so treated? [Atomic mass of Ca = 40]

(1) 3

(2) 2.7

(3) 5.4

(4) 2.4