The pKa, of a weak acid if titration progress is monitored as follows

(1) Data insufficient

(2) 8.15

(3) 3.88

(4) 4.28

A 1.458 g of Mg reacts with 80.0 ml of a HCI solution whose pH is –0.477. The change in pH after all Mg has reacted. (Assume constant volume. Mg = 24.3 g/mol.)(log 3 = 0.477)

(1) –0.176

(2) +0.477

(3) –0.2385

(4) 0.3

Find the $∆$pH (initial pH –final pH) when 100 ml 0.01 M HCl is added in a solution containig 0.1 m molesof NaHCO₃ solution (pH = 9 ) of negligible volume ( K_ai =10^–7, K_a, =10^–11 for H₂CO₃) :

(1) 6 + 2 log3

(2) 6 – log3

(3) 6 + 2 Log2

(4) 6 – 2 log3

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 of the above

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) $\frac{9}{11}$