The hydrogen ion concentration in a solution is expressed as pH. pH is the negative log of hydrogen ion concentration in a solution. The pH scale generally ranges from 0 to 14. The pH value of 7 is taken as neutral, less than 7 is acidic and more than 7 is basic. Buffer solutions resist any change in pH. They consist of an acid-base pair. The acidic buffer contains a weak acid and its salt with a strong base, e.g. acetic acid and sodium acetate. The basic buffer contains a weak base and its salt with a strong acid, e.g. ammonium hydroxide and ammonium chloride.

1. Find the pH of a solution containing an equal volume of 0.1 M NaOH and 0.01 M HCl.

(a) 7.0

(b) 2.0

(c) 12.65

(d) 1.04

2. FInd the solubility product (K_sp) of Ba(OH)₂, if the pH of a saturated solution of Ba(OH)₂ is 12.

(a) 5.0 × 10^-7

(b) 3.3 × 10^-7

(c) 5.0 × 10^-6

(d) 4.0 × 10^-6

3. Buffer solutions resist any change in pH. This is because ______.

(a) acids and alkalis in these solutions are shielded from attack by other ions

(b) these give unionised acid or base on reaction with added acid or alkali

(c) fixed value of pH

(d) large excess of H⁺ or OH^– ions

4. Which of the following solutions will act as a buffer?

(a) HNO₂ and NaNO₂

(b) HCl and KCl

(c) HNO₃ and NH₄NO₃

(d) NaOH and NaCl

5. Which of the following is the strongest conjugate base?

(a) Cl^–

(b) SO₄^2-

(c) CH₃COO^–

(d) NO₃^–

6. Find the pH of 0.1N NaOH solution.

(a) 13

(b) 10

(c) 12

(d) 11

7. Which of the following is the conjugate acid of NH₂^– ?

(a) NH₄⁺

(b) NH₄OH

(c) NH₃

(d) NH₂^–

8. What will be the concentration [OH^–] in the solution, if it is prepared by 20.0 mL of 0.050 M HCl with 30.0 mL of 0.10 M Ba(OH)₂?

(a) 0.0050 M

(b) 0.40 M

(c) 0.10 M

(d) 0.12 M

9. Which of the following solutions (equimolar) will have the highest pH?

(a) AlCl₃

(b) BaCl₂

(c) BeCl₂

(d) LiCl

10. This is not an acidic buffer.

(a) H₂CO₃ and Na₂CO₃

(b) CH₃COOH and CH₃COONa

(c) HClO₄ and NaClO₄

(d) H₃PO₄ and Na₃PO₄

Answer