Chemistry Question Papers for Class 11 on “Equilibrium – Buffer Solutions”.
1. Carbonic acid and sodium bicarbonate are present in blood as a buffer.
a) true
b) false
Answer: a
Clarification: A solution that resists the change in its PH value by the addition of a small amount of acid or base is called a buffer solution. The buffer system present in the blood is carbonic acid and sodium bicarbonate.
2. Which of the following is not an acidic buffer?
a) Acetic Acid-Sodium acetate
b) Boric acid-borax
c) Ammonium hydroxide-ammonium chloride
d) All are acidic buffers
Answer: c
Clarification: An acidic buffer has a pH value of less than 7, Acetic Acid-Sodium Acetate and boric acid-borax are examples of acidic buffers, but ammonium Hydroxide-ammonium chloride has a pH of greater than 7, so they are basic buffers.
3. Which of the following is an equation used to calculate the pH of a buffer solution for an acidic buffer?
a) pH = pKa + log[salt]/[acid]
b) pOH = pKa + log[salt]/[acid]
c) pH = pKb + log[salt]/[acid]
d) pH = pKa + log[salt][acid]
Answer: a
Clarification: Equation that is used to calculate the pH of a buffer solution for an acidic buffer is pH = pKa + log[salt]/[acid]. This equation is known as henderson-hasselbalch equation, it is used for making of buffer solutions.
4. Buffer solution is destroyed when _____________
a) addition of weak base
b) addition of strong acid or base
c) addition of weak acid
d) addition of a salt
Answer: a
Clarification: If the addition of a strong acid or base changes the pH of a buffer by unit, the buffer solution is assumed to be destroyed that is new pH = pKa ± 1; that means [salt]/[acid] or [acid]/[salt] = 10 or 1/10.
5. What is the buffer capacity if 3 moles are added in 5 litres of the solution to change the pH by 2 units?
a) 0.2
b) 0.5
c) 0.15
d) 0.3
Answer: d
Clarification: Buffer capacity is defined as the number of moles of acid or base added in one litre of the solution to change the pH by Unity. Therefore here buffer capacity = 3/5 divided by 2 = 0.6/2 = 0.3. The buffer capacity is given as 0.3.
6. Buffer capacity of a buffer is given as two units for a change in pH by Unity. Then what is the number of moles of acid or base, added in one litre of the solution?
a) 2
b) 0.5
c) 1
d) 4
Answer: a
Clarification: Buffer capacity is denoted by Φ = number of moles of acid or base added to one litre of the buffer by a change in pH. Here the change in pH is given by 1 and the buffer capacity is given by 2, therefore by substituting, we get that 2 moles of acid or base are added in one litre of the solution.
7. If 0.20 mol/L CH3COOH and 0.50 mol/L CH3COO– together make a buffer solution, calculate the pH of the solution if the acid dissociation constant of CH3COOH is 1.8 × 10-5.
a) 2.09
b) 5.14
c) 2.65
d) 3.98
Answer: b
Clarification: We have henderson-hasselbalch equation as pH = pKa + log[salt]/[acid]. So by substituting the concentrations of silent and acid along with the acid dissociation constant, we get pH = -log[1.8 × 10-5] + log [0.50mol/L]/[0.20mol/L] = 5.14.
8. Note that the pKa here is given by 4.752, a buffer is made using 0.8 M acetic acid and 1 M Sodium Acetate what do you think its pH is(log10/8 = 0.097)?
a) 4.84
b) 4.85
c) 4.849
d) 4.846
Answer: b
Clarification: According to the Henderson hasselbalch equation pH = pKa + log[salt]/[acid], if we substitute the concentration of salt as 1 M and the concentration of acid as 0.8 M, pH = 4.752 + 0.097 = 4.849 is the required answer.
9. If the pH of a substance is given by 3 then what is the pOH of the substance?
a) 3
b) 7
c) 14
d) 11
Answer: d
Clarification: We know that the sum of the pH and pOH of any substance is equal to 14 that is pH + pOH = 14. So here the pH of a substance is given by 3 the pH of the substance = 14 – 3 = 11, 11 is the required answer.
10. Which of the following do you think is a correct statement?
a) Ammonium hydroxide / ammonium chloride is an acidic buffer
b) boric acid / borax is an acidic buffer
c) henderson hasselbalch equation is given by pH = pKb + log[salt]/[acid]
d) PH + pOH = 4
Answer: b
Clarification: Ammonium hydroxide / ammonium chloride is a basic buffer, henderson hasselbalch equation is given by pH = pKa + log[salt]/[acid] and pH + pOH = 14. So the only correct statement is that boric acid / borax is an acidic buffer.
To practice Chemistry Question Papers for Class 11,