chemistry : class11 Effect on Degree of Ionization : Common ion effect : Equilibrium MCQ Questions and Answers
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Effect on Degree of Ionization
MCQ questions and answers.
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MCQ Questions
1. What happens to the degree of ionization of a weak electrolyte when a soluble electrolyte containing a common ion is added?
A.
It increases
B.
It decreases
C.
It remains exactly the same
D.
It becomes complete
Correct Answer:
It decreases
Explanation:
The added common ion shifts the ionization equilibrium of the weak electrolyte backward, thereby decreasing its degree of ionization.
2. When sodium acetate is added to acetic acid solution, the degree of ionization of acetic acid
A.
increases
B.
decreases
C.
becomes 100%
D.
does not change because sodium acetate is neutral
Correct Answer:
decreases
Explanation:
Sodium acetate provides acetate ions, which are common ions in the ionization of acetic acid. Their presence suppresses the ionization of acetic acid.
3. The degree of ionization of ammonium hydroxide decreases when ammonium chloride is added because ammonium chloride supplies
A.
chloride ions
B.
hydroxide ions
C.
ammonium ions
D.
hydrogen ions
Correct Answer:
ammonium ions
Explanation:
Ammonium hydroxide ionizes to produce ammonium ions and hydroxide ions. Ammonium chloride adds ammonium ions, causing suppression of ionization by the common ion effect.
4. For the equilibrium CH3COOH ⇌ H+ + CH3COO−, adding sodium acetate causes the concentration of CH3COO− to
A.
increase due to the common ion effect
B.
decrease to zero
C.
remain unchanged in every case
D.
become equal to the concentration of H+
Correct Answer:
increase due to the common ion effect
Explanation:
Sodium acetate dissociates and directly adds acetate ions, which are common ions in the ionization equilibrium of acetic acid. The increased acetate concentration suppresses further ionization of acetic acid.
5. Which solution shows a lower degree of ionization of acetic acid?
A.
Acetic acid in pure water
B.
Acetic acid containing sodium acetate
C.
Acetic acid diluted with more water
D.
Acetic acid heated mildly without adding a solute
Explanation:
Sodium acetate provides the acetate common ion, which shifts the ionization equilibrium of acetic acid toward the unionized form and lowers its degree of ionization.
6. The common ion effect on a weak electrolyte generally changes its degree of ionization in which direction?
A.
Toward greater ionization
B.
Toward lower ionization
C.
Toward complete ionization
D.
Toward no molecules at all
Correct Answer:
Toward lower ionization
Explanation:
An increase in the concentration of one of the ions already present in the ionization equilibrium shifts the equilibrium backward, reducing the degree of ionization.
7. In a solution of weak base NH4OH, addition of NH4Cl will
A.
increase the degree of ionization of NH4OH
B.
decrease the degree of ionization of NH4OH
C.
convert NH4OH into a strong base
D.
remove all NH4OH molecules
Correct Answer:
decrease the degree of ionization of NH4OH
Explanation:
NH4Cl supplies NH4+ ions, which are common to the ionization equilibrium of NH4OH. This common ion suppresses the ionization of NH4OH.
8. If the concentration of a common ion is increased in a weak electrolyte solution, the amount of unionized weak electrolyte generally
A.
decreases
B.
increases
C.
becomes zero
D.
remains unchanged in all conditions
Correct Answer:
increases
Explanation:
The common ion shifts the equilibrium toward the unionized weak electrolyte. Therefore, the degree of ionization decreases and the amount of unionized electrolyte increases.
9. Which pair demonstrates the common ion effect on the degree of ionization of a weak electrolyte?
A.
Acetic acid and sodium acetate
B.
Hydrochloric acid and sodium chloride
C.
Sodium hydroxide and potassium hydroxide
D.
Water and ethanol
Correct Answer:
Acetic acid and sodium acetate
Explanation:
Acetic acid is a weak electrolyte, and sodium acetate provides its common acetate ion. This lowers the degree of ionization of acetic acid.
10. Compared with pure water, acetic acid in a solution containing acetate ions has a degree of ionization that is
A.
higher
B.
lower
C.
always equal to 100%
D.
unrelated to the acetate ion concentration
Correct Answer:
lower
Explanation:
The added acetate ions act as common ions and shift the ionization equilibrium of acetic acid backward, reducing its degree of ionization.
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