chemistry : class11 Basic Buffer Action : Common ion effect : Equilibrium MCQ Questions and Answers
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Basic Buffer Action
MCQ questions and answers.
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MCQ Questions
1. What is a buffer solution?
A.
A solution that resists change in pH when small amounts of acid or base are added
B.
A solution that always has pH 7
C.
A solution that contains only a strong acid
D.
A solution that changes pH rapidly on dilution
Correct Answer:
A solution that resists change in pH when small amounts of acid or base are added
Explanation:
A buffer solution maintains nearly constant pH because its components react with added small amounts of acid or base.
2. Which pair forms an acidic buffer solution?
A.
Hydrochloric acid and sodium chloride
B.
Acetic acid and sodium acetate
C.
Sodium hydroxide and potassium chloride
D.
Nitric acid and potassium nitrate
Correct Answer:
Acetic acid and sodium acetate
Explanation:
An acidic buffer consists of a weak acid and its salt with a strong base, such as acetic acid and sodium acetate.
3. Which pair forms a basic buffer solution?
A.
Ammonium hydroxide and ammonium chloride
B.
Sodium hydroxide and sodium chloride
C.
Hydrochloric acid and potassium chloride
D.
Nitric acid and sodium nitrate
Correct Answer:
Ammonium hydroxide and ammonium chloride
Explanation:
A basic buffer contains a weak base and its salt with a strong acid, such as ammonium hydroxide and ammonium chloride.
4. In an acetic acid–sodium acetate buffer, which ion is mainly responsible for the common ion effect?
A.
Sodium ion
B.
Chloride ion
C.
Acetate ion
D.
Hydrogen ion
Correct Answer:
Acetate ion
Explanation:
Sodium acetate provides acetate ions, which are common to the ionization equilibrium of acetic acid and suppress its ionization.
5. When a small amount of hydrochloric acid is added to an acetic acid–sodium acetate buffer, the added hydrogen ions are mainly removed by reaction with:
A.
Acetic acid
B.
Acetate ions
C.
Sodium ions
D.
Water molecules only
Correct Answer:
Acetate ions
Explanation:
Acetate ions react with added hydrogen ions to form weak acetic acid, so the pH changes only slightly.
6. When a small amount of sodium hydroxide is added to an acetic acid–sodium acetate buffer, the hydroxide ions mainly react with:
A.
Acetic acid
B.
Acetate ions
C.
Sodium ions
D.
Chloride ions
Correct Answer:
Acetic acid
Explanation:
Acetic acid reacts with added hydroxide ions to form acetate ions and water, limiting the rise in pH.
7. In an ammonia–ammonium chloride buffer, which component reacts mainly with added hydroxide ions?
A.
Ammonia
B.
Ammonium ions
C.
Chloride ions
D.
Sodium ions
Correct Answer:
Ammonium ions
Explanation:
Ammonium ions react with added hydroxide ions to form ammonia and water, helping the basic buffer resist a rise in pH.
8. What happens to the ionization of a weak acid when its salt containing a common ion is added?
A.
It increases greatly
B.
It is suppressed
C.
It becomes complete
D.
It changes into ionization of a strong acid
Correct Answer:
It is suppressed
Explanation:
The common ion shifts the ionization equilibrium of the weak acid toward the unionized form, decreasing its ionization.
9. Why does an acetic acid–sodium acetate buffer show only a small pH change on adding a small amount of acid?
A.
The added acid evaporates
B.
Acetate ions react with the added hydrogen ions
C.
Sodium ions neutralize the acid directly
D.
Acetic acid becomes a strong acid
Correct Answer:
Acetate ions react with the added hydrogen ions
Explanation:
Acetate ions consume most of the added hydrogen ions by forming acetic acid, so the hydrogen ion concentration changes only slightly.
10. Which statement about the action of a basic buffer is correct?
A.
Its weak base reacts with added acid, while its conjugate acid reacts with added base
B.
It always keeps the solution exactly neutral
C.
It contains only a strong base
D.
It cannot react with added acid
Correct Answer:
Its weak base reacts with added acid, while its conjugate acid reacts with added base
Explanation:
In a basic buffer, the weak base removes added hydrogen ions and its conjugate acid removes added hydroxide ions, maintaining nearly constant pH.
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