Questions on Common Ion Effect
Multiple-Choice Questions: Common Ion Effect
1. What is the common ion effect?
A) The formation of a new compound when two salts are mixed
B) The shift in equilibrium due to the addition of an ion already present in the solution
C) The increase in solubility when a common ion is added
D) The precipitation of an insoluble salt
E) The complete dissociation of strong electrolytes
2. Which of the following demonstrates the common ion effect?
A) Adding NaCl to AgNO₃
B) Adding NaOH to NH₄OH
C) Adding NH₄Cl to NH₄OH
D) Adding KNO₃ to Pb(NO₃)₂
E) Adding HCl to NaOH
3. What is the result of the common ion effect on solubility?
A) Solubility increases
B) Solubility remains the same
C) Solubility decreases
D) It depends on temperature
E) It becomes zero
4. Adding NaF to a solution of HF will:
A) Increase HF ionization
B) Decrease HF ionization
C) Have no effect
D) Form a precipitate
E) Raise the pH significantly
5. Which ion is common to both CaF₂ and NaF?
A) Na⁺
B) Ca²⁺
C) F⁻
D) OH⁻
E) Cl⁻
6. In the presence of a common ion, Le Châtelier's principle predicts that:
A) The reaction will stop
B) Equilibrium shifts to favor ionization
C) Equilibrium shifts to reduce ion formation
D) The Ksp will increase
E) Solubility increases
7. When NH₄Cl is added to NH₄OH solution, what happens?
A) NH₄OH dissociation increases
B) OH⁻ concentration increases
C) NH₄OH dissociation decreases
D) pH increases
E) NH₄⁺ reacts with water to form acid
8. Which pair will exhibit the common ion effect?
A) NaCl and KBr
B) CH₃COOH and NaCl
C) CH₃COOH and CH₃COONa
D) HCl and NaOH
E) Ba(NO₃)₂ and AgNO₃
9. The common ion effect is a consequence of:
A) Neutralization reactions
B) Temperature variation
C) Le Châtelier’s Principle
D) Ionization energy
E) Redox potential
10. A solution contains AgCl. What will happen if NaCl is added?
A) AgCl dissolves more
B) AgCl ionizes completely
C) More AgCl precipitates
D) No change
E) Silver metal forms
11. Why does the addition of HCl decrease the solubility of Mg(OH)₂?
A) Common ion effect
B) Formation of complex ions
C) Reaction with OH⁻
D) Acid–base neutralization
E) Increase in temperature
12. Adding CH₃COONa to CH₃COOH causes:
A) Increased ionization
B) Formation of a buffer
C) Increased pH
D) Common ion effect and decreased ionization
E) More acetic acid
13. Which salt would reduce the solubility of AgBr the most?
A) NaNO₃
B) KCl
C) NaBr
D) K₂SO₄
E) NH₄NO₃
14. The solubility of a slightly soluble salt is generally reduced by:
A) Adding a strong acid
B) Adding a common ion
C) Increasing the temperature
D) Adding a catalyst
E) Changing pressure
15. Which of the following would NOT exhibit a common ion effect with CaCO₃?
A) Na₂CO₃
B) CaCl₂
C) H₂CO₃
D) NaCl
E) Ca(NO₃)₂
16. What happens to pH when NH₄Cl is added to NH₄OH?
A) pH increases
B) pH decreases
C) pH stays the same
D) Buffer is destroyed
E) Precipitate forms
17. The solubility of Fe(OH)₃ will be lowered by adding:
A) NaOH
B) HCl
C) FeCl₃
D) Both A and C
E) All of the above
18. Which one of the following combinations will NOT result in a common ion effect?
A) H₂CO₃ and Na₂CO₃
B) CH₃COOH and NaOH
C) NH₃ and NH₄Cl
D) NaF and HF
E) AgNO₃ and NaCl
19. Which of the following statements is true about Ksp and the common ion effect?
A) Ksp increases with more common ions
B) Ksp changes based on ion concentrations
C) Ksp remains constant at a given temperature
D) Ksp decreases when solubility decreases
E) Common ions eliminate Ksp
20. Adding Na₂SO₄ to BaSO₄ solution will:
A) Increase BaSO₄ solubility
B) Have no effect
C) Cause precipitation of BaSO₄
D) Form Ba(OH)₂
E) Change the Ksp of BaSO₄
- Questions on Nonreversible Reactions
- Questions on Le Châtelier's Principle
- Questions on Effect of Concentration, Temperature, and Pressure
Answer Key with Explanations
1. B – The common ion effect occurs when an ion already in solution causes a shift in equilibrium.
2. C – NH₄⁺ is common to both NH₄Cl and NH₄OH, reducing NH₄OH dissociation.
3. C – Common ions shift equilibrium and decrease solubility.
4. B – F⁻ is added, suppressing HF ionization by shifting equilibrium left.
5. C – F⁻ is the common ion between CaF₂ and NaF.
6. C – Le Châtelier's principle favors the reverse reaction to reduce added ions.
7. C – More NH₄⁺ shifts NH₄OH ⇌ NH₄⁺ + OH⁻ to the left, reducing OH⁻.
8. C – CH₃COOH and CH₃COONa share the CH₃COO⁻ ion.
9. C – The effect is based on Le Châtelier’s principle.
10. C – Cl⁻ from NaCl shifts equilibrium left, precipitating AgCl.
11. C – HCl adds H⁺, which neutralizes OH⁻, shifting solubility equilibrium.
12. D – CH₃COONa adds CH₃COO⁻, shifting equilibrium to reduce ionization.
13. C – NaBr shares the Br⁻ ion with AgBr, reducing its solubility most.
14. B – Common ions reduce solubility due to equilibrium shift.
15. D – NaCl shares no ion with CaCO₃ → no common ion effect.
16. B – NH₄⁺ increases, suppressing OH⁻ production → pH drops.
17. D – NaOH adds OH⁻; FeCl₃ adds Fe³⁺. Both promote precipitation.
18. B – NaOH neutralizes CH₃COOH, but OH⁻ is not a common ion to CH₃COOH.
19. C – Ksp depends only on temperature, not concentrations.
20. C – SO₄²⁻ is common to both salts; it reduces BaSO₄ solubility by precipitation.
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