chemistry : class11 Applications of Common Ion Effect : Common ion effect : Equilibrium MCQ Questions and Answers
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Applications of Common Ion Effect
MCQ questions and answers.
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MCQ Questions
1. What happens to the solubility of silver chloride when sodium chloride is added to its saturated solution?
A.
It increases greatly
B.
It decreases
C.
It remains unchanged
D.
It first increases and then becomes zero
Correct Answer:
It decreases
Explanation:
Sodium chloride provides chloride ions, which are common ions with silver chloride. The increased chloride-ion concentration shifts the dissolution equilibrium backward, decreasing the solubility of silver chloride.
2. Which substance is added to a saturated solution of calcium hydroxide to decrease its solubility by the common ion effect?
A.
Sodium hydroxide
B.
Sodium chloride
C.
Potassium nitrate
D.
Hydrochloric acid
Correct Answer:
Sodium hydroxide
Explanation:
Sodium hydroxide supplies hydroxide ions, which are common to calcium hydroxide. The increased hydroxide-ion concentration decreases the solubility of calcium hydroxide.
3. The common ion effect is used in qualitative analysis mainly to:
A.
Increase the solubility of all salts
B.
Separate ions by selective precipitation
C.
Convert acids into bases
D.
Increase the temperature of a solution
Correct Answer:
Separate ions by selective precipitation
Explanation:
Adding a common ion can reduce the solubility of a sparingly soluble salt and cause selective precipitation, helping separate different ions during qualitative analysis.
4. Why is hydrochloric acid added while passing hydrogen sulfide gas during the analysis of certain metal ions?
A.
To increase the concentration of sulfide ions
B.
To suppress the ionization of hydrogen sulfide
C.
To dissolve all metal sulfides
D.
To make hydrogen sulfide a strong oxidizing agent
Correct Answer:
To suppress the ionization of hydrogen sulfide
Explanation:
Hydrochloric acid supplies hydrogen ions, which are common ions for the ionization of hydrogen sulfide. This suppresses sulfide-ion formation and allows only very insoluble metal sulfides to precipitate.
5. Which salt can be added to a saturated solution of barium sulfate to decrease its solubility?
A.
Sodium sulfate
B.
Sodium nitrate
C.
Potassium chloride
D.
Ammonium nitrate
Correct Answer:
Sodium sulfate
Explanation:
Sodium sulfate provides sulfate ions, which are common to barium sulfate. The common ion effect shifts the dissolution equilibrium toward solid barium sulfate and lowers its solubility.
6. In the purification of common salt, the common ion effect can help in the crystallization of sodium chloride by adding:
A.
Hydrogen chloride gas
B.
Sodium hydroxide
C.
Potassium nitrate
D.
Calcium carbonate
Correct Answer:
Hydrogen chloride gas
Explanation:
Hydrogen chloride dissolves in the solution and supplies chloride ions, common to sodium chloride. This decreases the solubility of sodium chloride and promotes its crystallization.
7. Which ion should be added to a solution of lead(II) iodide to reduce its solubility?
A.
Potassium iodide
B.
Potassium nitrate
C.
Sodium chloride
D.
Ammonium sulfate
Correct Answer:
Potassium iodide
Explanation:
Potassium iodide provides iodide ions, which are common to lead(II) iodide. The common ion effect decreases the solubility of lead(II) iodide.
8. The common ion effect is useful in removing an unwanted ion from a solution by:
A.
Increasing the solubility of its salt
B.
Precipitating its sparingly soluble salt
C.
Changing its atomic number
D.
Increasing the volume of the solution
Correct Answer:
Precipitating its sparingly soluble salt
Explanation:
A suitable common ion lowers the solubility of a sparingly soluble salt containing the unwanted ion, causing that ion to precipitate and be removed from the solution.
9. Which reagent can decrease the solubility of magnesium hydroxide through the common ion effect?
A.
Magnesium chloride
B.
Sodium nitrate
C.
Potassium chloride
D.
Ammonium nitrate
Correct Answer:
Magnesium chloride
Explanation:
Magnesium chloride supplies magnesium ions, which are common to magnesium hydroxide. The increased magnesium-ion concentration decreases the solubility of magnesium hydroxide.
10. During selective precipitation, why is a common ion sometimes added slowly rather than all at once?
A.
To control the concentration of the precipitating ion
B.
To prevent any equilibrium from being established
C.
To increase the solubility of the precipitate
D.
To remove the solvent from the solution
Correct Answer:
To control the concentration of the precipitating ion
Explanation:
Adding the common ion slowly controls its concentration and allows the desired sparingly soluble salt to precipitate selectively while other salts remain dissolved.
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