Question

When ammonium chloride is added to ammonia solution, the pH of the resulting solution will be:

• A. increased
• B. seven
• C. decreased
• D. unchanged

Hint:

Common ion suppresses weak electrolyte ionization $\rightarrow$ Lower $[OH^{-}]$ $\rightarrow$ Lower pH.

Answer 1

The Correct Option is C

Step 1: Concept
This involves the common ion effect in a weak base/salt system.
Step 2: Analysis
Adding $NH_{4}Cl$ (common ion $NH_{4}^{+}$) suppresses the ionization of $NH_{4}OH$. This leads to a lower concentration of $[OH^{-}]$ ions.
Step 3: Conclusion
A decrease in hydroxide ion concentration leads to a decrease in pH.
Final Answer: (C)