WAEC - Chemistry (2008 - No. 25)
Which of the following compounds would dissolved in water to give a solution whose pH is less than 7?
AI(NO3)3
KNO3
N2O
NH3
Explicació
Aluminum nitrate (Al(NO3)3) is a salt that dissolves in water to produce hydrogen ions (H\(^+\)), which are acidic:
Al(NO\(_3\))\(_3\) → Al\(^{3+}\) + 3NO\(_3\)\(^-\)
Al\(^{3+}\) + 3H\(^2\)O → Al(OH)\(_3\) + 3H\(^+\)
The released hydrogen ions (H\(^+\)) increase the acidity of the solution, resulting in a pH less than 7.
The other options:
B. Potassium nitrate (KNO\(_3\)) is a neutral salt and does not affect the pH.
C. Nitrous oxide (N\(^2\)O) is a gas and does not dissolve in water to affect pH.
D. Ammonia (NH\(_3\)) is a base and would increase the pH of the solution (make it more alkaline).
So, aluminum nitrate (Al(NO3)3) is the correct answer.