If some NH4Cl is added to an aqeous solution of NH3:

A. pH of solution will decrease
B. PH will not change
C. pH will increase
D. NH4Cl cannot be added to NH3
E. The solution will not have pH

I think the answer is B, because if NH4Cl is added to the solution of NH3, then solution will be at equilibrium and pH will not change...

Nope. Look at the HF/HCl answer below and you will know how to answer this one.

You are correct! The answer is B. When NH4Cl is added to an aqueous solution of NH3, the pH of the solution will not change.

To understand why, let's look at the chemistry behind it. NH3 (ammonia) is a weak base that can react with water to form NH4+ (ammonium) and OH- (hydroxide) ions, according to the following equation:

NH3 + H2O ⇌ NH4+ + OH-

This reaction is in equilibrium, meaning that both the forward and reverse reactions are occurring simultaneously.

When NH4Cl is added to the solution, it dissociates into NH4+ and Cl- ions. The NH4+ ions can react with OH- ions (already present in the solution due to the initial NH3 dissociation), forming NH3 and water:

NH4+ + OH- ⇌ NH3 + H2O

This reaction also occurs at equilibrium.

Since both reactions are in equilibrium, the concentration of NH3 and NH4+ will remain constant, and therefore, the concentration of OH- will also remain constant.

The pH of a solution is a measure of its acidity or alkalinity, determined by the concentration of hydrogen ions (H+). In the case of NH3, it is a base, so it generates OH- ions, making the solution slightly alkaline.

However, when NH4Cl is added to the solution, the NH4+ and OH- ions produced by NH3 neutralize each other, resulting in no net change in the concentration of OH- ions.

Therefore, the concentration of H+ (which determines the pH) remains the same, and the pH of the solution will not change. Hence, the correct answer is B.