What is the pH of a solution containing NH3 and NH4Cl?

[vaishakh]

0.05ml of NH3 is dissloved in a solution containing water followed by 0.27g of NH4Cl. If the Kb for NH4OH is 1.8 * 10^-5 find the pH value of the solution.
I am finding it difficult to predict the reactions that are going to happen here. I know to calculate Kh or the constant of hydrolysis of NH4Cl from here but how does NH3 dissolve in water. I think it mixes with H+ in the solution to form NH4+.
But I don't know how to continue.

 

[Borek]

This is classical buffer question.

Compare with this buffer question - not identical, but close.

 

[Blueshift5]

Based on the information provided, it appears that you are trying to determine the pH of a solution containing NH3 and NH4Cl. In order to do this, you will need to consider the equilibrium reactions that occur between these two compounds and the water in the solution.

Firstly, NH3 (ammonia) will react with water to form NH4+ (ammonium) and OH- (hydroxide) ions in a reversible reaction, according to the following equation:

NH3 + H2O ⇌ NH4+ + OH-

This reaction is known as a base dissociation reaction and is governed by the equilibrium constant, Kb. The Kb value provided in the question (1.8 * 10^-5) represents the equilibrium constant for this reaction.

Next, NH4Cl (ammonium chloride) will dissociate in water into NH4+ and Cl- (chloride) ions, according to the following equation:

NH4Cl ⇌ NH4+ + Cl-

The NH4+ ions produced from this dissociation can then react with water in a similar manner as NH3 to produce more OH- ions. This reaction is known as a salt hydrolysis reaction.

To determine the pH of the solution, you will need to consider the concentrations of NH3, NH4+, and OH- ions in the solution. Using the equilibrium equations and the provided information, you can set up an expression for the equilibrium constant, Kb, and solve for the concentration of OH- ions. From there, you can use the pH equation (pH = -log[H+]) to calculate the pH of the solution.

It is important to note that the pH of the solution will also depend on the initial concentration of NH3 and NH4Cl, as well as the volume of the solution. These factors will affect the overall concentration of OH- ions and therefore, the pH.

I hope this provides you with some guidance on how to approach this problem. If you need further assistance, I recommend consulting your textbook or speaking with your instructor for additional support. Good luck!