CHEMISTRY: acid/base equilibrium

[applesnjanono]

Homework Statement

Calculate the end point pH when 50 mL 0.2 mol/L HCl solution reacts exactly with 50 mL 0.2 mol/L NH3 (equivalent to NH4OH) solution.

NH3 Kb=1.8x10^-5

The Attempt at a Solution

I have no idea how to even attempt this question. Can someone please help me? Thanks.

 

[Borek]

What is the composition of the solution at the end point? What ions are present? Only one them can change solution pH - which one?

 

[Blueshift5]

it is important to approach problems like this with a systematic and logical approach. The first step would be to understand the concept of acid-base equilibrium and the equations involved. In this case, the Henderson-Hasselbalch equation can be used to calculate the pH at the end point of the reaction. This equation relates the pH of a solution to the concentrations of the acid and its conjugate base.

Next, we can set up a balanced chemical equation to represent the reaction between HCl and NH3. This will help us determine the moles of each reactant and product involved in the reaction.

Then, using the given concentrations and volumes of the solutions, we can calculate the initial moles of HCl and NH3. From there, we can determine the limiting reactant and the amount of excess reactant present.

Using the Henderson-Hasselbalch equation, we can calculate the pH at the end point of the reaction, which is when the moles of the acid and base are equal. The pH at this point will be the end point pH.

It is also important to consider the Kb value of NH3 in this calculation, as it will affect the equilibrium and ultimately the end point pH. By plugging in the appropriate values into the Henderson-Hasselbalch equation, we can solve for the end point pH.

In summary, to solve this problem, we need to understand the concept of acid-base equilibrium, set up a balanced chemical equation, use the Henderson-Hasselbalch equation, and consider the Kb value of NH3. With these steps, we can calculate the end point pH when 50 mL 0.2 mol/L HCl solution reacts exactly with 50 mL 0.2 mol/L NH3 solution.