**What mass of ammonium chloride, NH4Cl, (Ka = 5.6 x 10^-10) must be added to exactly 500mL of 0.10M NH3 solution to give a solution with a pH of 9.00?**

**Concepts and reason**

The concept used to solve this problem is based on the chemical equilibrium.

The pH of solution is used to determine acidity and basicity of a solution.

**Fundamentals**

The pH of solution can be determine by Henderson-Hasselbalch equation as follow.

**Answer:**

Write the balanced equilibrium reaction as follow.

Now, Henderson-Hasselbalch equation for this reaction is written as follow.

**Explanation:**

The Henderson-Hasselbalch equation is used to calculate pH of solution by using concentrations of base and its conjugate acid.