`40mL` sample of `0.1M` solution of nitric acid is added to `20mL` of `0.3M` aqueous ammonia. What is the `pH` of the resulting solution? `(pK_b = 4.7447)`

Explanation

To solve the problem of finding the pH of the resulting solution when 40 mL of 0.1 M nitric acid is mixed with 20 mL of 0.3 M aqueous ammonia, we can follow these steps:

### Step 1: Calculate the moles of HNO3 and NH3
1. **Moles of HNO3**:
\[ \text{Moles of HNO3} = \text{Molarity} \times \text{Volume} = 0.1 \, \text{mol/L} \times 0.040 \, \text{L} = 0.004 \, \text{mol} = 4 \, \text{mmol} \]

...