<u>Answer:</u> The hydronium ion concentration in the solution is 
<u>Explanation:</u>
To calculate the molarity, we use the equation:

Moles hydrochloric acid solution = 0.060 mol
Volume of solution = 1 L
Putting values in above equation, we get:

The chemical reaction for aniline and HCl follows the equation:

<u>Initial:</u> 0.24 0.060 0.31
<u>Final:</u> 0.18 - 0.37
To calculate the pH of acidic buffer, we use the equation given by Henderson Hasselbalch:
![pH=pK_a+\log(\frac{[\text{conjugate acid}]}{[\text{base}]})](https://tex.z-dn.net/?f=pH%3DpK_a%2B%5Clog%28%5Cfrac%7B%5B%5Ctext%7Bconjugate%20acid%7D%5D%7D%7B%5B%5Ctext%7Bbase%7D%5D%7D%29)
![pH=pK_a+\log(\frac{[C_6H_5COO^-]}{[C_6H_5COOH]})](https://tex.z-dn.net/?f=pH%3DpK_a%2B%5Clog%28%5Cfrac%7B%5BC_6H_5COO%5E-%5D%7D%7B%5BC_6H_5COOH%5D%7D%29)
We are given:
= negative logarithm of acid dissociation constant of benzoic acid = 4.2
![[C_6H_5COO^-]=0.18M](https://tex.z-dn.net/?f=%5BC_6H_5COO%5E-%5D%3D0.18M)
![[C_6H_5COOH]=0.37M](https://tex.z-dn.net/?f=%5BC_6H_5COOH%5D%3D0.37M)
pH = ?
Putting values in equation 1, we get:

To calculate the hydronium ion concentration in the solution, we use the equation:
![pH=-\log[H_3O^+]](https://tex.z-dn.net/?f=pH%3D-%5Clog%5BH_3O%5E%2B%5D)
pH = 3.89
Putting values in above equation, we get:
![3.89=-\log[H_3O^+]](https://tex.z-dn.net/?f=3.89%3D-%5Clog%5BH_3O%5E%2B%5D)
![[H_3O^+]=10^{-3.89}=1.29\times 10^{-4}M](https://tex.z-dn.net/?f=%5BH_3O%5E%2B%5D%3D10%5E%7B-3.89%7D%3D1.29%5Ctimes%2010%5E%7B-4%7DM)
Hence, the hydronium ion concentration in the solution is 