Final answer:
To determine the pH after titrating ethylamine with HNO₃, conduct a stoichiometric calculation followed by using the base-dissociation constant and the Henderson-Hasselbalch equation if necessary.
Step-by-step explanation:
The pH of the titrated solution after adding 32.1 ml of 0.0522 M HNO₃ to 54.9 ml of 0.1049 m ethylamine (CH₃CH₂NH₂) can be determined by conducting a stoichiometric calculation followed by an application of the Henderson-Hasselbalch equation. Since ethylamine is a weak base with a base-dissociation constant (Kb) of 4.5 × 10⁻⁴ at 25°C, we must first compute the moles of ethylamine and moles of HNO₃ to find if the reaction has reached equivalence or if there is excess base or acid present. In this case, because ethylamine is a weak base, the reaction produces its conjugate acid, which significantly affects the pH of the solution.
To calculate the moles of ethylamine originally present, we use the formula:
- Moles of ethylamine = volume (in liters) × molarity
To calculate the moles of HNO₃ added:
- Moles of HNO₃ = volume (in liters) × molarity
If there is excess ethylamine, we use the Kb and the concentration of the excess ethylamine to find the pOH, then convert it to pH. If the solution contains excess HNO₃, its concentration determines the pH directly as it is a strong acid. In the case that the moles of ethylamine and HNO₃ are equal, the solution is at equivalence and the pH is determined by the hydrolysis of the ethylamine salt.