Find the pH when 100.0 mL of a 0.1 M dibasic compound B (pK_b1 = 4.00; pK_b2 = 8.00) was titrated with 11 mL of a 1.00 M HCl.

• A. 8.00
• B. 6.95
• C. 3.00
• D. 7.05

Answer: (B)

Verified step by step guidance

1. Calculate the initial moles of the dibasic compound B using the formula: \( \text{moles of B} = \text{volume (L)} \times \text{molarity (M)} \).
2. Calculate the moles of HCl added using the formula: \( \text{moles of HCl} = \text{volume (L)} \times \text{molarity (M)} \).
3. Determine the reaction between HCl and the dibasic compound B. Since HCl is a strong acid, it will react with the base in a 1:1 molar ratio, first neutralizing the first basic site.
4. Calculate the remaining moles of the base after the reaction with HCl. If there is excess HCl, it will further react with the second basic site.
5. Use the Henderson-Hasselbalch equation to find the pH of the solution. For the first equivalence point, use \( \text{pH} = \text{pKa1} + \log \left( \frac{[\text{base}]}{[\text{acid}]} \right) \), where \( \text{pKa1} = 14 - \text{pKb1} \).