Question

A 100.0 mL buffer solution is 0.110 mol/L in CH₃​NH₂​ and 0.135 mol/L in CH₃​NH₃​Br.

What mass of HCl will this buffer neutralize before the pH falls below 9.80? (Given Kb​(CH₃​NH₂​)=4.40×10⁻⁴)

Answer 1

The question about the capacity of a buffer solution to neutralize HCl before pH drops can be answered through the Henderson-Hasselbalch equation, using the given concentrations, the base's Kb value, and the desired pH.

Step-by-step explanation:

The student asks about the capacity of a buffer solution containing CH₃NH₂ and CH₃NH₃Br to neutralize HCl before the pH drops below 9.80. The key to answering this question is to use the Henderson-Hasselbalch equation to determine the pKa, and then, using stoichiometry, to calculate the amount of HCl that the buffer can neutralize. To calculate the pKa from the given Kb (which is 4.40 × 10⁻⁴ for CH₃NH₂), we use the equation pKa + pKb = 14.

With the pKa, the initial concentrations of the weak base and its conjugate acid, and the desired pH of 9.80, apply the Henderson-Hasselbalch equation to find the new ratios after neutralization. For this specific buffer, the buffering capacity will be determined by the amount of CH₃NH₃⁺ ions that can react with the HCl added. The problem requires converting moles to grams using HCl's molar mass.