8. Monoprotic Acid-Base Equilibria
Buffers
Multiple Choice
Which of the following molar ratios is the correct equilibrium ratio of BASE : ACID for a solution made of aniline (Kb = 3.8 x 10-10) and anilinium nitrate where the pH is 4.80?
A
1:2
B
3:5
C
7:2
D
2:1
E
5:3
Verified step by step guidance1
First, understand that aniline is a weak base and anilinium nitrate is its conjugate acid. The equilibrium involves the base (aniline) and its conjugate acid (anilinium ion).
Use the Henderson-Hasselbalch equation for a base: \( \text{pOH} = \text{pK}_b + \log \left( \frac{[\text{conjugate acid}]}{[\text{base}]} \right) \).
Calculate the pOH from the given pH: \( \text{pOH} = 14 - \text{pH} = 14 - 4.80 = 9.20 \).
Determine the \( \text{pK}_b \) from the given \( K_b \): \( \text{pK}_b = -\log(3.8 \times 10^{-10}) \).
Substitute the values into the Henderson-Hasselbalch equation and solve for the ratio \( \frac{[\text{conjugate acid}]}{[\text{base}]} \) to find the correct equilibrium ratio.
