The pH of a buffer can be predicted using the Hendersen-Hasselbach equation:
pH=pKa+ log([conjugate base][conjugate acid])
The choice of the conjugate acid-base pair (as you did in the previous questions) determines the pKa value to be used in the H-H equation. By varying the relative amounts of conjugate acid and base, it is possible to adjust the pH value of the buffer solution to the desire value. The ratio of [A-]/[HA] is defined as the buffer ratio.
If 0.100 L of a buffer solution is prepared by mixing 0.30 mol of formic acid (pKa = 3.74) and 0.60 mol of sodium formate in water, what is the buffer ratio in the resulting solution?
To determine the buffer ratio in the resulting solution, you need to find the ratio of the concentration of the conjugate base ([A-]) to the concentration of the conjugate acid ([HA]).
In this case, the conjugate acid is formic acid (HCOOH) and the conjugate base is sodium formate (HCOONa).
First, calculate the concentrations of the conjugate acid and base using the given amounts and the volume of the buffer solution:
Concentration of HCOOH ([HA]) = moles of HCOOH / volume of solution
= 0.30 mol / 0.100 L
= 3.00 M
Concentration of HCOONa ([A-]) = moles of HCOONa / volume of solution
= 0.60 mol / 0.100 L
= 6.00 M
Now, calculate the buffer ratio by dividing the concentration of the conjugate base ([A-]) by the concentration of the conjugate acid ([HA]):
Buffer ratio = [A-] / [HA]
= 6.00 M / 3.00 M
= 2.00
Therefore, the buffer ratio in the resulting solution is 2.00.