What is the Ka value of acetic acid from the pH of the buffered solution? pH=4.39 of 25ml of HC2H3O2 with .410g NaC2H3O2 added.
Ka = [H3O][C2H3O2] / [HC2H3O2]
Use the Henderson-Hasselbalch equation.
pH = pKa + log[(base)/(acid)]
Solve for pKa and convert to Ka.
To determine the Ka value of acetic acid (HC2H3O2) from the pH of the buffered solution, you will need to use the Henderson-Hasselbalch equation. This equation relates the pH of a buffered solution to the concentrations of the acid and its conjugate base.
The Henderson-Hasselbalch equation is as follows:
pH = pKa + log([A-]/[HA])
Where:
pH is the measured pH of the buffered solution
pKa is the negative logarithm of the acid dissociation constant (Ka)
[A-] is the concentration of the conjugate base (C2H3O2-)
[HA] is the concentration of the acid (HC2H3O2)
Given that the pH of the buffered solution is 4.39, you can rearrange the Henderson-Hasselbalch equation to solve for pKa:
pKa = pH - log([A-]/[HA])
However, before substituting the values into the equation, you need to find the concentrations of both the conjugate base ([A-]) and the acid ([HA]).
To find the concentration of the conjugate base, you need to determine the number of moles of sodium acetate (NaC2H3O2) that was added to the solution. You can do this by dividing the mass of NaC2H3O2 by its molar mass.
molar mass of NaC2H3O2 = atomic mass of Na + (2 x atomic mass of C) + (3 x atomic mass of H) + (2 x atomic mass of O)
Once you have the number of moles of NaC2H3O2, you can divide it by the total volume of the solution (25 mL) to get the concentration of the conjugate base ([A-]).
Next, you need to determine the concentration of the acid ([HA]). Since acetic acid is a weak acid, it does not fully dissociate in water. However, you can assume that its concentration is equal to the initial concentration of acetic acid before it reacts with any sodium acetate. This is known as the initial acid concentration.
Now, substitute the determined values into the equation for pKa:
pKa = 4.39 - log([A-]/[HA])
Finally, calculate the Ka value by taking the antilogarithm (inverse logarithm) of the pKa value:
Ka = 10^(-pKa)
By following these steps, you can determine the Ka value of acetic acid (HC2H3O2) from the pH of the buffered solution.