* Fixed Question
What is the PH of a buffer made by adding 8.20 grams of sodium acetate(NaCH3CO2) to 500 ml of 0.10 M(molarity) acetic acid(CH3CO2H). Ka for acetic acid is 1.8 x 10^-5.
Use the Henderson-Hasselbalch equation.
To find the pH of a buffer solution, we need to calculate the concentration of the acetate ion (CH3CO2-) and the acetic acid (CH3CO2H) after the sodium acetate is added to the acetic acid solution.
Let's go step by step:
Step 1: Calculate the number of moles of sodium acetate (NaCH3CO2).
Given:
Mass of sodium acetate = 8.20 grams
Molar mass of sodium acetate = 82.03 g/mol
We can use the formula:
moles = mass / molar mass
moles of sodium acetate = 8.20 g / 82.03 g/mol
Step 2: Calculate the concentration of the acetate ion (CH3CO2-) in the solution.
Given:
Volume of solution = 500 ml = 0.5 L
Molarity of acetic acid = 0.10 M
The sodium acetate dissociates in water into sodium ions (Na+) and acetate ions (CH3CO2-). Since 1 mole of NaCH3CO2 produces 1 mole of CH3CO2-, the concentration of CH3CO2- is the same as the concentration of NaCH3CO2.
Concentration of CH3CO2- = moles of sodium acetate / volume of solution
Step 3: Calculate the concentration of acetic acid (CH3CO2H) in the solution.
The initial molarity of acetic acid is already given as 0.10 M.
Step 4: Calculate the ratio of acetate to acetic acid.
Given the equation for the dissociation of acetic acid in water:
CH3CO2H ⇌ H+ + CH3CO2-
The Ka expression for acetic acid is:
Ka = [H+][CH3CO2-] / [CH3CO2H]
Since we are calculating the pH of a buffer solution, the [H+] concentration will approximately be equal to the concentration of CH3CO2- and [CH3CO2H].
Step 5: Calculate the pH of the buffer solution.
Given the Ka value for acetic acid is 1.8 x 10^-5.
Ka = [H+][CH3CO2-] / [CH3CO2H]
[H+] = [CH3CO2-] = [CH3CO2H] (approximation for a buffer solution)
Set up the equation:
1.8 x 10^-5 = [H+]^2 / [CH3CO2H]
Now we can solve for [H+].
Step 6: Calculate the pH.
pH = -log[H+]
Plug in the value of [H+] to find the pH.
By following these steps, you should be able to calculate the pH of the given buffer solution.