You have prepared a 400 mL of a .210 M acetate buffer solution with a pH of 4.44.
1. Determine the concentration of both the acetate and acetic acid in the solution.
2. If you made this solution using solid sodium acetate (MW = 136 g/mol) and liquid acetic acid (17.6 M, referred to as glacial acetic acid), what mass of sodium acetate is required and what volume of glacial acid is required?
I got part 1 but could not figure out part 2.
I could have used your numbers if you had given pKa and ratio base/acid you used. As it is you must check what I have; it may not agree with the constants you used.
pH = pKa + log (base)/(acid)
4.44 = 4.75 + log (base)/(acid)
I obtained b/a = 0.49 or
(base) = 0.49(acid)
Then a + b = 0.210
Solve those two equations to obtain
(acid) = 0.14M
(base) = 0.07M
The volume of the solution is 400 mL or 0.400 L.
mols acid = 0.14 x 0.400 = 0.056
mols base = 0.07 x 0.400 = 0.028
Then grams acid = mols x molar mass and use density to determine volume acetic acid.
grams base = mols base x molar mass sodium acetate.
You may need to work through the whole problem again using the values of your first calculation. Post your work if you get stuck or have questions.
To determine the required mass of sodium acetate and the volume of glacial acetic acid to prepare the buffer solution, we need to use the concept of the mole to mole ratio.
1. Determine the concentration of both acetate and acetic acid:
In a buffer solution, the concentration of the weak acid (acetic acid) and its conjugate base (acetate) are equal. We know the initial volume of the solution (400 mL) and the molar concentration (0.210 M). To find the moles of both acetate and acetic acid, we can use the formula:
moles = concentration x volume (in liters)
moles of acetate = (0.210 M) x (0.400 L) = 0.084 moles
moles of acetic acid = (0.210 M) x (0.400 L) = 0.084 moles
2. Determine the mass of sodium acetate:
The mole to mole ratio between sodium acetate (NaC2H3O2) and acetic acid (C2H4O2) is 1:1. This means that for every 1 mole of acetic acid, we need 1 mole of sodium acetate.
To find the mass of sodium acetate required, we can use the formula:
mass = moles x molecular weight
mass of sodium acetate = 0.084 moles x 136 g/mol = 11.44 grams
So, you would need approximately 11.44 grams of sodium acetate to prepare the buffer solution.
3. Determine the volume of glacial acetic acid:
To find the volume of glacial acetic acid required, we need to calculate the moles of acetic acid and use the molarity formula:
moles = concentration x volume (in liters)
0.084 moles = (17.6 M) x (volume of glacial acetic acid)
Rearranging the equation to solve for the volume:
volume of glacial acetic acid = 0.084 moles / 17.6 M = 0.0048 L or 4.8 mL
So, you would need approximately 4.8 mL of glacial acetic acid to prepare the buffer solution.
In summary, to prepare a 400 mL acetate buffer solution with a pH of 4.44:
- You would need approximately 11.44 grams of sodium acetate.
- You would need approximately 4.8 mL of glacial acetic acid.