posted by Lauren on .
Calculate the amounts and pH values for preparing the following acetic acid/acetate buffer solution.
1.) In the first step, If you plan to prepare a 2.00 M sodium acetate in 200.0 mL distilled water, how many grams of sodium acetate should be added in water?
2.) B. In the 2nd step, if 1.00M acetic acid will be added in the above solution, what will the pH value of the acetic acid/sodium buffer solution be? Assuming the change in volume will not be significant when all the chemicals are added, and the dissociation value (Ka) of acetic acid is 1.78x10-5
3.) C. If you plan to use the above stock solution from the 2nd step to prepare a new buffer solution in pH=4.50, how many additional moles of acetic acid should be added in this 200.0 mL solution. Assuming the change in volume will not be significant?
I think something is missing here. I don't get the connection between step 1 and step 2 and the final product.
To prepare 200 mL of 2.00 M sodium acetate, you will need 0.2 x 2 = 0.4 mol sodium acetate and that x molar mass = about 33 grams (but you need to go through and do it more accurately).
2) There is no indication of the amount of acetic acid added.
200.0 mL = 0.20 L
Molarity = moles of solute/liter of solution
2.00M = moles of solute/0.20 L
Moles of solute = 2.00M x 0.20 L = 0.40 moles sodium acetate
Grams of solute = moles of solute x molar mass
Grams of solute = 0.40 moles x 82.03 g/mol = 32.8 grams sodium acetate