Question

a student needed 1000 ml of a 0.10 buffer of ph 4.0. calculate the amount of sodium acetate and acidic acid needed for this solution

Answer 1

I assume you meant acetic acid (and not acidic acid). Also, I assume you mean to add M so that the sentence reads .....1000 mL of a 0.10 M buffer (I have added M).
Use the Henderson-Hasselbalch equation.
pH = pKa + log [(base)/{acid)]
pKa = 4.74 for acetic acid.
You want pH = 4.00. Substitute 4.00 and 4.74 appropriately in the equation and calculate (base)/(acid). I found B/A = 0.182 or B = 0.182*A.

So we take 1000 mL of 0.1 M acetic acid (M x L = 0.1 mole). Use the ratio you calculated to determine moles base and go from there to grams sodium acetate. Post your work if you get stuck. I think the answer is about 1 or 2 grams NaC2H3O2.