You need to produce a buffer solution that has pH 5.12. You already have a solution that contains 10millimoles of acetic acid. How many millimoles of solid sodium acetate will you need to add to this solution? (The pKa of acetic acid is 4.74)
Can someone help me answer this? (I don't have an answer for it though)
2007-03-11 09:38:41 · 1 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
Use the Henderson Hasselbalch equation for buffers
pH =pKa +log[conjugate base]/[acid]
Here the conjugate base is CH3COO- and the acid is CH3COOH. Since concentration= mole/V, the ratio of the concentrations is also a ratio of mole (V is the volume of the solution, it is the same for both concentrations thus it is simplified in the ratio). Also the convertion factor from mmole to mole is also simplified. Thus the equation can be rewritten as
pH= pKa + log( mmole CH3COO- / mmoleCH3COOH )
you know all except for mmole CH3COO-, so just substitute and you'll find the mmole of CH3COO-.
Finally mmole CH3COONa =mmole CH3COO- (since the salt dissociates 100%) and you have your answer.
2007-03-11 10:51:41 · answer #1 · answered by bellerophon 6 · 0⤊ 0⤋