What is the pH after adding HCl to the buffer solution?

[ahhppull]

Homework Statement

A 200.0 mL buffer solution is 0.280 M in acetic acid and 0.280 M in sodium acetate. What is the pH after addition of 0.0050 mol of HCl?

Homework Equations

pH = pKa + log[base]/[acid]

The Attempt at a Solution

I have a problem with the significant figures. The website won't accept my answer. Or maybe I'm just wrong.

The initial ph is 4.74 and when HCl is added, the concentration of sodium acetate decreases by .0050 and the concentration of acetic acid increases by .0050

Therefore the equation becomes pH = 4.74 + log [.275]/[.285]

My answers I have inputted were 4.72 and 4.73

 

[ahhppull]

Nvm, no help needed. I figured out what the problem is.

 

[Borek]

Would be nice if you can tell what it was.

 

[ahhppull]

Oh, I did the problem wrong. The right was to do it was:

.28 M acetic acid x .200 L = .056 moles acetic acid
.056 moles acetic acid + .005 moles (from HCl) = .061 moles acetic acid

.28 M sodium acetate x .200 L = .056 moles sodium acetate
.056 moles sodium acetate - .005 moles = .051 moles sodium acetate

pH = 4.74 + log [.051]/[.061]
pH = 4.67