I need some help in this question please check what i have done

[lioric]

Homework Statement

A 1.00dm³ buffer sollution contains 0.5 mol of ethanoic acid and 1.00 mol sodium ethanoate.

CH₃COOH: Ka= 1.8x10^-5

Calculate pH of solution
Calculate change in pH when 1cm³ of 1M HCl is added
Calculate change in pH when 2cm³ of 1.5M KOH is added

Homework Equations

pH=pKa + log [A^-/HA]

The Attempt at a Solution

pH=pKa + log [A^-/HA]

So pH= 4.7 + log [1/0.5] (I changed Ka to pKa)

pH=5.046

Is that ok?


The next part is confusing


A^- + HCl → HA + Cl^-

Initial conc.
A^-= 1M
HCl =(What do i write for HCl conc)
HA= 0.5

 

[Borek]

1^st part is OK.

For the second and third simply assume reaction (A^- protonation or HA neutralization) went to completion and concentrations can be calculated from a simple stoichiometry. This is not 100% accurate, but works in most cases.

 

[epenguin]

For first part doesn't [A^-]/[HA] = 1?

 

[Borek]

Why? Questions states explicitly 1 mole of A^- and 0.5 mole of HA.

 

[epenguin]

Why? Questions states explicitly 1 mole of A^- and 0.5 mole of HA.

Ah yes I had hastily read it for totals of all forms.

 

[lioric]

thank you very much i figured it out