[govibe]

"How many moles of NaOH must be added to 1.0 L of 1.8 M HC2H3O2 to produce a solution buffered at each pH?

    (a) pH = pKa

    (b) pH = 3.79

    (c) pH = 5.16
"

I know that NaOH is a strong base and will completely dissociate into Na+ and OH-. HC2H3O2 is a weak base. The ions in the solution are HC2H3O2, Na+, and OH-. However, I'm not sure what the chemical equation that will occur in the problem...

[Kryolith]

It's hard to identify what "HC2H3O2" means. It's better to write "CH₃COOH". A buffer is a solution of a weak acid and its salt. Example:

You have 0.5 mol NaOH and 1 mol CH₃COOH in 1 litre. What you get is 0.5 mol/l CH₃COONa (sodium acetate) and 0.5 mol/l (unreacted) CH₃COOH.

To calculate the pH of buffer solutions look at

http://en.wikipedia.org/wiki/Henderson-Hasselbalch_equation

[govibe]

so the base dissocation is

CH3COOH + H2O -> OH- + CH3CO-

and you do an ICE (IRE) box? (since you know concentration of OH-)?

[Borek]

so the base dissocation is

CH3COOH + H2O -> OH- + CH3CO-

That's completely off. CH₃COOH is on a base, it is an acid.

[Kryolith]

An acid is a proton donator, a base a proton acceptor. If CH₃COOH (acetic acid) donates a proton to the an acceptor (=base) eg. water you have:

CH₃COOH + H₂O ------> CH₃COO^- + H₃O⁺

Every acid has a conjugated base and every base a conugated acid. So there are always acid/base pairs. In the reaction above:
CH₃COOH/CH₃COO^- (acid/base)
H₃O⁺/H₂O (acid/base)

For an acetate buffer, you have acetic acid and it's corresponding base acetate (which can be formed with the reaction CH₃COOH + OH^- --->...). To calculate its pH you have to find out the concentration of both, then insert them in the Henderson-Hasselbalch equation.

Try to work it out.

[govibe]

how does the NaOH come into play here... It breaks up into NA+ and OH- ions, neither of which are in the equation

CH3COOH + H2O ------> CH3COO- + H3O+

[Borek]

What happens when you mix acid (acetic) with a base (sodium hydroxide)?

[govibe]

^it will form water, but what's the equation that will form involving all of these species?

[Kryolith]

general:
acid + base ---> water + ??

acetic acid + sodium hydroxide ---> water + ??

What does ?? stand for?