[whatabohr]

My book explains this topic in a really convoluted manner. I get that NaC2H3O2 will be basic because C2H3O2- is the conjugate base of acetic acid. Thus, the acetate ion will have a strong affinity for H+, causing the solution to contain less H+ than OH- making the solution basic..

My book went into calculating Kb given the Ka for acetic acid (1.8E-5) and using the equation Ka * Kb = Kw

What I don't get is why the Kb for the acetate ion is only 5.6E-10... this is extremely low, thus indicating that the acetate ion would be a weak base and hardly dissociate. If it hardly dissociates, then the solution of sodium acetate would be neutral. This isn't true though, because we know that the acetate ion is a strong base and that the solution of sodium acetate is basic.

How does this make sense?!

[Dan]

This isn't true though, because we know that the acetate ion is a strong base and that the solution of sodium acetate is basic.

Acetate is generally considered a weak base - it is much weaker than hydroxide, for example. You could use the K_b data to calculate the pH of 1 M NaOAc to verify that the solution is basic despite the seemingly low K_b.

[Stovn0611]

Consider water as an example - write out the reaction if it was acting as a base, taking a proton away from another water molecule

H2O + H2O -> H3O+ + OH-
                   
Kb = [H3O+][OH-]

Since water is neutral, it has a pH of 7 so the concentration of the hydrogen ion is 10^-7M and [H+]=[OH-] since water is neutral.

Kb = (10^-7)(10^-7) = 10^-14 (also called Kw, the auto-ionization constant of water)

Since Kb for acetate is 5.6*10^-10, it is a significantly stronger(Kb of acetate is 56000x Kw of water) base than water and thus will influence the pH of the solution.

[opsomath]

It's not really true to say "I get that NaC2H3O2 will be basic because C2H3O2- is the conjugate base of acetic acid" That's an overly complicated way to think about it.

Forget about the numbers for a minute. Just think about what reactions it will do in water. Will it release H+ to increase the H3O+ concentration? No, because it has no hydrogens that can come off.

Now, will it increase the OH- concentration? Yeah, it sure will. If you draw the Lewis dot structure of acetate, like this:

http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch01/ch1-3-1.html

you'll see that it has a negatively charged oxygen. That can pull a proton off of water, in the reaction

CH3COO- + H2O -> CH3COOH + OH- .

This isn't an especially favorable reaction, but it is enough to contribute a bit of OH- and raise the [OH-] of water by a couple orders of magnitude (that concentration is very low in neutral water) so that a solution of pure sodium acetate will wind up being about pH 8-9.