What is [h3o +] in a solution made by dissolving 0.200 mole of sodium acetate (nach3coo) in enough water to make one liter of solution? ka for ch3cooh is 1.80 × 10−5 .

Well Na acetate dissolves in water to form a basic solution due to hydrolysis. The Aco-1 reacts with H2O to give HOAC and OH-1 according to the hydrolysis constant 1 x10^-14/1.8 X 10^-5 = 5.56 X 10^-10 
X^2/0.1-X = 5.56 X 10^-10 
X^2 = 5.56 X 10^-11 
X = 7.46 X 10^-6=OH pOH = 6 - log 7.46 = 5.13 
pH = 8.87 
so the [H+] = 1.35 X 10^-9 M 
I do not know what is wrong with this answer... unless you gave pH and they wanted as you gave above the H+ concentration ( that would give that pH ). 

Proof [H+][OH-1]= 1 X 10^-14 
(1.35 X 10^-9)( 7.46 x 10^-6 ) = 10.07 X 10 ^-15 = 1.07 X 10^-14 

A. volume stays constant. just took took the quiz