Ka = ------------
Substitute the given information, and solve for the unknown quantity.
1.75 X 10--5 mol/L = ----------------
Although the actual concentration of the acetic acid is less than 0.100 mol/L
after ionization, it is a negligible amount (less than 5 your future course work,
the amount of ionized acid or base in this type of problem should be
considered to be a negligible amount.
Substitute the variable x for H+ and C2H3O2- since for every dissociated molecule
of HC2H3O2, one hydrogen ion and one acetate radical are produced.
x2 = (1.75 X 10-5 mol/L) (0.100 mol/L) = 1.75 X 10-6 mol2/L2
x = [H ] = 1.32 X 10-3 mol/L
By convention, the equilibrium constants of weak electrolytes are written
without units. However, they do have units.
Section III. DISSOCIATION OF WATER
Although water is not an electrolyte, its molecules do have a limited tendency to
dissociate into H and OH ions.
HOH <====> H + OH
It can be shown that the tendency of water to dissociate is given by:
[H+] [OH ]
K = ----------
At 25C, the value of K is 1.8 X 10-16.