Friday, March 27, 2009

Water Equilibrium Constant and Acid Base Strength

Water Equilibrium Constant
Water is a very weak electrolyte. Ionization occurs in water:
H2O → H+ + OH-

K [H2O] = [H+] [OH-]
Kw = [H+] [OH-]
At a temperature of 25ºC, Kw = 1.10-14, so that [H+] = [OH-] = 1.10-7.
Acid solution [H+]> 1.10-7.
Base solution [OH-] < 1.10-7.

Acid Base Strength
Acid base strength expressed in H+ or OH- concentration. Acid with the high concentration of H+ has greater acid strength than with the acid H+ with low concentration. Similarly base with its concentration of OH-.
Example:
HCl → ....H+
....+ ...Cl-
0.1 M .. 0.1 M 0....0.1 M
H2SO4 → ....2H
+ ...+ ..SO42-
0.1 M .....0.2 M...... 0.1 M
At the same concentration (0.1 M), H2SO4 is more acid than HCl because the H2SO4 has greater H
+ concentration than HCl.

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