pH and pOH Acid Neutral Base

pH [H+] = 10-pH . . . . Hence “power of hydrogen.” pH = -log [H+] Low pH = acid pH = “power of hydrogen” Power is the math power, as in 10 to the second power = 102 [H+] = concentration of H+ ion (molarity) The higher the concentration, the stronger the acid, the lower the pH [H+] = 10-pH . . . . Hence “power of hydrogen.” Solving for pH: pH = -log [H+]

pH examples What is the pH of a solution if the H+ concentration is 3.4 X 10-3 M? pH = -log [H+] pH = -log (3.4 X 10-3 M) pH = 2.5 What is the H+ concentration of an acid with a pH of 3.0? [H+] = 10-pH [H+] = 10-3.0 [H+] = .0010 M or 1.0 X 10-3 M

pOH [OH-] = 10-pOH pOH = -log [OH-] Low pOH = base pOH = a measure of hydroxide ion concentration pOH is derived from pH [OH-] = concentration of OH- ion (molarity) The higher the concentration, the stronger the base, the lower the pOH [OH-] = 10-pOH Solving for pOH: pOH = -log [OH-]

pOH Examples What is the pOH of a solution if the OH- concentration is 3.4 X 10-6 M? pOH = -log [OH-] pOH = -log (3.4 X 10-6 M) pOH = 5.5 What is the OH- concentration of a base with a pOH of 2.0? [OH-] = 10-pOH [OH-] = 10-2 [OH-] = .010 M or 1.0 X 10-2 M

pH and pOH pH is a measurement of the [H+] pH = -log [H+] pOH is a measurement of the [OH-] pOH = -log [OH-] pH and pOH must equal 14 pH + pOH = 14 pOH can be found when you know pH and vise versa In pure water, pH and pOH are both 7. All aqueous solutions have a pH and a pOH.

Example If [H+] = 1.0 x 10-7 M, then what is the pH? pH = -log [H+] pH = -log (1.0 x 10-7) pH = 7.0 You must use the log key.

Example If the [OH-] is 5.01 x 10-4 M, what is the pOH? pOH = -log [OH-] pOH = -log (5.01 x 10-4) pOH = 3.30

Sample Problem In household bleach, the concentration of OH- ions is 5.00 x 10-2 M. What is the pH? pOH = -log [OH-] pOH = -log (5.00 x 10-2) pOH = 1.30 pOH + pH = 14 pH = 14 - 1.30 pH = 12.7