power of hydrogen

pH scale logarithmic scale If pH changes by factor of 1, expressing H+1 concentration, [H+1] If pH changes by factor of 1, [H+1] changes by factor of 10 pH = -log[H+1]

Molarity to pH To determine pH: express [H+1] in scientific notation remember, [ ] means concentration of whatever is inside brackets log is the power of 10

Molarity to pH for Pure water tiny bit of ionization in pure water: H2O  H+1 + OH-1 [H+1] = [OH-1] = 1 X 10-7 M pH = -log[H+1] = -(-7) = 7

pH 3 2 1 pH .001 M or 1 X 10-3 M 0.01 M 1 X 10-2 M 0.1 M 1 X 10-1 M 1 M 1X100 M [H+1]

pOH = 14 10 7 4 0

pH range 0 to 14 (7 is neutral) pH = 0, strongly acidic pH = 14, strongly basic

ACID or BASE? acids: [H+1]  [OH-1] bases: [OH-1]  [H+1]

Relationships of: pH, pOH, [H+1] and [OH-1] product of [H+1] and [OH-1] is always 1x10-1M add exponents when multiple in scientific notation sum of pH and pOH is always 14

pH + pOH = 14 pH = 3, pOH = 11 pH = 7, pOH = pH = 10, pOH = 7 5 13

if pH = 4 [H+1] = ? pOH = ? [OH-1] = ? 1 x 10-4 M 10 1x10-10 M

if the [OH-1] = 1 X 10-3 pOH = ? pH = ? [H+1] = ? 3 14 – 3 = 11 1x10-11 M

if the [H+1] = 1 x 10-5M pH = ? pOH = ? [OH-] = ? 5 14 – 5 = 9 1x10-9M

6 1x10-2 1x10-5 3 Acidic or Basic pOH [OH-] (M) pH [H+] 1x10-3 1x10-11 11 A 9 B 1x10-9 5 A 2 1x10-12 12 1x10-8 8 1x10-6 B

How to safely test pH use instruments – pH meter use indicators – litmus paper or liquid indicators see if substance reacts with a metal other than Cu, Ag, or Au NEVER “taste”

pH meters

Indicator (l) substance that changes color over narrow pH range use several indicators to narrow down pH range of substance See Table M