pH scale Logarithmic scale –expressing H +1 concentration, [H +1 ] If pH changes by factor of 1, [H +1 ] changes by factor of 10 pH = -log[H +1 ]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 log is the power of 10

Molarity to pH for Pure water there ’ s a tiny bit of ionization:  H 2 O  H +1 + OH -1 -7[H +1 ] = [OH -1 ] = 1 X M log[H +1 ]-7pH = -log[H +1 ] = -(-7) = 7

pH M or -3 1 X M 0.01 M or -2 1 X M 0.1 M or -1 1 X M 1 M or 0 1X10 0 M [H +1 ]

pH to Molarity pH = -log[H +1 ], solve for [H +1 ] -pH = log[H +1 ] antilog(-pH) = [H +1 ] say pH = 5, then –pH = -5 antilog(-5) = the –pH becomes the power of 10!the –pH becomes the power of 10!

pOH by analogy: pOH is defined as –log[OH -1 ] express [OH -1 ] in scientific notation if [OH -1 ] = 1.0 X M then pOH = -log(10 -3 ) = -(-3) = 3

pH + pOH = 14 pH = 3, pOH = pH = 7, pOH = pH = 10, pOH = pH = 9, pOH = pH = 1, pOH =

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

pH range 0 to 14 –with 7 being neutral pH = 0, strongly acidic pH = 14, strongly basic

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

if the [OH -1 ] = 1 X pOH = ? pH = ? [H +1 ] = ? pOH = -log[OH -1 ] = -log(10 -3 ) = -(-3) = 3 14 – 3 = 11 antilog(-11) = 1x M

i f the [H +1 ] = 1 x M pH = ? pOH = ? [OH - ] = ?5 14 – 5 = 9 antilog(-9) = 1x10 -9 M

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

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

Indicator substance that changes color over narrow pH range use several indicators to narrow down pH range of substance