power of hydrogen

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

pOH = increasing [H +1 ] increasing [OH -1 ] (pH goes down) (pH goes up) (more acidic) (more basic)

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

water can undergo self-ionization H 2 O(l) + H 2 O(l)  H 3 O +1 (aq) + OH -1 (aq) H 3 O +1 H 3 O +1 = hydronium ion OH -1 = OH -1 = hydroxide ion OR H 2 O(l)  H +1 (aq) + OH -1 (aq) H +1 H +1 = hydrogen ion = proton H +1 & H 3 O +1 used interchangeably

Acid, Base, or Neutral? all H 2 O contains some H +1 and some OH -1 ions –pure H 2 O: ion concentrations very low (1 x M) neutral solution: [H +1 ] = [OH -1 ] -7 [H +1 ] = [OH -1 ] = 1 X M log[H +1 ]-7 pH = -log[H +1 ] = -(-7) = 7 acidic solution: H +1 > OH -1 basic solution: OH -1 > H +1

Convert 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 10log is the power of 10 pH = -log[H +1 ] pH = -log[H +1 ]

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

Relationships: pH, pOH, [H +1 ], [OH -1 ] pH = power of H refers to [H +1 ] OR [H 3 O +1 ] pOH = power of OH refers to [OH -1 ]

Here’s the math! product of [H +1 ] and [OH -1 ] is always 1x M add exponents when multiply in scientific notation ex: (1 x M)(X) = 1 x M (X) = 1 x M sum of pH and pOH is always 14

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

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

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

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

Indicators liquid substances that change color over narrow pH range use several indicators to narrow down pH range of substance see Table M