power of hydrogen
DESCRIPTION
power of hydrogen. 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 ]. Molarity to pH. To determine pH: express [H +1 ] in scientific notation - PowerPoint PPT PresentationTRANSCRIPT
power of hydrogen
pH scalepH 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[HpH = -log[H+1+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 10log 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 10-7-7 M• pH = -log[Hlog[H+1+1]] = -(-7-7) = 7
pH
33221100pH
.001 Mor
1 X 10-3-3
M
0.01 Mor
1 X 10-2-2
M
0.1 Mor
1 X 10-1-1
M
1 Mor
1X1000 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) = 10-5
• 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 10-3 M • then pOH = -log(10-3) = -(-3) = 3
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 = 14pH + pOH = 14
• pH = 3, pOH = • pH = 7, pOH = • pH = 10, pOH =• pH = 9, pOH =• pH = 1, pOH =
1111774455
1313
•if pH = 4if pH = 4
• [H+1] = ?
• pOH = ?
• [OH-1] = ?
1010
1 x 101 x 10-4 -4 MM
1x101x10-10-10 M M
• if the [OH-1] = 1 X 10-3
• pOH = ?
• pH = ?
• [H+1] = ?
pOH = -log[OHpOH = -log[OH-1-1]]= -log(10= -log(10-3-3) = -(-3) = 3) = -(-3) = 3
14 – 3 = 1114 – 3 = 11
1x101x10-11-11 M M
• if the [H+1] = 1 x 10-5M
• pH = ?
• pOH = ?
• [OH-] = ?
55
14 – 5 = 914 – 5 = 9
1x101x10-9-9MM
6
1x10-2
1x10-5
3
Acidic or Basic
pOH[OH-](M)(M)
pH[H+](M)(M)
11111x101x10-3-3 1x101x10-11-11 AA
55991x101x10-9-9
BB
22 12121x101x10-12-12 AA
881x101x10-8-8 1x101x10-6-6 BB
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”
pH meters
Indicator
• substance that changes color over narrow pH range
• use several indicators to narrow down pH range of substance
• See Table M
