What is pH? - Port Washington School
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Transcript What is pH? - Port Washington School
What is pH?
Tells us the relative quantity of H+ ions (or
the acidity) in solution.
The greater the [H+] the lower the pH.
pH Values of Common Liquids
H+ and OH- in Pure Water
Self Ionization of Water: small quantity of water
molecules in a sample will self ionize.
Results in small, but equal [H+] and [OH-]
Concentration of these ions is 1 x 10-7 M (pH = 7)
Reversible reaction that is at equilibrium.
H 2O
H+
OH-
http://youtu.be/kW-Zk4zABzw
H+ + OH[H+] = [OH-]
When Acid is Added to Water
Increases the H+ concentration
As
H+ increases, OH- decreases
[H+] > [OH-]
H+
OH-
When Base is Added to Water
Increases OH- concentration
When
OH- increases, H+ decreases
[OH] > [H+]
H+
OH-
pH Scale
0
1
2
3 4 5
6
7 8 9 10 11 12 13 14
Basic
Acidic
Neutral
[H+]>[OH-]
[H+] = [OH-]
[OH-]>[H+]
Important Summary
Acidic:
[H+] > [OH-]
Basic:
[H+] < [OH-]
Neutral: [H+] = [OH-]
Pretty Hydrangeas
The color of hydrangea flowers depends
on the pH of the soil.
Calculating pH
pH = - log [H+]
From the French pouvoir hydrogene
(“hydrogen power” or power of hydrogen)
[H+]
pH
1 x 10-5 M
5
1 x 10-9 M
9
1 x 10-11 M
11
11
If the [H+] is 0.000001 M, what is the pH?
pH = 6
If the [H+] is 0.01M, what is the pH?
pH = 2
If the pH is 10, what is the [H+]?
[H+] = 1 x 10-10 M
If the pH is 4, what is the [H+]?
[H+] = 1 x 10-4 M
Calculating pOH
What if you are given the concentration of
a base?
Ex: .000001M LiOH
You need to find the pOH!!
pOH
pOH = -log [OH-]
Ex:
.000001M LiOH = 1 x 10-6
pOH = 6
Ex:
.0001M NaOH = 1 x 10-4
pOH = 4
How can you find pH of a Base?
Easy!!!
pH + pOH = 14
Ex:
.000001M LiOH = 1 x 10-6
pOH = 6
pH = 8
Ex:
.0001M NaOH = 1 x 10-4
pOH = 4
pH = 10
Kw or Equilibrium Constant
for Water
If you know the concentration of one ion you
can find the other!
[H+] x [OH-] = 1 x 10-14
If [H+] is .001M what is the [OH-]?
[1 x 10-3] x [OH-] = 1 x 10-14
[OH-] = 1 x 10-11
Everything keeps adding up to 14!!
What’s up with that?
Let’s Try It
You have a .001 HCl solution.
Find: [H+], [OH-], pH, pOH
Let’s Try It
You have a .000000001M NaOH solution.
Find: [H+], [OH-], pH, pOH
Equation Summary
pH = -log [H+ ]
[H+ ] = 10-pH
pH + pOH = 14
pOH = -log [OH- ]
[OH- ] = 10-pOH
[H+ ] x [OH- ] = 1x10-14
Acidic solution:
Neutral solution:
Basic solution:
pH < 7 pOH > 7
pH = 7 pOH = 7
pH > 7 pOH < 7
Let’s Practice
A solution with a pH of 2.0 has a hydronium ion
concentration ten times greater than a solution
with a pH of
(1) 1
(2) 3
(3) 0.20
(4) 20
Which statement correctly describes a solution with
a pH of 9?
(1) It has a higher concentration of H3O+ than OH–
and causes litmus to turn blue.
(2) It has a higher concentration of OH–
than H3O+ and causes litmus to turn blue.
(3) It has a higher concentration of H3O+ than OH–
and causes methyl orange to turn yellow.
(4) It has a higher concentration of OH–
than H3O+ and causes methyl orange to turn red.
What is the pH of a solution that has a
hydronium ion concentration 100 times greater
than a solution with a pH of 4?
(1) 5
(2) 3
(3) 2
(4) 6
Solution A has a pH of 3 and solution Z has a
pH of 6.
How many times greater is the
hydronium ion concentration in solution A than
the hydronium ion concentration in solution Z?
(1) 100
(2) 3
(3) 2
(4) 1000
When the pH of a solution changes from a pH of 5
to a pH of 3, the hydronium ion concentration is
1). 0.01 of the original content
2). 0.1 of the original content
3). 10 times the original content
4). 100 times the original content
As the pH of a solution is changed from 3
to 6, the concentration of hydronium ions
(1) increases by a factor of 3
(2) increases by a factor of 1000
(3) decreases by a factor of 3
(4) decreases by a factor of 1000
Honors Questions
If the pH of a solution is 3.25 find the pOH,
[H+], and [OH-].
If .065 mole of KOH is placed in 20 liters of
water, what is the resulting pH?
Crash Course pH and pOH
http://www.youtube.com/watch?v=LS67vS
10O5Y&safe=active
Acid Rain
(Not to be confused with
“Chocolate Rain”)
Acid Rain
Unpolluted rain has a
pH of 5.6
It is naturally acidic
due to the gases in the
air that dissolve in it.
Acid Rain
Rain with a pH below 5.6 is “acid rain“
pH of Rainwater
across United States in 2001
Sources of Acid Rain
Sources of Acid Rain
Power stations
Oil refineries
Coal with high S content
Car and truck emissions
Bacterial decomposition, and lightning
hitting N2
CO2 in the air forms carbonic acid
CO2 + H2O
H2CO3
This increases the [H+] of rain
H2CO3
H+ (aq) + HCO3-(aq)
Reactions with oxygen in air form SO3
2SO2 + O2
2 SO3
Reactions with water in air form acids
SO3 + H2O
H2SO4 sulfuric acid
NO + H2O
HNO2 nitrous acid
HNO2 + H2O
HNO3 nitric acid
Effects of Acid Rain
Effects of Acid
Rain
Leaches heavy metals like Al from soil,
which kills fish
Fish kills in spring from runoff due to
accumulation of large amounts of acid in
snow
Prevents shellfish from building strong shells
Dissolves waxy coatings that protect leaves
from bacteria
Corrodes metals, textiles, paper and leather
Honors: pH and pOH game
http://www.quia.com/rr/4051.html
Acid Rain Destroys National Monuments
http://news.discovery.com/videos/earth-acidrain-eating-washington-dc.html
Global Warming: CO2 and Ocean Acidity
http://planetgreen.discovery.com/videos/blue
-august-acid-in-the-water.html
Acid Rain Site produced by EPA
http://www.epa.gov/acidrain/education/site
_kids/
EPA Website Detailing Acid Rain Causes
and Effects as well as Legislation
http://www.epa.gov/acidrain/