Review 1: Written the conjugate base and acid for the following acids and bases.

1
Review 1 Written the conjugate base and acid for
the following acids and bases.
2
Review 2 Name the acid, base, conjugate acid and
base for each reaction.
CH3NH2 H2O ? CH3NH3 OH -
conjugate acid
base
acid
conjugate base
H3PO4 H2O ? H3O H2PO4 -
conjugate acid
conjugate base
base
acid
HC2H3O2 H2O ? H3O C2H3O2 -
base
acid
conjugate acid
conjugate base
CH3NH3 H2PO4 - ? H3PO4
CH3NH2
base
acid
conjugate acid
conjugate base
3
Some common Acids
Most acids are Oxyacids These are acids in which
the acidic hydrogen is attached to an oxygen.
Organic acids are ones that have a carbon atom
backbone. They commonly contain the carboxyl
group COOH. Acetic acid is an example
4
Water as an Acid and a Base
Some substances can act as both acids and bases,
they are called amphoteric. Water is an
example. Water can react with itself to form ions
H2O (l) H2O (l) ? H3O (aq) OH -
(aq) Acid base
Only two H2O molecules out of every billion
ionize. The concentration of is H3O and OH
- is 1.0 ? 10-7 mol L-1
The equilibrium expression for this reaction
is Kw H3O OH- this is called the
dissociation constant Kw (1.0 ? 10-7 )(1.0 ?
10-7) Kw (1.0 ? 10-14 )
Kw K constant w water
5
In pure water, H3O OH- 1 ? 10 7 Kw
(1 ? 10 7) (1 ? 10 7) 1 ? 10 14 Kw 1 ? 10
14
But at 25 ?C the Kw of any aqueous solution (no
matter what it contains) will equal 1.0 ? 10-14
. H3O ? OH- must 1 ? 10 14.
So if H3O goes up, OH- must go down so that
the product of the two is still 1 ? 10 14.
There are three possibilities in an aqueous
solution.
1. In a neutral solution H3O OH- 2. In an
acidic solution H3O ? OH- 3. In a basic
solution OH- ? H3O
6
Calculating Ion Concentrations in water
solutions Kw H3O OH- 1 ? 10 14
What is the H3O or OH- in each of the
following solutions, also state if the solution
is neutral, acidic, or basic. a. 1 ? 10 5 M OH-
b. 1 ? 10 7 M OH- c. 10.0 M H
a.
b.
c.
7
The pH Scale
The pH scale is used to compare the strength of
different acids and bases. The strength of an
acid is based on the H3O . But these values
are often very small numbers
To express small numbers conveniently, chemists
use the p scale which is based on logarithim
(base 10)
E.g. 1.0 ? 10-9 mol L-1
9.00 on the p scale
pH -logH
8
The pH Scale
pH -log H 1
pH -log H 14
H 1 ? 10 -14 0.00000000000001 mol L-1
H 1 ? 10 -1 0.1 mol L-1
9
So you can convert the concentrations of H and
OH- in solutions in terms of pH and pOH
pH - log H pOH - log OH-
pH pOH 14
So if you know the H then you can calculate
the pH of a solution.
10
(No Transcript)
11
Calculating the pH and pOH using a calculator
1. What is the pH of a solution where H 1.0 ?
10-9
Step 1 Enter the number 1.0 ? 10-9 Step 2
Push the log key -9.00 Step 3 Push the /- key
9.00
pH 9.00
2. What is the pOH of the above solution?
pH pOH 14
pOH 14 - pH 14 9.00
pOH 5.00
12
3. What is the pH of a solution with OH- 1.0 ?
10-6
Kw H3O OH- 1 ? 10 14
H 1 ? 10 14 / 1.0 ? 10-6 1.0 ? 10-8
Step 1 Enter the number 1.0 ? 10-8 Step 2
Push the log key -8.00 Step 3 Push the /- key
8.00
pH 8.00
4. Calculating H from the pH
Step 1 Enter the pH 7.0 Step 2 Push the
/- key -7.00 Step 3 Push the inv log
keys 1.0 ? 10-7
H 1.0 ? 10-7