SOL Review – May 6, 2013
Topic: Acid/Base Theory
Arrhenius Theory:
Acids: substances that produce H+ ions in solution
Examples: HCl, H2SO4, HNO3
Bases: substances that produce OH- ions in solution
Examples: NaOH, Ca(OH)2, KOH
Neutralization reaction:
When an acid is added to a base, the products are water and a salt.
Examples:
NaOH + HCl  H2O + NaCl
HNO3 + Ca(OH)2  H2O + Ca(NO3)2
Bronsted-Lowry Theory:
Acids: substances that donate a proton (H+)
Bases: substances that accept a proton (H+)
Example:
HC2H3O2 + NH3  C2H3O2- + NH4+
1
pH Scale:
H+ ion concentration
(M)
1
10-1
10-2
10-3
10-4
pH
value
0
1
2
3
4
10-5
5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
6
7
8
9
10
11
12
13
14
pH
pH = -log[H+]
[H+] = 10-pH
[H+]
OH- ion concentration
(M)
10-14
10-13
10-12
10-11
10-10
Examples
Hydrochloric acid
Stomach acid
Lemon juice
Vinegar, Coca-Cola, Beer
Tomatoes
Black Coffee, Normal
Rainwater
Urine
Pure water, Blood, Tears
Seawater
Baking soda
Great Salt Lake
Household Ammonia
Bicarbonate of Soda
Oven cleaner
Sodium Hydroxide
pH + pOH = 14
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
1
pOH
[OH-] = 10-pOH
Kw = [H+][OH-]
Kw = 1.0 x 10-14
10-9
pOH = -log[OH-]
[OH-]
2
Examples:
1. If the [H+] is 1.5 x 10-3 M, what is the [OH-]?
𝐾𝑤 = [𝐻 + ][𝑂𝐻 − ]
𝐾𝑤
= [𝑂𝐻 − ]
[𝐻 + ]
(1.0𝑥10−14 )
= [𝑂𝐻 − ] = 6.7𝑥10−12 𝑀
(1.5𝑥10−3 )
2. If the [H+] = 4.3 x 10-6 M, what is the pH?
𝑝𝐻 = − log[𝐻 + ]
𝑝𝐻 = − log(4.3𝑥10−6 )
𝑝𝐻 = 5.37
3. If the [H+] = 7.8 x 10-10 M, what is the pOH?
𝑝𝐻 = − log[𝐻 + ]
𝑝𝐻 = − log(7.8𝑥10−10 ) = 9.11
𝑝𝐻 + 𝑝𝑂𝐻 = 14
14 − 𝑝𝐻 = 𝑝𝑂𝐻 = 14 − 9.11 = 𝑝𝑂𝐻 = 4.89
4. If the pH is 5.61, what is the [OH-]?
𝑝𝐻 + 𝑝𝑂𝐻 = 14
14 − 𝑝𝐻 = 𝑝𝑂𝐻 = 14 − 5.61 = 𝑝𝑂𝐻 = 8.39
[𝑂𝐻 − ] = 10−𝑝𝑂𝐻
[𝑂𝐻 − ] = 10−8.39 = 4.07𝑥10−9 𝑀
3
Titration Process:
A titration is an experimental process that is used to determine the concentration of
substance, most often an acid or a base. A buret is used to add a specific amount of
the titrant to the solution that is being analyzed, the analyte. An indicator is used to
show the exact point when the analyte is neutralized by the titrant. An indicator is a
substance that changes color depending on the pH of the solution it is in. The most
common indicator is phenolphthalein. Phenolphthalein is fuchsia in basic solutions
and clear in acidic solutions. Another way to determine the endpoint of a titration is
by using litmus paper. There are two types of litmus paper: red litmus paper and
blue litmus paper. Red litmus paper turns blue when it is exposed to a basic
solution and stays red when it is exposed to an acidic solution. Blue litmus paper
turns red when it is exposed to an acidic solution and stays blue when it is exposed
to a basic solution.
At the endpoint of the titration (at the neutralization point), the moles of the acid
are equal to the moles of the base.
By knowing this relationship, you can determine the concentration of the analyte.
You can use the formula, M1V1 = M2V2
-This formula can only be used when the ratio of the acid to the base is 1:1
So for example, 25mL of a 1.5M solution of NaOH were used to completely
neutralize 15mL of HCl. What is the concentration of the HCl solution?
M1 = 1.5M NaOH
M2 = ? M HCl
M1V1 = M2
V2
V1 = 25mL NaOH
V2 = 15mL HCl
(1.5M)(25mL) = M2 = 2.5M HCl
(15mL)
Another example:
16.43mL of a 0.100M solution of HBr were used to completely neutralize 14.55mL of
KOH. What is the concentration of the basic solution?
M1 = 0.100M HBr
M2 = ? M KOH
M1V1 = M2
V2
V1 = 16.43mL HBr
V2 = 14.55mL KOH
(0.100M)(16.43mL) = M2 = 0.113M KOH
(14.55mL)
4