Acids and Bases
I. Electrolytes – substances that dissolve in water to form a solution that conducts electricity. Pure
water does not conduct electricity. Therefore if an aqueous solution conducts
water it must contain free positive and negative ions.
A. Ionic Solids – Soluble ionic compounds are electrolytes. Ionic compounds dissociate
in water to release positive and negative ions capable of conducting electricity.
H–O
H
1) Diagram
Na+ O – H
H
O
H
H Cl- H - O
H
2) Examples
NaCl
NH4Cl
Mg(NO3)2
NH4 NO3
KOH
B. Polar covalent molecules – Some polar covalent molecules containing hydrogen react with
wter to produce positive and negative ions capable of conduction electricity.
1) Example 1 HCl + H2O  H3O+ + Cl2) Example 2 CH3COOH + H2O  H3O+ + CH3COO-
3) A scientist by the name of Svante Arrhenius provided the first explanation for the
behavior of electrolytes in aqueous solutions. This lead him to the first explanation of
acid base behavior.
II. Acid and Base Properties
A. Experimental Properties of Acids
1. Aqueous solutions of acids can conduct electricity. Acids conduct electricity in relation to
their strength or the degree the degree they can ionize water.
Strong Acids HI, HBr,HCl HNO3 H2SO4 HClO4
Weak Acids HF, CH3COOH, citric acid, carbonic acid etc.
2. Acids cause color changes in acid – base indicators
i)
Litmus paper is _red in the presence of an acid
ii)
Phenolphthalein is colorless in the presence of acids
iii)
There are hundreds of acid base indicators
3. Dilute solutions of acids produce have sour tastes ( Its not a good idea to taste
anything in a lab)
4. Acids react with metals that are higher than it on the reactivity series chart to produce
hydrogen gas.
5. Acids react with bases to produce an ionic solid called a “salt” and water
Examples
i) NaOH(aq) + HCl(aq)  NaCl(aq) + H2O
ii) Ca(OH)2 + H2SO4(aq)  CaSO4(aq) + H2O
C. Bases Properties
1. Most bases are ionic compounds composed of a metal and the hydroxide
polyatomic ion that dissociate in water to produce positive and _negative ions. Bases are
electrolytes
Ammonia is also a base because it reacts with water to produce positive and negative ions
NH3(g) + H2O(l)  NH4+ + OHa) Strong bases are very soluble in water
b) Weak bases are only slightly soluble in water or only partially ionize in water.
2. Bases cause color changes in acid – base indicators
i)
Litmus paper is blue in the presence of a base
ii)
Phenolphthalein is magenta in the presence of bases
iii)
There are hundreds of acid base indicators
3. Aqueous solutions of bases feel slippery because they react with the
oils on your skin to form soap. Strong bases have caustic effects
on the skin.
4.
Bases react with acids to form a salt and water.
III. Equilibrium- the term equilibrium describes a system in which the forward process and reverse
process occur at the same rate
Equilibrium is usually established in closed
system in which the temperature,
pressure and concentrations are held constant
No observable changes can be observed even though the processes are occurring.
At Equilibrium concentrations of the reactants and products do not have to be the same but
the rate of formation of the products equals the rate of formation of the reactants.
A. Types:
1. Phase
H2O(l) < -- > H2O (g)
2. Solution
AgCl(s) <  Ag+1 (aq)
+ Cl- (aq)
3. Chemical
a)
HNO3(aq) + H2O(l) ----> H3O+ (aq)
+
NO3-(aq)
Equilibrium Constant K can be determined which can be used to determine the strength
of an acid.
Ka = [H3O+] [NO3-]
[HNO3]
b)
HNO2(aq) + H2O(l) ----> H3O+ (aq)
+
NO2-(aq)
Ka = [H3O+] [NO2-]
[HNO2]
c) A large Ka value indicates that an equilibrium consists mostly of products
A large Ka value indicates that the acid is strong
A small Ka value (negative exponent ) indicates a weak acid and
that the equilibrium consists mostly of reactants
B. pH scale discussion
H2O (l) + H2O  H3O+ (aq) + OHKw = [H3O+] [ OH-] = 1.0 x10-14
[H3O+]=[OH-] = 1.0 x10-7
pH = - log [H3O+]=-log [1.0 x10-7] = 7
Acidic
Neutral
Basic
acid
acid
neutral
base
base
H3 O+
OH-
.00001
.000000001
1.0x1O-5
1.0x1O-7
.000001
.00000001
1.0x1O-6
1.0x1O-7
.0000001
.0000001
1.0x1O-7
1.0x1O-7
.00000001
.000001
1.0x1O-8
1.0x1O-6
.000000001
.00001
1.0x1O-9
1.0x1O-5
pH
pOH
5
9
6
8
7
7
8
6
9
5
Fill in the following
Acidic
Neutral
Basic
H3 O+
OH-
pH
pOH
Acid
.15 M
1.5x10-13
.82
13.18
Base
4.0 x10-12 M
.0025 M
11.4
2.6
Acid
1.6 x10-5 M
6.3x10-10
4.8
9.2
Acid
1.6 x10-3 M
6.3x10-12
2.8
11.2
IV. Conceptual Definitions of acids and bases
A. Acids
1. Svante Arrehenius – An acid is a substance that yields hydrogen ions as the positive
Ion in a solution. A hydrogen ion is just a proton
a) Examples HBr  H+ + Br2. Bronsted – Lowry theory – Any substance that can donate a proton to another substance is an
acid. Acids are proton donars and therefore have one more_ hydrogen than there
base pair.
HNO3(aq) + H2O(l) ----> H3O+ (aq)
acid 1
base 2
acid 2
+
NO3-(aq)
base 1
CH3COOH + H2O  H3O+ + CH3COOacid 1
base 2
acid 2
base 1
B. Bases
1. Svante Arrehenius – A base is a substance that yields hydroxide ions as the negative
Ion in a solution. A hydroxide ion is OHa. Examples LiOH(s)  Li+ + OH2. Bronsted – Lowry theory – Any substance that accepts a proton to another substance is a
base. Bases are proton acceptors and therefore have one more hydrogen than there base
pair.
a) Examples
NH3(g) + H2O(l)  NH4+ + OHBase 1
acid 2
acid 1
base 2
Acid Base HW
1. a) A student spills a solution over there hand and onto their desk. The substance fills slippery.
The student should recognize this solution to be
a) a salt
b) neutral
c) basic
d) acidic
b) How would this substance react with a piece of magnesium?
c) Would this substance be able to neutralize a solution of household ammonia?.
d) What technique could be used to determine the concentration of this solution? Describe the
technique?
2. There are well over 100 known acid - base indicators. How does one acid - base indicator
differ from each other besides their colors.
3. a) What is the name of H2S (aq) ?
b) What is the name of H2SO3 (aq) ?
c) What is the name of H2SO4 (aq) ?
d) What is the name of Zn(OH)2 (aq) ?
4. Which of the following are acids? 4 answers
a) HNO2 (aq) b) C6H12O6 (aq)
f) NaCl
(aq)
g)
c) CH3CH2COOH (aq)
Sr(OH)2 (aq)
h)
d) KOH (aq)
H2CO3 (aq)
i)
HF (aq)
e) NH4OH (aq)
j) C2H5OH (aq)
5. Which of the above are bases? 3 answers ( Hint one of the substances is an alcohol not a
base because it does not release ions when dissolved in water )
6.
C6H5COOH + OH- -----> H2O
+
C6H5COO- + H3O+ -----> H2O
C6H5COO-
+
C6H5COOH
a) Label the conjugate acid base pairs in the above reactions
b) Which of the above substances would be considered amphoteric and why?
c) Why would a solution containing sodium benzoate (NaC6H5COO ) and
benzoic acid (C6H5COOH ) act as a pH buffer?
7. A student prepares a 1.0 M solutions of HBr (aq) , HCOOH (aq) and H2C2O4 (aq) ?
The Ka of the HBr is very large, the Ka of the HCOOH is 1.8 x 10-4 , and
the Ka of H2C2O4 is 1.8 x 10-10 .
a)
b)
Which of the above 1.0 M solutions would have the highest pH?
Produce the lowest concentration of hydronium ions?
8. Fresh egg white has a pH of 7.8.
a) What is the concentration of hydronium ions in egg whites?
b) What is the pOH of the egg whites?
c) What is the concentration of hydroxide ions in egg whites?
9. The hydronium ion concentration of a solution of rainfall is 2.4 x 10-6 M.
a) What is the pH of rainfall?
b) What is the pOH of rainfall?
c) What is the hydroxide concentration of rainfall?
10. Given the following data from the titration of Vinegar and sodium hydroxide what is the
concentration of the vinegar?
volume of vinegar
35.0 ml
initial volume of NaOH
25.2 ml
final volume of NaOH concentration of the NaOH
48.7 ml
.50 M
11. What volume of 2.0 M HCl (aq) can be neutralized by 50.0 ml of .50 M KOH (aq)?\
12. Write a balanced chemical equation for the reaction between barium hydroxide and sulfuric
acid? What type of salt is produced from the reaction? How do you know this?
Extra Credit
The Kw of water at 25 C is 1.0 x 10-14 and the concentration of Hydronium ions and
hydroxide ions is 1.0 x 10-7 M. The pH is 7 and the pOH is 7. The Kw of water is
5.47 x 10-14 at 50 C.
What are the concentrations of hydronium and hydroxide ions and the ph of the water at 50 C?