Reactions in Solution (Acids and Bases):
Chapter 10
Chem 101
Fall 2004
Chapter Outline
• Properties of Aqueous Solutions of Acids and
Bases
• The Arrhenius Theory
• The Hydronium Ion (Hydrated Hydrogen Ion)
• The BrØnsted-Lowry Theory
• The Autoionization of Water
• Amphoterism
• Strengths of Acids
Chem 101
Fall 2004
Chapter Outline
•
•
•
•
Acid-Base Reactions in Aqueous Solutions
Acidic Salts and Basic Salts
The Lewis Theory
The Preparation of Acids
Chem 101
Fall 2004
1
Strengths of Acids
• Ternary acid strength usually increases with:
• an increasing number of O atoms on the central
atom and
• an increasing oxidation state of central atom.
• Effectively, these are the same phenomenon.
• Every additional O atom increases the oxidation state of
the central atom by 2.
Chem 101
Fall 2004
Strengths of Acids
• For ternary acids having the same central atom:
the highest oxidation state of the central atom is usually
strongest acid.
• For example, look at the strength of the Cl ternary acids.
HClO < HClO2 < HClO3 < HClO4
weakest
strongest
Chem 101
Fall 2004
Acid-Base Reactions in Aqueous Solution
• There are four acid-base reaction
combinations that are possible:
•
•
•
•
Strong acids – strong bases
Weak acids – strong bases
Strong acids – weak bases
Weak acids – weak bases
Chem 101
Fall 2004
2
Acid-Base Reactions in Aqueous Solution
• Strong acids - strong bases
• forming soluble salts
• This is one example of several possibilities
hydrobromic acid + calcium hydroxide
• The molecular equation is:
2 HBr(aq) + Ca(OH)2(aq) → CaBr2(aq) + 2 H2O()
Chem 101
Fall 2004
Acid-Base Reactions in Aqueous Solution
• Strong acids-strong bases
• forming insoluble salts
• There is only one reaction of this type:
sulfuric acid + barium hydroxide
• The molecular equation is:
H2SO4(aq) + Ba(OH)2(aq) → BaSO4(s)+ 2H2O()
Chem 101
Fall 2004
Acid-Base Reactions in Aqueous Solution
• Weak acids - strong bases
• forming soluble salts
• This is one example of many possibilities:
nitrous acid + sodium hydroxide
• The molecular equation is:
HNO2(aq) + NaOH(aq) → NaNO2(aq) + H2O()
Chem 101
Fall 2004
3
Acid-Base Reactions in Aqueous Solution
• Weak acids - weak bases
• forming soluble salts
• This is one example of many possibilities.
acetic acid + ammonia
• The molecular equation is:
CH3COOH(aq) + NH3(aq) → NH4CH3COO(aq)
Chem 101
Fall 2004
The Lewis Theory
• Developed in 1923 by G.N. Lewis.
• This is the most general of the present day acid-base
theories.
• Emphasis on what the electrons are doing as opposed to
what the protons are doing.
• Acids are defined as electron pair acceptors.
• Bases are defined as electron pair donors.
• Neutralization reactions are accompanied by
coordinate covalent bond formation.
Chem 101
Fall 2004
The Lewis Theory
• One Lewis acid-base example is the ionization of
ammonia.
NH 3 + H 2O →
← NH 4+ + OH -
base acid
+
H
N
H
H
H
H
+
H
H
O
N
H
H
+
-
O
H
Chem 101
Fall 2004
4
The Lewis Theory
• A second example is the ionization of HBr.
HBr + H2O → H3O+ + Bracid
base
Br
+
H
+
_
H
Br
O
+
O
H
H
H
H
Acid - it accepts
the electron pair
Base- it donates
the electron pair
covalent coordinate
bond formed
Chem 101
Fall 2004
The Lewis Theory
• The reaction of sodium fluoride and boron
trifluoride provides an example of a reaction that
is only a Lewis acid-base reaction.
• It does not involve H+ at all, thus it cannot be an
Arrhenius nor a Brønsted-Lowry acid-base reaction.
NaF + BF3 → Na+ + BF4• You must draw the detailed picture of this reaction
to determine which is the acid and which is the
base.
Chem 101
Fall 2004
The Lewis Theory
_
F
+
Base - it donates
the electron pair
B
B
F
-
F
F
F
Acid - it accepts
the electron pair
F
F
F
coordinate covalent
bond formed
Chem 101
Fall 2004
5
The Preparation of Acids
• The binary acids are prepared by reacting the
nonmetallic element with H2.
H2(g) + Cl2(g) → 2HCl(g)
This reaction is performed in the presence of UV light.
• Volatile acids, ones with low boiling points, are
prepared by reacting salts with a nonvolatile acid
like sulfuric or phosphoric.
NaCl(s) + H2SO4(conc.) → NaHSO4(s) + HCl(g)
NaF(s) + H2SO4(conc.) → NaHSO4(s) + HF(g)
Chem 101
Fall 2004
The Preparation of Acids
• We must use phosphoric acid to make HBr and
HI.
NaBr(s) + H3PO4(conc.) → NaH2PO4(s) + HBr(g)
NaI(s) + H3PO4(conc.) → NaH2PO4(s) + HI(g)
Chem 101
Fall 2004
The Preparation of Acids
• Ternary acids are made by reacting nonmetal
oxides (acid anhydrides) with water.
SO2(g) + H2O() → H2SO3(aq)
N2O5(g) + H2O() → 2 HNO3(aq)
• Some nonmetal halides and oxyhalides react with
water to give both a binary and a ternary acid.
PCl5(s) + 4 H2O() → H3PO4(aq) + 5 HCl(aq)
POCl3() + 3 H2O() → H3PO4(aq) + 3 HCl(aq)
Chem 101
Fall 2004
6
Reactions in Aqueous Solution
(Calculations): Chapter 11
Chem 101
Fall 2004
Chapter Outline
Aqueous Acid-Base Reactions
• Calculations Involving Molarity
• Titrations
• The Mole Method and Molarity
• Equivalent Weights and Normality
Oxidation-Reduction Reactions
• The Half-Reaction Method
• Adding in H+, OH- , or H2O to Balance Oxygen or
Hydrogen
• Stoichiometry of Redox Reactions
Chem 101
Fall 2004
Titrations
Acid-base Titration Terminology
• Titration – A method of determining the
concentration of one solution by reacting it with a
solution of known concentration.
• Primary standard – A chemical compound which
can be used to accurately determine the
concentration of another solution. Examples
include KHP and sodium carbonate.
Chem 101
Fall 2004
7
Titrations
Acid-base Titration Terminology
• Standard solution – A solution whose
concentration has been determined using a
primary standard.
• Standardization – The process in which the
concentration of a solution is determined by
accurately measuring the volume of the solution
required to react with a known amount of a
primary standard.
Chem 101
Fall 2004
Titrations
Acid-base Titration Terminology
• Indicator – A substance that exists in different forms with
different colors depending on the concentration of the H+ in
solution. Examples are phenolphthalein and bromothymol
blue.
• Equivalence point – The point at which stoichiometrically
equivalent amounts of the acid and base have reacted.
• End point – The point at which the indicator changes color
and the titration is stopped.
Chem 101
Fall 2004
The Mole Method and Molarity
• Potassium hydrogen phthalate is a very good
primary standard.
• It is often given the acronym, KHP.
• KHP has a molar mass of 204.2 g/mol.
O
CH
HC
O
CH
C
C
OH
+
HC
O
C
CH
C
C
HC
C
HC
C
KOH
CH
OH
O - K+
O
+
H2 O
C
OH
a c i di c H
KHP
Chem 101
Fall 2004
8
The Mole Method and Molarity
• Calculate the molarity of a NaOH solution if 27.3
mL of it reacts with 0.4084 g of KHP.
NaOH + KHP → NaKP + H 2 O
Chem 101
Fall 2004
Next Class: Reactions in Aqueous
Solution (Calculations): Chapter 11
• Start OWL Homework
(Chapter 11)
• Finish Reading
Chapter 11
Chem 101
Fall 2004
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