Chapter 4
Copyright
© The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2
 A chemical reaction is the process by which one or more substances are changed into one or more different substances reactants products
(NH
4
)
2
Cr
2
O
7(s)
 N
2(g)
+ Cr
2
O
3(s)
+ 4H
2
O
(g)
“The reactant ammonium dichromate yields the products nitrogen, chromium (III) oxide and water”
 A CHEMICAL EQUATION represents, with symbols and formulas, the identifies and relative amounts of the reactants and products in a chemical equation

3
1.
2.
3.
4.
Evolution of heat and light is strong evidence that a chemical reaction has taken place! But, the evolution of heat or light by itself is not necessarily a sign of a chemical change since many physical changes also release either heat or light .
Production of gas!
(aka bubbles when two substances are mixed)
Formation of precipitate!
A solid that is produced as a result of a chemical reaction in solution and that separates from the solution is known as a precipitate
Color Change!

4
1.
2.
3.
The equation must represent all reactants and products.
The equation must contain the correct formulas for the reactants and products
The law of conservation of mass MUST be satisfied!!
Law of conservation of mass – atoms are neither created nor destroyed in ordinary chemical reactions
To equalized numbers of atoms, coefficients are added in front of the formulas where necessary

5
A + B ↔ C
C ↔ A + B
A + BC ↔ AC + B
AB + CD ↔ AD + CB




Acid + Base ↔ salt + water
Change of oxidation state
Hydrocarbon + O
2
↔ CO
2
+ H
2
O



Synthesis (Combination)
Decomposition
Single Replacement
Precipitation Reactions (Double
Replacement Reactions)
Neutralization Reactions (Acid/Base)
Redox Reactions
Combustion

6
Double Replacement Reactions
AB + CD ↔ AD + BC

A solution is a homogenous mixture of 2 or more substances
The solute is(are) the substance(s) present in the smaller amount(s)
The solvent is the substance present in the larger amount
Solution
Soft drink ( l )
Air ( g )
Soft Solder ( s )
7
Solvent
H
2
O
N
2
Pb
Solute
Sugar, CO
2
O
2
, Ar, CH
4
Sn aqueous solutions of KMnO
4

An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity.
A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity.
8 nonelectrolyte weak electrolyte strong electrolyte

9
Conduct electricity in solution?
Cations (+) and Anions (-)
Strong Electrolyte – 100% dissociation
NaCl ( s )
H
2
O
Na + ( aq ) + Cl ( aq )
Weak Electrolyte – not completely dissociated
CH
3
COOH CH
3
COO ( aq ) + H + ( aq )

CH
3
Ionization of acetic acid
COOH CH
3
COO ( aq ) + H + ( aq )
A reversible reaction. The reaction can occur in both directions.
Acetic acid is a weak electrolyte because its ionization in water is incomplete.
10

Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner.
11 d d +
H
2
O

12
Nonelectrolyte does not conduct electricity?
No cations (+) and anions (-) in solution
C
6
H
12
O
6
H
2
O
( s ) C
6
H
12
O
6
( aq )

Precipitate – insoluble solid that separates from solution precipitate
Pb(NO
3
)
2
( aq ) + 2KI ( aq ) PbI
2
( s ) molecular equation
+ 2KNO
3
( aq )
Pb 2+ + 2NO
3
+ 2K + + 2I PbI ionic equation
2
( s ) + 2K + + 2NO
3
-
Pb 2+ + 2I PbI
2
( s ) net ionic equation
K + and NO
3
are spectator ions
13
PbI
2

14
Pb 2+ + 2I PbI
2
( s )
PbI
2

15
Solubility is the maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature.

16
CdS PbS Ni(OH)
2
Al(OH)
3

17
Characterize the following compounds as
(a) soluble or (b) insoluble in water:
1.
2.
3.
4.
5.
CaCO
3
ZnSO
4
Hg(NO
3
)
2
HgSO
4
NH
4
ClO
4

1. Write the balanced molecular equation.
2. Write the ionic equation showing the strong electrolytes completely dissociated into cations and anions.
3. Cancel the spectator ions on both sides of the ionic equation
4. Check that charges and number of atoms are balanced in the net ionic equation
Write the net ionic equation for the reaction of silver nitrate with sodium chloride.
AgNO
3 ( aq )
+ NaCl
( aq )
Ag +
( aq )
+ NO
3
-
( aq )
+ Na +
( aq )
+ Cl -
( aq )
18 Ag +
( aq )
+ Cl -
( aq )
AgCl
( s )
+ NaNO
3 ( aq )
AgCl ( s ) + Na +
( aq )
+ NO
3
-
( aq )
AgCl ( s )

19
Predict what happens when a potassium hydroxide solution is mixed with a solution of sodium chloride. Write a net ionic equation for the reaction.

20
What do we expect to see if we add copper (II) sulfate to sodium hydroxide? Write the molecular equation, ionic equation, and net ionic equation.

21
What do we expect to see if we add copper (II) sulfate to sodium hydroxide? Write the molecular equation, ionic equation, and net ionic equation.

22
EXTRA PRACTICE
Predict what happens when a potassium phosphate solution is mixed with a solution of calcium nitrate. Write a net ionic equation for the reaction.

23
Predict what happens when a silver nitrate solution is mixed with a solution of potassium hydroxide. Write a net ionic equation for the reaction.

A + B ↔ C
C ↔ A + B
A + BC ↔ AC + B
AB + CD ↔ AD + BC




Acid + Base ↔ salt + water
Change of oxidation state
Hydrocarbon + O
2
↔ CO
2
+ H
2
O



Synthesis (Combination)
Decomposition
Single Replacement
Precipitation Reactions (Double
Replacement Reactions)
Neutralization Reactions (Acid/Base)
Redox Reactions
Combustion
24

25
Acid/Base Reactions
Acid + Base ↔ Salt + Water

Have a sour taste. Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid.
Cause color changes in plant dyes.
React with certain metals to produce hydrogen gas.
2HCl ( aq ) + Mg ( s ) MgCl
2
( aq ) + H
2
( g )
React with carbonates and bicarbonates to produce carbon dioxide gas
2HCl ( aq ) + CaCO
3
( s ) CaCl
2
( aq ) + CO
2
( g ) + H
2
O ( l )
26
Aqueous acid solutions conduct electricity.

27
Have a bitter taste.
Feel slippery. Many soaps contain bases.
Cause color changes in plant dyes.
Aqueous base solutions conduct electricity.
Examples:

Arrhenius acid is a substance that produces H + (H
3
O + ) in water
28
Arrhenius base is a substance that produces OH in water

29
Hydronium ion , hydrated proton, H
3
O +

A Br ønsted acid is a proton donor
A Br ønsted base is a proton acceptor base acid acid base
30
A Br ønsted acid must contain at least one ionizable proton!

Monoprotic acids
HCl H + + Cl -
HNO
3
H + + NO
3
-
CH
3
COOH H + + CH
3
COO -
Strong electrolyte, strong acid
Strong electrolyte, strong acid
Weak electrolyte, weak acid
Diprotic acids
H
2
SO
4
H + + HSO
4
-
HSO
4
H + + SO
4
2-
Triprotic acids
H
3
PO
4
H
2
PO
4
-
HPO
4
2-
H + + H
2
PO
4
-
H + + HPO
4
2-
H + + PO
4
3-
31
Strong electrolyte, strong acid
Weak electrolyte, weak acid
Weak electrolyte, weak acid
Weak electrolyte, weak acid
Weak electrolyte, weak acid

32

Identify each of the following species as a Br ønsted acid, base, or both. (a) HI, (b) CH
3
COO , (c) H
2
PO
4
-
HI ( aq ) H + ( aq ) + I ( aq ) Br ønsted acid
CH
3
COO ( aq ) + H + ( aq ) CH
3
COOH ( aq ) Br ønsted base
H
2
PO
4
( aq ) H + ( aq ) + HPO
4
2( aq )
H
2
PO
4
( aq ) + H + ( aq ) H
3
PO
4
( aq )
Br ønsted acid
Br ønsted base
33

34
Identify each of the following as either a
(a)
1.
2.
3.
4.
Brønsted acid, (b) Brønsted base, or (c) both.
PO
4
3-
ClO
2
-
NH
4
+
HCO
3
-

35
acid + base salt + water
HCl ( aq ) + NaOH ( aq ) NaCl ( aq ) + H
2
O
H + + Cl + Na + + OH Na + + Cl + H
2
O
H + + OH H
2
O

36
weak acid + base salt + water
HCN ( aq ) + NaOH ( aq ) NaCN ( aq ) + H
2
O
HCN + Na + + OH Na + + CN + H
2
O
HCN + OH CN + H
2
O

acid + base salt + water + CO
2
2HCl ( aq ) + Na
2
CO
3
( aq ) 2NaCl ( aq ) + H
2
O +CO
2
2H + + 2Cl + 2Na + + CO
3
2-
2H + + CO
3
2-
2Na + + 2Cl + H
2
O + CO
2
H
2
O + CO
2
37

A + B ↔ C
C ↔ A + B
A + BC ↔ AC + B
AB + CD ↔ AD + BC




Acid + Base ↔ salt + water
Change of oxidation state
Hydrocarbon + O
2
↔ CO
2
+ H
2
O



Synthesis (Combination)
Decomposition
Single Replacement
Precipitation Reactions (Double
Replacement Reactions)
Neutralization Reactions (Acid/Base)
Redox Reactions
Combustion
38

39
Synthesis Reactions:
Redox Reactions
A + B ↔ C
Decomposition Reactions: C ↔ A + B
Single Replacement Reactions: A + BC ↔ AC + B
Combustion Reactions: hydrocarbon + O
2
↔ CO
2
+ H
2
O

(electron transfer reactions)
2Mg 2Mg 2+ + 4e Oxidation half-reaction (lose e )
O
2
+ 4e 2O 2-
2Mg + O
2
+ 4e -
40
Reduction
2Mg + O
2
2Mg 2+ half-reaction (gain e
+ 2O
2MgO
2+ 4e -
)

41

Zn ( s ) + CuSO
4
( aq ) ZnSO
4
( aq ) + Cu ( s )
Zn Zn 2+ + 2e Zn is oxidized Zn is the reducing agent
Cu 2+ + 2e Cu Cu 2+ is reduced Cu 2+ is the oxidizing agent
Copper wire reacts with silver nitrate to form silver metal.
What is the oxidizing agent in the reaction?
42

The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred.
1. Free elements (uncombined state) have an oxidation number of zero.
Na, Be, K, Pb, H
2
, O
2
, P
4
= 0
2. In monatomic ions, the oxidation number is equal to the charge on the ion.
Li + , Li = +1 ; Fe 3+ , Fe = +3 ; O 2, O = -2
43
3. The oxidation number of oxygen is usually –2 . In H
2 and O
2
2it is –1 .
O
2
4.4

4. The oxidation number of hydrogen is +1 except when it is bonded to metals in binary compounds. In these cases, its oxidation number is –1 .
5. Group IA metals are +1 , IIA metals are +2 and fluorine is always –1 .
6. The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to the charge on the molecule or ion.
7. Oxidation numbers do not have to be integers.
Oxidation number of oxygen in the superoxide ion,
O
2
, is –½ .
HCO
3
-
What are the oxidation numbers of all the elements in HCO
3
?
O = – 2 H = +1
3x( – 2) + 1 + ?
= – 1
C = +4
44

45
The Oxidation Numbers of Elements in their Compounds

What are the oxidation numbers of all the elements in each of these compounds?
NaIO
3
IF
7
K
2
Cr
2
O
7
NaIO
3
Na = +1 O = -2
3x( -2 ) + 1 + ?
= 0
I = +5
7x(
IF
F =
-1
I =
7
-1
) +
+7
?
= 0
K
2
Cr
2
O
7
O = -2 K = +1
7x( -2 ) + 2x( +1 ) + 2x( ?) = 0
Cr = +6
46

47
Give the oxidation number for the underlined atoms or in each of the following species: a) d)
Mg
3
N
2
CO
3
2g) NaBH
4 b) CsO
2 e) C
2
O
4
2h) WO
4
2c) CaC
2 f) ZnO
2
2-

Synthesis/Combination Reaction
A + B C
0 0
2Al + 3Br
2
+3 -1
2AlBr
3
Decomposition Reaction
C A + B
+1 +5 -2
2KClO
3
+1 -1 0
2KCl + 3O
2
48

Combustion Reaction
A + O
2
0 0
S + O
2
B
+4 -2
SO
2
0 0
2Mg + O
2
+2 -2
2MgO
49

Displacement Reaction
A + BC AC + B
0 +1 +2
Sr + 2H
2
O Sr(OH)
2
0
+ H
2
+4
TiCl
4
0 0 +2
+ 2Mg Ti + 2MgCl
2
Hydrogen Displacement
Metal Displacement
0
Cl
2
-1 -1 0
+ 2KBr 2KCl + Br
2
Halogen Displacement
50

51
Hydrogen Displacement Reaction
M + BC MC + B
M is metal
BC is acid or H
2
O
B is H
2
Ca + 2H
2
O Ca(OH)
2
+ H
2
Pb + 2H
2
O Pb(OH)
2
+ H
2

52
Which of the following metals can react with water to produce
H
2
(g)?
a) Au b) Li c) d) e)
Hg
Ca
Pt

53
2
2
2
2
Halogen Displacement Reaction
0
Cl
2
-1 -1 0
+ 2KBr 2KCl + Br
2
I
2
+ 2KBr 2KI + Br
2

Disproportionation Reaction
The same element is simultaneously oxidized and reduced.
Example: reduced
0
Cl
2
+ 2OH oxidized
+1 -1
ClO + Cl + H
2
O
54

55
Classify each of the following reactions.
Ca 2+ + CO
3
2-
NH
3
+ H +
CaCO
3
NH
4
+
Zn + 2HCl ZnCl
2
+ H
2
Ca + F
2
CaF
2

56
Predict the outcome of the reactions represented by the following equations by using the activity series, and balance the equations.
Cu (s) + HCl (aq) 
I
2
(g) + NaBr (aq) 
Mg (s) + CuSO
4
Cl
2
(aq)
(g) + KBr (aq) 


57
Classify the following redox reactions by type:
P
4
Cl
2
+ 10Cl
2
2NO  N
2

+ 2KI  I
2
4PCl
+ O
2
5
+ 2KCl

58
Molarity
Dilutions
Gravimetric Analysis
Titrations

The concentration of a solution is the amount of solute present in a given quantity of solvent or solution.
M = molarity = moles of solute liters of solution
What mass of KI is required to make 5.00 x 10 2 mL of a 2.80 M KI solution?
volume of KI solution
M KI moles KI
M
KI grams KI
59
5.00x10
2 mL
1 L x
1000 mL x
2.80 mol KI x
1 L soln
166 g KI
1 mol KI
= 232 g KI

60
Calculate the mass in grams of sodium nitrate required to prepare 2.50 x 10 2 mL of a 0.707 M solution.

61
Preparing a Solution of Known Concentration

Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution.
Dilution
Add Solvent
62
Moles of solute before dilution (i)
M i
V i
=
=
Moles of solute after dilution (f)
M f
V f

How would you prepare 60.0 mL of 0.200 M HNO
3 from a stock solution of 4.00 M HNO
3
?
M i
V i
= M f
V f
M i
= 4.00 M M f
= 0.200 M V f
= 0.0600 L V i
= ? L
V i
=
M f
V f
M i
= 0.200
M x 0.0600 L
4.00 M
= 0.00300 L = 3.00 mL
Dilute 3.00 mL of acid with water to a total volume
63 of 60.0 mL.

64
Water is added to 25.0 mL of a 0.866 M KNO
3 solution until the volume of the solution is exactly 500 mL. What is the concentration of the final solution?

65
You have 505 mL of a 0.125 M HCl solution and you want to dilute it to exactly 0.100 M. How much water should you add?
(assume that the volumes are additive.)

66
1. Dissolve unknown substance in water
2. React unknown with known substance to form a precipitate
3. Filter and dry precipitate
4. Weigh precipitate
5. Use chemical formula and mass of precipitate to determine amount of unknown ion

A 0.5662 g sample of an ionic compound containing chloride ions and an unknown metal is dissolved in water, and treated with excess AgNO
3
. If 1.0882 g of AgCl precipitate forms, what is the percent by mass of Cl in the original compound?
% Cl

35.45
143.4
g Cl g AgCl

100 %

24 .
72 % mass of Cl

0.2472

1.0882
g

0.2690
g
This is the amount of Cl in the original sample, so
%Cl

0.2690
g
0 .
5662 g

100 %

47 .
51 %
67

68
A sample of 0.6760 g of an unknown compound containing barium ions (Ba 2+ ) is dissolved in water and treated with an excess of Na
2
SO
4
. If the mass of the BaSO
4 precipitate formed is 0.4105 g, what is the percent by mass of Ba in the original unknown compound?

In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete.
Equivalence point – the point at which the reaction is complete
Indicator – substance that changes color at (or near) the equivalence point
Slowly add base to unknown acid
UNTIL the indicator changes color
69

Titrations can be used in the analysis of
Acid-base reactions
H
2
SO
4
+ 2NaOH 2H
2
O + Na
2
SO
4
Redox reactions
5Fe 2+ + MnO
4
+ 8H +
70
Mn 2+ + 5Fe 3+ + 4H
2
O

What volume of a 1.420 M NaOH solution is required to titrate 25.00 mL of a 4.50 M H
2
SO
4 solution?
WRITE THE CHEMICAL EQUATION!
H
2
SO
4
+ 2NaOH 2H
2
O + Na
2
SO
4
M volume acid acid moles red rxn coef.
M moles base base volume base
25.00 mL x
4.50 mol H
2
SO
4
1000 mL soln x
2 mol NaOH
1 mol H
2
SO
4
71
1000 ml soln x
1.420 mol NaOH
= 158 mL

72
Calculate the concentration (in molarity) of a NaOH solution if
25.0 mL of the solution are needed to neutralize 17.4 mL of a
0.312 M HCl solution.

16.42 mL of 0.1327 M KMnO
4 solution is needed to oxidize 25.00 mL of an acidic FeSO
4 the molarity of the iron solution?
solution. What is
5Fe
WRITE THE CHEMICAL EQUATION!
2+ + MnO
4
+ 8H + Mn 2+ + 5Fe 3+ + 4H
2
O
M volume red red rxn moles red coef.
V moles oxid oxid
16.42 mL = 0.01642 L 25.00 mL = 0.02500 L
M oxid
0.01642 L x
0.1327 mol KMnO
4
1 L x
73
5 mol Fe 2+
1 mol KMnO
4 x
1
0.02500 L Fe 2+
= 0.4358 M

74
The SO
2 present in air is mainly responsible for the acid rain phenomenon. Its concentration can be determined by titrating against a standard permanganate solution as follows:
5SO
2
+ 2MnO
4
+ 2H
2
O  5SO
4
2+ 2Mn 2+ + 4H +
Calculate the number of grams of SO
2
7.37 mL of 0.00800 M KMnO
4 the titration.
in a sample of air if solution are required for