Course Name: General Chemist

2 for Engineering students

Course Code:
 Water Chemist
Learning Objectives:
 Students will learn a bout
the following:
 The distribution of Ea h’s
water
 Identify water’s structure
and prope ies
 Water pollution
 Water treatment
Water on Ea h
Water is a common chemical substance on Ea h.
Almost 75% of the planet is covered in water.
- 97% of that water is salt water ocean
- 3% is freshwater
- 68% of all freshwater is locked in ice caps
and
glaciers (although that is changing)
- 30% is ground water
- 2% is su ace water
- 87% of the su ace water is found in
lakes
- 11% is located in swamps
Chemical Structure of Water
Water is made up of one atom of
Oxyge
oxygen and two atoms of hydrogen.
n The oxygen atom in a water
Hydroge Hydroge molecule attracts electrons more
n n strongly than the hydrogen atoms.
The result is that the oxygen side of the molecule is slightly
negative while the hydrogen side is more positive.
The di erence in electrical charges on di erent sides of a
molecule is called polarity. Water is a polar molecule.
The Water Molecule
Hydrogen bonding
explains much about
the various prope ies
of water.
 Physical
Water and Chemical Prope ies of
States of WaterWater is the only substance found on Earth in all three states (phas
1. Liquid 2. Solid (Ice)

3. Gas (Steam or Vapor)

Physical States Vapor
Hydrological Cycle
• Hydrological cycle is also known as the “water
cycle”;
• it is the normal water recycling system on Ea h .
• Due to solar radiation, water evaporates, as the
steam rises in the atmosphere, it is being cooled,
condensed, and returned to the land and the sea
as precipitation.
• Precipitation falls on the ea h as su ace water.
• A par tof the water precipitating penetrates the
ground and moves downward through the
incisions, forming aquifers. Finally, a par tof the
States of Water
• Water molecules are constantly moving
• Temperature increase = Increase in movement
• When water molecules move faster, they tend to break their
hydrogen bonds.
This is called
Evaporation
States of Water
• When gas or vapor molecules slow down, they
clump or join together.

This is called
Condensation
States of Water
• As water changes from a liquid to a solid,
molecules form c stals.
In ice c stals, molecules are spaced
fu her apa .

Liquid Solid (Ice)

Water as a Solvent
• Since water can dissolve more things than any other natural
substance, it is known as the “ Universal Solvent”
• Prope ies of Solvents include:
• Interacts with other polar compounds
• Is repelled by non-polar compounds
• Small size allows it to saturate areas
• Can convey other substances in solutions
Water as a Solvent
• Water is especially good at dissolving salts
Salts form from the combination of pa icles with opposite
electrical charges (or ions)
EX. Na+ + Cl- = NaCl
Water as a Solvent
• When salt is placed in water,
the strongly charged salt ions
attract to the weaker charged
water molecules.
• Water molecules surround
each ion.
• Salt c stals fall apa , or
dissociates, and the salt
dissolves.
 Water pollution

 Any physical or chemical change in water that adversely affects the

health of humans and other organisms. Water pollution :
 Water quality: It is impo ant to utilize a good quality and unpolluted
water. The quality criteria may va depending on the use.

16
 Environmental Water Quality Parameters
Physical Prope ies: Color, odor, temperature, solids (residues), turbidity, oil content, and grease content.
Chemical Prope ies : pH - Conductivity - Dissolved oxygen (DO) - Nitrate - O hophosphate - Chemical
oxygen demand (COD) - Biochemical oxygen demand (BOD) – Pesticides

Figure1: pH meter Figure 2:Digital conductivity meters

Biological Prope ies : Bacteriological parameters: coliforms, fecal coliforms, speci c pathogens, and
viruses.
 Some Key water-quality parameters
1- pH
pH : is a measure of the concentration of hydrogen ions in the water.
This measurement indicates the acidity or alkalinity of the water.
pH is an intensity factor.
1- pH = 7: Neutral 2- pH < 7: Acidic 3- pH > 7: Alkaline or basic
- -Naturally occurring fresh waters have a pH range between 6.5 and 8.5.
- <4.0, severe danger of health effects due to dissolved toxic metal ions are expected. Water tastes
sour. At pH
- At pH>11.0 – severe danger of health e ects due to deprotonated species. Water tastes soapy.
- At pH 4.0 – 6.0, toxic e ects associated with dissolved metals, including lead, are likely to occur.

18
 2- Conductivity
Conductivity is the ability of the water to conduct an electrical current,
and is an indirect measure of the ion concentration.
 The more ions present, such as that of carbonate, bicarbonate,
chloride, suphate, nitrate, Na, K, Ca, and Mg, the more electricity
can be conducted by the water.
 This measurement is expressed in microsiemens per centimeter
(uS/cm) at 25°C. The target water quality range is 0 – 70

19
 3-
Turbidity
- Turbidity is a measure of the clarity of the water
- Turbidity it is the amount of solids suspended in the water
- It is a measure of the light scattering proper ties of water, thus an increase in
the amount of suspended solid pa icles in the water may be visually described
as cloudiness or muddiness
There are several methods of measuring turbidity and, in the past, the results
were frequently expressed in dif fe rent units. Nowadays, nephelometric
turbidity units (NTU) are almost always used.
4- Colour
Colour is a measure of the light absorbed by the
water. is measured by comparing the sample against a set of standard colour
Colour
solutions. There are also automated instruments which measure colour directly.
Normally, colour is ve pH dependent and it is good practice to also repo pH value.

20
 5- Temperature
Temperature a ects physical, chemical, and biological processes in water
 Chemical example: DO (Dissolved Oxygen) decreases as temperature
increases (raising the temperature of a freshwater stream from 20°C to 30°C
will decrease the DO saturation level from about 9.2 to 7.6 ppm )
6- Phosphorus (P)
 Total phosphate is used as an indicator of pollution from run-o in agricultural
or domestic sewage.
 Concentrations of 0.2 mg/L are common.
 Concentrationns of 0.05 eutrophication (increased nutrient mg/L indicate the
possibility of concentrations) and algal blooms are likely.
 Measured colorimetrically
7 21
Water Pollution
 Water Pollution
classi cations:
two major
• Point Source • Non-point
Source
Point Sources: • Non-point Sources
• Single large source • Di use source or many
• Can localize it to one smaller point sources
spot • Automobiles
•Industrial Plants • Fe ilizer on elds
- Sewage pipes
 Water Pollution Comes from Point
Point sources
•Located at speci c places
•Easy to identify, monitor, and
regulate
•Examples:

Oil Tanker Spill Sewage spills into the water

Water Pollution Comes from Nonpoint Sources
• Nonpoint sources
•Broad, di use areas
•Di cult to identify and control
•Expensive to clean up
•Examples:

Figure1. Acid rain by Industrial emission

 Water Pollution
• Water pollutants includes:
•Heavy metals
•Sediment
•Ce ain radioactive isotopes
•Heat
•Fecal coliform bacteria
•Phosphorus
•Nitrogen
•Pathogenic bacteria and viruses
 Water treatment
Reasons for Water Treatment:
The two main reasons for treating water are:
1) to remove those contaminants that are harmful to health.
2) to remove contaminants that make the water look, taste, or smell bad.
Guide to selection of water treatment processes:
1- Contaminant removal
2- Source water quality
3 - Reliability
4- Existing conditions
5- Process exibility
6- Costs
7- Distribution system water quality
27
Basic Water Treatment Unit Processes
• Water treatment requires chemical, physical, and sometimes biological processes
to remove contaminants.
• The more common processes used in potable water treatment are the chemical
and physical processes.
The chemical processes involved in potable water treatment include:
- Oxidation
- Coagulation
- Disinfection.
The physical processes include:
- Flocculation
- Sedimentation
- Filtration
- Adsorption
- Disinfection using ultraviolet light.
 Coagulation and occulation
present in water It focuses on the theory and practice of
destabilisation of fine solids
Solids being present in water in three main forms:
1- Suspended par ticles, 2- colloids and 3- dissolved
solids.
1- Coarse or ne pa icles are generally relatively simple
to remove by either settlement or ltration.
2- Dissolved solids cannot be removed by physical
treatment save by reverse osmosis (although some may
be removed where precipitation is possible).
3- Thus, removal of colloids is often the main objective
and most dif fic ult aspect of conventional water
treatment.
 Reverse Osmosis
• force water through membrane
• removes many contaminants

30
 Coagulation-Flocculation-
Sedimentation
The aim of coagulation and f locculation is to produce par ticles of a size
that can be removed by settlement, otation or ltration.
Some coagulants: Some coagulant aids:
aluminum sulfate, activated silica
ferric sulfate ferric clay polymers
chloride

31
Colloids themselves are split into two types: hydrophilic
or water-loving colloids, and hydrophobic or water-
hating colloids.

A coagulant is the chemical that is dosed to cause

par ticles to coagulate. Typically, these are aluminum or
iron salts and organic polymers may also be used as
coagulants.
Coagulation occurs extremely quickly. Flocculation is the
longer term process of forming larger par ticles from the
small pa icles formed by coagulation.
Water lecture
Choose the correct answer.
Question 1 Question 3
………………………... is made up of one The bond between hydrogen and oxygen in
atom of oxygen and two atoms of water is call ……..
hydrogen. A) Coordination bond
A) Acid B) Water B) Covalent bond
C) Base D) Salt C) Hydrogen bond



D) All above answers
Question 2

Water can be found in Question 4

states (phases):
A) Liquid
Water molecules are constantly moving, if
the temperature increase the movement
B) Solid …………..
A) Increase
C) Gas B) Decrease
D) All above answers C) Constant
D) Answers a & b


Choose the correct answer. Question 10
Question 6 If the water was polluted what we must
do?
When water molecules move faster, they tend A. Use water B. Treat water
to break their hydrogen bonds this call C. Dispose water D. Drink water
……………..
A) Condensation B) Evaporation Question 11
C) C stallization D) Filtration Water pollutants includes:
Question 7 A) Heavy metals
Since water can dissolve more things B) Sediment
than any other natural substance, it is C) Pathogenic bacteria and
known as ……….. viruses
A) Poor solvent B) Organic D) All above answers
solvent
C) Universal Solvent D) All above
answers

Question 9
Major classi cations of water pollution are
…….
A) Point source B) Non point source
D) Answers a & b E) Non of above
SOLID STATE
CHEMISTRY
 INTRODUCTION
Three phases of matter:
 Gas
 Liquid
 Solid
 Liquid
molecules

37
 Solid
molecules

38


What is solid?
• De nite shape.
• De nite volume.
• Highly incompressible.
• Rigid.
• Constituent pa icles held closely by strong
intermolecular forces.
• Fixed position of constituents.


TYPES OF SOLIDS
Two types (based upon atomic arrangement):
1. C stalline solid
A c stalline solid exists as small c stals, each c stal having a characteristic geometrical
shape. In a c stal, the atoms, molecules or ions are arranged in a regular, repeating three
dimensional
pattern called the c stal lattice.
Examples: Sugar and salt are c stalline solids
2. Amorphous solid
The constituent pa icles (atoms, molecules or ions) are arranged in irregular and
random shapes with sho range order c stalline lattice.
Examples are rubber, plastics and glass.
 DIFFERENCE BETWEEN CRYSTALLINE AND AMORPHOUS SOLIDS
C stalline solid Amorphous solid
• De nite geometrical shape • No de nite geometrical shape.
• Has long range order • Has sho range order
• De nite sharp melting point and heat of • No sharp melting point and heat of fusion
fusion
• They are Anisotropic • They are Isotropic
• Examples: NaCl, CsCl, diamond, qua z,…. • Examples: glass, rubber, plastics, cement
 ANISOTROPY
• The physical prope ies like electrical resistance or refractive index
show di erent values when measured along di erent directions in
the same c stal.
• The arrangement of pa icles is di erent in di erent directions.
 ISOTROPY
• The value of any physical prope y would be same along any directions.
• No long range order and the arrangement is irregular along all the
directions.


Types of c stal structures

(based upon bonding between building blocks)

• Ionic c stals
• Covalent c stals
• Molecular c stals
• Metallic c stals


Ionic c stals
•Positive and negative ions are the constituent pa icles.
•These ions are bound by strong electrostatic forces.
• Two types:
 These solids are hard and brittle in nature.
 They have high melting and boiling points.
 They are insulators in solid state.
 In aqueous solutions, they conduct electricity.
 Exampls: NaCl, CsF, …


Covalent c stals
• The constituent pa icles are neutral atoms.
• Atoms are held together by strong covalent bonds
• They are ve hard solids.
• High melting point.
• They are insulators.

• Examples: diamond graphite



Molecular c stals
• The constituent pa icles are neutral molecules.
• The molecules are held together by Vander Waal’s forces.
• Ve soft solids.
• Low melting point.
• Poor conductors of electricity.
• Examples: solid CO2 (d ice), ice,…


Metallic c stals
•The constituent- pa icles are positive metal ions surrounded by a
sea of mobile e .
•Soft to ve hard.
• Metals have high tensile strength.
• Good conductors of electricity.
• Malleable and ductile.
• Bonding electrons in metals remain delocalized over the entire
c stal.
• High density.
•Examples: Iron, Copper, gold,….
 CRYSTAL LATTICE
• A regular 3 dimensional arrangement of points in
space is called a c stal
• lattice
 CHARACTERISTICS OF CRYSTAL LATTICE
• Each point in a lattice is called lattice point or lattice site.
• Lattice site represents one constituent pa icle.
• The constituent pa icle may be an atom, a molecule or an ion.
• Lattice points are joined by straight lines which give the geomet of the
lattice.
 UNIT CELL
• Unit cell is the smallest repeating unit of a c stal
lattice which when repeated in di erent direction
generates the entire c stal
 CHARACTERISTICS OF UNIT CELL
• The dimensions are along the three edges a, b and c.
• These edges may or may not be mutually perpendicular.
• Angles between the edges a, b and c are α, β and γ.
• A unit cell is characterized by six parameters a, b, c, α, β and γ.
 PRIMITIVE AND CENTERED UNIT CELLS
1- PRIMITIVE UNIT CELL OR SIMPLE CUBIC
• The constituent pa icles are present at all the 8
corners of a cube.
2- CENTERED UNIT CELLS
A- BODY CENTERED CUBIC (BCC)
• The constituent pa icles are present at all the
corners as well as at the centre of the unit cell
 B- FACE CENTERED CUBIC (FCC)
• The constituent pa icles are present at all the corners
as well as at the centre of each of the six faces.
 C- END CENTERED CUBIC
• The constituent pa icles are present at all the corners
as well as at the centre of any two opposite faces
 SEVEN PRIMITIVE UNIT CELLS
• There are seven type of primitive unit cells according to
the unit cell parameters (a, b, c, and , α, β ,γ):
SEVEN PRIMITIVE UNIT CELLS
 BRAVAIS LATTICES
• The 14 possible 3 dimensional lattices in which the atoms are arranged to form a c stal are
called Bravais lattices.
• These lattices are named after the French physicist Auguste Bravais.
 NUMBER OF ATOMS IN A UNIT CELL
• In counting the number of atoms per unit cell, we must keep in mind that atoms on
corners of faces are shared with adjoining cells.
cells Therefore the number of atoms in a
cubic unit cell may be computed as follows.
• (1) Eight unit cells share each corner atom.
• Therefore the simple cubic unit cell contains the equivalent of one atom.

At each corner we have = 1/8 atom

At 8 corners we have = 1/8 × 8 = 1 atom

• (2) Each face-centred atom is shared by two unit cells. Therefore the face-centred
unit cell contains the equivalent of four atoms.
• At 8 corners, 1/8 each = 1 atom
• 6 face-centred sites, 1/2 each = 3 atoms
• Total equivalent atoms = 1 + 3 = 4
• (3) A body centred unit cell contains the equivalent of two atoms.
• At 8 corners at 1/8 each = 1 atom
• central unshared = 1 atom
• Total equivalent atoms = 1 + 1 = 2
 Summa : The Number OF ATOMS IN A UNIT CELL

 Simple cubic cell: 1atom/unit cell

 Body-centered cell: 2 atoms/unit cell of bcc
 Face-centered cell: 4 atoms/unit cell of fcc
 End face-centered cell: 2 atoms/unit cell
Questions
 • Which one of the following is non-c stalline or • Amorphous solids do not have
amorphous? (a) sharp melting point
(a) Diamond (b) characteristic geometrical shapes
(b) Graphite (c) regularity of the structure
(c) Glass (d) all of these
(d) Common Salt
• Which is not true about the solid state?
(a) they have de nite shape and volume
(b) they have high density and low compressibility •(a)Amorphous substances are isotropic because
(c) they have high attractive forces among molecules (b) they have same value of any prope y in all directions
they have di erent values of physical prope ies in
(d) they have high vapour pressure di erent directions
(c) they have de nite geometrical shape
(d) none of the above
• If there are 4 atoms in unit cell in a cubic system,
it is an example of
(a) simple cubic unit cell • A c stalline solid has
(b) body centred cubic unit cell (a) de nite geometrical shape
(c) face centred cubic unit cell (b) (b) at faces
(d) none of these (c) sharp edges
(d) all of these
• Cement
Pa (4): Kinetics

68
Kinetics
• A branch of physical chemist that studies
how fast a reaction happens (rate of reaction)
• Studies factors that change the speed (rate)
of chemical reactions.
• Studies the pathways of reaction progression:
from reactants to products.
• Studies how a reaction occurs (reaction
mechanism).
• Studies how much amounts (concentrations)
would be left after ce ain times.

69
Slow and Fast Reactions
• Chemical reactions having va ing speeds.
• Thermodynamics only tells about the spontaneity of the reaction but not the
timing of its occurrence.

70
Rate of Reaction
•

Rate Unit: (amount/unit time)

mol/L s-1, mol/L h-1 , mol/ s-1,
…
71
Calculating Reaction Rates from
Graphs
•

72
Calculating Reaction Rates from Equations
Reaction rates correspond to the stoichiomet coe cient (number of
moles) of the reactant/product in the net balanced chemical equation.
Reaction rates are obtained by dividing each reactant/product by its
stoichiomet coe cient.
Write all possible rate expressions for the following reaction:
N2 + 3H2 = 2NH3

73
Rate Law
•

74
Reaction Order
•

75
Examples of Reaction Orders
Reaction Rate law Reaction order
2H2O2(l)  O2(g) + 2H2O(l) R = k [H2O2] First order reaction
2NO(g) + Cl2(g) 2NOCl(g) R = k [NO] [Cl2] Second order
reaction
NO2(g)  NO(g) + ½ O2(g) R=k Second order
reaction
2NO(g) + 2H2(g) N2(g) + R = k [H2] Third order
2H2O(g) reaction

76
Example:
For a reaction:
X+Y M
with

a rate law: 2

R = k[X][Y]
a. Determine the order of
each species and the
overall reaction order
b. Calculate k if the
concentration of each
species is 1.0 M and
the rate of the reaction
is 0.2 M/min
77
How Can Reaction Rates be
Measured
• Measure change of amounts of either a reactant or a product
over time.
•Measure volume of gas evolved over time.
•Measures concentrations of species over time.
•Measures mass of species over time.
• Find the relation between initial amounts and changes in
concentrations after a time.
78
Example with Experimental Data
aA + bB  cC + dD T=273 K a. First order with respect to A: the rate
[A]0(M) [B] 0(M) Rate [M]/s doubled when the concentration doubled
Exp 1 0.1 1 0.035
Exp 2 0.1 2 0.070 b. First order with respect to B: the rate
Exp 3 0.2 1 0.140 doubled when the concentration doubled
a. What is the order with respect c. R = k [A][B]
to A? d. The overall order is 1+1 = 2 (2nd order)
b. What is the order with respect e. K = R/[A][B]= 0.140/(1 x 0.2) = 0.7 M-1s-1
to B?
c. What is the overall rate law
equation?
d. What is the overall order of the
reaction? 79
Activation Energy, Ea
• Reactions take place when
pa icles collide with enough
energy.
• Activation energy is the minimum
amount of energy needed for
pa icles to react.
• Each reaction has a di erent
activation energy.
• If pa icles collide with less than
the activation energy, they will not
react.

80
Reaction Diagram
• Consider the reaction of methyl isonitrile CH3NC  CH3CN
to acetonitrile.
• Energy changes during the
rearrangement of methyl isonitrile. The
energy di erence between products and
reactants is ∆E .
• The high point in the diagram is the
transition state.
• The specie at the transition state is called
the activated complex.
• The energy gap between reactants and
the activated complex is the activation
energy barrier (Ea).
81
Reaction Diagram Shapes

82
Factors A ecting Reaction Rates
• Temperature
• Concentrations/pressures of dissolved/gaseous reactants.
• Prescence of a catalyst
• Su ace area of solid reactants or catalyst.

83
Temperature and Rate
• As temperature increases, rate increases
• At higher temperatures, more molecules will have su cient kinetic energy to react.

In cold weather, car

batteries are likely to fail.
fail
The reaction to generate
electric current proceeds
more slowly than at higher
temperatures.

84
Concentration and Rate
• Molecules can only react (bonds
broken and new bonds formed) if they
collide with each other.
• More molecules (higher concentrations)
means more possible collisions.
• Molecules must collide with enough
kinetic energy and in the correct
orientation.
• Since concentration of reactants
decreases with time, collisions
decrease, the reaction rate gets slower
and slower until there is no reaction.

85
Catalysts and Rate
• Catalysts are substance that
speed up the rate of a reaction
by providing an alternative
reaction pathway with a lower
activation energy barrier.
• Catalysts are not used up in the
reaction.
• Catalysts can bypass the need
of high temperatures and Platinum is a catalyst in car exhausts. It conve
pressures, saving time and pollutants carbon monoxide and nitrogen oxide
money. into carbon dioxide and nitrogen
• Biological catalyst are a special
type of protein called enzymes.
86
Su ace Area and Rate
• The smaller the pieces, the larger the su ace area.
• By increasing the su ace area, more area is exposed for reactants pa icles
to collide with.

87
 Chapter
Problems
1. A branch of science that deals with the speed of
reactions and their mechanisms:

a. mechanics b.
thermochemist

c. thermodynamics d. kinetics
2. The reaction: 2HI → H2 + I2 is a(n) . .

a. unimolecular reaction b. bimolecular
reaction

c. rst order reaction d. second order
reaction
3. The reaction rate:

a. rate of appearance of reactants.
b. rate of appearance of reactants and products.

c. rate of disappearance of reactants.
d. rate of disappearance of products.
4. Unit of reaction:

a. mol-1 L-1 s
-1 -1 b. mol L s-1 c. mol L-1 s d.
L mol s
5. The rate law expresses the relationship between the
reaction rate and …
a. temperature b. activation energy 88
c. concentration d. su ace area
89
 Pa (5)
Electrochemist

90
Electrochemist and Redox
Reactions
Electrochemist :
It is a branch of physical chemist which study of the relationship between electricity
(e- ow) and chemical reactions (redox reactions).
Chemical reactions involved in electrochemist are:
Reduction
Redox Reactions, one type of reaction cannot occur without the other.
Oxidation
In redox reactions, electrons are transferred from one species to another. A species
losing electrons is said to be oxidized; one gaining electrons is said to be reduced.
The two processes together are called redox.
91
Electrochemist and Redox
Reactions OXIDATION
Loss of electron(s) by a species.

REDUCTION
Gain of electron(s) by a species.

 Oxidation no. increase.  Oxidation no. decrease.
 Reaction at Anode.  Reaction at Cathode.
 Example: Zn(S)  Zn2+(aq.) + 2e  Example: Cu2+(aq.) + 2e  Cu(S)
What will happen if a strip of zinc is immersed in a solution of copper sulfate?

92
 Electrochemist and Redox
Reactions

Cu2+ ions gains 2e and is reduced to Cu

metal
Cu is calledReduction
the oxidizing agent
Total reaction
(Redox reaction) Zn (s) + Cu2+(aq.)  Zn2+(aq.) + Cu(s)
Oxidation
Zn metal loses 2e and is oxidized to Zn2+ 93
ions
 Electrochemist and Redox
Reactions
•Oxidizing Agent: a substance that accept electrons from other substance, causing it to be oxidized.
•Reducing Agent: a substance that donate electrons to other substance, causing it to be reduced.
A redox reaction is the sum of an oxidation half-reaction and a reduction half-reaction.
Oxidation half-reaction: Zn(S)  Zn2+(aq.) + 2e
Reduction half-reaction: Cu2+(aq.) + 2e  Cu(S)
Overall redox reaction: Zn(S) + Cu2+(aq.)  Zn2+(aq.) + Cu(S)

94
 Example:
•Identify the oxidizing agent Mg is the reducing agent (Mg0 to

the reducing agent in the
and
reaction:

Mg2+).
Mg(S) + 2HCl(aq.)  MgCl2(aq.) + H+ is the oxidizing agent (H1+ to H0 )
H2(g)

95
Review of Oxidation Numbers
Oxidation Number: the number of charges the atom
would have in a molecule (or an ionic compound) if
electrons were transferred completely.
H2(g) + Cl2(g) → 2 HCl(g)
Oxidation state

96
Assigning Oxidation Numbers
 Free elements (uncombined state)  In these cases, its oxidation number is
have an oxidation number of “zero”. –1 (e.g. NaH). The oxidation number of
e.g. Na, Be, K, Pb, H2, O2, P4 hydrogen is +1 (e.g. HF) except when it
is bonded to metals in binary
 For mono-atomic ions, the oxidation compounds.
number is equal to the charge on the  Group IA metals are +1, IIA metals
ion. + are +2 and VIIA is always –1
e.g. Li = +1; Fe3+= +3; O2-= -2
 The oxidation number of oxygen2- is  The sum of the oxidation numbers of
usually – 2, except in H2O2 and O2 it all the atoms in a molecule or ion is
is – 1. equal to the charge on the molecule or
ion.
97
Example:
• What is the oxidation O = -2 S = ?

number of sulfur atom

in the S2O82- ion? [8x(-2)] + (2 X ?) = -2
A. +3 -16 + (2 X ?) = -2
B. +5 (2 X ?) = +14
C. +7
D. -2 S = (+14/2) = + 7
98
 Electrochemical Cell
It is used for the interconversion of electrical and chemical energy. An electrochemical
cell is a system or arrangement in which two electrodes are fitted in the same
electrolyte or in two different electrolytes, which are joined by a salt bridge.
(a)

Based on the nature of energy

conversion, electrochemical
cells are broadly divided as: (b)

99
 Galvanic Cell
Galvanic or Voltaic Cell: a device in which chemical energy is conve ed to electrical energy through spontaneous redox reaction.
Daniel Cell It is a typical voltaic Cell. It is a simple zinc-copper cell.
Flow of e-

Daniel Cell
100
Galvanic Cell
Cell Diagram or line notation

Oxidation+2(anode) Reduction
+2 (cathode)
Zn(s)/Zn (aq., 1 M) // Cu (aq., 1 M) /
Cu(s)
A line between electrode Junction between State, concentration.
and its solution (phase two half-cells
bounda ). Salt bridge.

101
 Example:
• For the cell below, write the reaction at Anode: Zn(s)  Zn+2(aq.) + 2e
anode

and cathode and also the Cathode: Ni2+(aq.) + 2e  Ni(s)
overall

cell reaction.
overall cell reaction: Zn(s) Ni2+(aq.)  Zn+2(aq.) + Ni(s)
Zn(s)/Zn2+ (aq., 1M) // Ni2+ (aq., 1M)/Ni(s)

102
Galvanic Cell
Cell Potential (E ):
Cell
The dif ference in electrical potential between the anode and
the cathode of an electrochemical cell is called:
cell voltage or
electromotive force (e.m.f.) or measured by a voltmeter
cell potential (Ecell)
Potential Unit:
1 Volt (V) = 1 J/C
E0cell = E0cathode - E0anode
103
 Galvanic Cell
Electrode Potential
How do we measure the potential of an electrode? Strongest
oxidizing
agents
By using a standard electrode
Voltmeter: measures the di erence between
cathode and anode potentials
An electrode to Standard electrode
be measured its potential is zero
(hypothetical value)
Standard Hydrogen
Electrode (SHE)
E0 = 0.00 V

Reduction potentials for Strongest

many electrodes have been reducing
measured and tabulated agents

104
 Galvanic Cell
Cell Potentials under Standard Conditions

105
Example:
Calculate the standard cell The Oxidation half-reaction (Anode): Zn(S) → Zn2+(aq) + 2e- E0Zn = - 0.76 V
potential of the following The Reduction half-reaction (Cathode): 2H+ (aq) + 2e- → H2 (g) E0H2 = 0.00 V
reaction:

 Zn2+(aq) + H2(g) The Overall Reaction Zn(s) + 2H+ (aq)

Zn2+(aq) + H2(g) Zn(s) + 2H+

(aq)
Eºcell = Eºcathode – Eºanode = (0.00) - (-0.76) = + 0.76 V

106
 Electrolytic Cell
Electrolysis: is the process that uses electric energy to force
a nonspontaneous chemical reaction to take place.
An electrolytic cell is the cell used to car out electrolysis.

Cell Type Chemical reaction Electric Energy

Galvanic spontaneous Produced
Electrolytic Nonspontaneous Consumed

107
Faraday

108
 Chapter
Problems
1. Separating redox equations is simpler if the equation is 7. A cell can be prepared from zinc and iron. What is the Eocell3+
separated into oxidation and reduction po ions. for -the cell2+thato forms from2+the following half reactions? Fe
a. True (b) False + e  Fe , E = 0.77 V; Zn + 2e  Zn, E = -0.76 V
- o
a. -1.53 V b. -0.01 V c. 0.01V d.
2. Oxidation is de ned as :
1.53 V
a. gain of an electron b. Gain of a 8. Which of the following does not denote the di erence in
proton
electrical potential between the anode and cathode?
c. loss of a proton d. loss of an a. cell voltage b. electromotive force
electron c. Voltmeter d. cell potential
3. An oxidizing agent will always
9. Calculate the free energy change per mole of Cu 2+ formed
a. increase in mass b. be reduced
in the following reaction at 25+ oC.
c. increase in oxidation number d. lose electrons Cu + 2 Ag  2 Ag + Cu2+.
4. The electrode at which oxidation occurs is called the:
Cu2++ + 2- e-  Cu Eoo = 0.34 V;
a. salt bridge. b. cathode.
Ag + e  Ag, E = 0.80 V.
c. anode. d. none of the a a. 0.46 kJ b. 89 kJ c. 44.5 kJ d.
bove. -89 kJ
5. The oxidation number of Mn is maximum in:
10. One of the di erences between a galvanic cell and an
a. MnO b. K2MnO4 c. Mn3O4 d. electrolytic cell is that in a galvanic cell
KMnO4. 2 a. an electric current is produced by a chemical reaction.
b. electrons ow toward the anode.
c. a non spontaneous reaction is forced to occur using an
9. A galvanic cell is prepared2+using zinc2+and iron. 3+Its cell electric current from an external source.
notation is as follows: Zn|Zn (1 M)||Fe (1 M), Fe (1M)|Pt. d. reduction occurs at the anode.
Which3+of the- following reactions occurs at2+ the cathode?
a. Fe + e 2+ Fe2+- b. Fe 2+Fe3+ +-e- 109
c. Zn  Zn + 2 e d. Zn + 2e  Zn
110


Course Name: General Chemist

2
Course Code: CHM1103