Chapter 1-Atomic Concept and Mole

7/31/2019 Chapter 1-Atomic Concept and Mole

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Atomic Concept and Mole

1. Matter

2. Atoms and Ions

3. Atomic and Molecular Mass

4. Mole Concept

5. Names of Chemical Compounds

6. Chemical Formula

7. Chemical Equation and Stoichiometry8. Volumetric Analysis

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Matter

Matter can be described as

anything that has mass and it

must take up space.

Examples

States of Matter

Classification of Matter

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States of Matter

Depending on its temperature,matter can be solid, liquid or

gas.


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Classification of Matter

MixturesPure Substances

Homogeneous Heterogeneous

Elements Compounds

IonsAtoms Molecules

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Atom

An atom is the smallest particledifferentiable as a certain

chemical element.

When an atom of an element is

divided, it ceases to be thatelement.

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Atoms

An atom consists of three sub-atomic

particles which are electrons,

protons and neutrons.

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The atomic number ( Z ) is the number of protons in thenucleus of each atom of an element ( Z = p ).

In a neutral atom the number of protons is equal to thenumber of electrons ( p = e ).

The mass number ( A ) is the total number of neutrons andprotons present in the nucleus of an atom of an element.In general the mass number is given by:

Mass number = number of protons + number of neutrons

= atomic number + number of neutrons

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The accepted way to denote the atomic

number and mass of an atom of an

element ( X ) is as

Mass number or

AXNucleon number

ZAtomic number orProton number

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Atom Example

(a) Sodium (Na),(b) Iron (Fe),

(c) Gold (Au),

(d) Oxygen (O),

(e) Hydrogen (H),

(f) Chlorine (Cl),

(g) Carbon (C).10


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Molecules

A molecule is the smallest indivisible

portion of a pure compound that

retains a set of unique chemical

properties.

A molecule consists of two or more

atoms bonded together.

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Molecules - examples

(a) Oxygen (O 2 ),

(b) Hydrogen (H 2 ),(c) Chlorine (Cl 2 ),

(d) Ozone (O 3 ),

(e) Water (H 2 O),

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IONIC COMPOUNDS

Sodium chloride (NaCl),

Magnesium oxide (MgO)

Sodium oxide (Na 2 O)

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Pure Substances

Any sample of matter can be

classified as a pure substance or

a mixture. A pure substance can be

either an element or a compound.

The composition of a pure substance

is definite and fixed.

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Pure Substances

Example:

2.Pure gold - an element.

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A chemical element or simply

element , is a substance that cannot

substances by ordinary chemical

methods.

The smallest particle of such an

element is an atom , which consistsof electrons centered around a

nucleus of protons and neutrons.

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Examples of elements

(a)Metals - Iron (Fe), Gold (Au),Silver (Ag), Mercury (Hg).

(a)Gases - Oxygen (O 2 ), Nitrogen (N 2 ),Chlorine (Cl 2 ), Helium (He),

Neon (Ne).

(a)Non-metals - Carbon (C).

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C d


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Compounds

A chemical compound is a chemical

substance formed from two or more

elements, with a fixed ratio

determining the composition.

For example, dihydrogen monoxide

(water) is a compound composed oftwo hydrogen atoms for every

oxygen atom, H 2 O.

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Mixtures

A mixture is a combination of two

or more substances, often chemicals,

in which the substances remain

chemically distinct, retaining their

particular composition and

properties.

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Mixtures

There are two types of mixtures:heterogeneous mixtures and

homogeneous mixtures.

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Heterogeneous Mixtures

A Heterogeneous Mixture does not have

uniform properties throughout; the

composition of one part (or phase) .

Example:1. A mixture of oil and water.

2. A mixture of nuts and cake.

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Homogeneous Mixtures

An Homogeneous Mixture is the samethroughout. It has uniform composition

and appearance throughout.

Example:1. A cup of hot coffee.

2. A mixture of alcohol and water.

3. A solution.

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A d I


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Atoms and Ions

An atom consists of three sub-atomic

particles which are electrons,

protons and neutrons.

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A d I


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Atoms and Ions

An ion is an atom or group of atoms

with a net electric charge.

H +

Cl - Na + H +O 2 -

H +

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At d I


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Atoms and Ions

A negatively charged is known as

an anion, and a positively charged

is known as a cation.

Cation Anion

H +

H +

O 2 -O 2-

Na +Cl -H +

H +

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Cations & anions

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At i d M l l M


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Atomic and Molecular Mass

A tomic mass is the mass of one atomexpressed in units ( atomic mass unit ,amu) where 1 amu is equal to 1/12 th

of the actual mass of carbon-12.

Atomic mass is also called as

relative atomic mass or atomicweight.

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Relative Atomic Mass

Relative Atomic Mass is unitless. It is the

atomic mass (amu) divided by the mass

of one C-12 atom (amu).

Relative atomic mass = atomic mass (amu) x 12mass of 12 C (12)

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Average Atomic Mass


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Average Atomic Mass

Most elements have several naturally

occurring isotopes with differentabundance.

The atomic mass shown in the

periodic table for an element is

actually a weighted average of the

masses of all isotopes of the element.

Example 129

Average Atomic Mass


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Average Atomic Mass

- Example 1 -

Bromine :

50.69% bromine - 79, mass = 78.9183

49.31% bromine - 81, mass = 80.9163

? Average atomic mass of Br

= (50.69% x 78.9183)

+ (49.31% x 80.9163)

=79.9035

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Average Atomic Mass


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Average Atomic Mass

- Example 2 -

Magnesium :

78.99% magnesium-24, mass = 23.9850

10.00% magnesium-25, mass = 24.9858

11.01% magnesium-26, mass = 25.9826

? Average atomic mass of Mg

= (78.99% x 23.9850) + (10.00% x 24.9858)

+ (11.01% x 25.9826)= 24.3050

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Average Atomic Mass: Exercise


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Average Atomic Mass: Exercise

Isotopes Mass Abundance (%)6 Li 6.015 7.59

7 Li 7.016 92.41

16 O 15.995 99.75717 O 16.999 0.038

18 O 17.999 0.205

Calculate the average atomicmass of lithium and oxygen.

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Carbon 12


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Carbon - 12

Carbon-12 is the most abundant (98.89%)of the two stable isotopes of the elementcarbon. It contains 6 protons, 6 neutronsand 6 electrons.

Carbon-12 is of particular importance asit is used as the standard from which allother isotopes' atomic weight is measured

and thus the measurement of Avogadro'snumber.

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Molecular Mass
http://www.chemistrydaily.com/chemistry/Protonshttp://www.chemistrydaily.com/chemistry/Protons


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Molecular Mass

The molecular mass of a substance(less accurately called molecular

weight and abbreviated as MW ) is

substance, relative to the unified

atomic mass unit u (equal to 1/12

the mass of one atom of carbon-12).

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Molecular Mass


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Molecular Mass

calculated as the sum of the

atomic masses of all the atoms of

any one molecule.The molar mass of a substance is

numerically equal to the molecular

mass, but expressed in mass unitsper mole (e.g. grams per mole)

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Molecular Mass


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Molecular Mass

For example: the atomic mass of hydrogen

is 1.00784 u and that of oxygen is 15.9994

u; therefore, the molecular mass of water

with formula H 2 O is (2 x 1.00784 u) +

15.9994 u = 18.01508 u.

Therefore, one molecule of water weighs

18.01508 u, and one mole of water weighs

18.01508 grams.

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Molecular Mass


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Molecular Mass

Molecular mass or molar mass areused in stoichiometry calculations.

Since molecules are created bychemical reactions , not nuclearreactions , a molecule's molecularmass exactly equals the sum of the

atomic masses of its constituentatoms.

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Mole Concept


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Mole Concept

The mole (symbol: mol) is one of theseven SI base units and is commonly

used in chemistry.

Mole of substance A = Mass of substance A(g)

Formula Mass of A(g.mol -1 )

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Mole Concept


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Mole Concept

It measures the amount of substance

of a system and is defined as the

amount ofsubstance that contains

as many elementary entities as there

are atoms in exactly 12 grams

carbon-12.

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Mole Concept
http://www.chemistrydaily.com/chemistry/Amount_of_substancehttp://www.chemistrydaily.com/chemistry/Amount_of_substance


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Mole Concept

This quantity is known asAvogadro's number and is

approximately 6.0221415 x 103.

N A = 6.022 x 10 23

or6.02 x 10 23

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Names of Chemical Compo nds


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Names of Chemical Compounds

Different kinds of compounds are named

by different rules. Ordinary table salt is

named sodium chloride because of its

formula, NaCl.

But common table sugar is named

-D-fructofuranosyl- -D-lucopyranoside.[Please don't worry about it!]

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Names of Chemical Compounds


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p

Binary Compounds Acid

(nonmetals)

Ionic CompoundsSalts

PolyatomicHydratesIons

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Names of Binary Compound


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Names of Binary Compound

Chemical Name Symbol

Dinitrogen pentoxide N 2 O 5

Carbon tetrachloride CCl 4

Nitrous oxide N 2 O

Ammonia NH 3

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Names of Ionic Compound


Potassium sulfide K 2 S

Iron(II) sulfide FeS

Calcium chloride CaCl 2

Zinc nitrate Zn(NO 3 ) 2

Sodium sulfate Na 2 SO 4

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Names of Hydrates


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Names of Hydrates

Chemical Name

Symbol

Sodium carbonate Na 2 CO 3 .10H2 Odecahydrate (washing

soda)

Magnesium sulfate MgSO 4 .7H 2Oheptahydrate(epsom salt)

Calcium sulfate dihydrate CaSO 4 .2H 2

O(gypsum)Sodium tetraborate Na 2 B 4 O 7 .10H

2 Odecahydrate (borax)

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N f P l t i I


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Names of Polyatomic Ions


Cr 2 O 72-Dichromate

ClO 4-Perchlorate

ClO -Hypochlorite

HCO 3-BicarbonateSO 42-Sulfate

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Names of Acid


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Names of Acid


Hydroiodic acid HI

Hydrosulfuric acid H 2 S

Phosphoric acid H 3 PO 4

Phosphorus acid H 3 PO 3

Chlorous acid HClO 2

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Names of Salts


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a es o Sa ts


Sodium Fluoride NaF

Sodium Sulfite Na 2 SO 3

Sodium bicarbonate NaHCO 3

Sodium Na 2 HPO 3

monohydrogenphosphite

Potassium chlorate KClO 3

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Names of Binary Compounds


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1. Write an appropriateformula for

(a) dinitrogen pentoxide

(b) carbon tetrachloride(c) nitrous oxide

(d) ammonia

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Names of Binary Compounds


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2. Write the chemical namefor(a) NO 2

(b) SO 3

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Names of Ionic Compounds


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What are the names for thecompounds

(a) K 2 S

(b) FeS(c) CaCl 2

(d) Zn(NO 3 ) 2

(e) Na 2 SO 4

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Names of Hydrates


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1. Write formulas for the following

hydrates.

(a) Sodium carbonate decahydrate

(washing soda)

(b) Magnesium sulfate heptahydrate(Epsom salt)

(c) Calcium sulfate dihydrate

(gypsum)

(d) Sodium tetraborate decahydrate(borax)

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Names of Hydrates


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2. Write the chemical names for the

following hydrates.

(a) CoCl 2 .6H 2 O

(b) CuSO 4 .5H 2 O

(c) Na 2 S 2 O 3 .5H 2O

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y

Write formulas for thefollowing ions.

(a) chromate

(b) perchlorate

(c) hypochlorite

(d) bicarbonate(e) sulfate

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y

Write names for thefollowing ions.(a) PO 43-

(b) Cr 2 O 72-

thiocyanatedichromatethiosulfatephosphatechlorite(c) S 2 O 3 2-

(d) SCN -

(e) ClO 2-

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Names of Acids


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Write names for thefollowing acids.

(a) HF(b) H 2 SO 3

(c) H 2 CO 3

(d) CH 3 COOH(e) HClO

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Names of Acids


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Write formulas for thefollowing acids.

(a) Hydroiodic acid

(b) Hydrosulfuric acid

(c) Phosphoric acid

(d) Phosphorous acid(e) Chlorous acid

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Names of Salts


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Write names for thefollowing typical salts.

(a) NaF(b) Na 2 SO 3

(c) NaHCO 3

(d) Na 2 HPO 3

(e) KClO 3

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Chemical Formula


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There are two types of chemical

formulas:

(a) Empirical Formula,

(b) Molecular Formula .

Empirical formula and molecular

formula are used for different purposes.

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Empirical Formula


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The Empirical Formula gives the simplestwhole-number ratio of atoms of each

element present in a compound.

Example:

Acetylene (C 2 H 2 ) and benzene (C 6 H 6 )

- the simplest ratio C : H = 1 : 1

Empirical Formula = CH

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Molecular Formula


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The Molecular Formula gives the actual

number of atoms of each element present

in a molecule.

Example:a) Acetylene - C 2 H 2

b) Benzene - C 6 H 6

c) Glucose - C 6 H 6 O 6

d) Water - H 2 O

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Exercise 1


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When analyzed, an unknown compound

gave these experimental results: C, 54.0%;H, 6.00%; O, 40.0%. Four different

students used these values to calculate the

empirical formulas shown here. Which

answer is correct? Why did some students

not get the correct answer?(a) C 4 H 5 O 2 (c) C 7 H 10 O 4

(b) C 5 H 7 O 3 (d) C 9 H 12 O 5

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A process in which one or more substances is changed into oneor more new substances is a chemical reaction


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or more new substances is a chemical reaction

A chemical equation uses chemical symbols to show what

happens during a chemical reaction

3 ways of representing the reaction of H 2 with O 2 to form H 2O

productsreactants 63

How to "Read" Chemical Equations


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2 Mg + O 2 2 MgO

2 atoms Mg + 1 molecule O 2 makes 2 formula units Mg

2 moles Mg + 1 mole O 2 makes 2 moles MgO

48.6 grams Mg + 32.0 grams O 2 makes 80.6 g MgO

2 grams Mg + 1 gram O 2 makes 2 g MgO Is thiscorrect?

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Balancing Chemical Equations


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1. Write the correct formula(s) for the reactants on the

left side and the correct formula(s) for the product(s)

on the right side of the equation.

Ethane reacts with oxygen to form carbon dioxide and water

C 2 H 6 + O 2 CO 2 + H 2 O

2. Change the numbers in front of the formulas

( coefficients ) to make the number of atoms of each

element the same on both sides of the equation. Donot change the subscripts.

NOT2C 2 H 6 C 4 H 12

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Balancing Chemical Equations...contd

3 S b b l i h l h i l


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3. Start by balancing those elements that appear in only onereactant and one product.

C 2 H 6 + O 2 start with C or H but not OCO 2 + H 2 O

1 carbon2 carbonmultiply CO 2 by 2on righton left

C 2 H 6 + O 2 2CO 2 + H 2 O

6 hydrogen 2 hydrogenmultiply H 2 O by 3

on left on rightC 2 H 6 + O 2 2CO 2 + 3H 2 O

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Balancing Chemical Equations..contd


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4. Balance those elements that appear in two or more

reactants or products.

multiply O 2 by 7C 2 H 6 + O 2 2CO 2 + 3H 2 O2

4 oxygen + 3 oxygen = 7 oxygen2 oxygenon right(3x1)on left (2x2)

remove fractionC 2 H 6 + 7 O 22CO 2 + 3H 2 O

multiply both sides by 22

2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O

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Balancing Chemical Equations.contd


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5. Check to make sure that you have the same number of

each type of atom on both sides of the equation.

2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O

Reactants Products

4C 4C

12 H 12 H

14 O 14 O

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Mass Changes in Chemical Reactions


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1. Write balanced chemical equation

2. Convert quantities of known substances into moles3. Use coefficients in balanced equation to calculate the number of

moles of the sought quantity

4. Convert moles of sought quantity into desired units69

Methanol burns in air according to the equation

2CH 3 OH + 3O 2 2CO 2 4H 2 O


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2CH 3 OH + 3O 2 2CO 2 + 4H 2 O

If 209 g of methanol are used up in the combustion,what mass of water is produced?

grams CH 3 OH moles CH 3 OH moles H 2 O grams H 2

molar mass molar masscoefficientsCH 3 OH H 2 Ochemical equation

4 mol H 2 O 18.0 g H 2 O1 mol CH 3 OH=209 g CH 3 OH x x x

32.0 g CH 3 OH 2 mol CH 3 OH 1 mol H 2 O

235 g H 2 O

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Chemical Equation and Stoichiometry

(Exercise)


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1. Write the balanced equation for thecombustion of ethyl alcohol:

C 2 H 5 OH (l) + O 2 (g) CO 2 (g) + H 2 O (l)

Answer

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Chemical Equation and Stoichiometry

(Exercise)


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Determine the number of grams oflead(II) sulfide, PbS, that can be oxidised

by 5.22 mol of oxygen gas according to

the following equation.

2PbS(s) + 3O 2 (g) 2PbO(s) + 2SO 2 (g)

Answer

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Volumetric Analysis


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Concentrations of Solutions

Dilution

Titration

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Molarity ( M )

The most widely used to quantify

the concentration of solutions.

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Molarity ( M )

The molarity of a solution is

defined as

moles solutesMolarity= volume of solution ( L )

nor M =V

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Molarity - Exercise 1


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Calculate the molarity of a

solution made by dissolving

23.4 g of sodium sulphate in

enough water to form 125 mL ofsolution.

Answer

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Molarity - Exercise 2

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How many grams of sodium

sulphate, Na 2 SO 4 are required to

make 0.350 L of 0.500 M Na 2 SO 4 ?

Answer

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Dilution


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Solutions that are used routinelyin the laboratory are often

purchased or prepared in

concentrated form. They are calledas stock solutions .

Example: 12M HCl

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Dilution


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Solutions of lower concentrationscan be obtained by adding water.

This process is called as dilution .

Formula( Initial molarity )( initial volume ) = ( final molarity )( final volume )

or M 1 V 1 = M 2 V 2

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Exercise

How many milliliters of 3 0 M


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How many milliliters of 3.0 M

H 2 SO 4 are required to make 450mL of 0.10 M H 2 SO 4 ?

Answer

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Titration

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How can we determine the

concentration of a solution?

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Titration


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One common way is to use a secondsolution of known concentration ,

called a standard solution , that

undergoes a specific chemicalreaction of known stoichiometry

with the solution of unknown

concentration .

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This procedure is known as titration .

Example:


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aA + bB cC + dD

Formula( molarity of solution A )( volume of solution A ) ( molarity of solution B )( volume of solution B )=

a b

M a V a M b V b=or

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Exercise

What is the molarity of an


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What is the molarity of an

automobile battery acid, H 2 SO 4

solution if 22.53 mL of the acid

neutralizes 42.11 mL of 1.923 M

sodium hydroxide, NaOH?

Answer

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Chapter 1-Atomic Concept and Mole