scb121 1 introduction to chemistry revision) kfs

8/6/2019 SCB121 1 Introduction to Chemistry Revision) KFS

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SCB121 CHEMISTRY 2

COMMONWEALTH OF AUSTRALIA

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Source Material:Blackman et al., Chemistry, Wiley, 2008.Brown, LeMay, et al., Chemistry: The Central Science, Pearson, 2006.Chang, R., General Chemistry; The Essential Concepts 3rdEd., McGraw-Hill, 2003.Zumdahl, S. and Zumdahl S., Chemistry 6thEd., Houghton Mifflin Company, NY, 2003.Lecture notes courtesy of Dr John McMurtrie.

Introduction to Chemistry

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Kathryn Fairfull-Smith Lecture Set 1: Blackman et al. Chapters, 1 & 2

The Scientific Method

A systematic approach to solving problems

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Hierarchy: Hypothesis Law Theory

Matter

Anything that has mass and takes up space.

Exists in three states

Solid rigid, definite shape

Liquid fluid, able to assume shape of container

Gas fluid, expands indefinitely to fill a volume

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solid

liquid

gas


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Matter

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Matter

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Atoms are the building blocks of matter.

Each element is made of the same kind of atom.

A compound is made of two or more different kinds of elements.

Pure Substances, Elements & Compounds

Pure substance Matter that has distinct properties and acomposition that doesnt vary from

sample to samplee.g. table salt, sodium chloride, NaCl

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Pure substances are either elements or compounds

Elements

Element A substance that cannot bedecomposed into simpler substancese.g. oxygen gas, O2

A substance that contains atoms of only one element

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113 elements currently known

83 occur naturally on earth

(the rest are man made e.g. plutonium)

Check out www.webelements.com


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Elements

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Symbol 1st letter (capital), 2nd letter (lower case)

Latin Natrium (Na) = sodium, Ferrum (Fe) = iron, Aurum (Au) = gold

Arranged in periodic table

From Brown, LeMay et al. Pearson, 2006.

Title

NON-METALS

METALS

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METALLOIDS

Compounds

hydrogen

oxygen

+

H2H2

O2

Compound A substance that is composed of two ormore different elements i.e. two or moredifferent kinds of atoms, e.g. water, H2O

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The elemental composition of a pure compound is always the same.This is known as the Law of Constant Composition(or Law of DefiniteProportions) Joseph Proust (1754 - 1826)

water

H2O

H2O

The elements hydrogen andoxygen combine (or react) toproduce water

Compounds

sodium + chlorine sodium chloride

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element

element

compound


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Mixtures

There are two types:

mixture combination of two or more substances in which eachsubstance retains its own chemical identity and can

be separated from each other

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- heterogeneous: a mixture which does not have the samecomposition, properties and appearance throughout,e.g. muesli, oil in water

- homogeneous: a mixture which is uniform throughout,e.g. vanilla ice-cream, scotch in water

Classification of Matter

14heterogeneous

a homogeneous (solution)


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Properties of Matter

Intensive Properties

Independent of the amount of the substance that is

present.Density, temperature, boiling point, colour, etc.

Consider the final tem erature when a beaker of water

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at 50C is added to another beaker of water also at 50C

Extensive Properties

Dependent upon the amount of the substance present.

Mass, volume, energy, etc.

Consider the energy released when 1 kg of TNTexplodes compared to the energy released when 2 kgexplodes

Properties of Matter

Physical Properties

Can be observed without changing a substance intoanother substance.

Boiling point, density, mass, volume, etc.

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Chemical Properties

Can onlybe observed when a substance is changed intoanother substance.

Flammability, corrosiveness, reactivity with acid, etc.

Changes of Matter

Physical Changes

Changes in matter that do not change the composition of asubstance.

Changes of state, temperature, volume, etc.

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2 and water in steam (gas)

Chemical Changes

Changes that result in new substances.

Combustion, oxidation, decomposition, etc.

Bonds between atoms are broken and new bonds are formed

Chemical Reactions (Chemical Change)

20In the course of a chemical reaction, the reacting

substances are converted to new substances.


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SI Units

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Systme International dUnits

Uses a different base unit for each quantity

Metric

Metric System

Prefixes convert the base units into units that

are appropriate for the item being measured.

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SI Units: Length and Mass

The SI base unit of lengthis the metre (m)

Massis a measure of the amount of material in an object.

The SI base unit of mass is the kilogram (kg).

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Chemists generally work with grams of material

1 kg = 1000 g = 1 103 g

Mass vs. Weight

Massis a measure of the quantity of matter in an object

Weightis the force that gravity exerts on an object

Mass is measured using scales or a balance

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(ironically in a procedure called weighing)

The terms mass and weight are often used interchangeably andtherefore incorrectly!


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Mass vs. Weight

The mass of a man on the moon is equalto the mass of the same man on earth.

25The weight of a man on the moon is less than the weight of thesame man on earth due to the lower gravitational pull of the moon

SI Units: Temperature (Kelvin)

The Kelvin is the SI unit of temperature

The Celsius scale divides the rangebetween the freezing point (0C) andboiling (100C) of water into 100 degrees

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K = C + 273.15

Kelvin is an absolute scale

Relationship between C and K

0 K is absolute zero = -273.15C

What are 25C and 100Cin units of Kelvin?

Derived SI Units: Volume

volume is length (m) cubed

SI Unit for volume = cubic metres (m3)

In chemistry we typically work with

volumes in less than a cubic meter

1 cm3 = (1 10-2 m)3 = 1 10-6 m3

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1 dm3 = (1 10-1 m)3 = 1 10-3 m3

A common non-SI Unit is the Litre (L)

A Litre is the volume occupied by

one cubic decimetre (i.e. 1 dm3

= 1 L)

1 L = 1 dm3 = 1000 mL

1 cm3 = 1 mL

Derived SI Units: Density

density mass of an object divided by its volume

density =

mass

volume

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=m

V

SI Unit is the kilogram per cubic metre (kg m-3)

In chemistry we typically use grams per cubic centimetre (g cm-3)

Recall that 1 g cm-3 = 1 g mL-1


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Uncertainty in Measurements

Different measuring devices have different

uses and different degrees of accuracy.

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Uncertainty in Measurements

Measured quantities are reported in such a way that only thelast digit is uncertain.

All digits of a measured quantity, including the uncertain one,are called significant figures.

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The greater the number of significant figures the greater is thecertainty of the measurement.

Significant Figures

All nonzero digits are significant,e.g. 123.45

Zeros between two significant figures are themselves significant,e.g. 103.405

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Zeros at the beginning of a number are never significant,e.g. 00123.45 = 123.45

Zeros at the end of a number are significant if a decimal point iswritten in the number, e.g. 123.450 has six significant figures but

123450 has only five significant figures

Significant Figures

When addition or subtraction is performed, answers arerounded to the least significant decimal place.

2.343 + 3.2 = 5.5

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When multiplication or division is performed, answers arerounded to the number of digits that corresponds to the leastnumber of significant figures in anyof the numbers used in thecalculation.

5.45 2.447 = 13.3


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Significant Figures

6 mL 6 1 mL 1 significant figure

i.e. true value is between 5 and 7 mL

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6.0 mL 6.0 0.1 mL 2 significant figures

6.00 mL 6.00 0.01 mL 3 significant figures

i.e. true value is between 5.9 and 6.1 mL

i.e. true value is between 5.99 and 6.01 mL

Accuracy and Precision

Accuracy refers to the proximity of ameasurement to the true value of a quantity.

Precision refers to the proximity of severalmeasurements to each other.

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Tutorial Exercises

CHELP: TUTORIAL SET A - MODULE 1

Definitions, scientific notation, SI units, unit

conversions

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The following slides contain additional information on:Natural abundance of the elements.Separation of mixtures.Handling numbers, scientific notation, unit conversions.Atomic structure and radioactivity.

Natural Abundance of the Elements

earths crust

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of the elements in earths

crust, only oxygen is abundantin living systems

living systems


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Separation of Mixtures

1. Distillation

Separates

homogeneous

mixture on the

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basis of differences

in boiling point.

Separation of Mixtures

2. Filtration

Separates solid substances from liquids and solutions.

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Handling Numbers

Chemists often use very large and very small numbers

e.g. 1 gram of hydrogen contains

602 200 000 000 000 000 000 000 hydrogen atoms

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and each hydrogen atom has a mass of

0.00000000000000000000000166 grams

It is cumbersome and impractical to use numbers in this way

Scientific Notation

All numbers can be expressed in the form

N 10n

Nis a number between 1 and 10

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n is an exponent that can be a positive or negative integer

568.7 = 5.687 102

0.00000772 = 7.72 10-6

Practice addition, subtraction, multiplication and division


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scb121 1 introduction to chemistry revision) kfs

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