Download The Physical Properties And Physical Changes of Substances

The Physical Properties And Physical Changes of
Substances
A.
Definitions In Science
1.
Science is the observation, identification, description, experimental
investigation, and theoretical explanation of natural phenomena.
We gather information about our surrounding through the use of
our senses: sight, smell, hearing, taste, and touch.
Over hundreds of years, people have developed tools that enhance
our senses and allow us to gather information that would otherwise
be impossible. Information usually takes one of two forms:
QUALITATIVE information is NON-NUMERICAL
information (Descriptions)
QUANTITATIVE information is NUMERICAL information
(Measurements)
Assign 1-3
In Chemistry, you must be able to collect information and describe
substances in many different ways. To ensure that we are using a
common vocabulary, some important terms must be defined:
• An OBSERVATION is qualitative information collected
through the direct use of our senses.
• An INTERPRETATION (or “inference”) is an attempt to put
meaning into an observation.
Sometimes our interpretations of what we observe is biased by
our expectations and prior knowledge.
VERSION: September 10, 2000
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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Do you see a
young lady
or an old
hag?
Do you see a
young lady
or an old
hag?
Which of the two
lines is
longer?
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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Which of the
cylinders is the
largest?
It is possible that two people may not observe the same thing.
For this reason, scientists insist that observations be repeated
several times by more than one person.
http://www.youtube.com/watch?v=vJG698U2Mvo
• A DESCRIPTION is a list of the properties of something.
• DATA is quantitative information, which is experimentally
determined or obtained from references.
• An EXPERIMENT is a test or a procedure that is carried out in
order to discover a result.
• A HYPOTHESIS is a SINGLE, UNPROVEN assumption or
idea which attempts to explain why nature behaves in a specific
manner. When put forward, hypotheses are tentative but, if they
survive testing, eventually gain general acceptance.
• A THEORY is a set of hypothesis that ties together a large
number of observations of the real world into a logically
consistent and understandable pattern. In other words, a theory
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
is a TESTED, REFINED, and EXPANDED explanation of
why nature behaves in a given way.
OBSERVATIONS → HYPOTHESIS → THEORY
Scientific Method
• A LAW is a broad generalization or summary statement which
describes a large amount of experimental evidence stating how
nature behaves when a particular situation occurs.
2.
The following are general characteristics of HYPOTHESES:
• Hypotheses are normally single assumptions.
• Hypotheses are narrow in their scope of explanation.
• When originally proposed, hypotheses are tentative (being
based on very incomplete evidence) but may become generally
accepted after more complete testing.
e.g. HYPOTHESES OF GASES:
(i)
All gases are made up of tiny, fast moving particles.
(ii)
The tiny particles of a gas transfer some of their energy
when they collide with other particles or with the
container.
(iii) The tiny particles in a gas act like miniature billiard
balls and the entire system undergoes no net change in
energy when particles collide.
3.
The following are general characteristics of THEORIES:
• Theories are composed of one or more underlying hypotheses.
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CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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• Theories are broad in scope and may have subtle implications
which are not foreseen when they are proposed because they
provide explanations for entire “fields” of related behaviour.
• Theories are sometimes called models because they often
provide a concrete way to examine, predict, and test the
workings of nature.
• A theory cannot be “proven” but it may have such a tremendous
record of explanation and prediction that we place a high
probability on its correctness as a model capable of describing
reality.
• Theories must be “falsifiable”; that is, they must make testable
predictions about the behaviour of the system under NEW
conditions.
e.g. KINETIC THEORY OF GASES
Gases behave the way they do because they are made up of
point-like particles, which are constantly moving, colliding,
and exchanging energy.
4.
The following are general characteristics of LAWS:
• Laws summarize the results of many experiments or
observations and state what will happen when a specific
situation occurs.
• Laws do not try to explain why something occurs.
• Laws are not “proven theories”. Laws are often stated before
any theory exists to explain why the law is true.
e.g. BOYLE’S LAW states that if the temperature is unchanged,
the greater the pressure applied to a sample of gas, the
smaller its volume.
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
CHARLES’ LAW states that if the applied pressure is
unchanged, the greater the temperature of a sample of gas,
the greater its volume.
ASSIGN 4-11
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CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
B.
The Physical Properties of Matter
1.
CHEMISTRY is the study of matter and its interactions.
7
MATTER is defined as anything that has mass and occupies
space. (Matter is what makes up everything other than energy.)
Hence, chemistry may be better described as the science concerned
with the properties, composition, and behaviour of matter.
2.
SUBSTANCES are things that have a unique and identifiable set
of properties. A PHYSICAL PROPERTY of a substance is a
property that can be found without creating a new substance.
e.g. Density, colour, hardness, and melting point
A CHEMICAL PROPERTY is the ability of a substance to
undergo a chemical reaction and change into new substances,
either by itself or with other substances.
e.g. Hydrogen gas can burn in air to produce water.
3.
Physical properties can be either intensive or extensive.
An INTENSIVE PROPERTY is a physical property that does not
depend on how much of the substance is present. (e.g. density,
melting temperature)
An EXTENSIVE PROPERTY is a physical property that does
depend on the amount of substance present. (e.g. mass and
volume)
Intensive properties can be used to identify a substance while
extensive properties cannot be used to identify substances.
Assign 13-15
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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4. Matter can exist in three common states or “PHASES”: solid,
liquid, and gas. The three common phases of mater each have a
unique set of properties which allow a given substance to be
classified.
a. http://phet.colorado.edu/en/simulation/states-of-matter
5. (a) SOLIDS
Solids are rigid and DO NOT readily change their shape.
Solids experience very small changes in volume (expand)
when heated or subjected to pressure.
In a solid, the particles are packed closely together into a
given volume. The particles are highly organized and rigid
which requires the particles to be in direct contact with each
other. In general solids are NOT compressible.
(b)
LIQUIDS
Liquids conform to the shape of their container and experience
only slight changes in volume when heated or subjected to pressure
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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In a liquid, the particles remain in close contact with each
other but have enough room to slide past one another easily
and prevent an organized packing. Because the particles of a
liquid are in close contact, they are also NOT compressible.
(c)
GASES
Gases conform to the shape of their container but unlike
solids or liquids they occupy the entire volume of the
container. Gases experience drastic changes in volume
when heated or subjected to pressure.
In a gas, the particles are widely separated and only contact
each other during collisions. Most of the volume of a gas is
EMPTY SPACE. Because the large separation of particles
can be decreased, gases are compressible.
5.
Some other physical properties of matter include:
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
HARDNESS the ability of a solid to resist abrasion or
scratching.
MALLEABILITY the ability to be rolled or hammered into thin
sheets.
DUCTILITY the ability to be stretched or drawn into wires.
LUSTRE the manner in which a solid surface reflects
light. Lustres can vary from metallic to
admantine (diamond-like), glassy, oily, pearly,
silky, or dull.
VISCOSITY the resistance of fluid to flow (thickness).
DIFFUSION the mixing of fluids (gases and liquids) as a
result of random motion within the fluid.
VAPOUR the gaseous material formed by the evaporation
of a substance below its boiling point
VAPOUR the pressure created by the vapour evaporating
PRESSURE (VP) from a liquid.
BOILING POINT the temperature at which a liquid changes state
(BP) to a gas.
MELTING POINT the temperature at which a solid changes state to
(MP) a liquid.
Assign 16-20 all and 21-31 odd
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CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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C._______________________ The Classification of Matter
1.
The physical properties of a substance can be used to classify or
organize the substances into a number of categories. Recall the
following terms:
(a)
ELEMENT is a substance, which cannot be separated into
simpler substances as a result of any chemical process.
e.g. silver metal, hydrogen gas, copper metal
(b)
ATOM is the smallest possible unit of an element, which
retains the properties of the element.
e.g. silver (Ag), hydrogen (H), copper (Cu)
(c)
MOLECULE is a group of two or more atoms joined
together by chemical bonds.
e.g. water (H2O), ethanol (CH3CH2OH), sodium carbonate
(Na2CO3)
(d)
ION is an atom or molecule which possesses an electrical
charge (positive or negative).
e.g. sodium ion (Na+), chloride ion (Cl-), nitrate ion (NO3-),
calcium ion (Ca2+)
(e)
PARTICLE is the general term used to describe a small bit
of matter such as an atom, molecule, or ion.
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
2.
12
Substances can be classified according to the following flowchart.
ALL SUBSTANCES
HOMOGENEOUS
(only one phase)
PURE SUBSTANCE
(constant composition)
ELEMENT
COMPOUND
HETEROGENEOUS
(more than one phase)
HOMOGENEOUS
MIXTURE
(variable composition)
SOLUTION
MECHANICAL
MIXTURE
(variable composition)
A HOMOGENEOUS substance is a substance consisting of only
one phase.
e.g. air, water, salt water, a piece of iron
A HETEROGENEOUS substance is a substance consisting of
more than one phase.
e.g. pencil, gravel, human being
A PURE SUBSTANCE is a substance that is homogeneous and
has an unchangeable composition.
e.g. sugar, water, copper, iron
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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A MIXTURE is a system made up of two or more substances with
variable composition.
e.g. salt dissolved in water, sugar in coffee
A MECHANICAL MIXTURE is a heterogeneous mixture of two
or more substances.
e.g. gravel, sand and iron filings, a pencil
A SOLUTION is a homogenous mixture of two or more
substances. There are several different types of mixtures:
TYPE OF SOLUTION
EXAMPLE
gas—in—gas
air (oxygen, nitrogen…)
gas—in—liquid
soda pop (demo outside)
liquid—in—liquid
water and alcohol
solid—in—liquid
salt water
solid—in—solid
alloys (metals melted
together)
For a solution, the solvent is the component of the solution in
greater quantity while the solute is the component in smaller
quantity.
Elements are substances that cannot be separated into simpler
substances by chemical processes.
e.g. substances in the periodic table — H, Pb, C, O, Ag …
Compounds are substances composed of two or more types of
atoms but only one type of “molecule” is present.
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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e.g. NaCl, H2O, C6H12O6
PURE SUBSTANCE = unchanging physical properties
HOMOGENEOUS MIXTURE = changeable composition but
each particular composition has unchanging, uniform physical
properties.
HETEROGENEOUS MIXTURE = each component present has
different physical properties regardless of composition.
Assign 33-44
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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D.
The Physical Separation of Substances
1.
There are many different methods that can be used to separate one
substance from another. All the methods however, take advantage
of differences in the physical properties of the substances
involved.
A.
HAND SEPARATION
A mechanical mixture can often be separated by hand or by
the use of a sieve or magnet.
e.g. magnets can be used to separate iron filings from sand
B.
FILTRATION
Filtration allows the separation of liquids from solids; that is,
of mechanical mixtures involving liquids and solids.
Filtration CANNOT however, be used to separate dissolved
solids from liquids (solutions).
Demo CuSO4 and sand in water
The material which remains on the filter paper is called the
RESIDUE and the liquid which passes through the filter
paper is called the FILTRATE.
e.g. sand can be filtered from a sand/water mixture
C.
EVAPORATION
Evaporation involves allowing the liquid in a SOLID–IN–
LIQUID solution to evaporate or be boiled away, leaving the
solid.
e.g. water can be evaporated from salt water to leave behind
the salt
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
D.
16
DISTILLATION
Distillation separates liquid–in–liquid solutions based on
differences in boiling points.
When a liquid–in–liquid solution is heated in a distillation
setup, the liquid with the lowest boiling point boils first. The
vapor produced is at the exact temperature of the liquid and
ascends to the top the of the DISTILLATION FLASK,
passes the thermometer, enters the side arm of the flask and
contacts the cold inner surface of the CONDENSER. The
gas cools and condenses back into a liquid form, dropping
out the end of the condenser as a purified liquid called a
DISTILLATE.
e.g. a water/ethanol mixture can be separated by distillation
Demo CuSO4(aq) with CH3OH
E.
SOLVENT EXTRACTION
Separates substances based on their solubilities in different
solvents. In the simplest case, this method uses a liquid that
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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dissolves one or more of the solids present but leaves others
undissolved. In a more complicated situation, several solvent
extractions may be necessary.
e.g. salt and sand can be separated by adding water
demo CuSO4 in oil and extract to water.
F.
RECRYSTALLIZATION
Recrystallization is a variation on the method of
EVAPORATION in which the solid in a solid–in–liquid
solution is separated in a pure and CRYSTALLINE state. A
SATURATED solution of a desired solid is prepared in a
suitable solvent. The solvent is allowed to slowly evaporate
causing some of the desired solid to come out of solution as
crystals; however, not all the solvent is allowed to evaporate.
The crystals that are formed can then be separated by HAND
SEPARATION or FILTRATION.
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
G.
GRAVITY SEPARATION
This method separates solids from a mechanical mixture
based on their density. Sometimes this method may involve
a centrifuge, which whirls a test tube around at extremely
high speeds forcing finely dispersed solids to the bottom of
the test tube. A centrifuge works best with small volumes of
liquid.
Demo sand, sawdust and water
18
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
H.
19
PAPER, COLUMN, AND THIN LAYER
CHROMATOGRAPHY
Each of paper, column, and thin layer chromatography works
similarly and used to separate small amounts of SOLID–IN–
LIQUID solutions containing two or more dissolved solids
(SOLUTES), which are colored, or can be reacted to form
colors. Paper chromatography uses a sheet of absorbent
paper. Thin layer chromatography (TLC) uses a thin
absorbent layer of dried silica gel on a sheet of glass or
plastic. Column chromatography uses beads of resin or silica
beads. In each of these methods a developing solvent
referred to as the MOBILE PHASE carries the solute along
the absorbent STATIONARY PHASE. The solutes separate
as a result of their varying solubilities in the mobile phase
and their AFFINITY (attraction) for the stationary phase.
demo felt pens
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
2.
SUMMARY OF SEPARATION METHODS
MIXTURE
METHOD
Hand separation
WHEN TO USE METHOD
Large chunks present among other solids
Gravity
separation
The density of the desired solids is much different from the
density of the other solids.
Solvent
extraction
One solid preferentially dissolves in a particular solvent
SOLID in SOLID
SOLID in LIQUID
MIXTURE
Chromatography
The solids are coloured, present in small amounts and are
soluble in some solvent or mixture of solvents
Hand separation
A few large pieces of solid are present in the liquid
Gravity
separation
Filtration
Solid particles are present in LARGE amount of liquid
METHOD
WHEN TO USE METHOD
Evaporation
SOLID in LIQUID
LIQUID in
LIQUID
Assign- 45-58
Solid particles are present in a SMALL amount of liquid
The solid is wanted and the liquid is not
Distillation
The liquid is wanted; the solid may or may not be wanted
Solvent
extraction
An immiscible added solvent preferentially dissolves at least
one but not all of the solids present
Recrystallization
One dissolved solid is much less soluble than the others
present (if any); the liquid is not wanted
Chromatography
Small amounts of more than one coloured solid are present;
the liquid present is not wanted
Distillation
Two or more liquids are present and have different boiling
temperatures
Solvent
extraction
An immiscible added solvent preferentially dissolves at least
one but not all of the liquids present
20
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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E. _____________________________________ Phase Changes
1.
Substances can undergo two kinds of changes, chemical or
physical. Chemical changes produce a set of chemicals, which is
different from the set of chemicals, which existed before the
change. A physical change does not change the set of chemicals
involved.
A CHEMICAL CHANGE is a change in which new substances
are formed.
A PHYSICAL CHANGE is change in the phase of a substance,
such that no new substances are formed.
Chemical changes are frequently accompanied by physical
changes. For example, hydrogen gas and oxygen gas react to form
liquid water
2.
In general, continued heating of a solid produces the following
temperature behaviour.
boiling
freezing
g
l <—> g
melting
s <—> l
condensing
s
freezing
Notice that the temperature does not change during a phase change
such as melting and boiling.
CHEMISTRY 11 — UNIT III THE PHYSICAL PROPERTIES…
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A.
MELTING TEMPERATURE is the temperature at which a
solid changes into the liquid phase.
B.
FREEZING TEMPERATURE is the temperature at which
a liquid changes into the solid phase. At the
MELTING/FREEZING temperature the solid and liquid
phases co-exist.
C.
BOILING TEMPERATURE is the temperature at which a
liquid changes into the gas phase.
D.
CONDENSATION TEMPERATURE is the temperature at
which a gas changes into the liquid phase. At the
BOILING/CONDENSING temperature the liquid and gas
phases co-exist.
As time goes on, heat is constantly entering the substance
represented in the above graph.
On the sloping portions of the graph, all the heat is used to warm
the substance so the temperature rises.
On the level portions of the graph, the substance contains so
much heat energy that it cannot absorb more heat and stay in the
same phase. The added heat is used, for example, to break up the
solid and allow a liquid to form. All the heat is used to change
phase so the temperature does not change and the graph levels off.
Assign 59-63
Read page 62-64
Assign 64-68