MATTER
Chemistry is an integral part of the science curriculum both at the
high school as well as the early college level. At these levels, it is
often called 'general chemistry' which is an introduction to a wide
variety of fundamental concepts that enable the student to acquire
tools and skills useful at the advanced levels, whereby chemistry is
invariably studied in any of its various sub-disciplines. Scientists,
engaged in chemical research are known as chemists.
Chemistry contributes to other disciplines. In engineering, many of
the materials we work with have been synthesized by chemists.
Some of these materials are organic. They could be familiar plastics
like polyethylene or the more esoteric plastics used in unbreakable
windows and nonflammable clothing.
Other materials, including
metal alloys and semiconductors are inorganic in nature. In the
career of medicine or pharmacy, we have to become familiar with
the properties of aqueous solutions, which include blood and other
body fluids.
Chemists today are involved in the synthesis of a
variety of life-saving products. These range from drugs used in
chemotherapy
to
new
antibiotics
used
against
resistant
microorganisms.
Chemistry is the scientific study of interaction of chemical
substances that are constituted of atoms or the subatomic particles:
protons, electrons and neutrons.
Atoms combine to produce
molecules or crystals. Chemistry is often called "the central science"
because it connects the other natural sciences, such as astronomy,
physics, material science, biology, and geology.
The genesis of chemistry can be traced to certain practices, known
as alchemy, which had been practiced for several millennia in
various parts of the world, particularly the Middle East.
The structure of objects we commonly use and the properties of the
matter we commonly interact with, are a consequence of the
properties of chemical substances and their interactions. For
example, steel is harder than iron because its atoms are bound
together in a more rigid crystalline lattice; wood burns or undergoes
rapid oxidation because it can react spontaneously with oxygen in a
chemical reaction above a certain temperature; sugar and salt
dissolve in water because their molecular/ionic properties are such
that dissolution is preferred under the ambient conditions. The
transformations that are studied in chemistry are a result of
interaction
either
between
different
chemical
substances
or
between matter and energy. Traditional chemistry involves study of
interactions between substances in a chemistry laboratory using
various forms of laboratory glassware.
A chemical reaction is a
transformation of some substances into one or more other
substances. It can be symbolically depicted through a chemical
equation. The number of atoms on the left and the right in the
equation for a chemical transformation is most often equal. The
nature of chemical reactions a substance may undergo and the
energy changes that may accompany it are constrained by certain
basic rules, known as chemical laws.
Energy and entropy considerations are invariably important in
almost all chemical studies. Chemical substances are classified in
terms
of
their
structure,
phase
as
well
as
their
chemical
compositions. They can be analyzed using the tools of chemical
analysis, e.g. spectroscopy and chromatography.
History
Ancient Egyptians pioneered the art of synthetic "wet" chemistry up
to 4,000 years ago. By 1000 BC ancient civilizations were using
technologies that formed the basis of the various branches of
chemistry, such as; extracting metal from their ores, making pottery
and glazes, fermenting beer and wine, making pigments for
cosmetics and painting, extracting chemicals from plants for
medicine and perfume, making cheese, dying cloth, tanning leather,
rendering fat into soap, making glass, and making alloys like bronze.
The genesis of chemistry can be traced to the widely observed
phenomenon of burning that led to metallurgy- the art and science
of processing ores to get metals (e.g. metallurgy in ancient India).
The greed for gold led to the discovery of the process for its
purification, even though, the underlying principles were not well
understood -- it was thought to be a transformation rather than
purification. Many scholars in those days thought it reasonable to
believe that there exist means for transforming cheaper (base)
metals into gold. This gave way to alchemy, and the search for the
Philosopher's Stone, which was believed to bring about such a
transformation by mere touch.
Greek atomism dates back to 440 BC, as what might be indicated by
the book De Rerum Natura (The Nature of Things) written by the
Roman Lucretius in 50 BC. Much of the early development of
purification methods is described by Pliny the Elder in his Naturalis
Historia.
Some consider medieval Arabs and Persians to be the earliest
chemists, who introduced precise observation and controlled
experimentation into the field, and discovered numerous chemical
substances. The most influential Muslim chemists were Geber (d.
815), Al-Kindi (d. 873), Al-Razi (d. 925), and
Al-Biruni (d.
1048). The works of Geber became more widely known in Europe
through Latin translations by a pseudo-Geber in 14th century Spain,
who also wrote some of his own books under the pen name "Geber".
The contribution of Indian alchemists and metallurgists in the
development of chemistry was also quite significant.
The emergence of chemistry in Europe was primarily due to the
recurrent incidence of the plague and blights there during the so
called Dark Ages. This gave rise to a need for medicines. It was
thought that there exists a universal medicine called the Elixir of
Life that can cure all diseases, but like the Philosopher's Stone, it
was never found.
For some practitioners, alchemy was an intellectual pursuit, over
time, they got better at it. Paracelsus (1493-1541), for example,
rejected the
4-elemental theory and with only a vague
understanding of his chemicals and medicines, formed a hybrid of
alchemy and science in what was to be called iatrochemistry.
Similarly, the influences of philosophers such as Sir Francis Bacon
(1561-1626) and René Descartes (1596-1650), who demanded
more rigor in mathematics and in removing bias from scientific
observations, led to a scientific revolution. In chemistry, this began
with Robert Boyle (1627-1691), who came up with an equations
known as the Boyle's Law about the characteristics of gaseous state.
Chemistry indeed came of age when Antoine Lavoisier (1743-1794),
developed the theory of Conservation of mass in 1783; and the
development of the Atomic Theory by John Dalton around 1800. The
Law of Conservation of Mass resulted in the reformulation of
chemistry based on this law and the oxygen theory of combustion,
which was largely based on the work of Lavoisier. Lavoisier's
fundamental contributions to chemistry were a result of a conscious
effort to fit all experiments into the framework of a single theory. He
established the consistent use of the chemical balance, used oxygen
to overthrow the phlogiston theory, and developed a new system of
chemical nomenclature and made contribution to the modern metric
system. Lavoisier also worked to translate the archaic and technical
language of chemistry into something that could be easily
understood by the largely uneducated masses, leading to an
increased public interest in chemistry. All these advances in
chemistry led to what is usually called the chemical revolution. The
contributions of Lavoisier led to what is now called modern
chemistry - the chemistry that is studied in educational institutions
all over the world. It is because of these and other contributions
that Antoine Lavoisier is often celebrated as the "Father of Modern
Chemistry".
The later discovery of Friedrich Wöhler that many
natural substances, organic compounds, can indeed be synthesized
in a chemistry laboratory also helped the modern chemistry to
mature from its infancy.
The discoveries of the chemical elements has a long history from the
days of alchemy and culminating in the creation of the periodic table
of the chemical elements by Dmitri Mendeleev (1834-1907) and
later discoveries of some synthetic elements.
Matter is anything that has both mass and volume (occupies space).
A more rigorous definition is used in science: matter is what atoms
and molecules are made of. Matter is commonly said to exist in four
states (or phases): solid, liquid, gas and plasma; other phases, such
as Bose–Einstein condensates, also exist. In everyday human
environments, matter is closely related to (and in many contexts
equivalent to) mass. For example, a car would be said to be made of
matter, as it occupies space, and has mass.
In the realm of relativity, matter can be equated to energy via the
equation E = mc2. In the realm of cosmology, other forms of matter
and energy, such as dark matter and dark energy are invoked to
explain the behavior of the observable universe.
The international standards organization Bureau International des
Poids et Mesures uses the terminology "amount of substance",
rather than "matter". A scientific definition of "matter" that is based
upon its physical and chemical structure is: matter is what atoms
and molecules are made of, meaning anything made of protons,
neutrons, and electrons.
The common definition in terms of occupying space and having mass
is in contrast with most physical and chemical definitions of matter,
which rely instead upon its structure and upon attributes not
necessarily related to volume and mass. James Clerk Maxwell
discussed matter in his work Matter and Motion. He carefully
separates "matter" from space and time, and defines it in terms of
the object referred to in Newton's first law of motion. In the 19th
century, the term "matter" was actively discussed by a host of
scientists and philosophers, and a brief outline can be found in
Levere. A textbook discussion from 1870 suggests matter is what is
made up of atoms.
Three divisions of matter are recognized in science: masses,
molecules and atoms.
A Mass of matter is any portion of matter
appreciable
by
the
senses.
A Molecule is the smallest particle of matter into which a body can
be divided without losing its identity. An Atom is a still smaller
particle produced by division of a molecule.
Phases of ordinary matter
In bulk, matter can exist in several different forms, or states of
aggregation, known as phases,
depending on ambient pressure,
temperature and volume. A phase is a form of matter that has a
relatively uniform chemical composition and physical properties
(such as density, specific heat, refractive index, and so forth). These
phases include the three familiar ones (solids, liquids, and gases), as
well as more exotic states of matter ( such as plasmas, superfluids,
supersolids, Bose-Einstein condensates, ...). A fluid may be a liquid,
gas or plasma. There are also paramagnetic and ferromagnetic
phases of magnetic materials. As conditions change, matter may
change from one phase into another. These phenomena are called
phase transitions, and are studied in the field of thermodynamics. In
nanomaterials, the vastly increased ratio of surface area to volume
results in matter that can exhibit properties entirely different from
those of bulk material, and not well described by any bulk phase.
Phases are sometimes called states of matter, but this term can lead
to confusion with thermodynamic states. For example, two gases
maintained at different pressures are in different thermodynamic
states (different pressures), but in the same phase (both are solids).
Solid
Solids are characterized by a tendency to retain their structural
integrity; if left on their own, they will not spread in the same way
gas or liquids would. Many solids, like rocks and concrete, have very
high hardness and rigidity and will tend to break or shatter when
subject to various forms of stress, but others like steel and paper
are more flexible and will bend. Solids are often composed of
crystals, glasses, or long chain molecules (e.g. rubber and paper).
Some solids are amorphous such as glass. A common example of a
solid is the solid form of water, ice. Thus, a solid phase has a rigid
shape and a fixed volume.
Liquid
In a liquid, the constituents frequently are touching, but able to
move around each other. So unlike a gas, it has cohesion and
viscosity. Compared to a solid, the forces holding constituents
together are weaker, and it is not rigid, but adapts a shape decided
by its container. Liquids are hard to compress. A common example is
water. Thus liquid phase has a fixed volume and it takes on the
shape of the container.
Gas
A gas is a state of aggregation without cohesion; a vapor. Thus a gas
has no resistance to changing shape (beyond the inertia of its
constituents, which have to be knocked aside). The distance
between constituent particles is flexible, determined, for example,
by the size of a container and the number of particles, not by
internal forces. A common example is the vapor form of water,
steam. Thus gaseous phase has neither a fixed volume nor a rigid
shape; it takes on both the volume and the shape of the container.
Plasma
Plasma is a fourth state of matter consisting of an overall chargeneutral mix of electrons, ions and neutral atoms. The plasma
exhibits behavior peculiar to long range Coulomb forces in which the
particles move in electromagnetic fields generated by and selfconsistent with their own motions. The sun and stars are plasmas,
as is the Earth's ionosphere, and plasmas occur in neon signs.
Plasmas of deuterium and tritium ions are used in fusion reactions.
The term plasma was applied for the first time by Tonks and
Langmuir in 1929, to the inner regions of a glowing ionized gas
produced by electric discharge in a tube.
Bose–Einstein condensate
This state of matter was first discovered by Satyendra Nath Bose,
who sent his work on statistics of photons to Albert Einstein for
comment. Following publication of Bose's paper, Einstein extended
his treatment to massive particles fixed in number, and predicted
this fifth state of matter in 1925. Bose–Einstein condensates were
first realized experimentally by several different scientific groups in
1995 for rubidium, sodium, and lithium, using a combination of laser
and evaporative cooling.
Bose–Einstein condensation for atomic
hydrogen was achieved in 1998.
The Bose–Einstein condensate is a liquid-like superfluid that occurs
in at low temperatures in which all atoms occupy the same quantum
state. In
low-density systems, it occurs at or below 10−5 K.
Fermionic condensate
A fermionic condensate is a superfluid phase formed by fermionic
particles at low temperatures.
It is closely related to the Bose-
Einstein condensate under similar conditions. Unlike the Bose-
Einstein condensates, fermionic condensates are formed using
fermions instead of bosons. The earliest recognized fermionic
condensate described the state of electrons in a superconductor; the
physics of other examples including recent work with fermionic
atoms is analogous. The first atomic fermionic condensate was
created by Deborah S. Jin in 2003. These atomic fermionic
condensates are studied at temperatures in the vicinity of 50-350nK.
A hypothetical fermionic condensate that appears in theories of
massless fermions with chiral symmetry breaking is the chiral
condensate or the quark condensate.
Core of a neutron star
Because of its extreme density, the core of a neutron star falls under
no other state of matter. While a white dwarf is about as massive as
the sun (up to 1.4 solar masses, the Chandrasekhar limit), the Pauli
exclusion principle prevents its collapse to smaller radius, and it
becomes an example of degenerate matter. In contrast, neutron
stars are between 1.5 and 3 solar masses, and achieve such density
that the protons and electrons are crushed to become neutrons.
Neutrons are fermions, so further collapse is prevented by the
exclusion principle, forming so-called neutron degenerate matter.
Quark-gluon plasma
Gluons are elementary particles that cause quarks to interact, and
are indirectly responsible for the binding of protons and neutrons
together in atomic nuclei. The quark-gluon plasma is a hypothetical
phase of matter, a phase of matter as yet not observed, supposed to
exist in the early universe and to have evolved into a hadronic-gas
phase. At extremely high energy the strong force is anticipated to
become so weak that the atomic nuclei break down into a bunch of
loose quarks, which distinguishes the quark-gluon phase from
normal plasma. In collisions of relativistic heavy ions, it is hoped to
observe a phase transition from the nuclear, hadronic phase to a
matter phase consisting of quarks and gluons. So far, experimental
results have shown that such collisions form a dense hadronic
fireball of high energy density well localized in space.
Structure of ordinary matter
In particle physics, fermions are particles which obey Fermi–Dirac
statistics. Fermions can be elementary, like the electron, or
composite, like the proton and the neutron. In the Standard Model
there are two types of elementary fermions: quarks and leptons,
which are discussed next.
Quarks
Quarks are a particles of spin -1⁄2, meaning that they are fermions.
They carry an electric charge of −1⁄3 e (down-type quarks) or +2⁄3 e
(up-type quarks). For comparison, an electron has a charge of −1 e.
They also carry colour charge, which is the equivalent of the electric
charge for the strong interaction. Quarks also undergo radioactive
decay, meaning that they are subject to the weak interaction.
Quarks are massive particles, and therefore are also subject to
gravity (Table 1-1).
Table (1-1): Quark properties.
Quark properties
Electri
Name
Symb Spi
ol
n
c
Mass
Mass
charg (MeV/c comparab
e
2)
(e)
Up-type quarks
le to
Antipartic
le
Antipartic
le
symbol
Up
u
1⁄
2
+2⁄3
Charm
c
1⁄
2
+2⁄3
1.5 to
~5
3.3
electrons
1160 to
~1
1340
proton
169,10
Top
t
1⁄
2
+2⁄3
0 to
173,30
0
Antiup
u
Anticharm
c
Antitop
t
Antidown
d
~ 180
protons or
~1
tungsten
atom
Down-type quarks
Down
Strang
e
Botto
m
d
1⁄
2
−1⁄3
s
1⁄
2
−1⁄3
b
1⁄
2
−1⁄3
3.5 to
~ 10
6.0
electrons
70 to
~ 200
Antistran
130
electrons
ge
4130 to
~5
Antibotto
4370
protons
m
s
b
Quark structure of a proton: 2 up quarks and 1 down quark.
Baryonic matter
Baryons are strongly interacting fermions, and so are subject to
Fermi-Dirac statistics. Amongst the baryons are the protons and
neutrons, which occur in atomic nuclei, but many other unstable
baryons exist as well. The term baryon is usually used to refer to
triquarks — particles made of three quarks. "Exotic" baryons made
of four quarks and one antiquark are known as the pentaquarks, but
their existence is not generally accepted.
Baryonic matter is the part of the universe that is made of baryons
(including all atoms). This part of the universe does not include dark
energy, dark matter, black holes or various forms of degenerate
matter, such as compose white dwarf stars and neutron stars.
Microwave light seen by Wilkinson Microwave Anisotropy Probe
(WMAP), suggests that only about 4.6% of that part of the universe
within range of the best telescopes (that is, matter that may be
visible because light could reach us from it), is made of baryionic
matter. About 23% is dark matter, and about 72% is dark energy.
A comparison between the white dwarf IK Pegasi B (center), its Aclass companion IK Pegasi A (left) and the Sun (right). This white
dwarf has a surface temperature of 35,500 K.
Degenerate matter
In physics, degenerate matter refers to the ground state of a gas of
fermions at a temperature near absolute zero. The Pauli exclusion
principle requires that only two fermions can occupy a quantum
state, one spin-up and the other spin-down. Hence, at zero
temperature, the fermions fill up sufficient levels to accommodate
all the available fermions, and for the case of many fermions the
maximum kinetic energy called the Fermi energy and the pressure of
the gas becomes very large and dependent upon the number of
fermions rather than the temperature, unlike normal states of
matter.
Degenerate matter is thought to occur during the evolution of heavy
stars. The demonstration by Subrahmanyan Chandrasekhar that
white dwarf stars have a maximum allowed mass because of the
exclusion principle caused a revolution in the theory of star
evolution. Degenerate matter includes the part of the universe that
is made up of neutron stars and white dwarfs.
Leptons
Leptons are a particles of spin-1⁄2, meaning that they are fermions.
They carry an electric charge of −1 e (electron-like leptons) or 0 e
(neutrinos). Unlike quarks, leptons do not carry colour charge,
meaning that they do not experience the strong interaction. Leptons
also undergo radioactive decay, meaning that they are subject to
the weak interaction. Leptons are massive particles, therefore are
subject to gravity (Table 1-2).
Table (1-2): Lepton properties.
Lepton properties
Electr
Name
Symb Spi
ol
n
ic
Mass
Mass
charg (MeV/c compara
e
2)
ble to
Antiparticl
e
Antipartic
le
symbol
(e)
Electron-like leptons[47]
Electro
n
e−
1⁄
2
−1
0.5110
Muon
μ−
1⁄
2
−1
105.7
Tauon
τ−
1⁄
2
−1
1,777
1
electron
~ 200
electrons
~2
protons
Antielectro
n
e+
(positron)
Antimuon
μ+
Antitauon
τ+
Neutrinos[48]
Electro
n
neutrin
νe
1⁄
2
0
<
Less than
Electron
0.0004
a
antineutrin
60
thousand
o
Νe
o
th of an
electron
Muon
neutrin
Less than
νμ
1⁄
2
0
< 0.19 half of an antineutrin
o
electron
Tauon
(or tau
Νμ
o
Tauon
neutrin
o
Muon
Less than
ντ
1⁄
2
0
< 18.2
~ 40
electrons
neutrin
o)
antineutrin
o
(or tau
Ντ
antineutrin
o)
Other types of matter
Ordinary matter is divided into luminous matter (the stars and
luminous gases and 0.005% radiation) and nonluminous matter
(intergalactic
gas
and
about
0.1%
neutrinos
and
0.04%
supermassive black holes). Ordinary matter is uncommon. Modeled
after Ostriker and Steinhardt.
Matter, in the scientific definition, constitutes about 4% of the
energy of the observable universe. The remaining energy is
theorized to be due to exotic forms, of which 23% is dark matter
and 73% is dark energy (Figure 1-1).
Figure (1): The fractions of energy in the universe contributed by
different sources.
Dark matter
In astrophysics and cosmology, dark matter is matter of unknown
composition that does not emit or reflect enough electromagnetic
radiation to be observed directly, but whose presence can be
inferred from gravitational effects on visible matter. Observational
evidence of the early universe and the big bang theory require that
this matter have energy and mass, but is not composed of either
elementary fermions (as above) OR gauge bosons. As such, it is
composed of particles as yet unobserved in the laboratory (perhaps
supersymmetric particles).
Dark energy
In cosmology, dark energy is the name given to the antigravitating
influence that is accelerating the rate of expansion of the universe.
It is known not to be composed of known particles like protons,
neutrons or electrons, nor of the particles of dark matter, because
these all gravitate.
Fully 70% of the matter density in the universe appears to be in the
form of dark energy. Twenty-six percent is dark matter. Only 4% is
ordinary matter. So less than 1 part in 20 is made out of matter we
have observed experimentally or described in the standard model of
particle physics. Of the other 96%, apart from the properties just
mentioned, we know absolutely nothing.
Exotic matter
Exotic matter is a hypothetical concept of particle physics. It covers
any material which violates one or more classical conditions or is not
made of known baryonic particles. Such materials would possess
qualities like negative mass or being repelled rather than attracted
by gravity.
Classification of matter
Matter can be classified into two categories; pure substances and
mixtures. Pure substance has a fixed composition and a unique set
of properties.
It could be element or compound. Mixtures may
composed of two or more substances.
They can be either
homogeneous or heterogeneous.
Elements
An element is a type of matter which cannot be broken-down into
two or more pure substances. There are 112 known elements, of
which 91 occur naturally.
Many elements are familiar to all of us.
The charcoal used in
outdoor grills is nearly pure carbon. Electrical wiring is often made
from copper. Many household utensils are made of aluminum. The
shiny liquid in the thermometers you use is still another metallic
element, mercury.
Ultra pure silicon has become the basis for
semiconductor industry.
In chemistry, an element is identified by its symbol (Table 1-3).
This consists of one or two letters, usually derived from the name of
the element. Thus the symbol for carbon is C; that for aluminum is
Al.
Sometimes the symbol comes from the latin name of the
element or one of its compounds. The two elements copper and
mercury, which were known in ancient times, have the symbols Cu
(cuprum) and Hg (hydrargyrum). Table (00000), lists the name and
symbols of the elements that we will be most concerned with in this
course.
Table (1-3): Names and symbols of some of the more familiar
elements:
Element
Symbol
Element
Symbol
Aluminum
Al
Lithium
Li
Antimony
Sb
Magnesium
Mg
Argon
Ar
Manganese
Mn
Barium
Ba
Mercury
Hg
Beryllium
Be
Neon
Ne
Bismuth
Bi
Nickel
Ni
Boron
B
Nitrogen
N
Bromine
Br
Oxygen
O
Cadmium
Cd
Phosphorus
P
Calcium
Ca
Platinum
Pt
Carbon
C
Plutonium
Pu
Cesium
Ce
Potassium
K
Chlorine
Cl
Rubidium
Rb
Chromium
Cr
Selenium
Se
Cobalt
Co
Silicon
Si
Copper
Cu
Silver
Ag
Fluorine
F
Sodium
Na
Gold
Au
Strontium
Sr
Helium
He
Sulfur
S
Hydrogen
H
Tin
Sn
Iodine
I
Uranium
U
Iron
Fe
Titanium
Ti
Krypton
Kr
Xenon
Xe
Lead
Pb
Zinc
Zn
Compounds
A compound is a pure substance that contains more than one
element.
Water is a compound of hydrogen and oxygen.
The
compounds methane, acetylene, and naphthalene all contain the
elements
carbon
and
hydrogen,
Compounds have fixed compositions.
in
different
proportions.
That is, a given compound
always contains the same element in the same percentages by mass.
A sample of pure water contains precisely 11.19% hydrogen and
88.81% oxygen. In contrast, mixtures can vary in composition. For
example, a mixture of hydrogen and oxygen might contain 5, 10, 25,
or 60% hydrogen, along with 95, 90, 75, or 40% oxygen.
The properties of compounds are very different from those of the
elements they contain.
Ordinary table salt, sodium chloride, is a
white, unreactive solid.
It contains the two elements Na and Cl.
Sodium is a shiny, extremely reactive metal.
Chlorine is a
poisonous, greenish-yellow gas. Clearly, when these two elements
combine to form sodium chloride, a profound change takes place.
Many different methods can be used to resolve compounds into their
elements, e.g. heating and electrolysis.
Mercury (II) oxide, a
compound of mercury and oxygen, decomposes to its elements
when heated to 600 °C.
Water, a compound of hydrogen and oxygen, separates to its
elements when passes an electric current through it (electrolysis).
Electrolysis process is usually done when the compound present in a
liquid state.
Mixtures
A mixture contains two or more pure substances combined in such a
way that each substance retaines its chemical identity. When you
shake iron fillings with powdered sulfur, a mixture is formed; the
two elements are chemically unchanged. In contrast, when sodium
is exposed to chlorine gas, a compound, sodium chloride, is formed;
the two elements lose their chemical identity.
Types of mixtures
There are two types of mixtures, homogeneous and heterogeneous
mixtures.
Homogeneous or uniform mixtures
The composition of this mixture, is the same throughout. Another
name for a homogeneous mixture is a solution. A solution is made
up of a solvent, the substance present in largest amount, and one or
more solutes. Most commonly, the solvent is a liquid, while solutes
may be solids, liquids, or gases. Soda water is a solution of carbon
dioxide (solute) in water (solvent). Sea water is a more complex
solution in which there are several solid solutes, including NaCl, the
solvent is water. It is also possible to have solutions in the solid
state. Brass (yellow copper) is a solid solution containing the two
metals copper (67-90%) and zinc (10-33%).
Heterogeneous or nonuniform mixtures
The composition of this mixture is vary throughout. Most rocks fall
into this category. In a piece of granite, several components can be
distinguished, differing from one another in color.
Separation methods
Many different methods can be used to separate the components of
a mixture from one another.
A couple of methods that you may
have carried out in the laboratory are filtration and distillation.
Filtration, is used to separate a heterogeneous solid-liquid mixture.
The mixture is passed through a barrier with fine pores such as filter
paper.
Distillation, is used to resolve a homogeneous solid-liquid
mixture. The liquid vaporizes, leaving a residue of the solid in the
distilling flask. Pure liquid is obtained by condensing the vapor. A
more
complex
but
more
versatile
separation
method
is
chromatography to separate all kinds of mixtures. Chromatography
takes advantage of differences in solubility and/or extent of
adsorption on a solid surface.
In gas-liquid chromatography, a
mixture of volatile liquids and gases is introduced into one end of a
heated glass tube. As little as 1µl of sample may be used. The tube
is packed with an inert solid whose surface is coated with viscous
liquid. An unreactive "carrier gas", often helium, is passed through
the tube.
The components of sample gradually separate as they
vaporize into the helium or condense into the viscous liquid. Usually
the more volatile fractions move faster and emerge first; successive
fractions activate a detector and recorder. The end result is a plot
such as chromatogramic graph.
Properties of substances
Every pure substance has its own unique set of properties that serve
to distinguish it from all other substances. A chemist most often
identifies an unknown substance by measuring its properties and
compairing them to the properties recorded in the chemical
literature for known substances.
Chemical properties, observed when the substance takes part in a
chemical reaction, a change that converts it to a new substance. For
example, the fact that mercury (II) oxide decomposes to mercury
and oxygen upon heating to 600 °C can be used to identify it.
Physical properties. Observed without changing the chemical
identity of a substance. One such property is color; the fact that
K2CrO4 is yellow serves to distinguish it from a great many other
substances.
We consider four physical properties that you may well have
occasion to measure in the general chemistry laboratory; density,
melting point, boiling point and solubility.
Density
The density of a substance is the ratio of mass to volume:
Density = mass / volume,
d = m/v
For liquids or gases, density can be found in a straightforward way
by measuring, indepenently, the mass and volume of a sample.
For liquids, density is most often expressed in g/mL; for gases, g/L
is more common.
For solids, density is a bit more difficult to determine. The mass of
the solid sample is found in the usual way;
its volume is found
indirectly. To find the volume of insoluble solids, add the solid to a
flask of known volume, v, and determine the volume of water, vm ,
required to fill the flask.
The volume of the solid = v-vm
and then
d = m / ( v-vm)
Example:
To determine the density of ethyl alcohol, a student pipets a 5.0 mL
sample into an empty flask weighing 15.246 g. He finds that the
mass of the flask + ethyl alcohol = 19.171 g. Calculate the density
of ethyl alcohol.
Solution:
Mass of ethyl alcohol = 19.171 g – 15.246 g = 3.925 g
Volume of ethyl alcohol = 5.0 mL
Density = 3.925 g / 5.0 mL = 0.785 g / mL
Melting point
The melting point is the temperature at which a substance changes
from the solid to the liquid state.
If the substance is pure, the
temperature stays constant during melting. This means that, for a
pure substance, the melting point is identified with the freezing
point. Ice melts at 0 °C ; pure water freezes at that same temp.
Boiling point
The boiling point of a liquid is the temp at which bubbles filled with
vapor form within the liquid.
Boiling point depends on the pressure above the liquid. The normal
boiling point is the temperature at which a liquid boils when the
pressure above it is one atmosphere. For pure liquid, temperature
remains constant during the boiling process.
If you find that a colorless liquid freezes at 0 °C and boils at 100 °C
(at 1 atm pressure), chances are the liquid is water. To be sure, you
might check the density, which should be 0.997 g/ml at 25 °C.
Melting
point
and
boiling
point, like
density,
are
intensive
properties.
Solubility
The extent to which a substance dissolves in a particular solvent can
be expressed in various ways. A common method is to state the
number of grams of the substance that dissolves in 100 g of solvent
at a given temperature. At 20 °C, about 32 g of KNO3 dissolves in
100 g of water. At 100 °C, the solubility of this solid is considerably
greater, about 246 g/100g of water.
Example:
Taking the solubility of potassium nitrate, KNO3 , to be 246 g/100g
of water at 100 °C and 32 g /100g of water at 20 °C, calculate:
(1) The mass of water required to dissolve 100 g of KNO3 at 100 °C.
(2) The amount of KNO3 that remains in solution when the mixture
in (1) is cooled to 20 °C
Solution:
246 g KNO3
100 g H2O at 100 °C
32 g KNO3
100 g H2O at 20 °C
100 g KNO3
x
g H2O at 100 °C
(a) The mass of water required = 100 g KNO3 x 100 g H2O / 246 g
KNO3
= 40.7 g water
Therefore,
100 g KNO3
40.7 g H2O at 100 °C
32 g KNO3
100 g H2O at 20 °C
x g KNO3
40.7 g H2O at 20 °C
x g KNO3 = 32 x 40.7 / 100 = 13.0 g KNO3
The amount of KNO3 that remains = 100- 13 = 87 g
Therefore, 87 g of KNO3 Crystallizes out of solution when the
temperature drops from 100 °C to 20 °C
References
Sally M Walker & Andy King (2005). What is Matter?. Lerner
Publications. p. 7.
John Kenkel, Paul B. Kelter, David S. Hage (2000). Chemistry: An
Industry-based Introduction with CD-ROM. CRC Press. p. 2.
Kent A. Peacock (2008). The Quantum Revolution: A Historical
Perspective. Greenwood Publishing Group. p. 47.
Martin H. Krieger (1998). Constitutions of Matter: Mathematically
Modeling the Most Everyday of Physical Phenomena. University of
Chicago Press. p. 22.
Trevor Harvey Levere (1993). "Introduction". Affinity and Matter:
Elements of Chemical Philosophy, 1800-1865. Taylor & Francis.
P. M. Chaikin, T. C. Lubensky (2000). Principles of Condensed Matter
Physics. Cambridge University Press. p. xvii.
Walter Greiner, Mikhail G. Itkis (2003). Structure and Dynamics of
Elementary Matter: Proceedings of the NATO Asi on Structure and
Dynamics of Elementary Matter, Camyuva-Kemer (Antalya), Turkey,
from 22 September to 2 October 2003. Springer.
Paul Sukys (1999). Lifting the Scientific Veil: Science Appreciation
for the Nonscientist. Rowman & Littlefield. p. 87.
Bogdan Povh, Klaus Rith, Christoph Scholz, Frank Zetsche, M.
Lavelle (2004). "Part I: Analysis: The building blocks of matter".
Particles and Nuclei: An Introduction to the Physical Concepts (4rth
ed.). Springer.
B. Carithers, P Grannis (1995). "Discovery of the Top Quark". Beam
Line (SLAC) 25 (3): 4–16.
Lee Smolin (2007). The Trouble with Physics: The Rise of String
Theory, the Fall of a Science, and What Comes Next. Mariner Books.
p. 67.
The W-boson mass is 80.43 GeV; see Figure 1C. Caso, MW
Grünewald, & A Gurtu (March 2008). "The mass and width of the W
boson". Particle Data Group.
I.J.R. Aitchison, A.J.G. Hey (2004). Gauge Theories in Particle
Physics. CRC Press. p. 48.
S. R. Logan (1998). Physical Chemistry for the Biomedical Sciences.
CRC Press. pp. 110-111.
Peter J. Collings (2002). "Chapter 1: States of Matter". Liquid
Crystals: Nature's Delicate Phase of Matter. Princeton University
Press.
D. H. Trevena (1975). "Chapter 1.2 Changes of phase". The Liquid
Phase. Taylor & Francis.
Toshiaki
Makabe,
Z.
Petrović
(2006).
Plasma
Electronics:
Applications in Microelectronic Device Fabrication. CRC Press. p. 1.
C. K. Birdsall, A. Bruce Langdon (2005). Plasma Physics via
Computer Simulation. CRC Press. p. xvii.
J. A. Bittencourt. Fundamentals of Plasma Physics. Springer. p. 2.
Gordon Fraser (2006). The New Physics for the Twenty-first
Century. Cambridge University Press. p. 238.
Jean Letessier, Johann Rafelski (2002). "A New Phase of Matter?".
Hadrons and Quark-gluon Plasma. Cambridge University Press.
Jean-Pierre Luminet, Alison Bullough, Andrew King (1992). Black
Holes. Cambridge University Press. p. 75.
Jeremiah P. Ostriker and Paul Steinhardt New Light on Dark Matter
K Pretzl (2004). "Dark Matter, Massive Neutrinos and Susy
Particles". Structure and Dynamics of Elementary Matter (Walter
Greiner ed.). p. 289.
Ken Freeman, Geoff McNamara (2006). "What can the matter be?".
In Search of Dark Matter. Birkhäuser. p. 105.
Mark H. Jones, Robert J. Lambourne, David John Adams (2004). An
Introduction to Galaxies and Cosmology. Cambridge University
Press. p. 21; Figure 1.13.