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Absolute zero
The temperature scale used in science is the
Kelvin scale. 0 Kelvin is the theoretical
zero point where substances possess no thermal energy. 0 K is equal to -273.25 oC
or -459.67 oF.
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Accuracy
The closeness of a measurement to the true value.
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Acid Rain
SO3 and SO2 gases are produced during
combustion of sulfur-containing fossil fuels and smelting operations. When these oxides,
react with moisture (i.e. rain), sulfuric and sulfurous acids are produced. The result is an
increased acidity of the rain water known as "acid rain". Sulfuric acid in the rain water reacts with
structural materials such as
limestone and
marble to form calcium sulfate, which is then washed away in the rain.
Acid rain also breaks down of structures composed of metals such as steel. Sulfuric acid
reacts with many organic compounds, including those in plants. For humans, their lungs are very
susceptible to irritation.
Rain in unpolluted air is slightly acidic because of the presence of CO2. But rain in
some areas has been found to have a
pH of about 2, due mainly to the presence of sulfuric acid.
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Acids
A substance that produces hydrogen ions in water.
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Acidic solution
An aqueous solution in which
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Actinide series
A group of 15 radioactive elements including
actinium atomic number=89 through
lawrencium atomic number=103. In general,
artificial methods using high-energy bombardment are used to generate them.
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Activity series of metals
The arrangement of metals in order
of decreasing activity. Thus, each element in the series displaces
any element below it from its salt or acid.
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Alkali metals
All the Group IA elements (except hydrogen) in the
periodic table. They are:
They are strongly corrosive in the presence of moisture and react explosively
with water to produce a caustic metal hydroxide.
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Alkaline earth metals
All the Group IIA elements in the periodic
table.They are:
This group of metals is moderately reactive and is harder and less volatile than
the alkali metals. The elements all burn in air to give the
oxide.
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Allotrope
A different crystalline or molecular form of the same
element. Usually one allotrope is more stable than another at a particular
pressure and temperature.
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Alpha-particle
A He2+ ion emitted at a high velocity by a radioactive
substance. Alpha particles are used to cause nuclear disintegration reactions.
In radiation chemistry, alpha radiation is a form of radiation consisting of helium nuclei.
An atom of radium gives off one alpha particle
in decaying to radon. Alpha particles are used to bombard other
nuclei in creating artificial radioactivity and are the least damaging to human
tissue of all radioacitve emanations.
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Alum
Alum is a type of double salt obtained by crystallizing
mixtures in correct proportions. Examples are:
- Potash alum or alum - aluminum potassium sulfate
- ammonium alum - aluminum ammonium sulfate
- chrome - chromium(III) potassium sulfate.
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Amalgam
A liquid or solid alloy or mixture of mercury with another component, which is
usually a metal. The component metal must be soluble in
mercury. Examples are
lithium,
sodium,
potassium, and
cesium.
A well-known use of amalgams is for the repair of tooth decay; in this case, the amalgam contains
silver and
tin, forming a paste which sets quickly to a hard mass. Industrial
applications of amalgams containing other componetns are in silvering mirrors, in special
techniques in metallurgical analysis, and as catalysts.
Silver and
gold are recovered from ores by the amalgam process. The metal is
recovered by distilling off the
mercury.
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Angstrom
An angstrom is a unit of length.
| 1 angstrom (Å) = 10-10 meter |
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Anhydrous salt
A salt that has no water of hydration.
For example, CuSO4 is the anhydrous salt of CuSO4· 5H2O (copper (II) sulfate pentahydrate).
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Anion
A negatively charged
ion.
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Anode
In any electrochemical cells, the anode is the terminal at which electrons
flow out of the system. It is the terminal at which
oxidation takes place.
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Anodizing
An electrolytic method of applying a strongly
adherent film or coating of oxygen on the surface of a metal, especially
aluminum.
This is accomplished by passing an electric current through a bath containing sulfuric or chromic
acid as electrolyte. The negatively charged oxygen ions formed are
deposited on the positively charged aluminum
anode, building up a film of controllable thickness
which increases the corrosion resistance of the metal.
Anodizing is a thus a type of electrodeposition. Such films can absorb particles of added colourant, so that
the metal is in effect dyed by this method.
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Antiknock agent
About 1923, a toxic liquid, tetraethyllead
(Pb(C2H5)4), was introduced into internal-combustion engine fuel
as a gasoline antiknock additive. Its use was to
increase the octane number of the fuel and thus prevent pre-ignition knocking.
Up until the mid-1970s, the principal antiknock agent was tetraethyllead.
The use of this antiknock agent proved to be an environmental hazard. Not only did tetraethyllead
posion the catalytic converters, but the poisonous fumes which evolved polluted the air in urban areas.
Today, oxygenated hydrocarbons are used as antiknock agents. One of the most cost-effective
is methyl t-butyl ether (MTBE).
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Aqueous solution
A solution obtained by dissolving a
compound in a solvent, specifically water. Any other solvent used
does not result in an aqueous solution.
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Atom
An electrically neutral particle that is made up of the fundamental
particles of matter.
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Atomic mass
Atomic mass of an element is the mass of the
naturally occurring mixture of isotopes of the element. It has the units of:
The formula to calculate atomic mass from isotopic data is:
| atomic mass = | (the fraction of isotope 1)(mass of isotope 1) + |
| (the fraction of isotope 2)(mass of isotope 2) + |
| (the fraction of isotope 3)(mass of isotope 3) + ... |
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Atomic Mass Unit (amu)
An atomic mass unit
is used to express the masses of individual atoms. It is defined
as 1/12 of the mass of a carbon-12 (12C) atom.
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Aqua Regia
An extremely strong
oxidizing solvent used chiefly in metallurgical
analysis. It composed of:
- one part concentrated nitric acid, HNO3, and
- three parts of hydrochloric acid, HCl.
It is capable of dissolving metals such as
palladium ,
platinum , and
gold . The term literally means "ruling water".
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Atomic number
Atomic number is the number of protons in the nucleus
of the atom. For an electrically neutral atom, this is also the number of electrons
outside the nucleus.
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Atomic orbitals
An atomic orbital describes the electron
charge density or the probability of finding an electron in an atom.
The several kinds of orbitals (s, p, d, f, ...)differ in the
shapes of the electron clouds they describe.
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Avogadro's number
The number of particles in exactly 12 grams
of 12C is 6.022137 x 1023, or 1
mole.
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Bases
Any substance that releases hydroxide (OH-) ions when dissolved in water.
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Beta-particle
An electron emitted by a radioactive substance as it decays.
They have moderate energy and can be damaging to human tissue. Effective shielding
can be obtained with thin metal sheets. Collectively, such particles are often called
beta rays or beta radiation.
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Niels Bohr
In 1913, a Danish physicist (1885-1962), Niels Bohr, proposed
that, based on the model of the hydrogen atom, electons in an atom have
their energies restricted to certain values, or specific energy levels .
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Boiler scale
A deposited layer or incrustation of calcium carbonate
or calcium sulfate on the lining of boilers or in water pipes, resulting from prolonged contact
with hard water. This impairs the efficiency of the boiler and clogs feed lines and ultimately
may block them completely.
The best prevention is to test the water for hardness and to demineralize or "soften" by
ion exchange methods.
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Boiling point
The temperature at which a substance undergoes
a phase transition from a liquid to a gas. Sometimes it is called the normal boiling point. It
is the temperature at which this phase transition occurs at 1 atmosphere.
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Brass
An alloy of
zinc and
copper.
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Bronze
An alloy of
copper, with
tin, and
antimony,
phosphorus or other components. The alloy usually contains 0.5-10% tin.
This alloy is generally harder, stronger in compression, and more corrosion-resistant than
brass.
Some copper-rich alloys containing no tin are also called bronzes. Examples are:
- aluminum bronzes, with
up to 10% aluminum. They are strong, resistant to corrosion and wear and can be worked cold or hot.
- silicon bronzes, with up to 1-5% silicon. They are high resistant to corrosion.
- beryllium bronzes, with about 2% beryllium. They are very hard and strong.
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Bronze Age
A period of human culture between the
Stone Age and the
Iron Age, marked by the use of bronze implements and
weapons.
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Buckminsterfullerene
In the late 1980s, researchers discovered this
new allotrope of carbon. The molecule
is known as buckminsterfullerene, named after the scientist/philosopher
R. Buckminster Fuller.
The molecule is spherical, shaped like a soccer-ball, and has
a formula of C60. Informally it is called a "bucky ball".
The original evidence came from samples of soot. Recently, findings reveal the molecule
even in geological samples formed by the meteor impact that occurred around the
time when the dinosaurs became extinct.
Did you know? ...
The Science World "golf ball" in Vancouver British Columbia is actually a
geodesic dome, the design of which was created by American inventor R. Buckminster Fuller (1895-1983).
Fuller patented 28 inventions in his lifetime; perhaps the
most famous is the geodesic dome which was patented on June 29, 1954. One of the most famous
geodesic domes in the world was the American pavilion at Expo '67 in Montreal.
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Calomel Electrode
A half cell having a
mercury electode coated with mercury (I) chloride called
calomel. The electrode is in an electrolyte consisting
of potassium chloride and saturated mercury (I) chloride solution. Its standard electrode
potential against the hydrogen electrode is accurately known (to be - 0.2415 V at 25 oC)
and this voltage is relatively stable.
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Calorie
The calorie is the quantity of heat required to change
the temperature of one gram of water by one degree
Celsius.
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Catalyst
An element or compound that accelerates the rate of a chemical
reaction but is neither changed nor consumed by it.
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Cathode
In any electrochemical cells, the cathode is the terminal at which electrons
enter the system. It is the terminal at which
reduction takes place.
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Cation
An ion with a positive
charge.
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Celsius
A temperature scale based on a value of 0oC for the melting
point of ice and 100oC as the boiling point of water.
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Cesium atomic clock
An atomic clock makes use of an atomic resonance to control the
periodic phenomenon. The atomic clock is a very good clock because these resonances are determined
by the atom's properties rather than by man-made counting mechanisms. The unit of time, the
second, is defined in terms of this atomic resonance of cesium, and the national
standards of time and frequency for the United States and other countries are cesium clocks. Independent
cesium clocks can maintain synchronism with one another to better than 10-6 of a second
after one year's operation. This is more than 100,000 times more predictable than the earth's
rotation on its axis.
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Charge
A fundamental property of electrons (having -1 charge)
and protons (having +1 charge).
"+1", and "-1" are a relative scale. The actual charge is measured in
coulombs.
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Chemical Change
A chemical change is a chemical reaction
in which a sample of matter is transformed into completely different
substances.
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Chemical Property
Chemical properties describe types of
changes a substance can undergo to change into other substances.
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Chloralkali Process
The chloralkali process for the production of
chlorine from sea water uses mercury as the
cathode and as the solvent for the
sodium metal that forms. When the sodium
amalgam is removed and treated with water,high-purity NaOH is formed.
This method is phased out in some countries as some of the recycled
mercury is lost in the industrial waste water.
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Chlorofluorocarbons, CFCs
In the lower atmosphere, CFCs are chemically inert chlorine- and fluorine-
containing compounds that are used as air-conditioner refrigerants and aerosal
propellants. When CFCs reach the stratosphere, they absorb ultraviolet photons and break into
species which are very reactive. One such species is atomic chlorine. The Cl atoms react
with stratospheric ozone and breaks down the ozone layer.
Atmospheric scientists have documented more than 80% ozone depletion over the South Pole during certain
times of the year and there is evidence of ozone thinning over the North Pole as well. More than 1 million
tons of CFCs are released from air conditioners and spray cans each year. International agreements plan
to phase out CFC production before the end of the century. This plan brings up questions whether
there are other alternatives for refrigerants, or if we can do with less air conditioning?
If CFC production were to stop now, there are amounts which are already released that have not
yet reach the stratosphere. So, the ozone will continue to deplete for the next 100 years.
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Compound
A substance made up of two or more elements in a definite ratio.
It can be broken down into its constituent elements by chemical reactions.
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Contact Process
an industrial process for the manufacture of sulfuric acid.
Concentrated sulfuric acid, (approx. 18 moles/L), is produced in ton quantities in the following way:
- Step 1: Sulfur is burnt in air to produce
sulfur dioxide, SO2. This reaction releases a large amount
of heat which is used to generate steam and electricity.
- Step 2:
The sulfur dioxide is
oxidized to sulfur trioxide, SO2,on a
vanadium pentoxide
catalyst.
- Step 3:
The sulfur trioxide is dissolved in concentrated sulfuric aid to produce oleum (fuming
sulfuric acid, H2S2O7.
- Step 4:
The oleum is reduced in strength by adding water to produce twice as much sulfuric
acid as used in the previous step.
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Copper sweetening
Copper sweetening is a process that changes
mercaptans molecules into disulfides
compounds, which are less odorous. The process involves using a mixture of
Cu+ and Cu+2 ions as catalysts. The sweetening
process does not lower the sulfur content.
Disulfides are very viscous and are usually left in the heavy fuel oil fraction.
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Core electrons
Electrons in the inner shells of the atom are called
the core electrons. For example, silicon has 14 electrons. It has
10 core electrons and 4
valence electrons.
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Coulombs
The
SI unit of electrical charge. The actual charge of a proton is
1.6 x 10-19 coulombs. The actual charge of an electron is - 1.6 x 10-19 coulombs.
Since atomic particles have charges which are integral multiples of
1.6 x 10-19 coulombs, it is convenient to use a relative scale based on
the actual charge of 1.6 x 10-19 coulombs.
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Covalent bond
This type of bonding is usually found between
non-metallic elements. In the formation of
the covalent bond, electrons are shared between
the atoms. As a result, covalent compounds have relatively lower
melting points and do not conduct electricity as a solid, liquid or in
aqueous solutions.
The smallest unit of a compound formed by covalent bonds is a
molecule.
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Cracking process
Cracking is the process by which heavy high-boiling oils
are converted to low-boiling gasoline.
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Critical temperature
The temperature below which a gas can be liquefied by
applying pressure and above which no amount of pressure is sufficient to bring about
liquefaction.
Liquefaction is more difficult for gases such as oxygen and nitrogen because they have
very low critical temperatures.
Here is a summary of the critical temperatures of some gases. Critical temperature should not
be confused with
boiling points of the substance.
| Substance | Critical Temperature (oC) | Boiling Point (oC) |
|---|
| Xenon | 16.6 | -107.1 |
|---|
| Krypton | -63.8 | -152.30 |
|---|
| Oxygen | -118 | -182.962 |
|---|
| Argon | -122.3 | -185.7 |
|---|
| Nitrogen | -150 | -195.8 |
|---|
| Neon | -229 | -195.8 |
|---|
| Hydrogen | -239.9 | -252.87 |
|---|
| Helium | -267.9 | -268.934 |
|---|
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Cyclotron
A circular enclosed chamber in which the energy of charged
particles can be increased by application of an alternating electric field. A magnetic field
is used to keep the particles in a spiral path within the enclosed chamber.
The cyclotron was developed in the 1930's to provide a means of bombarding atomic nuclei and
accelerated deuterons. It has also been used to create synthetic elements belonging to the
actinide series. Vancouver, British Columbia is the home of
the largest cyclotron in the world. It is Canada's national meson research facility,
TRIUMF .
