The Celsius scale of temperature, is the scale named after the
Swedish astronomer Andes Celsius, where the temperature range between
the melting point at standard pressure of ice and the boiling point
of water has been divided into 100 degrees. The melting point of
ice is taken as zero degrees and written as 0 degC. The boiling
point of water is therefore taken as 100 degrees and written as
Portland cement, so called because after setting it resembles
Portland stone, is made by heating a mixture of lime stone and
clay, which is then ground to a fine powder. Limestone containing
more than 5 per cent of clay on burning forms a lime, which
gives a hydraulic mortar (i.e. cement) which hardens
Ceramics are inorganic materials, such as pottery, enamels
A chain is a linear combination of the same type of atom
in a molecule. In straight chain molecules, the atoms are arranged
in a line, with each atom in the chain linked to one preceding atom
and one succeeding atom of the same type. In branched chain molecules,
groups are attached to a central straight chain, and the group is
called a side chain. A closed chain molecule is a chain where the
atoms are linked in a ring structure; otherwise, the molecule
has an open chain molecule.
A chain reaction is a multi-step sequence of chemical reactions in
which a product of the first step is used as a reagent in the
second step, and a product of the second step is used as a reagent
in the third step, etc.. In general, chain reactions are
free radical reactions.
For example, the reaction of bromine with methane in the presence
of light is an example of a chain reaction. The mechanism by which
the reaction proceeds is as follows.
- The first step is called the Initiation of the reaction.
- The absorption of light breaks the covalent bond holding
together the bromine atoms together in the bromine molecule
and produces free bromine atoms (i.e. bromine free radicals,
Br2 ==> Br* + Br* (1)
- The Propagation of the Reaction
- involves repeating steps (2) and (3), where the bromine free
radical then removes a hydrogen atom from
a molecule of methane to produce a methyl free radical and
a molecule of hydrogen bromide.
Br* + CH4 ==> CH3* + HBr (2)
The methyl radical then attacks a bromine molecule to
produce a molecule of methyl bromide and to regenerate a
bromine free radical, which proceeds to react as in step (2).
CH3* + Br2 ==> CH3Br + Br* (3)
- The Termination of the Reaction
- is the final step and results when these steps can are stopped by the chance
recombination of free radicals as in (4).
Br* + CH3* ==> CH3Br (4) or
Br* + Br* ==> Br2
CH3* + CH3* ==> C2H6
Chaos is the widely diverse range of behaviour which non-linear
dynamic systems exhibit under different initial conditions.
Charle's Law is the empirical relationship, which states that
which states that for an ideal gas at constant pressure, its
volume is proportional to its absolute temperature.
This relationship applies to ideal gases only. Real gases
deviate considerable form this ideal relationship.
It is called after Jacques Alexandre Cesar
Chemical bonds are the forces that hold atoms together in
a molecule are called chemical bonds.
A Chemical Bond is the attractive force between two atoms
in a molecule. These bonds keep the molecule intact as an entity.
In 1916AD, the two kinds of chemical bonds which were known
were described as the Ionic Bond by
Walter Kossel (Germany) and the Covalent
Bond by G.N.Lewis (University of California).
These ionic and covalent bonds arise from the tendency of atoms
to attain a stable configuration of electrons for each atom in a
molecule, by either the transfer or the sharing of electrons between
atoms. Because a molecule consists of at least two atoms with
positively charges nuclei and negatively electronic clouds about these
atoms, there are electrostatic interactions between the various particles of
the atoms in the molecule.
The chemical oxygen demand is the quantity of oxygen
required to destructively oxidise the organic matter in a sample.
It is expressed in mg COD per Liter.
A chemical change is a process which results in the production of one
or more new materials. The system within which the process takes
place is called a chemical system. A chemical change is also known
as a chemical reaction, where one substance is converted into one or
more different substances. When sodium and chlorine react to produce
sodium chloride, a chemical reaction has taken place.
Chemical equilibrium is a state of dynamic equilibrium is set up
when the rate of the forward reaction is equal to the rate of
the back reaction.
A chemical formula shows the number and types of atoms that are
present in a molecule.
A chemical symbol is assigned to every element, which represents
one atom (occasionally, one mole) of that element. The symbols of
the elements which were known in earlier days were derived from
Latin names. Many of the initial letters of the elements; others have a
second letter where there is more than one starting with the small letter. Example include
The simplest type of chloro-organic compounds are the
chloroalkanes, which find extensive use as solvents in industry.
Dichloromethane, CH2Cl2, (i.e. Methylene Chloride)
Carbon Tetrachloride, CCl4
Chromatography is a technique for analysing or separating mixtures of
gases, liquids, or dissolved substances. In general, all types of chromatography
involve two distinct phases, (a) a stationary phase (i.e. the adsorbent
material) and (b) moving phase (i.e. the eluting solvent). The separation
depends on competition for molecules of sample between the moving
phase and the stationary phase.
- Adsorption Chromatography
- is a technique for the separation and
analysis of mixtures of gases, liquids, or dissolved substances. In the case of
liquid adsorption chromatography, a vertical glass tube is packed with
an adsorbing material, (e.g. Alumina, Al2O3, or Silica Gel, SiO2), the sample
is poured onto the top of the column and then continuously transported down
through the column with a solvent, in a process called Elution.
Different components of the sample are adsorbed to different extents and
move down the column at different rates. The usual method is to collect
the liquid (i.e. the eluatent) in fractions, as it passes out from the column.
- Column Chromatography
- is the oldest chromatographic technique. The apparatus consists of a glass
tube (approximately about 20mm ( 250mm) which has a glass frit at the
bottom of the tube and a stopcock. A thin layer of coarse, clean sand
is placed over the frit, and the chosen adsorbent (usually alumina or silica) is
then placed in the tube as a slurry.
The sample under analysis (i.e. the mixture) is poured into the top of the column and
continuously washed through with an eluting solvent. Fractions are collected. As the mixture
is passed through the column, its components separate into zones of material (i.e. bands)
with a space between each zone. A band represents a fraction of homogeneous material
either a pure compound or a group of compounds behaving as a single compound on the
- Gas Liquid Chromatography, GLC,
- is the experimental technique used to separate volatile materials for analysis.
- High Performance Liquid Chromatography, HPLC,
- is the chromatographic technique for separating and analysing mixtures
of substances, using a packed column containing microsperes coated with the
stationary phase and where the mobile phase is pumped through the
column with a high pressure pump. The emergence of each component of
the sample under analysis from the column is monitored using one of a
number of different detectors.
- Paper Chromatography
- is a technique for analysing mixtures by chromatography, in which
the stationary phase is the layer of water on the absorbent paper. After
the mixture has been spotted at the bottom of the paper, solvent is allowed to
rise up the paper by capillary action to some arbitrary height. The paper
is then dried, and the individual components are identified by physical (e.g. ultraviolet light) or chemical (e.g. some chemical spray) methods.
- Thin Layer Chromatography, TLC,
- is the chromatographic technique for separating and analysing
mixtures of substances, using a thin layer of stationary phase attached
to a glass plate and using the passage of liquid up the plate by capillary
action as the mobile phase.
As well as the structural isomerism, which was illustrated in the
alkane series, a new type of isomerism is possible in the
alkene series. There is not free rotation about the carbon to
carbon double bond, and therefore there are two distinct isomers
possible, depending on the layout of the groups attached to the
carbons involved in the double bond.
The cis-isomer and the trans-isomers are distinct chemical compounds
and they have different physical properties and chemical properties.
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