Coagulation is the process in which colloidal particles come
together to form lager masses. Coagulation can be brought
about by adding ions to neutralize the charges stabilizing the
colloid. Ions with a high charge are particularly effective.
Another example of ionic coagulation is in the formation of
river deltas, which occurs when colloidal silt particles in
rivers are coagulated by ions in sea water. Heating is another
way of coagulating certain colloids.
Coal is a brown or black carbonaceous deposit derived from the
accumulation and alteration of ancient vegetation, which originated
largely in swamps or other moist environments. As the vegetation
decomposed it formed layers of peat, which were subsequently
buried. Under the increased pressure and the resulting
higher temperatures the peat was transformed into coal.
Coal gas is a gas produced by the destructive distillation of
coal, and contains approximately 50% hydrogen, 35% methane and
8% carbon monoxide.
The by products of the production of coal gas are coal tar
Coal tar is a material obtained from the destructive distillation
of coal in the production of coal gas. The crude tar contains a
large number of organic compounds (e.g. benzene, naphthalene,
methylbenzene, etc.), which can be separated by fractional
Coke is an impure form of carbon, which is obtained as a byproduct
from the destructive distillation of coal.
Colorimetric analysis is a quantitative analysis of solutions
by estimating the colour produced by the reaction of the sample
under analysis with a reagent and comparing it with the colours
produced by known standard solutions.
The halogen molecules are all coloured due to the absorption of
visible light. This absorption of light results in the
excitation of outer electrons to higher energy levels.
The energy required to bring about these electronic transitions
follows the same pattern as the ionisation potential values for
the elements. Thus, the energy required to bring about such a
transition in the smaller fluorine atom is much larger than the
energy required for the same transition for the larger iodine
atom. Fluorine absorbs the higher energy violet light and
transmits yellow light whilst the iodine absorbs the lower
energy yellow light and transmits violet light.
The combined gas law is the mathematical relationship between
the pressure, volume and temperature of a fixed quantity of
an ideal gas, which states that the product of the pressure, P, and
the volume, V, of one mole of gas is equal to the product of
the gas constant, R, and the absolute temperature, T.
P V = R T
The combined gas law is derived from Boyle's
Law and Charles's Law.
Common groups which are derived from hydrocarbons include :
A substance is said to undergo a physical change when it
changes from one state to another. The changes of water
when it is boiled or frozen are examples of physical
changes. When water is heated until it boils, bubbles
of gas rise through the hot liquid. We know this gas
as steam. If the steam that is produced when water is
boiled is cooled down to room temperature, a
liquid (i.e. water) is formed. If water is cooled much
below room temperature, a solid known as ice is formed.
Whenever a process takes place with the production of
one or more new materials, the process itself is
called a chemical change or a chemical reaction. This
process takes place within a chemical system. In a
chemical reaction, the initial materials called
reactants, and these are replaced as a result of the
chemical change by a new set of materials called
products. In order to distinguish between a physical
and chemical change, it is necessary to find out if a new substance
has been formed. If a new substance has been formed in
the change, a chemical change has taken place.
As matter may undergo changes which may be either physical
changes or chemical changes, the following table indicates
the differences between physical and chemical changes.
Characteristics of a physical change
- This may be a change from solid to liquid to gas,
or solid to gas no new kind of matter being formed.
- This change of state is reversible,
e.g. gas to liquid to solid.
- No change in weight.
Characteristics of a chemical change
- A new type of matter is formed.
- This change is not easily reversible.
- The weight of each reacting substance changes, although
the total weight remains unchanged.
There are a number of differences in the physical properties of
chemical compounds which depend on the type of bonds which are
present in the molecules of the compound. These differences are
summarised in the table below.
- Ionic Compounds
- Formed by transferring electrons
- High melting and boiling points
- Form lattices
- Dissolve in water
- Do not dissolve in organic solvents
- Conduct electricity when melted or dissolved in water
- Strong forces holding whole ionic structure together
- Covalent Compounds
- Formed by sharing electrons
- Low melting and boiling points
- No lattices, except diamond and graphite
- Do not dissolve in water
- Dissolve in organic solvents
- Do not conduct electricity (graphite is the only exception)
- Atoms in molecule held by strong forces, but
weak forces between the molecules.
- Properties related to those of the constituents.
- Composition is variable.
- Constituents can be mechanically separated.
- Properties need not be related to constituents.
- Composition is fixed and can be represented by a formula.
- Constituents cannot be mechanically separated.
A component is a distinct chemical species in a mixture. If there are
no chemical reactions between the components in a mixture, the number
of components is the number of distinct chemical species.
A compound is a substance composed of two or more elements that are
bound together by chemical bonds. A compound cannot be broken
down into its individual elements of which it is composed by
physical means. However, a compound can be broken down to the
elements of which it is composed by chemical means.
Calcium chloride Calcium, Chlorine
Calcium oxide Calcium, Oxygen
Sodium chloride Sodium, Chlorine
Hydrogen oxide Hydrogen, Oxygen
Iron oxide Iron, Oxygen
Just as every element has its own symbol, every compound has its
own formula. The formula identifies the elements present in the
compound and the number of atoms of each kind that are in a
molecule of the compound.
As all compounds are made from elements, so the elements are the
building blocks of compounds. When a compound is formed by
the combination of elements, this reaction is called a
Unlike the elements, compounds can be split up into simpler
substances (i.e. the elements of which they are composed). The
splitting up of compounds into simpler substances is called
Compound ions are groups of atoms which remain unchanged through
a series of chemical reactions, but which are incapable of independent
existence. They have an overall charge. Examples include the
carbonate ion, CO3(-.-), nitrate ion, NO3(-), ammonium ion, NH4(++), etc.
Concentration is the quantity of dissolved substance per unit
quantity of solvent in a solution. The mass concentration is the
mass of solute per unit volume of solvent. The molal concentration
is the amount of substance per unit mass of solvent.
Condensation is the change of a vapour or gas into a liquid. The
change of phase is accompanied by the evolution of heat.
Condensation reaction are those chemical reactions in which two
molecules combine to form a larger molecule with elimination of a
small molecule, typically water, during the course of the reaction.
A condenser, (i.e. a Liebig Condenser) consists of a straight glass
tube enclosed in a glass jacket through which water is passed.
The condenser speeds the cooling and condensing process, when vapour
passes through the condenser's center tube and is cooled by the
water flowing around the condenser's outer jacket.
A coductimetric titration is one in which the electrical conductivity
of the reaction mixture is continuously monitored as one reactant is
added. The equivalence point (i.e. the end-point of the titration)
is the point at which the conductivity undergoes a sudden change.
No text prepared for this topic yet
Two definitions are associated with the term, configuration.
- Configuration is the arrangement of atoms or groups of atoms in a molecule, or
- Configuration is the arrangement of electrons about the nucleus of an atom.
A conical flask is used for titration's to facilitate the return of
liquid splashed onto the walls of the flask to the body of the liquid
at the bottom of the flask.
Conjugated bonds describe the alternating pattern of double and
single bonds, or triple bonds and single bonds, in a molecule.
In such molecules, there is some delocalisation of electrons into
the pi orbitals of the carbon atoms linked by the single bond.
Consolute temperature is a temperature at which two partially
miscible liquids become fully miscible as the temperature
The contact process is used for manufacturing sulphuric acid and
fuming sulphuric acid from sulphur dioxide, which is made by
burning sulphur or by roasting sulphide ores and oxygen (in
the form of air) which combine to form sulphur trioxide in
the presence of a Catalyst.
The reaction is exothermic and the conditions are controlled to keep the
temperature at 450 degC.
The catalyst used is valadium (V) oxide (V2O5). The sulphur trioxide
is dissolved in sulphuric acid to form fuming sulphuric acid, this
S(s) + O2(g) ==> SO2(g)
2SO2(g) + O2(g) ==> 2SO3(g)
SO3(g) + H2SO4(l) ==> H2S2O7(l)
This Oleum is then diluted with water into concentrated sulphuric
H2S2O7(l) + H2O (l) ==> 2 H2SO4(l)
A continuous spectrum consisting of a band of coloured
light is produced when a narrow beam of sunlight is
allowed to pass through a prism. In a continuous
spectrum, each colour merges into the next, so that it
is difficult to say where one colour ends and the next
colour begins. Each colour corresponds to radiation of different
Convection is the process by which heat is transferred from one
part of a fluid to another by movement of the fluid itself. There
are two methods in which this can be carried out. One is by natural
convection, in which movement occurs as a result of gravity, the
hot part of the fluid expands, become less dense and is displaced
by the colder denser part of the fluid as this drops below it.
Forced convection is where hot fluid is transferred from one
region to another by a pump.
A coordination complex is a compound in which molecules or ions
form coordinate bonds to a central metal atom or Ion.
The complex may contain positive ions, negative ions or neutral molecules. The
formation of such coordination complexes is typical behaviour of Transition Metals.
Corrosion is the chemical changes which occurs in a material
over time due to its contact with air or moisture, and which
result in the loss of physical strength and the mechanical properties
of the material, rendering it unsuitable for its intended use.
For example, metals are oxidised in moist air to their oxides
which have low mechanical strength.
Corrosion cells are the arrangements of electrodes and solutions
which result in electrochemical changes to the contents of the cells.
The coulomb is the charge carried by a current of one ampere
flowing for a period of one second.
A coupling reaction is a chemical reaction in which two molecules
join together to form a single product.
A covalent bond is the principal type of bond between atoms whose
are of almost equal (i.e. it is formed by sharing electrons between any two constituent
atoms in a molecule such as the elements in the middle of the periodic table, who
do not lose or gain electrons easily). Thus, in the covalent
bond, the Electron Pair in the covalent
bond is shared equally between the atoms, so that stable outer shells are created
in each atom by this sharing.
For example, in the chlorine molecule each chlorine atom contributes
one electron from its outer shell to form a shared pair, thus
giving both a stable outer shell.
The atoms in carbon dioxide are also covalently bonded. Each oxygen
atom shares two pairs of electrons with the carbon atom. Thus,
there is a double covalent bond between the carbon atom and
each oxygen atom.
The chlorides of non-metals (e.g. phosphorus trichloride) are covalent
With the exception of carbon tetrachloride, these chlorides fume
in air and are readily hydrolysed to yield either an acid or an
For example, phosphorus trichloride fumes in air
PCl3 + 3 H2O ==> H3PO3 + 3 HCl
Cracking is the process of breaking down chemical compounds at
high temperature. The term is applied particularly to the
cracking of hydrocarbons in the kerosene fraction obtained
from petroleum refining to give smaller hydrocarbons. This
process involves the decomposition of petroleum fractions
into hydrocarbons of lower molecular weight, by heating them
under pressure in the presence of a suitable Catalyst.
Critical pressure is the pressure of a fluid at its critical state.
The critical state of a fluid is when the liquid and gas phase
both have the same density. In the critical state, the fluid
is at its critical temperature, critical pressure and critical volume.
The critical temperature is the temperature above which a gas
cannot be liquefied by an increase in pressure.
The critical volume is the volume occupied by a fixed mass of a fluid
in its critical state.
Crude oil is the material extracted from oil wells, and which
is subjected to a refining process to isolate various grades of fuels.
Crystal lattice are the regular pattern of atoms, ions or molecules
in a crystalline substance.
Crystallisation is the precipitation of crystals of a solid from a
supersaturated solution on cooled, when the solvent is unable to
hold all the solute in solution.
Crystals are solids with regular polyhedral shape. All crystals of
the same substance grow so that they have the same angles between
A cubic lattice is name for the unit cell of solid crystalline
structure of Sodium Chloride, NaCl.
Cyclo- is the prefix used in chemical nomenclature to designate
a cyclic compound.
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