5. Conductance of Electrolyte
5
We have seen that electrolyte solutions conduct electric currents through them
by movement of the ions to the elecrtodes. The power of electolytes to conduct
electric currents is termed conductivity or conductance. Like metalic
conductors,
electrolytes obey Ohm’s Law. According to this law, the current l flowing through
a metalic conductors is given by the relation,
l=E/R
where E is the potential difference at two ends (in volts); and R is the resistance
measured ohms Ω, we can write as,
R α 1/A
or, R = ρ × 1/A
where ρ ‘rho’ is a constant of proportionality and is called specific conductance.
It is defined as: the conductance of cc of solution of an electrolyte. The units of
specific conductance is 1/ Ω × 1/cm
6. Concept of E.M.F
6
The flow of electron through the circuit is determined by the ‘push’ of
electrons at the anode & ‘attraction’ of electrons at the cathode. These two
forces constitute the ‘electrical pressure’ that sends electrons through the
circuit. It is known as electromotive forces or cell potential. The emf of cell
potential is measured in units of volts (V) and is also referred to as cell
voltage.
The emf of a cell can be calculated from the half-cell potentials of the two
cells(anode & cathode) by using the following formula ,
Eo
cell = Eo
cathode - Eo
anode
= Eo
R - Eo
L
Eo
cell = Eo
Rduction - Eo
oxidation
7. Electrode Potential
7
When a metal (electrode) is immersed in a solution containing the ions of
that metal, a potential difference is set up between the metal and its ions
in the solution. This potential difference is referred to as "ELECTRODE
POTENTIAL".
If a copper plate is dipped in a solution of copper sulphate (CuSO4) a
potential difference is set up between copper and Cu+ -ions which is known
as electrode potential.
Electrode potential may be positive or negative depending upon the
nature of electrode.
8. Relation Between Electrical &
Chemical Energies
8
There are three basic components: positive electrode (cathode, or
"positive terminal"), negative electrode (anode or "negative
terminal"), and electrolyte.
When the positive and negative terminals are connected so that
electrons (electricity) can flow between them (usually by a wire),
chemical reactions occur at the electrodes. These reactions release
excess electrons at the anode which flow to the cathode.
The chemical reactions occur between the electrolyte and the cathode
and between the electrolyte and the anode. Different types of
batteries use different materials for the these three components.
9. Figure : Batteries transform
chemical energy into electrical
energy.
We can get electrical energies from chemical reactions. So, it
is the relation between two of these.
10. Interfacial Phenomena &
Complexation
When phases exist together , the boundary between
two of them is termed an interface.
The properties of the molecules forming the
interface are often sufficiently from those in the bulk
of each phase that they are referred to as forming an
interfacial phase.
Very often it is desirable or necessary in the
development of pharmaceutical dosage forms to
produce multi-phasic dispersions by mixing together
two or more ingredients that are not mutually
miscible and capable of forming homogeneous
solutions. Examples of such dispersions include :
Suspensions – solid in liquid
Emulsions – liquid in liquid
Foams – vapor in liquids
10
11. What does Complexation mean?
Complexation is the combination of individual atom groups, ions or
molecules to create one large ion or molecule. One atom or ion is the focal
point of the complex. This central atom contains empty electron orbitals
that enable bonding with other atoms as well as unshared electrons.
The last stage in complexation involves the sum of individual components'
charges. Therefore, there can be zero, negative and positive charges in a
complex within a solution.
To ensure that proper complexation takes place, certain factors should be
observed:
Ionic strength
Temperature
pH
Competing ions
When these factors are properly controlled, obtaining more accurate
complexation values is the major result
14. A very large molecule, such as a polymer or protein, consisting of many
smaller structural units linked together. Also called super-molecule.
A molecule of high relative molecular mass, the structure of which
essentially comprises the multiple repetition of units derived, actually
or conceptually, from molecules of low relative molecular mass.
And the macro/super/large molecule maintain a system , this system
is known as macromolecular system
