The reciprocal of resistance (R ) is known as conductane (c )
`l/R=k xx(l)/(l//A)`
`c=k xx(l)/(l//A)`
`to` The conductance or the current conducting capacity of an electrolytic solution can be expressed as
i) Specific conductance (k), ii) Molar conductivity `(^^_(m))`
i) Specific conductance : The conductance of the solution enclosed between two parallel electrodes of unit area of cross section separated by unit distance is called specific conductance (k).
ii) Molar conductivity `(^^_(m)):` The conductivity of a volume of solution containing one gram molecular weiht of the electrolyte placed between two parallel electrodes separated by a distance of unit length of 1 meter is called molar conductivity `(^^_(m))`
Relation between conductivity and molar conductivity :
`^^_(m) =k/c,therefore c=` constant
Measurement of electrical conductance :
`to` The resistance of a metallic wire can be measured with a wheatstone bridge.
`to` In measuring the resistance of an electrolytic solution tow problems are identified.
i) On passing direct current (DC) through the solution charges the composition of the solution due to electrolysis.
ii) A solution cannot be connected to the mmeasuring bridge like a metallic wire.
` to` ii) A solution cannot be connected to the measuring bridge like a metallic wire.
`to` First proble solved by using AC instead of DC.
`to` Second problem solved by using specilly designed vessel called conductivity cell.
By using above cells,
Resistance `R=(l)/(k xxA)`
l = distance between electrodes : A = Area of cross section, k = conductivity `l/A` = cell constant `=G^(**)`
`therefore G^(**)=l/A =Rxxk`
The cell constant `(G^(**))` is determinded by measuring the resistance of the cell containing a solution whose conductivity is already known
`to` Cell constant once determined, used for measuring the resistance (or) conductivity.
`to` The set up for the measurement of the resistance is shown in following figure.
Unknown resistance `R_(2) =(R_(1)R_(4))/(R_(3))`
Conductivity of solution `(k) =("Cell constant " (G^(**)))/(R)`
Molar conductivity `^^_((m))=k/c =(k (S cm ^(-1)))/(1000(Lm^(-3))xx"Molarity (moles//lit)")`
