Conductivity of solution

5 min readNov 14, 2022

Why to learn this topic? What are the applications of Conductance of solution in our life?

Ohhhooo, too many questions?

Let’s see, it’s applications-

Now a days big problem-Water quality .

As water is a universal solvent , so it contains dissolved substances. Water treatment is important to us because the availability of fresh water is 0.3 % of fresh water is found in the surface water of lakes, rivers etc. limited source in the earth and the demand and utility is high.

It is important for health – The harmful chemicals, metal and other contaminants present in water are dangerous for the health of humans and other organisms living on this planet.

so in water treatment this technique is used , to check the purity of water.

From this technique you will come to know how much dissolved substances, chemicals, and minerals are present in the water.

Higher amounts of these impurities will lead to a higher conductivity

Before starting this topic , you should know,

What is Conductance of solution?

The ability of any ion to transport charge depends on the mobility of the ions.

conductance is affected by factors like

i)the charge on ion,

ii)size of ion

iii)mass of ion

iv)extent of solvation

v)Concentration of ions

vi)Nature of electrolyte

Need to know some terms used in this topics

Conductance- ( c) It is the reciprocal of resistance and it is written as,

C = 1/R,

put unit of resistance in this formula ,you will get unit of Conductance.

Therefore the unit of conductance is reciprocal of ohm or mho (ohm-1)

Yes ,understood

Specific resistance (ρ):- It is defined as a resistance offered by a cube of unit length of it to the passage of electricity through it.

Mathematically R α l/a or R=ρ.l/a, As l=1cm and a=1cm2 then, R= ρ

Therefore, ρ = R. a/l

ρ =ohm.cm2/cm = ohm.cm

Hence, unit of ρ is ohm.cm

Types of Conductance-

i) Specific conductance

ii)Equivalent conductance

iii)Molar conductance

To determine this we have to use conductivity cell , which contains two parallel Platinum electrodes which have cross sectional area 1 cm2 and which are kept 1 cm apart.

Specific conductance (k):- It is defined as the conductance of solution between two parallel electrodes which have cross sectional area 1 cm2 and which are kept 1 cm apart.

It is the reciprocal of Specific Resistance. It just similar definition of conductance.

K = 1/ ρ

The unit of specific conductance (K) will be mho.cm-1

Cell constant: — The ratio of (l/a) is called cell constant.

K = C. (l/a)

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i. e. Specific conductance = Measured conductance(C) x Cell constant (l/a)

therefore,

cell constant =Specific conductance/Measured conductance

The unit of cell constant is cm-1

Equivalent conductance (λv):- It is defined as the conductance of a solution containing one gram equivalent of an electrolyte at any particular concentration, when placed between two electrodes 1 cm apart.

λv = K x 1000/C

= (ohm-1.Cm-1) x Cm3.gm-equiv-1

λv = ohm-1.cm2.gm-equiv-1

λv = mho.cm2.gm-equiv-1

Molar conductance (µ):- It is the conductivity of the solution containing

1 mole of the electrolyte, when placed between two large electrodes 1cm apart.

µ = K x V = K x 1000/Molarity

Therefore unit

µ = ohm-1.cm-1.cm3 mol-1

µ = mho.cm2.gmol-1

Effect of Dilution on Conductance-

On dilution , volume of solution increases.

Thus, the number of ions per ml decreases and hence Specific conductance decreases.

Molar conductance and equivalent conductance is defined for 1 mole or 1 gm equivalent of ions. Thus on dilution, ions get more apart and mobility of ions increases which leads to increase in Molar conductance and equivalent conductance of the solution.

Means , On dilution Specific conductance decreases and Molar conductance and equivalent conductance increases.

Effect of temperature on Conductance-

All three types of conductance(Specific conductance, Molar conductance and equivalent conductance) increase with increase in temperature. Because of increase in temperature dissociation increases.