Page 32 - Chemistry - XI

Chemical Equilibrium (
4 Chemical Equilibrium ( Ionic Ionic
Equilibrium in Solutions
Equilibrium in Solutions ))

EXPERIMENT - 13

Objective
Study of the shift in equilibrium between ferric ions and thiocyanate ions by increasing/decreasing the
concentration of either of the ions.

a b c d e f g
Look Vertically Downwards

Fig. 13.1: Placing of Test Tubes

Principle/Theory
In a reversible reaction, chemical equilibrium is a state at which two opposing processes involving a

chemical change balance each other under specifi c conditions of temperature, pressure and concentration,
i.e. at the equilibrium point, the rate of the forward reaction and the rate of the backward reaction becomes
equal, e.g. in a reaction between ferric ion (Fe ) and thiocyanate (SCN ) ion
3+
–
aq
3 2
()
(
aq
Fe () SCNaq [ FeSCN)] ()
( Blood redcolour)
[Fe(SCN)] 2+
At equilibrium, the equilibrium constant K may be written as K =
[Fe ][SCN ]
–
3+
If concentration of Fe and SCN increases, equilibrium will shift towards the right hand side, i.e. in
3+
–
forward direction. If NH Cl is added at the equilibrium point, equilibrium will shift towards the left hand
4
side, i.e. towards backward direction.
Materials Required
Test tubes, boiling tubes, beaker (250 mL), dropper, test tube stand, glass rod, FeCl solution, and ammonium Test tubes, boiling tubes, beaker (250 mL), dropper, test tube stand, glass rod, FeCl 3
thiocyanate solutionthiocyanate solution

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