Chemical Equilibrium

Materials Required

The Procedure

Real Lab Procedure

  • Take 10 ml of 0.1 M FeCl3 solution in a measuring cylinder and pour it into a clean beaker.
  • To this, add 10 ml of 0.1 M KSCN using a measuring cylinder.
  • A deep red colour is obtained due to the formation of the complex, [Fe(SCN)(H2O)5]2+ (aq).
  • Dilute the deep red solution by adding 50 ml of distilled water.
  • Take four test tubes and label them as A, B, C and D.
  • Add 10 ml of the deep red solution to each test tube using a measuring cylinder.
  • Place the test tubes in the test tube stand.
  • Add 5 ml of distilled water into test tube A; 5 ml of 0.1 M FeCl3 solution to test tube B; 5 ml of 0.1 M KSCN solution to test tube C and 5 ml of 0.1 M KCl solution into the test tube D.
  • Shake all the test tubes well.
  • Now compare the intensity of the colours in the test tubes, B, C and D with the red colour in test tube A taken as the reference test tube.

Simulator Procedure (as performed through the Online Labs)

  • You can select the test solution from the 'Select the test solution' drop down list.
  • You can select the control tube from the 'Select the control tube' drop down list.
  • Drag the dropper containing the reagent towards any one of the test tube to pour the reagent into it.
  • You can see the inference of different tests by clicking on the inference icon.
  • The chemical reaction and equilibrium constant can be seen on the side menu.
  • You can redo the experiment by clicking on the 'Reset' button.

Observations

Observations are given in the table.

 Test tube

 Substances added at equilibrium

 Change in colour

Effect on the concentration of [Fe(SCN)(H2O)5]2+

 Shift of equilibrium

A

5 ml of water

Reference colour

-

-

B

5 ml of 0.1 M FeCl3 solution

Colour deepens

Increases

Towards right

C

5 ml of 0.1 M KSCN solution

Colour deepens

Increases

Towards right

D

5 ml of 0.1 M KCl solution

Colour becomes lighter

Increases

Towards left

Conclusions

  • The intensity of red colour corresponds to the concentration of complex [Fe(SCN)(H2O)5]2+ and if the concentration of this ion increases, the colour intensity will also increase.
  • Increase in concentration of either of the reactants (Fe3+ ions or SCN- ions) shifts the equilibrium in the forward direction (towards right).
  • Decrease in concentration of any of the reactants shifts the equilibrium in the backward direction (towards left).

Precautions

  • Use test tubes of almost identical diameter.
  • Dilute solutions of thiocyanate should be used.
  • The intensity of colour of a solution should be compared by keeping it and the reference side by side and then observing them from the top of the test tube.  

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