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.