Five Colors from One Solution

Five 250-mL beakers, four 50-mL beakers, five dropping pipettes, safety glasses, protective gloves. 

1 % methanolic phenolphthalein solution, Na2C03, FeCb 6 H2O, NH4SCN, K4[Fe(CN)6] 3 H2O, distilled water. 

1 mL of the phenolphthalein solution is added to 100 mL of water in the first beaker. The colorless solution is now poured into the second beaker, which contains 5 drops of a 5 % soda solution it turns to a reddish violet. This liquid is now poured into the third beaker, which contains 5 drops of a 50 % FeCb solution, and the color changes to a yellowish ochre. The fourth beaker contains 20 drops of a 30% NH+SCN solution, which causes a further color 

The indicator phenolphthalein, which is colorless in neutral solution, turns reddish-violet in the presence of the basic soda solution. In the third beaker the H30 ions set free in the hydrolysis of the iron(IIl) salt bind the OH ions from the soda solution, leading to decolorisation of the phenolphthalein at the same time the solution turns yellow because of the presence of the hydrolysed iron(III) species (eqns. la, b)  

In the fourth beaker iron(III) salts form deep red complexes such as [Fe(SCN)(H20)5] with the SCN ions. The extreme stability of Prussian blue dominates in the fifth beaker, so that the deep blue color brings the series to a close. Deviations from the given concentrations can lead to slight differences in the effects due to the formation of precipitates or mixed colors. 

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