Chapter 1: Chemical Equilibrium Part 5 SABIS Grade 11 (Level M) Chemistry

1.2 Demonstration of the FeSCN²⁺ System

1. 25cm3 of 0.002 M KSCN and 25cm3 of water are placed into a small beaker. You also have a dropper bottle contains Fe(NO3)3. Write down the ions present in each solution.

2. Three to four drops of Fe(NO3)3 are now placed into the beaker and stirred. Write down your observations.

3. Look at a bottle of KNO3 and note its color.

4. What possible explanation is there for the color change in point 2 above?

5. The color is due to hydrated thiocyanoiron (III) ion:

Fe3+(aq) + SCN–(aq) ⇌ FeSCN2+(aq)

6. The colored solution is divided into 4 test tubes.

a) The first is used as reference.

b) Some crystals of KSCN are added to the second. Give a possible explanation for the intensification of color. How could this have happened without adding more Fe3+(aq)?

c) Three drops of 0.2M Fe(NO3)3 are added to the third tube. Give a possible explanation for the intensification of color. How could this have happened without adding more SCN–(aq)?

d) A few Na2HPO4 crystals are added to the fourth tube. This compound reacts with the Fe3+(aq) ions, effectively removing them from the solution (i.e. it decreases the [Fe3+(aq)]). Write down your observations. Give a possible explanation.

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Chapter 1: Chemical Equilibrium  Part 6 SABIS Grade 11 (Level M) Chemistry