Title:Interpretation of reaction by the Le Chatelier’s principle
Objective:To determine the factors that affecting the equilibrium position
Iron(III) ions and thiocyanate ions (NCS-) react in solution to produce thiocyanatoiron(III) (FeNCS2+), a complex ion, according to the equation :
Fe3+(aq) + NCS-(aq) [pic] FeNCS2+(aq)
yellow colourless blood red
The colour produced by the complex ion indicates the position of equilibrium. In this experiment, iron(III) chloride solution, potassium thiocyanate solution and solid ammonium chloride were added to the mixture solution to find out the factors that affecting the equilibrium position.
Two drops of iron(III) chloride solution and two drops of potassium thiocyanate solution were mixed together in a test-tube and then about 10cm3 of deionized water was added to form a pale orange-brown solution. After that, the solution was divided into four equal parts in four test-tube. Two drops of iron(III) chloride solution were added to one test-tube and two drops of potassium thiocyanate solution were added to the second test-tube. Then the colour of the solutions in these two test-tube were compared with the untouched test-tube. Two spatula-measure of solid ammonium chloride were then added to a third test-tube and was stirred well. The colour of this solution was compared with the untouched tube.
1.The colour of the solution in the test-tube which two drops of iron(III) chloride solution were added was deeper than the untouched tube. When the concentration of Fe3+(aq) ions was increased, according to Le Chatelier’s principle, the equilibrium position shifted to right in order to decrease the concentration of Fe3+(aq) ions. Thus the deep red equilibrium mixture became deeped in colour.
2.The colour of the solution in the test-tube which two drops of potassium thiocyanate solution were added was more...