Interpretation of Reaction by Le Chatelier's Principle

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Experiment 11

Date: 28-3-2011

Title: Interpretation of reaction by the Le Chatelier’s principle

Objective: To determine the factors that affecting the equilibrium position

Introduction:
Le Chatelier’s principle states that if a system in equilibrium is subjected to a change, the equilibrium position of the system will shift in a direction to minimize the effect of the change.

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) à 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 the affecting the equilibrium position.

Procedure:
Two drops of iron(III) chloride solution and potassium thiocyanate solution were mixed together in a test-tube and then 5cm³ of deionized water was added to form a pale orange-brown solution. After that, the solution was divided into four equal partsin four aliquots in four test-tubes. A drop of iron(III) chloride solution and potassium thiocyanate solution were added to the first test-tube and the second test-tube respectively. A spatula-measure of solid ammonium chloride was then added to the third test-tube and was stirred well. The colour of the solution was compared with the untouched tube.

Result:



Data Analysis:
Fe3+(aq) + NCS-(aq) à FeNCS2+(aq)
Yellow colourless blood red
The untouched tube was a pale orange-brown colur, which was representative of an equilibrium between both sides.

The colour of the solution in the test-tube which a drop of iron(III) chloride solution was added was darker than the untouched tube. When the concentration of Fe3+ ion s was increased, according to Le Chatelier’s principle, the equilibrium...
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