Equilibrium Lab application

Topics: Chemistry, Ion, Potassium Pages: 6 (1484 words) Published: March 23, 2014
Lab O6 – Equilibrium Lab Application

Purpose: An introduction to the qualitative aspects of chemical equilibrium. Starting with a reaction at equilibrium, one will change the concentration of various ions present in the equilibrium, and record the states of the changing equilibrium through observation. Theory:

Equilibrium- the point at which a solution has become perfectly saturated; when their forward and reverse reaction rates are equal Concentration- a measurement of how much solute is dissolved in a solution, measured in molarity (M) Reversible reaction-represented by a double arrow, a reaction the works in both the forwards and reverse directions Closed system- an environment in which nothing in the reaction will be able to escape. Must be part of an actual equilibrium expression Common Ion- when a substance is added to equilibrium and it has one ion in common, it will most likely affect to equilibrium in one way or another as a precipitate may form Control dish- the initial equilibrium to which all modified solutions will be compared Equilibrium Shift- when a system in equilibrium is affected by an external stress, the reactants and products shift to minimize the effects of the stress Stresses- alterations made to a system in regards to concentration, pressure and volume, temperature or the addition of a catalyst

Materials:
1- 150ml beaker
4- 250ml beakers
0.0020M potassium thiocyanate, KSCN, (aq)
10 drops of Fe(NO3)
Crystals of solid KSCN
Crystals of solid Na2HPO4
Safety goggles
Lab book

Sketch of apparatus:

Procedure:
1. In the first table, write down a description of what KSCN and Fe(NO3)3 look like. 2. Clearly mark the 4 beakers, 1 thru 4, to ensure you know what substance is added to each beaker. 3. Observe a solution of potassium nitrate KNO3. Describe the appearance of the solution in the first table. 4. Put approximately 25 ml of 0.0020M potassium thiocyanate solution, KSCN, in a 150ml beaker. Add approximately 25ml of distilled water to this same beaker. 5. Ad 5-6 drops of the Fe(NO3)3 to the same 150ml beaker. Gently swirl the mixture. Describe what you see in the first table. 6. Pour equal amounts of this solution in to the 4- 250ml beakers 7. Use beaker 1 as your control dish, the one that will have nothing added to it, to which you will compare the other solutions in regards of colour. 8. Experiment 1: in beaker 2, add 2-3 small crystals of solid KSCN. Describe the results in the second table. 9. Experiment 2: in the third beaker, add 3 drops of Fe(NO3)3 solution, swirl to get and record the results in the second table. 10. Experiment 3: in the fourth beaker, add 5 to 10 small crystals of Na2HPO4, a few at a time. Stir as you add them, and then describe the results in the second table.

**Note: it will be helpful to place the beakers on a white piece of paper, in order to see the colour properly.

Variables:
Independent variable- substances added to control solution
Dependent Variable- equilibrium shift
Control- the initial solution, mixture of Fe(NO3)3 + KSCN, forming the equilibrium of Fe3++ SCN- FeSCN
Constants- the FeSCN as the initial solution

Observations and Data:

Table One: *rough data at back of lab*
Solution
KSCN
KNO3
Fe(NO3)3
Ions Present
[K+] and [SCN-]
[K+] and [NO3-]
[Fe3+] and [NO3-]
Colour
Clear
Clear
Light orange/yellow

Table Two: *rough data at back of lab*

Control dish
Experiment one
Experiment two
Experiment three
Ions Present
[Fe3+], [K+], [SCN-], [NO3-]
[Fe3+], [K+], [SCN-], [NO3-]
[Fe3+], [K+], [SCN-], [NO3-]
[Na+], [HPO42-], [Fe3+], [K+], [SCN-], [NO3-]
Colour
Light orange-yellow
Dark Red
Dark orange
Clear

Observations:
The solid KSCN crystals did not dissolve completely in the solution, but the colour still changed readily The colour of the solution when we added more KSCN became very quickly a dark, blood red, nearly black. When we added...
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