Chapter+12+Lab

**Equilibrium and Le Chatelier's Principle** Le Chatelier's Principle states :

**If an equilibrium system is subjected to a stress, the system will react to remove the stress.**

To remove a stress, a system can only do one of two things: form more products using up reactants, or reverse the reaction and form more reactants, using up products. In this experiment you will form several equilibrium systems. Then, by putting different stresses on the systems, you will observe how equilibrium systems react to a stress.

**General procedure**

1) Using the generalizations you have developed in the [|concept attainment] on Le Chatelier's principle, predict which way you think the equilibrium will shift for each change . 2) Then, carry out the reaction to verify your prediction.

**Chemicals for all procedures and reactions**

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 * Sodium chloride, NaCI(s) Hydrochloric acid, HCI, 12 M
 * Potassium thiocyanate, KSCN, 0.002 M Hydrochloric acid, HCI, 0.1 M
 * Bromothymol blue indicator solution Sodium hydroxide, NaOH, 0.1 M
 * Potassium thiocyanate, KSCN(s) Iron(M) nitrate, Fe(N03)3, 0.2 M
 * Silver nitrate, AgN03. 0.1 M Ethanol, C2H5OH(l)
 * Cobalt(II) chloride, CoCl2*6H2O(s) Disodium hydrogen phosphate, Na2HP04(S)
 * Equipment
 * Test tubes, 13 x 150-mm Test tube rack
 * Beaker, 100 mL Graduated cylinders
 * Stirring rod Funnel, filter paper, and holder for funnel

1. **An Equilibrium in a Saturated Solution** The first reaction you will study is a dissolving reaction to form a saturated solution that is at equilibrium. Examine the following reaction. Read the procedure below and predict what the effect of increasing [Cl-] ( adding concentrated HCl ) will be.
 * Specific Procedures **
 * NaCl(s) || [[image:http://www.saskschools.ca/curr_content/chem30/images/darrow.gif width="20" height="10"]] || Na+(aq) || + || Cl-(aq) ||


 * Procedure;**

2. **An Acid-Base Indicator Equilibrium**
 * Pour some solid NaCl into a 13 x 100-mm test tube and fill the tube 3/4 full of distilled water.
 * Cork and shake to form a saturated solution.
 * If all the NaCl dissolves, pour some additional NaCl (s) in the, tube and shake until a saturated solution with some excess solid is obtained.
 * Filter the solution into a second test tube.
 * To this saturated solution of NaCl, add some Cl- ions in the form of concentrated HCl Record and explain the results.

Acid-base indicators are large organic molecules that can gain and lose hydrogen ions to form substances that have different colors. The reaction of the indicator bromothymol blue can be illustrated as follows:


 * HIn(aq) || [[image:http://www.saskschools.ca/curr_content/chem30/images/darrow.gif width="20" height="10"]] || H+(aq ) || + || In-(aq) ||
 * yellow ||  ||   ||   || blue ||

In this reaction HIn is the neutral indicator molecule, and In- is the indicator ion after the molecule has lost a hydrogen ion. Equilibrium reactions can easily be forced to go in either direction. Read the procedure below and predict the effect of decreasing [H+ ] will be on the colour of the equilibrium.
 * Procedure;**

3. **A Complex Ion Equilibrium**
 * Fill a small test tube about half-full of distilled water.
 * Add several drops of bromothymol blue indicator solution.
 * Add 5 drops of 0.1 M HCl and stir This will increase the amount of H+ in solution. **Note the color of the indicator.**
 * Next add 0.1 M NaOH drop by drop with stirring until no further color change occurs.
 * Adding OH ions causes the H+ ion concentration to decrease as the ions combine to form water molecules. Again, note the color.
 * See if you can add the right amount of acid to this test tube to cause the solution to be green in color after it is stirred (half of the indicator is blue and half is yellow).

An equilibrium system can be formed in solution with the following ions:


 * Fe3+(aq) || + || SCN-(aq) || [[image:http://www.saskschools.ca/curr_content/chem30/images/darrow.gif width="20" height="10"]] || FeSCN2+(aq) ||
 * ** gold coloured ** ||  || colorless ||   || ** red-brown ** ||

The iron ion (Fe 3+) is gold coloured and the thiocyanate ion (SCN-) is colourless; however, the ion that forms from their combination, the FeSCN2+ ion, is colored a dark red-brown(almost blood red in colour). It is the color of this ion that will indicate how the equilibrium system is being affected. Read the procedure below and predict what the following changes will cause to happen.

Test a) Increase [SCN-] Test b) Increase [Fe 3+] Test c) Lower [Fe 3+]
 * Procedure:**

Test a) To the second test tube add 2-3 crystals of solid KSCN. Describe the results. > Test b) To the third test tube add 6 drops of Fe(N03)3 solution. Stir and describe the results. > Test c) To the fourth test tube add small crystals of NaHP04, a few at a time. Stir and note the results. Phosphate ions PO43-, have the ability to form complex ions with Fe3+, which has the same effect as **removing Fe3+ from solution.** 4. **Inquiry: An Equilibrium with Cobalt Complex Ions** In this section we will investigate the equilibrium between two different complex ions of cobalt. The reaction is endothermic:
 * Pour about 25 mL of 0.0020 M KSCN solution (a source of SCN- ion) into a beaker.
 * Add 25 mL of distilled water and 5 drops of 0.20 M Fe(N03)3 solution.
 * Swirl the solution and note the following: the color of the KSCN solution, the color of the Fe(N03)3 solution, and the color of the resulting complex ion.
 * You will stress the equilibrium system that has resulted in several ways. Pour equal amounts of the solution from the beaker into four test tubes. **The solution in the first test tube will be the reference solution.**
 * Co(H2O)62+(al) || + || 4 Cl-(aq) || + || Heat || [[image:http://www.saskschools.ca/curr_content/chem30/images/darrow.gif width="20" height="10"]] || CoCl42-(al) || + || 6 H20(l) ||
 * pink ||   ||   ||   ||   ||   ||  blue  ||   ||   ||
 * Caution **

Silver Nitrate causes stains on skin and clothing Wash off spills with soap and water immediately. Measure about 50 mL of ethanol into a beaker.**
 * Ethanol is flammable. Turn off all flames.


 * To create the equilibrium mixture add 2.00 grams of Cobalt (II) chloride to 50 ml of ethanol. in a small beaker**

Predict the effect on the colour of the equilibrium mixture that each of the following changes or tests will have.**
 * Create a procedure that will stress the equilibrium in the following ways. Clearly indicate how each test will be performed.

Test a) Heating the equilibrium Test b) Cooling the equilibrium Test c) Adding Silver Nitrate to the equilibrium (silver ions lower [Cl-] in the equilibrium) Test d) Add solid sodium chloride (NaCl: this raised [Cl-]) Test e) Add water to the equilibrium mixture.


 * Perform the 5 tests separate test tubes (13 x 100)
 * Be sure to include a control in a sixth test tube, so as to compare any colour change that occurs
 * Use approximately 5 ml of equilibrium solution for each test.
 * Record your results.
 * Did your results match your predictions?