LeCHATELIER’S PRINCIPLE
The purpose of this experiment is to observe the effect of altering concentration or temperature on the position of equilibrium.
Procedure
Part 1. HIn (aq) ⇌ H1+ (aq) + In1– (aq)
1. Fill one disposable pipet with 1 M HCl and a second disposable pipet with 1 M NaOH (be sure you won’t mix them up). Put about 2 cm of deionized water into each of two large clean test tubes. Add three drops of indicator solution to each tube.
2. Add a drop of HCl to one test tube, mix by flicking, and record the color. Add a drop of NaOH to the other test tube, mix, and record the color.
3. Add 1-2 drops of NaOH to the first test tube, mixing after each drop, until the color changes. Record the color. Add 1-2 drops of HCl to the test tube, mixing after each drop, until the color changes again. Record the color.
4. Add 1-2 drops of HCl to the second test tube, mixing after each drop, until the color changes. Record the color. Add 1-2 drops of NaOH to the test tube, mixing after each drop, until the color changes again. Record the color.
Part 2. Co(H2O)62+ (aq) + 4 Cl1– (aq) ⇌ CoCl42– (aq) + 6 H2O (l) ∆H = +50 kJ/mol
5. Make a hot water bath on the hot plate (setting 4), and an ice bath in the foam bucket.
6. Add a Beral pipetful 0.15 M CoCl42– in methanol into a large clean dry test tube. 4.87g of oven dried Co(H2O)6 which looks blue instead of purple, dissolved in 250 mL of water. Record the color of the CoCl42– solution, then use another Beral pipet to add drops of deionized water, one at a time, mixing after each drop, just until the color changes to pink. Do not add too much water.
7. Place the test tube in the hot water and observe the color. If you do not observe a color change, you added too much water; try again with a clean dry test tube. Move the tube to the ice bath and observe the color again.
Part 3. AgCl (s) ⇌ Ag1+ (aq) + Cl1– (aq)
8. Add a Beral pipetful of saturated AgCl solution to a small test tube. AgCl is made by using 0.1 M NaCl and add 0.1M AgNO3 until there is a percipate. Be sure you get only the solution, none of the solid settled at the bottom.
9. Add a drop of 0.1 M AgNO3 solution to the test tube and record your observations.
Analysis
Part 1. HIn (aq) ⇌ H1+ (aq) + In1– (aq)
1. Write the chemical equation for the equilibrium and its Kc expression. Under the H1+ write the color of the indicator with a drop of HCl. Under the HIn, write the color of the indicator with a drop of NaOH. its color in solution, based on your observations in step 1.
2. Describe how adding NaOH and HCl to each tube affects the concentration of H1+ ions; interpret this in terms of how the change in [H1+] shifts the composition of the mixture at equilibrium.
Part 2. Co(H2O)62+ (aq) + 4 Cl1– (aq) Û CoCl42– (aq) + 6 H2O (l) ∆H = +50 kJ/mol
3. Write the chemical equation for the equilibrium, adding energy to the appropriate side of the equation. The CoCl42– ion is a deep blue color and the Co(H2O)62+ ion is a pink color; write the color under the formula for each ion.
4. Describe how adding and removing energy shifts the composition of the solution at equilibrium, as revealed by the color changes.
Part 3. AgCl (s) ⇌ Ag1+ (aq) + Cl1– (aq)
5. Write the chemical equation for the equilibrium and its Kc expression. Interpret your observation of the effect of adding AgNO3 to the solution in terms of how the change in [Ag1+] shifts the composition of the mixture at equilibrium.
Discussion
Draw a general conclusion about the effect of adding or removing a reactant or product on the equilibrium. Briefly identify sources of error in the data.