Project: Chemical Equilibrium Lab Potential Credits: /20 Name: Goal and Instructions: To observe the macroscopic properties of chemical systems at equilibrium and to explain the observations obtained by applying Le Chatelier s principle. Begin by watching this video: Chemical Equilibrium. Thymol Blue Data and Observations: There are two equilibrium reactions at work here: 1) Thymol blue (blue) + H + Thymol blue (yellow) (Color change between ph 8.0-9.6) 2) Thymol blue (yellow) + H + Thymol blue (red) ) (Color change between ph 1.1-2.8) 1. What is the original color of the Thymol blue in the video? 2. What is the lowest possible ph the original solution could have? Explain how you know 3. Complete table 1 below. For the shift column, use Right if the equilibrium shifts towards the products and Left if the equilibrium shifts towards the reactants. The stress ion is the component of the solution added that affects the equilibrium. Table 1: Equilibrium Stresses Solution Added Stress Ion Color Change Shift HCl More HCl NaOH More NaOH Page 1 of 5
Thymol Blue Questions: 1. Explain how adding HCl causes the shift it does. 2. Explain how adding NaOH causes the shift it does. Hint: You must mention a reaction that creates water in your explanation. 3. If you increased the concentration of HCl or NaOH used, how would that affect the number of drops required before you saw a color change? Thiocyanatoiron(III) Ion Data and Observations: In this section we will be looking at changes to the following equilibrium: Fe 3+ (aq) (yellow) + SCN - (aq) (colorless) FeSCN (aq) (blood-red) Chloride ions are colorless. Potassium ions are also colorless. The above equilibrium can be created by mixing an Iron (III) chloride solution with a potassium thiocyanate solution. Based on this information and the colors in the equilibrium above answer the first two questions. 1. What color would an FeCl 3 solution be? 2. What color would a KSCN solution be? 3. What color do you get when you mix FeCl 3 and KSCN as shown in the video for the control test tube? Page 2 of 5
4. Complete table 2 below. For the shift column, use Right if the equilibrium shifts towards the products and Left if the equilibrium shifts towards the reactants. The stress ion is the component of the solution added that affects the equilibrium. Solution Added Stress Ion Spectator Ion Color Change Shift KCl Test Tube B Fe(NO 3 ) 3 Test Tube C KSCN Test Tube D NaOH Test Tube E Thiocyanatoiron(III) Ion Questions: 1. What is a spectator ion? 2. Using Le Chatelier's principle, explain why the reaction shifts the direction it does when Fe 3+ is added. 2. When NaOH is added, there is a color change to light yellow and a precipitate forms. Using Le Chatelier's principle, explain why the reaction shifts the direction it does when NaOH is added. Page 3 of 5
Copper(II) Complexes Data and Observations: In this section there will be three equilibriums to consider: When a small amount of NH 3 is first added, it reacts with water to form ammonium (NH 4+ ) ions and hydroxide ions: Equilibrium 1: NH 3(aq) + H 2 O (l) NH 4 + (aq) + OH (aq) Copper(II) ions can then form a precipitate with the hydroxide ions that are formed: Equilibrium 2: Cu (aq) (light blue) + 2OH (aq) Cu(OH) 2(s) Copper(II) ions in water are known to exist as tetraaquocopper(ii) ions (Cu(H 2 O) 4 ), which give a solution a pale blue color. When more ammonia (NH 3 ) is added to this solution, a new equilibrium develops: Equilibrium 3: Cu(H 2 O) 4 (aq) (light blue) + 4NH 3(aq) Cu(NH 3 ) 4 (aq) (dark blue) + 4H 2 O (l) The complex ion Cu(NH 3 ) 4, called the tetraamminecopper(ii) ion, is a deep blue color. It is also known that H + ions from acid will react with NH 3 and decrease the [NH 3 ]. 1. Complete Table 3 below. CuSO 4 +3 drops of NH 3 (ammonia) More NH 3 HCl added Color observed Page 4 of 5
Copper(II) Complexes Questions: 1. Explain using the equilibrium from the previous page why a precipitate forms when a few drops of ammonia are added to the copper (II) sulphate solution. 2. Using equilibrium concepts, explain the color change observed when HCl is added to the Cu(NH 3 ) 4 ion. Concluding Questions: 1. State Le Chatelier's Principle. 2. If the concentration of a reactant is increased, what is the effect on the equilibrium and why does it occur? 3. If the concentration of a reactant is decreased, what is the effect on the equilibrium and why does it occur? Page 5 of 5