E5 Chemical Equilibria: Le Chatelier's Principle Report Form Name: Partner's Name: (if any) Lab Section: MW/TTH/M-TH/F (circle) Advanced Study Assignment 1. Why is Le Chtelier's principle important in chemical equilibrium? 2. The intense color of chromate and dichromate ions is due to ligand to metal charge transfer rather than the d-d electronic transitions we studied in Chapter 23. (a) What are the colors of these two ions? chromate- dichromate- (b) How are the two ions related? 3. Methyl orange and phenolphthalein are organic molecules that are used as acid-base indicators. Such indicators can also be used to indicate direction of change when equilibrium systems are subjected to stress. (a) Use Hin to symbolize the unionized form of an indicator and write a balanced equation in water to represent its ionization (b) Provide the pH range of the indicators described above along with the color of the acid(unionized) and basic(ionized) form of each indicator. Indicator: Indicator: pH range pH range colors: acid colors: acid base base 4. A complex ion is formed when Fe3+ solution is combined with a thiocyanate solution. (a) Select the ion responsible for the blood-red color in the solution. (b) The experimental directions call for heating the cobalt(II) chloride solution in a beaker of hot water under fume hood. Why is this extra precaution necessary? 5. Last parts of the experiment are concerned with equilibria of saturated solutions and the applications of chemical equilibria to solubility equilibria. (a) How is the saturated solution of barium chromate formed? (b) What is examined in the reaction for the formation of calcium oxalate? -6