Lab 17 Molar Solubility – Common-Ion Effect Procedure Caution: The saturated Ca(OH)2 solution and saturated Ca(OH)2 solution with CaCl2 added have been prepared for you. Do not stir or mix the saturated solutions! > Note: Record the exact concentration of the standardized 0.05 M HCl for use in your calculations. 1. Prepare a clean 50 mL buret for titration. Rinse the buret and tip with three 5 mL portions of the standardized 0.05 M HCl solution and discard. Fill the buret with standardized 0.05 M HCI, remove the air bubbles in the buret tip, and, after 10–15 seconds, read and record the initial volume using all certain digits (from the labeled calibration marks on the buret) plus one uncertain digit (the last digit which is the best estimate between the calibration marks). Place a sheet of white paper beneath the receiving flask to make the end point of the titration easier to see. Part A – Molar Solubility and Solubility Product of Calcium Hydroxide 2. Obtain a sample of saturated Ca(OH)2 solution (without added CaCl2) from your instructor. 3. Pipet 25 mL of the saturated Ca(OH). solution into a 125 mL flask and add 2 drops of methyl orange indicator. 4. Titrate the Ca(OH)2 solution to the methyl orange endpoint, where the color changes from yellow to red. Remember, the addition of HC1 should stop within one-half drop of the end point. Read and record the final volume of standard HCl in the buret. 5. Titrate two additional 25 mL aliquots of the saturated Ca(OH)2 solution. Data Analysis Calculate the molar solubility and solubility product of Ca(OH)2 for each trial and report their average values. Part B – Molar Solubility of Calcium Hydroxide in the Presence of a Common Ion 6. Repeat Steps 2–5 using a sample of saturated Ca(OH)2 solution containing added CaCl2. 7. Discard all of the reaction mixtures and HCl solution in the buret into the sink, followed by a generous supply of tap water. Rinse the buret twice with tap water and twice with deionized water.