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Determining the K of Calcium Hydroxide Complete the data table and answer the questions in the data analysis. Calcium hydroxide is an ionic solid that is sparingly soluble in water. A saturated, aqueous, solution of Ca(OH)₂ is represented in equation form as shown below. Ca(OH)2 (s) + Ca (aq) + 2OH(aq) The solubility product expression describes, in mathematical terms, the equilibrium that is established between the solid substance and its dissolved ions in an aqueous system. The equilibrium expression for calcium hydroxide is shown below. Kup-[Ca][OH-] The constant that illustrates a substance's solubility in water is called the K, All compounds, even the highly soluble sodium chloride, have a Kp. However, the Ksp of a compound is commonly considered only in cases where the compound is very slightly soluble and the amount of dissolved ions is not simple to measure. Your primary objective in this experiment is to test a saturated solution of calcium hydroxide and use your observations and measurements to calculate the Ksp of the compound. You will do this by titrating the prepared Ca(OH): solution with a standard hydrochloric acid solution. By determining the molar concentration of dissolved hydroxide ions in the saturated Ca(OH)2 solution, you will have the necessary information to calculate the Ke HOL
Data Table by HE Volume of Ca(OH)2 Concentration of HCI Initial pH 1. Equivalence point 2. Volume of HCI added at the equivalence point 3. Moles HCI 4. Moles of OH (moles OH = moles H') 5. Moles of Ca²+ ions. Hint: 1 mol Ca²+ = 2 mol OH 6. Ksp expression for Ca(OH)2 7. Ksp for Ca(OH)2 8. Ksp from Appendix C 12.5 0.05 mol/L TRIAL #1 15.0 ml. 3.5x10-4 7.00 mL 3.5 x 10-4 7.00 mL 6,4x10-6 mol 6.5 x 10-6 15.0 ml. 0.05 mol/L 12.0 TRIAL #2 7.50 mL 7.50 mL 3.75×10 mol mol 3.75x10 175x 10-4 mol 1.875 x 164 mol 4 Ksp= [Ca ²+ ] [OH-] = [Ca] [or] 7.8×106 mol 6.5 x 10-6
Data Analysis 1. Calculate the [OH-] from the results of your titrations. Explain your calculations. Hint: moles of OH/0.015 L 3.5x14 13 3.75×10-4 13 11000 = *0234 mol % (con. of OH) -x1000-0.025 mol/L 2. Using stoichiometry, calculate the [Ca). Explain you calulations. Hint: moles of Ca/0.015 L 3. Calculate the Kp for calcium hydroxide. Explain your calculations 4. Find the accepted value of the K for calcium hydroxide and compare it with your valuc. Discuss any discrepancy and suggest possible sources of experimental error.