*Determination of Ksp, G, H and S for Ca(OH)2Group 2; (MF, 7:00-10:00 AM)

Engada, Renz Aldaine S.Macalos, Mary Grace G.Pacalna, Almira Hannah B.Pulpul, Charlene G.

*Presentation OutlineIntroductionTheoretical BackgroundObjectivesMethodologyProposed Data SheetPossible Sources of Error

*IntoductionThe solubility of hydroxides is easily determined through a titration with a suitable acid. From the molar solubility, the solubility equilibrium constant, Ksp, can be calculated and from this the G for the dissolution of the material can be determined. Using G values at two different temperatures, the enthalpy and entropy changes can also be estimated. With knowledge of these constants, G and Ksp can be calculated at any temperature between 0 C and 100 C.

*Theoretical BackgroundThe solubility of an ionic substance in a solvent can be thought of as a reaction where the solid dissociates into ions in solution.Ca(OH)2(s) Ca2+(aq) + 2 OH-(aq)Equilibrium has been established and the solid removed, the concentration of hydroxide can be determined via an acid/base titrationHCl(aq) + OH-(aq) H2O(l) + Cl-(aq)

*Theoretical BackgroundThe concentration of hydroxide ion in a saturated solution of Ca(OH)2 is found by titration with standardized hydrochloric acid. Since HCl is a strong acid and H+ and OH- react with 1:1 stoichiometry, we can use:MHClVHCl = MOH-VOH-The molar solubility of the salt is equal to half of the hydroxide ion concentration

*Theoretical BackgroundThe equilibrium constant, Ksp, for Ca(OH)2 is:Ksp = [Ca2+][OH-]2The Gibbs Free Energy, G, is related to the equilibrium constant (Ksp) byG = -RT ln KspTo find the enthalpy (H) and entropy (S) changes, the following equation is used G = H - TS

*ObjectivesTo determine the Equilibrium constant, Ksp at room temperatureTo determine the Equilibrium constant, Ksp at 100 CTo determine the G and use this to determine H and S for the salvation of calcium hydroxide.

MethodologyA. Materials Needed125-mL E. flasks50, 100, 250-mL beakers10-mL pipet and aspiratorburetBuchner funnelFilter flaskFilter paperHeating equipments

B. Chemicals NeededStandardized 0.025 M HCIBromothymol blue solutionSolid and saturated Ca(OH)2, (room temp and boiling)

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MethodologyC. ProcedurePart One Preparation of 0.025 M HCl Solution

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MethodologyPart Two Determining Ksp at Room Temperature

Methodology

Methodology

*MethodologyPart Three Determining Ksp at 100 C

*Methodology

*Methodology

*Proposed Data SheetTable 1. Determination of the solubility of Ca(OH)2 at room temp

Trial 1Trial 2Trial 3TemperatureMolarity of HClVolume of HCl usedMoles of OH- in sampleVolume of SampleMolarity of OH-Molarity of Ca2+KspAve KspG

*Proposed Data SheetTable 2. Determination of the solubility of Ca(OH)2 at 100C

Trial 1Trial 2Trial 3TemperatureMolarity of HClVolume of HCl usedMoles of OH- in sampleVolume of SampleMolarity of OH-Molarity of Ca2+KspAve KspG

Proposed Data Sheet*Table 3. Determination of H and S

HS

*Possible Sources of Error