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Determination of Ksp, ΔG˚, ΔH˚ and ΔS˚ for Ca(OH)2

Group 2; (MF, 7:00-10:00 AM)

Engada, Renz Aldaine S.

Macalos, Mary Grace G.

Pacalna, Almira Hannah B.

Pulpul, Charlene G.

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Presentation Outline Introduction Theoretical Background Objectives Methodology Proposed Data Sheet Possible Sources of Error

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Intoduction

The 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 ΔG˚ for the dissolution of the material can be determined. Using ΔG˚ values at two different temperatures, the enthalpy and entropy changes can also be estimated. With knowledge of these constants, ΔG˚ and Ksp can be calculated at any temperature between 0 ˚C and 100 ˚C.

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Theoretical Background The 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 titration

HCl(aq) + OH-(aq) H2O(l) + Cl-(aq)

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Theoretical Background The 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

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Theoretical Background The equilibrium constant, Ksp, for Ca(OH)2

is:

Ksp = [Ca2+][OH-]2

The Gibbs Free Energy, ΔG˚, is related to the equilibrium constant (Ksp) by

ΔG˚ = -RT ln Ksp

To find the enthalpy (ΔH˚) and entropy (ΔS˚) changes, the following equation is used

ΔG˚ = ΔH˚ - TΔS˚

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Objectives To determine the Equilibrium constant,

Ksp at room temperature To determine the Equilibrium constant,

Ksp at 100 °C To determine the ΔG° and use this to

determine ΔH° and ΔS° for the salvation of calcium hydroxide.

MethodologyA. Materials Needed 125-mL E. flasks 50, 100, 250-mL

beakers 10-mL pipet and

aspirator buret Buchner funnel Filter flask Filter paper Heating equipments

B. Chemicals Needed Standardized 0.025 M

HCI Bromothymol blue

solution Solid and saturated

Ca(OH)2, (room temp and boiling)

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MethodologyC. Procedure

Part One – Preparation of 0.025 M HCl Solution

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MethodologyPart Two – Determining Ksp at Room Temperature

Methodology

Methodology

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MethodologyPart Three – Determining Ksp at 100 °C

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Methodology

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Methodology

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Proposed Data Sheet

Trial 1 Trial 2 Trial 3

Temperature

Molarity of HCl

Volume of HCl used

Moles of OH- in sample

Volume of Sample

Molarity of OH-

Molarity of Ca2+

Ksp

Ave Ksp

ΔG°

Table 1. Determination of the solubility of Ca(OH)2 at room temp

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Proposed Data Sheet

Trial 1 Trial 2 Trial 3

Temperature

Molarity of HCl

Volume of HCl used

Moles of OH- in sample

Volume of Sample

Molarity of OH-

Molarity of Ca2+

Ksp

Ave Ksp

ΔG°

Table 2. Determination of the solubility of Ca(OH)2 at 100°C

Proposed Data Sheet

ΔH°

ΔS°18

Table 3. Determination of ΔH° and ΔS°

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Possible Sources of Error