Thermodynamics quantities of calcium hydroxide
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Transcript of Thermodynamics quantities of calcium hydroxide
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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