Solubility Product Constant of PbI2

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Solubility Product Constant of PbI2
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Experimental Objective

• Determine the solubility product constant
  (equilibrium constant) of PbI2
• PbI2(s)) ? Pb2(aq) 2I-(aq)
• Ksp I-2Pb2

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Experimental Procedure Overview

• Volumetrically prepare 100 mL of 0.25 M lead
  nitrate by direct addition
• Volumetrically prepare 50 mL of 0.10 M potassium
  iodide by direct addition
• Titrate lead nitrate with potassium iodide to
  saturation point
• Pb(NO3)2 2KI ? 2KNO3 PbI2

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Prepare 0.25M Lead Nitrate Solution

• 100 mL volumetric flask
• Direct addition of solid lead nitrate
• One solution per two students
• Place in buret

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Prepare 0.10M Potassium Iodide Solution

• 50 mL volumetric flask
• Direct addition of solid potassium iodide
• One solution per two students
• Divide into two clean, dry test tubes (one test
  tube per student)

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Titrate lead nitrate with potassium iodide to
saturation point

• Add KI dropwise from calibrated Pasteur pipet to
  25.00 mL Pb(NO3)2
• Pb(NO3)2 2KI ? 2KNO3 PbI2
• Observe yellow turbidity at saturation point

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Pasteur Pipet

• Calibrate
• Maintain constant drop size
• Hold vertically
• Maintain constant pressure

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Observe Saturation Point

• Beaker on black benchtop
• Constant stirring with stirring rod
• Persistent yellow precipitate

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Five Trials -Varying dilutions of Pb(NO3)2

• 0.01M, 0.02M, 0.05M, 0.10M, 0.25M (reverse order
  suggested in lab manual)
• Dispense 0.25M lead nitrate from buret
• Dispense appropriate water for dilution from
  buret

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Waste Handling

• All solutions should be discarded in liquid waste
• Do not overflow liquid waste

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Data Analysis

• Activity of ions Effective concentration
• Effective concentration
• Not necessarily equal to actual concentration
• solute-solute interactions
• Solute-solvent interactions
• Close to actual concentration at infinite
  dilution

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Data Analysis Concentration of ions
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Data Analysis - Ksp of each Trial

• Ksp I-2Pb2

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Data Analysis - Ksp at infinite dilution

• Plot log Ksp vs Concentration of Lead Cation
• Extrapolate plot to concentration 0