CHEM 01LC Lecture Notes - Lecture 5: Potassium Nitrate, Lead, Nonmetal
CHEM 01LC Experiment 5: Solubility Product
●Experimental Purpose
○The purpose of this experiment is to determine the Ksp (solubility product) for lead
iodide after spectrophotometrically measuring the molar solubility
●Solubilities of Salts
○Salt: an ionic compound comprised of a metal and a nonmetal
■Soluble if its solubility (molar concentration) is ≥ 0.1 M
■Slightly soluble if its solubility is between 0.01 M and 0.1 M
■Insoluble if its solubility is < 0.01 M
●Solubility of Lead Iodide
○Insoluble salt ( < 0.002 M at 20℃)
○Equation for reaction:
■PbI2(s) ⇌ Pb2+(aq) + 2I-(aq)
○Equilibrium constant expression:
■K = [Pb2+] [I-]2
●K = Ksp (solubility product)
○No units expressed
●Solubility product: equilibrium constant corresponding to the
dissolution of a slightly soluble or insoluble ionic compound in
water
●2 ways to establish equilibrium
○Mix solutions of Pb(NO3)2 and KI
■[I-] determined experimentally
●Determine [Pb2+] from stoichiometric relationship
●Determine Ksp for lead iodide
○Determining [I-]
■Separate solid PbI2 from solution
■Oxidize I- ions to I2 with KNO2
■Measure absorbance of I2, relate to iodide ion concentration
●KNO2 vs. KNO3
○Potassium nitrate (KNO3): inert electrolyte
■Serves to maintain a constant ionic strength in various solutions
○Potassium nitrite (KNO2): oxidizes I- to I2
■Oxidation reaction:
●2NO2
- + 2H+ + 2I- → 2NO(g) + 2H2O + I2
●Waste Disposal
○LEAD ION IS TOXIC
■Do NOT pour any solutions or solids from this experiment into the sink
Document Summary
The purpose of this experiment is to determine the k sp (solubility product) for lead iodide after spectrophotometrically measuring the molar solubility. Salt : an ionic compound comprised of a metal and a nonmetal. Soluble if its solubility (molar concentration) is 0. 1 m. Slightly soluble if its solubility is between 0. 01 m and 0. 1 m. Insoluble if its solubility is < 0. 01 m. Insoluble salt ( < 0. 002 m at 20 ) Solubility product: equilibrium constant corresponding to the dissolution of a slightly soluble or insoluble ionic compound in water. Oxidize i - ions to i 2 with kno 2. Measure absorbance of i 2 , relate to iodide ion concentration. Serves to maintain a constant ionic strength in various solutions. Potassium nitrite ( kno 2 ): oxidizes i - to i 2. + 2h + + 2i - 2no(g) + 2h 2 o + i 2. Do not pour any solutions or solids from this experiment into the sink.
