Chemistry 112 - Study Guide - Test 3

Chemistry 112 - Study Guide - Test 3 - Chapter 17: - Write...

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Chapter 17: - Write Expressions for K sp : Example : CaC 2 O 4  Ca 2+ (aq) + C 2 O 4 2- (aq) K sp = [Ca 2+ ][ C 2 O 4 2- ] - Calculating K sp from Solubility Information: * Impute Molar concentrations for the K sp  Equation. Example : 1.0 L Sample of a saturated calcium oxalate solution, CaC 2 O 4 , contains 0.0061g of the salt at 25°C. Calculate the K sp . Molarity of CaC 2 O 4 = (0.0061g/ 1.0L) x (1 mol CaC 2 O 4 /128g CaC 2 O 4 ) = 4.8 x 10 -5 mol CaC 2 O 4 /L Example: The mineral Fluorite is calcium fluoride, CaF 2 . Calculate the solubility of calcium fluoride in water from the K sp = 3.4x10 -11 . CaF 2 (s)  Ca 2+ (aq) + 2 F - (aq) K sp = [Ca 2+ ][ F - ] 2 Initial: 0 0 Change: +x +2x Equilibrium: x 2x 3.4x10 -11 = (x)(2x) 2 4x 3 = 3. 4x10 -11 x = cube root[3. 4x10 -11 ] = 2.0x10 -4 M NOTE: Molarity = moles/ volume Common ion Effect: The shift in an ionic equilibrium caused by the addition of a solute that provides an ion that takes part in the equilibrium. * Assumption: (Initial concentration) / (K sp ) > 100; then (+ x) is negligible. - Write Expressions for Equilibrium Constant (Q c ): Example: PbCl 2  Pb 2+ (aq) + 2Cl 2- (aq) Q c = [Pb 2+ ] I [Cl 2- ] 2 i ^ If Q c > K sp Precipitate ^ If Q c < K sp no Precipitate ^ If Q c = K sp Saturated - Predict if a Precipitate will form: Example: The concentration of calcium ion in blood plasma is 0.0025M. If the concentration of oxalate ion is 1.0x10 -7 M, do you expect calcium oxalate to precipitate? K sp for calcium oxalate is 2.3x10 - 9 . Q c = [Ca 2+ ] i [C 2 O 4 2- ] I Q c = (0.0025M)(1.0x10 -7 M) =2.5x10 -10 Q c = 2.5x10 -10 < 2.3x10 -9 = K sp = no precipitate will form ^ If Q c > K sp Precipitate ^ If Q c < K sp no Precipitate ^ If Q c = K sp Saturated
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Fractional Precipitation: The technique of separating two or more ions from a solution by adding a reactant that precipitates first on ion, then another, and so forth. * Ex. Slowly adding K 2 CrO 4 to a solution containing Ba 2+ and Sr 2+ - After most of the Ba 2+ has precipitated then Sr 2+ precipitates. NOTE: K sp  must be very different. -pH Effect on Solubility: * If more soluble in an acidic solution = Low pH * If the anion is the conjugate base of a weak acid then solubility is affected by pH. Example: C 2 O 4 2- (aq) + H 3 O + (aq)  HC 2 O 4 - (aq) + H 2 O (l) HC 2 O 4 - is conjugate to a weak base = react with H 3 O + - Complex Ion Formation: is formed when a metal ion from a Lewis base attaches to a coordinate covalent bond. - Formation Constant (K f ): the equilibrium constant for the formation of a complex ion from the aqueous metal ion and the ligands. * A large value means the complex ion is very stable. NOTE: DO NOT NEED TO KNOW HOW TO DO K F  CALCULATIONS.
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This lab report was uploaded on 04/16/2008 for the course CHEM 111 taught by Professor Hartshorn during the Fall '06 term at St. Thomas.

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Chemistry 112 - Study Guide - Test 3 - Chapter 17: - Write...

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