5-Precipitation Equilibria

# 5-Precipitation Equilibria - PrecipitationReactions...

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Precipitation Reactions Important Concepts: K sp molar solubility - 2 (aq) 4 (aq) (s) 4 2 CrO Ag 2 CrO Ag + + ] [CrO ] [Ag K 2 4 2 sp - + = ] [CrO S solubility molar 2 4 - = = Molar solubility=moles of solid dissolved per liter ] [Ag S 2 + =

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Mass-Balance Equation in Precipitation Reactions Solubility= Σ(equilibrium concentrations of one of the salt species) For a solution saturated in AgCl: - + + → Cl Ag s AgCl ) ( ] [ ] [ - + = Cl Ag ] [ 2 ] [ 2 4 - + = CrO Ag 2 4 4 2 2 ) ( - + + → CrO Ag s CrO Ag •For a solution saturated in Ag 2 CrO 4 : S (mol/l)=[Ag + ]=[Cl - ] S (mol/l)=1/2[Ag + ]=[CrO 4 -2 ] 4 K S 1/3 sp = ( 29 S 1/2 sp K =
• Calculate the molar solubility of Mg(OH) 2 in water. 14 3 12 2 2 10 1 ] ][ [ 10 1 . 7 ] ][ [ - - + - - + × = = × = = OH O H K OH Mg K w sp

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Calculate the molar solubility of Mg(OH) 2 in water 12 E 7.1 ] ][OH [Mg K 2 2 sp - = = - + - (aq) 2 (aq) (s) 2 2OH Mg Mg(OH) + + 2 ] [OH ] [Mg s Solubility Molar 2 - + = = 3 2 sp 4s (2s) s K = = 04 E 1.21 4 K s 3 sp - = = 11 4.13E 2s K ] [OH K ] O [H w w 3 - = = = - + 10.38 pH =
How does fixing the pH have an effect on the molar solubility of Mg(OH) 2   ? 12 E 7.1 ] ][OH [Mg K 2 2 sp - = = - + - (aq) 2 (aq) (s)

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## This note was uploaded on 12/03/2011 for the course CHEM 2211 taught by Professor Facundofernandez during the Fall '09 term at Georgia Institute of Technology.

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5-Precipitation Equilibria - PrecipitationReactions...

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