chapter-19 lecture-5

chapter-19 lecture-5 - Factors Factors Which Affect...

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Factors Which Affect Solubility t ilib i [ M p X q ( s ) p M n+ ( aq ) + q X z- ( aq ) Important solution factors which may affect the solubility of nic substances in water At equilibrium K sp = M n+ ] p [ X z- ] q ionic substances in water Temperature - solubility is temperature dependent Common ions - the presence of common ions in solution lowers solubility pH - solution pH can affect solubility if the anion of the ionic solid (i.e., X) is the conjugate base of a weak acid Complex ions - ammonia reacts with many metal ions in solution through complexation reactions 19-39
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Common Ion Effect -- occurs when the ionic solid is dissolved in a solution which already contains a common ion Example : what is the solubility of PbCl 2 in a 0.100 M NaCl(aq) olution? p =12X10 -5 solution? K sp 1.2 X 10 Chloride ion is common to both Na Cl and Pb Cl 2 and is called the common ion SOLUTION: PbCl 2 (S) Pb 2+ (aq) + 2 Cl - (aq) Concentration ( M ) Initial - 0 0.1 Change Equilibrium - - + S +2 S S 0.1+2 S Assume S <<0.1 , and the [Cl - ] remains constant at 0.100 M through the greatly abundant chloride ion contributed by NaCl K p =1.2 X 10 -5 = [Pb 2+ ][Cl - ] 2 = [Pb 2+ ] 0.100 2 19-40 sp s = [Pb 2+ ] = 1.2 X 10 -5 /0.100 2 = 1.2 x 10 -3 M
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PROBLEM: In previous sample problem, we calculated the solubility of Ca(OH) 2 in water. What is its solubility in 0.10 M Ca(NO 3 ) 2 ? K sp of Ca(OH) 2 is 6.5x10 -6 . LAN: et up a reaction equation and table for the dissolution of Ca(OH) PLAN: Set up a reaction equation and table for the dissolution of Ca(OH) 2 . The Ca(NO 3 ) 2 will supply extra [Ca 2+ ] and will relate to the molar solubility of the ions involved. + SOLUTION: Ca(OH) 2 ( s ) Ca 2+ ( aq ) + 2OH - ( aq ) Concentration ( M ) Initial hange -0 . 1 0 0 2 Change Equilibrium - - + S +2 S 0.10 + S 2 S K p = 6.5x10 -6 = (0.10 + S )(2 S ) 2 = (0.10)(2 S ) 2 Assume: S << 0.10 S = Check the assumption: .0 < 5.0% 4.0x10 -3 x 100 = 4 10 5 6 5 x . = 4.0x10 -3 19-41 4.0% 5.0% 0.10 M
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Effect of pH on Solubility __ Apply Le Chatelier’s Principle to determine pH effect ! Some anions of solids may undergo hydrolysis Example of non-reactive ionic solid AgCl( s ) Ag + ( aq ) + Cl - ( aq ) Cl - or Ag + do not undergo hydrolysis, equilibrium position is ot affected by the addition of H not affected by the addition of H 3 O + one of the ions formed is a conjugate base of a weak acid, If one of the ions formed is a conjugate base of a weak acid, then hydrolysis occurs Example of reactive solid PbF ( s ) Pb 2+ ( aq ) + 2F - ( aq ) 2 F - ( aq ) + H 2 O( l ) HF( aq ) + OH - ( aq ) Fluoride ion is the conjugate base of the weak acid HF 19-42
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This note was uploaded on 07/31/2010 for the course CHEM CHEM 01C taught by Professor Unknown during the Spring '10 term at UC Riverside.

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chapter-19 lecture-5 - Factors Factors Which Affect...

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