A K sp Pb 2 Cl 2 B K sp Pb 2 Cl C K sp Pb 2 2 Cl D K sp PbCl Cl E K sp Pb Cl 2

A k sp pb 2 cl 2 b k sp pb 2 cl c k sp pb 2 2 cl d k

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A) K sp = [Pb 2+] [Cl ] 2 B) K sp = [Pb 2+ ] [Cl ] C) K sp = [Pb 2+ ] 2 [Cl ] D) K sp = [PbCl + ] [Cl ] E) K sp = [Pb + ] [Cl 2 ] 2 19 ) ( 2 ) ( b (s) 2 2 aq Cl aq P PbCl
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Example What is the K sp value of a solution made of 0.0012 mols PbI 2 (s) dissolves in 1.0 L water. 20 2 2 ] ][ [ I Pb K sp 0.0012M 0 0 2 (0.0012) 0.0012 -0.0012 0M 0.0012M 0.0024M 2 ] 0024 . 0 ][ 0012 . 0 [ sp K 9 10 9 . 6 x K sp I C E ) ( 2I ) ( Pb (s) PbI 2 2 aq aq
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Solubility vs. Solubility Product Solubility: number of grams of solute that dissolves to form a saturated solution Molar solubility: number of moles of solute that dissolve to form a liter of saturated solution Unit = mols/L Solubility-Product, K sp : equilibrium constant for ionic solid and its saturated solution Unit= g/L 21
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22 Example If the K sp of Pb(OH) 2 is 1.2x10 -5 , calculate the molar solubility. 2 2 ] ][ [ OH Pb K sp ) ( 2 ) ( b (s) ) ( 2 2 aq OH aq P OH Pb 2 5 ] 2 ][ [ 10 2 . 1 x x x 3 5 4 10 2 . 1 x x M x 014 . 0 x 0 0 2 (x) +x -x 0M x 2x I C E
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Factors Affecting Solubility There are 3 factors affecting solubility: 1. The presence of a common ion 2. pH of the solution 3. The presence or absence of complexing agents 23
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Factors Affecting Solubility 1. Common-Ion Effect: Solubility of the partially soluble salt is decreased when a common ion is added Le Châtelier’s principle ) ( 2 ) ( (s) 2 2 aq F aq Ca CaF Adding more F ( such as NaF ), or Ca 2+ ( such as CaCl 2 ) the equilibrium shifts to offset the increase, shifts to the left The solubility of CaF 2 decreases 24
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Example What is the molar solubility of Pb(OH) 2 in 0.20M Pb(NO 3 ) 2 ? 25 ) ( 2 ) ( b (s) ) ( 2 2 aq OH aq P OH Pb 0.20 0 x 2x 0.20+x 2x 2 2 ] ][ [ OH Pb K sp 5 10 2 . 1 x ] 4 [ ] 20 . 0 [ 10 2 . 1 2 5 x x M x x 3 10 87 . 3 I C E 2 ] 2 ][ 20 . 0 [ x x x -x 0M Pb(OH) 2 only = 1.4x10 -2 M Decreased
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Factors Affecting Solubility 2. pH: Substances with acidic salts are more soluble in basic solutions Substance with basic salt , are more soluble in acidic solution Such as adding HCl to CaF 2 26
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Factors Affecting Solubility Again we apply Le Châtelier’s principle: CaF 2 ( s ) Ca 2+ ( aq ) + 2F - ( aq ) F - ( aq ) + H + ( aq ) HF( aq ) If HCl is added , H + reacts with F - , the equilibrium shifts to the right and CaF 2 dissolves As pH decreases, [H + ] increases and solubility increases Ca(OH) 2 (S. Base) HF (W. Acid) Basic salt 27
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Factors Affecting Solubility 3. Complex Ions: metal ions can act as Lewis acids and form complex ions with Lewis bases in the solvent Equilibrium constant is called the formation constant , K f The formation of these complex ions increases the solubility of these salts (aq) C (aq) Ag AgCl(s) l (aq) NH A (aq) 2NH (aq) A 2 3 3 g g K sp = 1.6 × 10 10 (aq) C (aq) H A (aq) H 2 AgCl(s) - 2 3 3 l N g N K = 2.72x10 -3 K f = 1.7 x 10 7 28
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Example In which of the following aqueous solutions would you expect AgI to have the highest solubility? A) pure water B) 0.050 M BaI 2 C) 0.050 M NaI D) 0.050 M KI E) 0.010 M AgNO 3 29 ) ( ) ( g gI(s) aq I aq A A
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Precipitation and Separation of Ions To decide if a precipitate will form: calculate the reaction quotient , Q ( actual conditions ), and compare it to the solubility product constant , K sp If Q = K sp , system is at
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