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8/14/2019 Unidad IV Eqsolubilidadalumnos
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UNIDAD IV. EQUILIBRIOS DE
SOLUBIBLIDAD
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Reacciones de precipitacin
Los iones solubles sepueden combinar para
formar un compuesto
insoluble.
Se produce laprecipitacin.
Ag+(aq) + Cl-(aq) AgCl(s)
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Ag+(aq) + NO3-(aq) + Na+(aq) + I-(aq)
AgI(s) + Na+(aq) + NO3-(aq)
Iones espectadores
Ecuacin inica neta
AgNO3(aq) +NaI (aq) AgI(s) + NaNO3(aq)
Reaccin de precipitacin global:
Ecuacin inica neta:
Ag+(aq) + I-(aq) AgI(s)
Ecuacin inica neta:
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Reglas de solubilidad
Compuestos solubles:
Li+, Na+, K+, Rb+, Cs+ NH4+
NO3- ClO4
- CH3CO2-
Todos los de losmetales alcalinos y elion
amonio.
Nitratos, percloratosy acetatos
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Reglas de solubilidad
Hidrxidos y sulfuros HO-, S2- Excepto los metales alcalinos y los iones amonio.
Los sulfuros de los alcalinotrreos son solubles. Los hidrxidos de Sr2+ y Ca2+ son un poco solubles.
Carbonatos y fosfatos CO32-, PO4
3- Excepto los de los metales alcalinos y las sales de amonio.
Compuestos insolubles:
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Temperature and Solubility
Solid solubility and temperature
solubility increases withincreasing temperature
solubility decreases with
increasing temperature
12.4
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Fractional crystallizationis the separation of a mixture of substances into pure components
on the basis of their differing solubilities.
Suppose you have 90 g KNO3
contaminated with 10 g NaCl.
Fractional crystallization:
1. Dissolve sample in 100 mL ofwater at 600C
2. Cool solution to 00C
3. All NaCl will stay in solution (s =
34.2g/100g)
4. 78 g of PURE KNO3will
precipitate (s = 12 g/100g). 90
g 12 g = 78 g
12.4
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Temperature and Solubility
Gas solubility and temperature
solubility usually decreaseswith increasing
temperature
12.4
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Solubility Equilibria
16.6
AgCl (s) Ag+(aq)+ Cl-(aq)
Ksp= [Ag+][Cl-] Kspis the solubility product constant
MgF2(s) Mg2+(aq)+ 2F-(aq) Ksp= [Mg
2+][F-]2
Ag2CO3(s) 2Ag+(aq)+ CO3
2-(aq) Ksp= [Ag+]2[CO3
2-]
Ca3(PO4)2(s) 3Ca2+(aq)+ 2PO4
3-(aq) Ksp= [Ca2+]3[PO3
3-]2
Dissolution of an ionic solid in aqueous solution:
Q= Ksp Saturated solution
Q< Ksp Unsaturated solution No precipitate
Q> Ksp Supersaturated solution Precipitate will form
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Molar solubility(mol/L) is the number of moles of solute dissolved in 1 L of a saturated
solution.
Solubility(g/L)is the number of grams of solute dissolved in 1 L of a saturated solution.
16.6
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What is the solubility of silver chloride in g/L ?
AgCl (s) Ag+(aq)+ Cl-(aq)
Ksp= [Ag+][Cl
-]Initial (M)
Change (M)
Equilibrium (M)
0.00
+s
0.00
+s
s s
Ksp= s2
s= Ksp
s= 1.3 x 10-5[Ag+] = 1.3 x 10-5M [Cl-] = 1.3 x 10-5M
Solubility of AgCl =1.3 x 10-5 mol AgCl
1 L soln
143.35g AgCl
1 mol AgCl
x = 1.9 x 10-3g/L
Ksp= 1.6 x 10-10
16.6
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If 2.00 mL of 0.200 MNaOH are added to 1.00 L of 0.100 MCaCl2, will a
precipitate form?
16.6
The ions present in solution are Na+, OH-, Ca2+, Cl
-.
Only possible precipitate is Ca(OH)2(solubility rules).
Is Q> Kspfor Ca(OH)2?
[Ca2+]0= 0.100 M [OH-]0= 4.0 x 10-4M
Ksp= [Ca2+][OH
-]2= 8.0 x 10-6
Q= [Ca2+]0[OH-]0
2 = 0.10 x (4.0 x 10-4)2= 1.6 x 10-8
Q< Ksp No precipitate will form
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The Common Ion Effect and Solubility
The presence of a common ion decreases the solubility of the
salt.
What is the molar solubility of AgBr in (a) pure water and (b) 0.0010 MNaBr?
AgBr (s) Ag+(aq)+ Br-(aq)
Ksp= 7.7 x 10-13
s2= Ksp
s= 8.8 x 10-7
NaBr (s) Na+ (aq)+ Br-(aq)
[Br-] = 0.0010 M
AgBr (s) Ag+(aq)+ Br-(aq)
[Ag+] = s
[Br-] = 0.0010 + s0.0010
Ksp= 0.0010 x s
s= 7.7 x 10-10
16.8
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Complex Ion Equilibria and Solubility
A complex ionis an ion containing a central metal cation bonded to one or more molecules
or ions.
Co2+(aq)+ 4Cl-(aq) CoCl4(aq)2-
Kf=[CoCl4]
[Co2+][Cl-]4
2-
Theformation constant or stability constant (Kf)is the equilibrium constant for the
complex ion formation.
Co(H2O)6 2+ CoCl42-
16.10
Kfstability ofcomplex
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16.10
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16.11
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Qualitative
Analysis of
Cations
16.11
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Flame Test for Cations
lithium sodium potassium copper
16 11