DUAL EQUILIBRIUM PROBLEMS
Write out these full solutions on a separate piece of paper!
1. Consider a solution in which AgCl and Ag2CrO4 are in dual equilibrium.
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[Cl-] = 4.0 x 10 M. Find [Ag+] and [CrO42-].
2. Fe (OH)2 and FeS are in simultaneous equilibrium in solution.
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Find all [ion] if [OH-]= 6.0 x 10 M.
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3. What concentration of SO4 must exist to produce a precipitate in a solution
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of 1.0 x 10 M Ra(NO3)2 ? RaSO4 has a Ksp = 4.0 x 10 .
ANSWER: 4.0 x 10
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M
4. A solution is saturated with both AgCl and Ag2CrO4.
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If AgCl has a Ksp = 1.1 x 10
and Ag2CrO4 has a Ksp = 1.7 x 10 , determine
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all ion concentrations if [CrO4-2] = 1.0 x 10 M.
+
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ANSWER: [Ag ] = 4.1 x 10 M and [Cl ] = 2.7 x 10 M
DUAL EQUIL. PROBLEMS – What precipitates first?
1. Ba(NO3)2 is added to a solution containing both 0.0100 M K2CO3 and
0.0010 M Na2SO4.
What precipitates first?
What is the [ion] when the second ppt. commences?
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2. A solution contains [Br -1] = 2.00 x 10 M and [Cl -1] = 1.00 x 10 M .
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If, for AgCl, in these experimental conditions Ksp = 1.56 x 10
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And, for AgBr, in these experimental conditions Ksp = 3.25 x 10
What precipitates first as Ag+ is added to the solution of bromide and chloride?
What will the concentrations of bromide, chloride, and silver ions be, when the
second precipitate starts forming?
ANSWER: For AgCl ppt to form, we need [Ag + ] > 1.56 x 10 -8 M
For AgBr ppt to form, we need [Ag + ] > 1.63 x 10 -8 M;
Since the [Ag + ] limit for AgCl will be reached first as Ag + is added to the solution, AgCl
will ppt first. The second ppt is AgBr and will commence when the [Ag + ] reaches
1.63 x 10 -8 M. This occurs when [Br - ] = 2.0 x 10 -5 M (as given) and [Cl - ] = 9.6 x 10 -3 M.
3. A solution contains 3.5 x 10-3 M IO3-(aq) and 6.4 x 10-4 M CO3-2(aq). Identify the precipitate
that will form first upon addition of Ag+(aq) to the solution. Find the concentration of the ions
when the second precipitate starts forming.
ANSWER: For AgIO3(s) precipitation, we need [Ag+(aq)] > 9.1 x 10-6 M. For Ag2CO3(s)
precipitation, we need [Ag+(aq)] > 1.1 x 10-4 M. The first precipitate formed will be AgIO3(s).
The second ppt is Ag2CO3(s) and will commence when:
[Ag+(aq)] = 1.2 x 10-4 M (as calculated),
[CO3-2(aq)] = 6.4 x 10-4 M (as given) and,
[IO3-(aq)] = 2.8 x 10-4 M when Ag2CO3(s) starts to precipitate.
ANOTHER LOOK AT PRECIPITATION PROBLEMS
Write out these full solutions on a separate piece of paper!
1.
If we mix 300. mL of 0.075 M Na2SO4 and 200. mL of 0.045 M
Ba(NO3)2 , will a precipitate form?
2.
Equal volumes of 0.040 M Cu2SO4 and 0.00060 M NaI are
mixed. Will a precipitate form?
3.
200. mL of 0.000060 M Al2(SO4)3 is mixed with 300. mL of
0.00010 M Pb(NO3)2 . Does a precipitate form?
4.
Will precipitate form if 10. mL of a 0.010 M NaCl is mixed with
30. mL of 0.020 M Ag2SO4?
AgCl has a Ksp value of 1.6 x 10 -10 .
ANS: Ksp 1.6 x 10 -10 < Ktrial 7.5 x 10
5.
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so a ppt forms
Will a precipitate form if 750. mL of 2.0 x 10-2 M MgCl2(aq) is
mixed with 2.50 L of 0.010 M Cs2CO3(aq)?
ANS: Ksp < Ktrial so a ppt forms