QUIZ CHAPTER #16
Student’s Name
1. Cation C and anion A form an ionic compound X for which Ksp = 4s3, where s is the molar
solubility of the ionic compound X. Which of Figures I–III represent(s) an unsaturated aqueous
solution of compound X?
a) only I
b) only II
c) only III
d) both II and III
2. If 315 mL of 1 × 10−4 𝑀 Ca(NO3)2 is mixed with 315 mL of 1 × 10−4 𝑀 NaF, what will
occur? For CaF2, 𝐾𝑠𝑝 = 3.4 × 10−11 .
Ca(NO3 )2(𝑎𝑞) + 2 NaF(𝑎𝑞) → 2 NaNO3(𝑎𝑞) + CaF2(𝑠)
a) No precipitate will form.
b) Sodium nitrate will precipitate.
c) Calcium nitrate will precipitate.
d) Calcium fluoride will precipitate.
𝑚𝑜𝑙 𝐹 − = 𝑚𝑜𝑙 𝑁𝑎𝐹 = 0.315 𝐿 × 1 × 10−4 𝑀 = 3.15 × 10−5 𝑚𝑜𝑙
𝑚𝑜𝑙 𝐶𝑎2+ = 𝑚𝑜𝑙 Ca(NO3 )2 = 0.315 𝐿 × 1 × 10−4 𝑀 = 3.15 × 10−5 𝑚𝑜𝑙
𝑉(𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛) = 315 𝑚𝐿 + 315 𝑚𝑙 = 630. 𝑚𝐿 = 0.630 𝐿
[𝐶𝑎2+ ] =
3.15 × 10−5 𝑚𝑜𝑙
= 5 × 10−5 𝑀,
0.630 𝐿
[𝐹 − ] =
3.15 × 10−5 𝑚𝑜𝑙
= 5 × 10−5 𝑀
0.630 𝐿
𝑄 = [𝐶𝑎2+ ][𝐹 − ]2 = 5 × 10−5 × (5 × 10−5 )2 = 1.25 × 10−13 < 3.4 × 10−11
𝑄 < 𝐾𝑠𝑝 , no precipitation
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3. You have two salts, AgX and AgY, with very similar Ksp values. You know that Ka for HX is
much greater than Ka for HY. Which statement will be true?
a) AgX and AgY are less soluble in acidic solution than in pure water.
b) AgX is more soluble in acidic solution.
c) AgX and AgY are equally soluble in acidic solution.
d) AgY is more soluble in acidic solution.
4. Solid KCN is added to a solution composed of 0.10 M Ag+ and 0.10 M Zn2+ just until a
precipitate forms. What is the composition of this initial precipitate? 𝐾𝑠𝑝 (AgCN) = 2.2 × 10−16
and 𝐾𝑠𝑝 ( Zn(CN)2 ) = 3 × 10−16 .
a) The precipitate is pure Zn(CN)2.
b) The precipitate is pure AgCN.
c) The precipitate is a mixture of AgCN and Zn(CN)2.
d) The precipitate is a mixture of KCN and AgCN.
[𝐶𝑁 − ] =
𝐾𝑠𝑝 (AgCN) 2.2 × 10−16
=
= 2.2 × 10−15 𝑀
[𝐴𝑔+ ]
0.10
[𝐶𝑁 − ] = √
𝐾𝑠𝑝 (Zn(𝐶𝑁)2 )
3 × 10−16
√
=
= 5.5 × 10−8 𝑀
[𝑍𝑛2+ ]
0.10
If [𝐶𝑁 − ] < 2.2 × 10−15 𝑀, then no precipitation occurs
If 2.2 × 10−15 𝑀 < [𝐶𝑁 − ] < 5.5 × 10−8 𝑀, then AgCN precipitates, but Zn(CN)2 does not.
If [𝐶𝑁 − ] > 5.5 × 10−8 𝑀, both AgCN and Zn(CN)2 precipitate.
Since KCN was added just until an initial precipitate forms, its composition must be pure AgCN.
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5. An aqueous solution of Ag(CN)−
2 is made by combining 0.0100 moles AgNO3 with 1.00 mole
NaCN and diluting to 1.000 L. What is the molar concentration of Ag+ in the solution?
−
−
18
Ag +
(𝑎𝑞) + 2 CN(𝑎𝑞) ⇄ Ag(CN)2(𝑎𝑞) , 𝐾𝑓 = 5.6 × 10
a) 0.010 M
b) 𝟏. 𝟗 × 𝟏𝟎−𝟐𝟏 𝑴
c) 5.8 × 1016 𝑀
d) 1.7 × 10−17 𝑀
−
−
Ag +
(𝑎𝑞) + 2 CN(𝑎𝑞) ⇄ Ag(CN)2(𝑎𝑞)
0
0.98
0.0100
Change (M): +𝑥
+2𝑥
−𝑥
Initial (M):
Equilibrium (M):
𝐾𝑓 =
𝑥
0.98 + 2𝑥
0.0100 − 𝑥
[Ag(CN)−
0.0100 − 𝑥
0.0100
2]
=
≈
= 5.6 × 1018
+
−
2
2
[Ag ][CN ]
𝑥(0.98 + 2𝑥)
𝑥(0.98)2
𝑥 = [Ag + ] = 1.9 × 10−21 𝑀
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