CHEMISTRY 12 – DETERMINING SOLUBILITY, SOLUBILITY EQUATIONS, SELECTIVE
PREIPITATION & QUALITATIVE ANALYSIS WORKSHEET
1) Determine whether the following salts are high solubility or low solubility: (1 mark each)
(a) CuI2
high
(b) Na2CO3
high
(c) NH4Cl
high
(d) Ba(OH)2
low
(e) KNO3
high
(f) (NH4)3PO4
high
(g) Al2S3
low
(h) PbSO4
low
(i) CuCl
low
(j) PbBr2
low
(k) MgS
high
(l) Be(OH)2
low
(m) (NH4)2SO3
high
(n) CuI2
high
(o) BaS
high
(p) Sr(OH)2
high
(q) PbCl2
low
(r) Fe3(PO4)2
low
(s) SrSO4
low
(t) K2S
high
2) For the following combinations, identify (place a ü) whether a precipitate is produced or not: (1
mark each)
ppt forms
ppt does not form
ü
(a)
NaBr
&
AgNO3
(b)
KCl
&
FeSO4
ü
(c)
(NH4)2SO4
&
K2CO3
ü
(d)
KOH
&
CaCl2
(e)
MgI2
&
SrS
(f)
BaCl2
&
AlPO4
(g)
NH4Cl
&
CuSO4
(h)
AgNO3
&
Sr(OH)2
(i)
CaCl2
&
MgS
(j)
Na2CO3
&
BeS
ü
(k)
AlBr3
&
Cu2SO4
ü
ü
ü
ü
ü
ü
ü
3) Write a formula equation, complete ionic equation and net ionic equation for the following reactions:
(3 marks each)
(a) Na2SO3 (aq) + CaBr2 (aq) → ?
Na2SO3 (aq) + CaBr2 (aq) → 2 NaBr (aq) + CaSO3 (s)
2 Na+ (aq) + SO32- (aq) + Ca2+ (aq) + 2 Br- (aq) → 2 Na+ (aq) + 2 Br- (aq) + CaSO3 (s)
Ca2+ (aq) + SO32- (aq) → CaSO3 (s)
(b) Bi(NO3)3 (aq) + NaOH (aq) → ?
Bi(NO3)3 (aq) + 3 NaOH (aq) → Bi(OH)3 (s) + 3 NaNO3 (aq)
Bi3+ (aq) + 3 NO3- (aq) + 3 Na+ (aq) + 3 OH- (aq) → Bi(OH)3 (s) + 3 Na+ (aq) + 3 NO3- (aq)
Bi3+ (aq) + 3 OH- (aq) → Bi(OH)3 (s)
(c) Pb(C2H3O2)2 (aq) + K2SO4 (aq) → ?
Pb(C2H3O2)2 (aq) + K2SO4 (aq) → PbSO4 (s) + 2 KC2H3O2 (aq)
Pb2+(aq) + 2 C2H3O2- (aq) + 2 K+ (aq) + SO42- (aq) → PbSO4 (s) + 2 K+ (aq) + 2 C2H3O2- (aq)
Pb2+(aq) + SO42- (aq) → PbSO4 (s)
(d) FeSO4 (aq) + (NH4)2S (aq) → ?
FeSO4 (aq) + (NH4)2S (aq) → FeS (s) + (NH4)2SO4 (aq)
Fe2+ (aq) + SO42- (aq) + 2 NH4+ (aq) + S2- (aq) → FeS (s) + 2 NH4+ (aq) + SO42- (aq)
Fe2+ (aq) + S2- (aq) → FeS (s)
(e) K2CO3 (aq) + Sr(NO3)2 (aq) → ?
K2CO3 (aq) + Sr(NO3)2 (aq) → 2 KNO3 (aq) + SrCO3 (s)
2 K+(aq) + CO32- (aq) + Sr2+(aq) + 2 NO3- (aq) → 2 K+ (aq) + 2 NO3- (aq) + SrCO3 (s)
Sr2+(aq) + CO32- (aq) → SrCO3 (s)
(f) CuSO4 (aq) + FeCl3 (aq) → ?
3 CuSO4 (aq) + 2 FeCl3 (aq) → 3 CuCl2 (aq) + Fe2(SO4)3 (aq)
3 Cu2+(aq) + 3 SO42-(aq) + 2 Fe3+(aq) + 6 Cl-(aq) → 3 Cu2+(aq) + 6 Cl-(aq) + 2 Fe3+(aq) + 3 SO42-(aq)
There is no net ionic equation since no precipitate is produced
(g) NaI (aq) + AgNO3 (aq) → ?
NaI (aq) + AgNO3 (aq) → NaNO3 (aq) + AgI (s)
Na+(aq) + I-(aq) + Ag+(aq) + NO3-(aq) → Na+(aq) + NO3-(aq) + AgI (s)
Ag+(aq) + I-(aq) → AgI (s)
(h) Al2(SO4)3 (aq) + CaCl2 (aq) → ?
Al2(SO4)3 (aq) + 3 CaCl2 (aq) → 2 AlCl3 (aq) + 3 CaSO4 (s)
2 Al3+(aq) + 3 SO42-(aq) + 3 Ca2+(aq) + 6 Cl-(aq) → 2 Al3+(aq) + 6 Cl-(aq) + 3 CaSO4 (s)
Ca2+(aq) + SO42-(aq) → CaSO4 (s) since the 3 coefficients that are in front of all of the chemical
species can be removed so that the reaction is written in lowest terms
4) A solution is prepared by mixing equal moles of Ba(NO3)2, K2SO4 and BaS and precipitation occurs.
Identify the precipitate(s) and write the net ionic equation(s) for the reaction(s). (2 marks)
Solve this question by finding all of the new possible combinations between cations and anions and
then finding which of these will produce a low solubility salt. The only combination that produces a
precipitate is BaSO4 (s) therefore the net ionic equation is Ba2+(aq) + SO42- (aq) → BaSO4 (s).
5) Identify a cation that could be added to an aqueous mixture containing SO42- and S2- to separate the
ions by precipitating one of them? (1 mark)
Ca2+, Ba2+ or Sr2+
6) Identify a solution that could be used to separate the cations Al3+ and Ba2+ from each other by
precipitation? (1 mark)
Since the question specifies a “solution”, the answer needs to be a molecule. The answer would be
SO42- or S2- combined with an alkali ion, for example Na2SO4 or Na2S.
7) Identify a solution that could be used to separate the anions SO42- and CO32- from each other by
precipitation? (1 mark)
Since the question specifies a “solution”, the answer needs to be a molecule. There are a lot of
possible answers for this question. The answer would be anything other than an alkali ion, H+, NH4+
(since those 3 do not produce precipitates with either of the anions), Ag+, Ca2+, Sr2+, Ba2+ or Pb2+
(since those would produce precipitates with both of the anions) combined with NO3-, for example
Al(NO3)3.
8) A solution is prepared containing both 0.2 M OH- and 0.2 M PO43- ions. An equal volume of a
second solution is added in order to precipitate only one of these anions. Identify a cation that the
second solution must contain? (1 mark)
Sr2+
9) Devise a scheme to individually precipitate and remove the cations from a solution containing Mg2+,
Sr2+ and Pb2+. As a part of your scheme, provide the compounds added, the net ionic equations and
the method of removal. (4 marks)
Your table should look like this:
Mg2+
Sr2+
Pb2+
Cl✖
SO42✖
S2✖
✖
ppt
ppt
✖
OHppt
✖
ppt
ppt
ppt
CO32ppt
ppt
ppt
Having the correct order of adding the chemicals is worth 1 mark, saying “filter & continue” is
worth 1 mark, having the correct net ionic equations is worth 1 mark and having the correct
compounds is worth 1 mark.
For example:
Step 1: Add NaCl (Pb2+ (aq) + 2 Cl- (aq) → PbCl2 (s)) then filter & continue
Step 2: Add Na2SO4 (Sr2+ (aq) + SO42- (aq) → SrSO4 (s)) then filter & continue
Step 3: Add NaOH (Mg2+ (aq) + 2 OH- (aq) → Mg(OH)2 (s))
10) Devise a scheme to individually precipitate and remove the cations from a solution containing OH-,
S2- and Br-. As a part of your scheme, provide the compounds added, the net ionic equations and the
method of removal. (4 marks)
There are a lot of possible answers to this question, but this is one example.
Your table should look like this:
OHS2Br-
Ag+
ppt
ppt
ppt
Be2+
ppt
✖
✖
Al3+
ppt
ppt
✖
Having the correct order of adding the chemicals is worth 1 mark, saying “filter & continue” is
worth 1 mark, having the correct net ionic equations is worth 1 mark and having the correct
compounds is worth 1 mark.
Step 1: Add Be(NO3)2 (Be2+ (aq) + 2 OH- (aq) → Be(OH)2 (s)) then filter & continue
Step 2: Add Al(NO3)2 (2 Al3+ (aq) + 3 S2- (aq) → Al2S3 (s)) then filter & continue
Step 3: Add AgNO3 (Ag+ (aq) + Br- (aq) → AgBr (s))
11) A solution contains the cations Pb2+, Ba2+ and Fe2+. Devise a scheme to individually precipitate two
of the cations and separate them from the solution. As part of your answer, provide the compounds
added, the net ionic equations and the method of removal. (4 marks)
Your table should look like this:
Pb2+
Ba2+
Fe2+
Clppt
✖
✖
SO42ppt
ppt
✖
S2ppt
✖
ppt
OHppt
ppt
ppt
CO32ppt
ppt
ppt
Having the correct order of adding the chemicals is worth 1 mark, saying “filter & continue” is
worth 1 mark, having the correct net ionic equations is worth 1 mark and having the correct
compounds is worth 1 mark.
Step 1: Must be to remove the Pb2+ therefore add NaCl (Pb2+ (aq) + 2 Cl- (aq) → PbCl2 (s)) then filter &
continue
Step 2: Could be to either remove the Ba2+ therefore add Na2SO4 (Ba2+ (aq) + SO42- (aq) → BaSO4 (s))
then filter & continue or could be to remove the Fe2+ therefore add Na2S (Fe2+ (aq) + S2- (aq) → FeS (s))
then filter & continue
Since the questions says to only remove two of the cations, it is allowable to leave the third cation in
the solution
12) An experiment is conducted to identify an unknown cation that is present in each of four beakers.
(1 mark)
Which of the
following could be
the unknown cation?
Ag+
Ba2+
Fe3+
Be2+
13) A reagent that may be used to separate Cl- from S2- by precipitation is (1 mark):
A
KNO3
C
Pb(NO3)2
B
AgNO3
D
Al(NO3)3
14) A solution contains both Ag+ and Mg2+ ions. During selective precipitation, these ions are removed
one at a time by adding (1 mark)
A
OH- followed by S2-
C
SO42- followed by Cl-
B
I- followed by OH-
D
NO3- followed by PO43-
15) A precipitate forms when a 0.20 M solution containing an unknown cation is added to SO42-, but not
when an equal volume is added to S2-.
What is the possible identity of the
unknown cation? (1 mark)
Ca2+, Sr2+ or Ba2+
16) A solution contains 0.2 M Zn2+ and 0.2 M Sr2+. An equal volume of a second solution was added,
forming a precipitate with Sr2+ but not with Zn2+. What is present in the second solution? (1 mark)
SO4217) A solution containing an unknown cation was added to three solutions and the following
observations were recorded:
What is the identity of the unknown cation? (1 mark)
Sr2+
18) Consider the following experiment:
What anion could the unknown solution
contain? (1 mark)
Cl-, Br-, I-, S2- or OH-