SKOOG - SOLUCIONÁRIO CAPÍTULO 12

Prévia do material em texto

Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
Chapter 12 
12-1 (a) A colloidal precipitate consists of solid particles with dimensions that are less than 
10-4 cm. A crystalline precipitate consists of solid particles with dimensions that at least 
10-4 cm or greater. As a consequence, crystalline precipitates settle rapidly, whereas 
colloidal precipitates remain suspended in solution unless caused to agglomerate. 
(b) In gravimetric precipitation, the analyte is converted to a sparing soluble precipitate, 
which is then filtered, washed free of impurities, and then converted into a product of 
known composition by suitable heat treatment. In gravimetric volatilization, the analyte 
is separated from other sample constituents by converting it to a gas of known 
composition. 
(c) Precipitation is the process by which a solid phase forms and is carried out of solution 
when the solubility product of a chemical species is exceeded. Coprecipitation is a 
process in which normally soluble compounds are carried out of solution by precipitate 
formation. 
(d) Coagulation, or agglomeration, is the process by which colloidal particles coalesce to 
form larger aggregates. Peptization refers to the process by which a coagulated colloid 
reverts to its original dispersed state. Heating, stirring and adding an electrolyte can 
coagulate colloidal suspensions. Washing the coagulated colloid with water often 
removes sufficient electrolyte to permit the re-establishment of repulsive forces that favor 
return to the colloidal state. 
(e) Occlusion is a type of coprecipitation in which a compound is trapped within a pocket 
formed during rapid crystal formation. Mixed-crystal formation is also a type of 
coprecipitation in which a contaminant ion replaces an ion in the crystal lattice. 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
(f) Nucleation is a process in which a minimum number of atoms, ions or molecules 
associate to give a stable solid. Particle growth is a process by which growth continues 
on existing nuclei. Precipitation by nucleation results in a large number of small particles. 
Precipitation by particle growth results in a smaller number of large particles. 
12-2 (a) Digestion is a process in which a precipitate is heated in the presence of the solution 
from which it was formed (the mother liquor). Digestion improves the purity and 
filterability of the precipitate. 
(b) Adsorption is the process by which ions are retained on the surface of a solid. 
(c) In reprecipitation, the filtered solid precipitate is redissolved and reprecipitated. 
Because the concentration of the impurity in the new solution is lower, the second 
precipitate contains less coprecipitated impurity. 
(d) Precipitation from a homogeneous solution is a technique by which a precipitating 
agent is generated in a solution of the analyte by a slow chemical reaction. Local reagent 
excess does not occur and the resultant solid product is better suited for analysis than 
precipitate formed by direct addition of precipitating reagent. 
(e) The counter-ion layer describes a layer of solution containing sufficient excess 
negative ions that surrounds a charged particle. This counter-ion layer balances the 
surface charge on the particle. 
(f) Mother liquor is the solution from which a precipitate is formed. 
(g) Supersaturation describes an unstable state in which a solution contains higher solute 
concentration than a saturated solution. Supersaturation is relieved by precipitation of 
excess solute. 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
12-3 A chelating agent is an organic compound that contains two or more electron-donor 
groups located in such a configuration that five- or six-membered rings are formed when 
the donor groups complex a cation. 
12-4 Relative supersaturation can be regulated through control of reagent concentration, 
temperature and the rate at which reagents are combined. 
12-5 (a) There is positive charge on the surface of the coagulated colloidal particles. 
(b) The positive charge arises from adsorbed Ag+ ions. 
(c) -3NO ions make up the counter-ion layer. 
12-6 SHCONHCHOHCSNHCH 223243 ++ ←→ 
The slow hydrolysis of thioacetamide can be used to generate a source of hydrogen 
sulfide gas. Hydrogen sulfide gas is then involved in the equilibria below: 
−+
←
→−
−+
←
→
++
++
2
32
322
SOHOHHS
HSOHOHSH
 
The S2- generated can then be used to precipitate Ni2+ in the form of NiS. 
12-7 Peptization is the process by which a coagulated colloid returns to its original dispersed 
state as a consequence of a decrease in the electrolyte concentration of the solution in 
contact with the precipitate. Peptization can be avoided by washing the coagulated 
colloid with an electrolyte solution rather than pure water. 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
12-8 Chloroplatinic acid, H2PtCl6, forms the precipitate K2PtCl6 when mixed with K+ but does 
not form analogous precipitates with Li+ and Na+. Thus, chloroplatinic acid can be used 
to separate K+ from a mixture containing Li+ and Na+. 
12-9 Note: M stands for molar or atomic mass in the equations below: 
(a) 
4
2
BaSO
SO
42 BaSOmassSOmass M
M×= 
(b) 
722 OPMg
Mg
722
2
OPMgmassMgmass
M
M×= 
(c) 
32OIn
In
32
2OInmassInmass
M
M×= 
(d) 
62PtClK
K
62
2PtClKmassKmass
M
M×= 
(e) 
22 )SCN(Cu
Cu
22
2)SCN(CumassCumass
M
M×= 
(f) 
43
2
OMn
MnCl
432
3
OMnmassMnClmass
M
M×= 
(g) 
2
43
PbO
OPb
243 3
PbOmassOPbmass
M
M×= 
(h) 
52
1122
OP
OPU
521122 OPmassOPUmass M
M×= 
(i) 
32
2742
OB
OH10OBNa
322722 2
OBmassOH10OBNamass
M
M ⋅×=⋅ 
(j) 
OH6)OHC()UO(NaZn
ONa
29232322
2923232
2
2
OH6)OHC()UO(NaZnmassONamass
⋅
×⋅=
M
M
 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
12-10 
%59.60%100
sampleimpureg2500.0
mole
KClg55.74
AgClmole1
KClmole1
g32.143
AgClmole1AgClg2912.0
mole
g55.74
mole
g32.143
KClAgCl
=×
⎟⎠
⎞⎜⎝
⎛×⎟⎟⎠
⎞
⎜⎜⎝
⎛×⎟⎟⎠
⎞
⎜⎜⎝
⎛×
== MM
 
12-11 
mole
g15.237
mole
g96.101
24432 )SO(AlNHOAl
== MM 
(a) 
244
244
244
244
3
244
3
32
244
32
32
32
)SO(AlNH%102%100
g910.0
)SO(AlNHmole
)SO(AlNHg15.237)SO(AlNHmole10925.3
)SO(AlNHmole10925.3
OAlmole
)SO(AlNHmole2
OAlg96.101
OAlmole1OAlg2001.0
=×
××
×=××
−
−
 
(b) 3232 OAl%0.22%100sampleimpureg910.0
OAlg2001.0 =× 
(c) 
Al%6.11%100
sampleimpureg910.0
mole
Alg981.26Almole10925.3
mole10925.3)SO(AlNHmole.noAlmole.no
2
3
244
=×
××
×==
−
−
 
12-12 
23
23
23
24
23
24
24
24
)IO(Cug828.0
)IO(Cumole1
)IO(Cug35.413
OH5CuSOmole1
)IO(Cumole1
OH5CuSOg67.249
OH5CuSOmole1OH5CuSOg500.0
=×
⋅×⋅
⋅×⋅
 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
12-13 
3
3
3
23
3
24
23
24
24
24
KIOg342.0
KIOmole1
KIOg214
)IO(Cumole1
KIOmole2
OH5CuSOmole1
)IO(Cumole1
OH5CuSOg67.249
OH5CuSOmole1OH5CuSOg2000.0
=××
⋅×⋅
⋅×⋅
 
12-14 (Note: In the first printing of the text, the answer in the back of the book was in error.) 
AgIg178.0
AgImole
AgIg773.234AgImole1057.7
AgImole1057.7
AlImole1
AgImole3
AlIg770.407
AlImole1AlI201.0sampleg512.0AgImole.no
4
4
33
3
3
=××
×=×××=
−
−
 
12-15 The precipitate V2O5·2UO3 gives the greatest mass from a given quantity of uranium. 
12-16 322332 AlCl2OH3CO3HCl6)CO(Al +++ ←→ 
Al%60.2%100
sampleimpureg8102.0
Alg02105.0
Alg02105.0
Almole
Alg98.26
)CO(Almole1
Almole2
COmole3)CO(Almole1
COg01.44
COmole1COg0515.0
3322
332
2
2
2
=×
=
××××
 
12-17 42 CdSOO2CdS ←
→+ 
mole1061.5
CdSOmole1
CdSmole1
g47.208
CdSOmole1CdSOg117.0CdSOmole.noCdSmole.no
4
4
4
44
−×=
××==
 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
The number moles H2S is equal to number moles CdS. 
SH%025.0%100
sampleimpureg0.75
SHg0191.0
g0191.0
SHmole1
SHg08.34mole1061.5SHmass
2
2
2
24
2
=×
=××= −
 
12-18 
C%23.17%100
sampleg2121.0
Cmole1
Cg011.12
BaCOmole1
Cmole1
g34.197
BaCOmole1BaCOg6006.0
3
3
3
=×
×××
 
12-19 
5914
5914
59145914
ClHC%589.1
%100
sampleg000.5
ClHCmole1
ClHCg72.354
AgClmoles5
ClHCmole1
g37.143
AgClmole1AgClg1606.0
=
×
×××
 
12-20 (Note: In the first printing of the text, the answer in the back of the book was in error.) 
22
22
22
2
2223
23
265
2
265
265
265
2
ClHg%16.41%100
sampleg8142.0
ClHgmole1
ClHgg09.472
Hgmole2
ClHgmole1Hgmol104198.1
Hgmol104198.1
)IO(Hgmole1
Hgmole5
)IO(Hgg75.1448
)IO(Hgmole1)IO(Hgg4114.0
Hgmol
=×
⎟⎟⎠
⎞
⎜⎜⎝
⎛ ×××
×=××
=
+
+−
+−
+
+
 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
12-21 
KI%12.2
%100
sampleimpureg97.1
mole
KIg00.166
)IO(Bamole1
KImole2
g13.487
)IO(Bamole1)IO(Bag0612.0
mole
g00.166
mole
g13.487
23
23
23
KI)IO(Ba 23
=
×
⎟⎠
⎞⎜⎝
⎛×⎟⎟⎠
⎞
⎜⎜⎝
⎛×⎟⎟⎠
⎞
⎜⎜⎝
⎛×
== MM
 
12-22 
3
33
PtNH
NH%74.38%100
sampleimpureg2115.0
mole
NHg0306.17
Ptmole1
NHmole2
g08.195
Ptmole1Ptg4693.0
mole
g08.195
mole
g0306.17
3
=×
⎟⎠
⎞⎜⎝
⎛×⎟⎟⎠
⎞
⎜⎜⎝
⎛×⎟⎟⎠
⎞
⎜⎜⎝
⎛×
== MM
 
12-23 
3
33
2
2
3
32
22
AlClMnO
AlCl%24.26
%100
sampleimpureg1402.1
mole
AlClg34.133
Clmole3
AlClmole1
MnOmole1
Clmole2MnOmol10366.3
mol10366.3
g94.86
MnOmole1)MnOg3521.0g6447.0(MnOmol
mole
g34.133
mole
g94.86
32
=
×
⎟⎟⎠
⎞
⎜⎜⎝
⎛ ⎟⎠
⎞⎜⎝
⎛×⎟⎟⎠
⎞
⎜⎜⎝
⎛×⎟⎟⎠
⎞
⎜⎜⎝
⎛××
×=⎟⎟⎠
⎞
⎜⎜⎝
⎛×−=
==
−
−
MM
 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
12-24 Let Sw = mass of sample in grams 
sampleg412.0
%20
%100
mole
SOg064.96SOmole1057.8
samplegS
SO%20%100
samplegS
mole
SOg064.96SOmole1057.8
SOmole1057.8
BaSOmole1
SOmole1
g39.233
BaSOmole1BaSOg200.0
mole/g064.96mole/g39.233
2
42
4
4
w
2
4
w
2
42
4
4
2
4
4
4
2
44
4
SOBaSO 244
=
×××
=
==
××
×=××
==
−
−−
−
−
−−
−−
−
−MM
 
The maximum precipitate weight expected given this sample weight, 
4
4
2
4
4
2
4
2
4
BaSOg550.0
mole1
BaSOg39.233
SOg1
BaSOmole1
g064.96
SOmole1
sampleg100
SOg55sampleg412.0
=
×××× −
−−
 
12-25 Let Sw = mass of sample in grams. 
The higher percentage of Ni in the alloy sample is selected because this corresponds to 
maximum amount expected precipitate. 
sampleg102.0
%35
%100
mole
Nig693.58Nimole1006.6
samplegS
Ni%35%100
samplegS
mole
Nig693.58Nimole1006.6
Nimole1006.6
)NOHHC(Nimole1
Nimole1
g92.288
)NOHHC(Nimole1)NOHHC(Nig175.0
mole/g693.58mole/g92.288
4
w
w
4
4
2264
2264
2264
Ni)NOHHC(Ni 2264
=
×××
=
==
××
×=
××
==
−
−
−
MM
 
 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
12-26 
Let Sw = mass of sample in grams 
(a) 
sampleg239.0
%68
%100ZrClg16259.0samplegS
ZrCl%68%100
samplegS
mole1
ZrClg03.233
AgClmole4
ZrClmole1
g32.143
AgClmole1AgClg400.0
mole/g03.233mole/g32.143
4
w
4
w
44
ZrClAgCl 4
=×=
=×
×××
== MM
 
(b) 
AgClg494.0
mole1
AgClg32.143
ZrClmole1
AgClmole4
g03.233
ZrClmole1
sampleg100
ZrClg84sampleg239.0
4
44 =××××
 
(c) 
g406.0
%40
%100ZrClg16259.0samplegS
%40
samplegS
%100ZrClg16259.0ZrCl%
4
w
w
4
4
=×=
=×=
 
 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
 
12-27 
 A B C D 
1 Problem 12-27 
2 
3 Coefficient Matrix Constant Matrix 
4 1.823 1.578 1.505
5 1 1 0.872
6 
7 Inverse Matrix Solution Matrix 
8 4.0816327 -6.4408200 0.526465306
9 -4.0816300 7.4408160 0.345534694
10 
11 Mass of Sample % KBr % NaBr 
12 0.872 39.6 60.4
13 
14 Spreadsheet Documentation 
15 A8:B8=MINVERSE(A4:B5) 
16 D8:D9=MMULT(A8:B9,D4:D5) 
17 C12=100*D9/A12 
18 D12=100*D8/A12 
 
12-28 
 A B C D 
1 Problem 12-28 
2 
3 Coefficient Matrix Constant Matrix 
4 1 1 0.443
5 1 0.6104698 0.3181
6 
7 Inverse Matrix Solution Matrix 
8 -1.5671952 2.5671952 0.122357321
9 2.5671952 -2.5671952 0.320642679
10 
11 Mass of Sample Mass AgCl % Cl % I 
12 0.6407 0.1223573 4.72 27.05
13 
14 Spreadsheet Documentation 
15 A8:B8=MINVERSE(A4:B5) 
16 D8:D9=MMULT(A8:B9,D4:D5) 
17 B12=D4-D9 
18 C12=100*D9/A12 
19 D12=100*D8/A12 
 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
12-29 
52
5252
4
4
4
4
44
44
OPPbMoO
OP%089.2
%100
sampleg1969.0
mole1
OPg94.141
Pmole2
OPmole1
PbMoOmoles12
Pmole1PbMoOmol109565.6
PbMoOmol109565.6
g14.367
PbMoOmole1PbMoOg2554.0PbMoOmol
mole/g94.141mole/g14.367
524
=
×
⎟⎟⎠
⎞
⎜⎜⎝
⎛ ××××
×=×=
==
−
−
MM
 
12-30 
2
2
2
33
2
3232
33
3232
COKMgCOCO
COg498.0
mole1
COg010.44mole0113.0COmass
mole0113.01046.41076.6COmole
g21.138
COKmole1
sampleg100
COKg42sampleg500.1
g31.84
MgCOmole1
sampleg100
MgCOg38sampleg500.1
COKmoleMgCOmoleCOmole
mole/g21.138mole/g31.84mole/g010.44
3232
=×=
=×+×=
⎟⎟⎠
⎞
⎜⎜⎝
⎛ ××
+⎟⎟⎠
⎞
⎜⎜⎝
⎛ ××=
+=
===
−−
MMM
 
12-31 
AgClmole1022804.3
OH6MgClmole1
AgClmoles2OH6MgClmole1061402.1
AgClmole1013268.4
g32.143
AgClmole1AgClg5923.0
OH6MgClmole1061402.1
OPMgmole1
OH6MgClmoles2
g55.222
OPMgmole1OPMgg1796.0
mole/g32.203mole/g44.58mole/g55.222
3
22
22
3
3
22
3
722
22722
722
OH6MgClNaClOPMg 22722
−−
−
−
•
×=⋅ו×
×=×
⋅×
=⋅××
=== MMM
 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
OH6MgCl%69.47
%100
sampleg881.6
mL0.50
mL0.500
mole1
OH6MgClg32.203OH6MgClmole1061402.1
NaClmole100464.9
AgClmole1
NaClmole1AgClmole)10228.31013268.4(
22
22
22
3
433
⋅=
×
×⋅ו×
×=××−×
−
−−−
 
NaCl%68.7%100
sampleg881.6
mL0.50
mL0.500
mole1
NaClg44.58NaClmole100464.9 4
=×
××× −
 
12-32 
,reagentlimitingtheisIOBecause
IOmole10516.1
NaIOmole1
IOmole1
g89.197
NaIOmole1NaIOg300.0
Bamole10188.8
OH2BaClmole1
Bamole1
g26.244
OH2BaClmole1OH2BaClg200.0
mole/g13.487mole/g89.197mole/g26.244
3
3
3
3
33
3
24
22
2
22
22
)IO(BaNaIOOH2BaCl 23322
−
−−
−
+−
+
⋅
×=××
×=
⋅×
⋅×⋅
=== MMM
 
(a) 
23
234
23
4
3
23
)IO(Bag369.0
mole1
)IO(Bag13.487mole10580.7)IO(Bamass
mole10580.7
2
mole10516.1)IO(Bamoles
=××=
×=×=
−
−
−
 
(b) 
( )
OH2BaClg0149.0
mole1
OH2BaClg26.244OH2BaClmole1008.6OH2BaClmass
mole10080.6mole)10580.7()10188.8(remainingOH2BaClmole
22
22
22
5
22
544
22
⋅=
⋅×⋅×=⋅
×=×−×=⋅
−
−−−
 
Fundamentals of Analytical Chemistry: 8th ed. Chapter 12 
12-33 
,reagentlimitingtheisAgBecause
CrOAgg5125.0
mole1
CrOAgg730.331
CrOKmole1
CrOAgmole1
g190.194
CrOKmole1CrOKg300.0
CrOAgg4882.0
mole1
CrOAgg730.331
AgNOmole2
CrOAgmole1
g873.169
AgNOmole1AgNOg500.0
mole/g190.194mole/g730.331mole/g873.169
42
42
42
4242
42
42
42
3
423
3
CrOKCrOAgAgNO42423
+
=
×××
=
×××
=== MMM
 
(a) 4242 CrOAgg488.0CrOAgmass = 
(b) 
( )
42
42
42
5
42
533
42
CrOKg0142.0
mole1
CrOKg190.194CrOKmole10331.7CrOKmass
mole10331.7mole)10472.1()10545.1(remainingCrOKmole
=
××=
×=×−×=
−
−−−