CHM202 General Chemistry and Laboratory II
Laboratory 8
Inorganic Qualitative Analysis
Name
Section
Group
Unknown #
Results
1. Tests for Silver (I) Ion (Group I)
Start with
30 drops of
sample [1.2]
2 Drops
6M HCl
[1.2]
No Precipitate
Precipitate
Known - Contact
Instructor
Unknown - Go to
2.1 (test for Cu2+)
[1.3]
Centrifuge
then add
1 drop 6M HCl
[1.3]
Centrifuge and
separate solid
and solution
[1.4]
Solid
Add 6 drops
6M NH3, mix
[1.5]
Ag+ ID - White ppt?
Known
Unknown
Additional
Precipitate?
Repeat 1.3
until no more
ppt is observed
[1.3]
Some solid remains
Add 3 drops NH3
[1.5]
Solution
Save for 2.1
[1.4]
Centrifuge and
Solution
Ag+ Confirm.
separate solid
and solution
[1.6]
Add 6M HNO3
Precipitate should
form [1.6]
Known
Unknown
The known solution tested
positive for silver (I) ion
YES
NO
The unknown solution tested
positive for silver (I) ion
YES
NO
2. Tests for Copper (II) Ion (Group II)
Start with
solutions from
1.3 or 1.4
Add 6M NH3
until basic [2.1]
Estimate volume
+ .6mL; add 1 drop
HCl per mL of soln
Test pH< 2
[2.2]
Add 12 drops TA
Heat 8-10 min
[2.3]
Cu+2 ID - Black ppt?
Known
No Precipitate
Known - Contact
Instructor
Unknown - Go to
3.1 (test for Zn2+)
[2.4]
Solid
Add 20 drops
6M HNO3
Heat 2-3 min
Centrifuge and
separate [2.7]
Unknown
Precipitate
Centrifuge
separate solid
and solution
[2.4]
Solution
Add 3 drops TA
Heat 5 minutes
Centrifuge if ppt
Combine solid with
solid from 2.4 [2.5]
Combined Solids
Add 20 drops of
Distilled Water, Mix
Centrifuge/separate [2.6]
Solution
Save for 3.1
[2.5]
Solution
Add 6M NH3
until basic,
add 6M HOAc
until acidic
[2.8]
Est. vol.
+ 0.6 mL
drops of HCl =
pH <2?
(If not add more HCl)
Solution
Discard
to waste [2.6]
Cu2+ Confirm.
Add 10 drops of K4Fe(CN)6
Red-brown ppt confirms Cu2+
Heat content 3 min if no ppt. [2.9]
Known
Unknown
The known solution tested
positive for copper (II) ion
YES
NO
The unknown solution tested
positive for copper (II) ion
YES
NO
3. Test for Zinc Ion (Group III)
Start with solutions
from 2.4 or 2.5
Add 10 drops 6M HCl
Add 6M NH3 until
basic [3.1]
Add 12 drops
Thioacetamide
Heat 8-10 min [3.3]
No Precipitate
Known - Contact
Instructor
Unknown - Go to
4.1 (test for Ca2+)
[3.4]
Zn2+ ID - White ppt?
Known
Unknown
Precipitate
Centrifuge
separate solid
and solution
[3.4]
Solution
Add 3 drops TA
Heat 5 minutes
Centrifuge if ppt
Combine solid with
solid from 3.4 [3.5]
Combined Solids
Add 20 drops of
Water + 2 drops of
6M NH3, Mix, Centrifuge
and Separate [3.6]
Solution
Save for 4.1
[3.5]
Solid Add 20
drops 6M HNO3
Heat 2-3 min
Centrifuge and
separate [3.7]
Add 5 drops
6M NH3
pH must be > 9
If not add more
NH3 [3.2]
Add 6M NH3
until basic,
add 6M HOAc
until acidic
[3.8]
Solution
Discard to
waste [3.6]
Zn2+ Confirm.
Add 10 drops of K4Fe(CN)6
White ppt confirms Zn2+ [3.9]
Heat 3 min if no ppt.
Known
Unknown
The known solution tested
positive for zinc (II) ion
YES
NO
The unknown solution tested
positive for zinc (II) ion
YES
NO
4. Tests for Calcium Ion (Group IV)
Start with
solutions from
3.4 or 3.5 [4.1]
Add 10 drops
3M (NH4)2CO3
[4.1]
Ca2+ ID - White ppt?
Known
Unknown
No Precipitate
Known - Contact
Instructor
Unknown - Test
Complete (neg.
for Ca2+) [4.1]
Precipitate
Centrifuge
Separate solid
Add 10 drops
water, mix, Centrifuge
Separate solid [4.2]
Solution
Add 6M NH3
until basic
[4.4]
Ca2+ Confirm.
Add 10 drops K4Fe(CN)6 or
Add 10 drops K2C2O4
White ppt? If no, heat [4.4]
White ppt? [4.5]
If a white precipitate forms from either confirmation
test then calcium ion was present in the solution.
Known
Solid
Add 5 drops
6M HOAc or
more if not
dissolved [4.3]
Unknown
The known solution tested
positive for calcium ion
YES
NO
The unknown solution tested
positive for calcium ion
YES
NO
Questions
1.
Write the Ksp expression for each of the precipitation reactions used to identify each group and
calculate the concentration of the anion required to precipitate a 0.1 M cation solution for each
of these.
2.
Predict if the following conditions would result in the formation of a precipitate:
a) 0.0025 M Fe3+ at pH 6.00
b) 0.0025 M Ba2+ and a 1.25 x 10-4 M solution of sodium sulfate
c) 0.05 M Ca2+ and a 1.25 x 10-4 M solution of cesium phosphate
3. Determine the equilibrium concentration of the following:
a) The cobalt ion concentration of a saturated solution of CoS
b) The pH of a saturated Zn(OH)2 solution
c) The lead (II) ion concentration of a saturated solution of PbCl 2.