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E-11
Once the precipitates have settled
(i.e. after 15 minutes), compare the heights of the precipitates in these
3 test
tubes. Record the results on
your Observations Sheet, including the height (in
millimeters) of the precipitate in
the test tubes, for Parts II A.1,
II A.2, and II A.3. Empty these test tubes
into the toxic waste beaker, and rinse
the tubes with water.
B.
Relative Solubility of Pb(NO3)2,
PbCl2 , PbCrO
4
and PbS.
1.
Using automatic dispensers, combine
0.5 mL of 1.0 M Pb(NO3)2
with 0.5 mL of
1.0 M
NaCl in an 18
x 150
mm test tube (the medium size). Record your observations.
2.
Add 5 drops of 0.50
M Na2CrO
4
to the above test tube. The
5 drops are approximately equal to 0.25 mL
volume. Record your observations.
3.
Next, add 1.0 mL of 1.0
M Na2S to the test tube containing
the solution and precipitate from II B.2 above.
Stir vigorously. Record your
observations.
4.
Determine if these reactions will
occur in the reverse order. Do this by combining 0.50 mL of
1.0 M Pb(NO3)2
with 1.0 mL of 1.0 M Na2S
in a second clean 18
x 150
mm test tube. Mix the contents of
the test tube thoroughly and then
add 0.5 mL of 0.50 M Na2CrO
4
to the test tube. What do
you observe?
Record your observations.
5.
Next add 0.5 mL of 1.0
M NaCl to the solution in the above test tube (step B 4.)
Record your observations
Immediately dispose of these solutions
and precipitates in the toxic waste container in the fume
hood. Do not keep these waste
solutions at your bench!
Part III. Effect of Temperature
on Equilibrium Involving Cobalt(II) Complex Ions
Use the demonstration sealed tubes
of the 0.40 M cobalt(II) equilibrium solution
(containing both [CoCl
4
]²
-
(aq)
and [Co(H2O)
6
]
2+
(aq)
) found on
the Instructor’s bench, to perform the experiment below.
Record the colour of
the solution on your observation
sheet. Keep one test tube of the solution at room temperature to
use for a
reference colour.
Place the second test tube containing
the cobalt(II) equilibrium solution in an ice bath prepared in a 100 mL
beaker and allow 1 minute for the
temperature of the solution to decrease. Record your observations.
Put the third test tube of the
cobalt(II) equilibrium solution into the hot water bath set up for general
use. Allow
1 minute for the temperature of
the solution to increase, then record your observations.
Determine whether the colour changes
are reversible. On your Observations Sheet, describe how you tested
for
this.
EMPTY YOUR TOXIC WASTE BEAKER
INTO THE DESIGNATED TOXIC WASTE CONTAINER
IN THE FUMEHOOD.
Wash all
your glassware thoroughly before returning
it to your drawer. Remember to turn in the
original copy
of the Observations Sheet to your
laboratory instructor before leaving.
