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E-12
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 1.0 mL of 1.0 M Pb(NO3)2 with 1.0 mL of
1.0 M NaCl in an 18 x 150 mm test tube (the medium size). Record your observations.
2.
Add 10 drops of 0.50 M Na2CrO
4
to the above test tube. The 10 drops are approximately equal to 0.5 mL
volume. Record your observations.
3.
Next, add 2.0 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 1.0 mL of
1.0 M Pb(NO3)2 with 2.0 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 1.0 mL of 0.50 M Na2CrO
4
to the test tube. What do you observe?
Record your observations.
5.
Next add 1.0 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 2 minutes 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
one 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.
