PERFORMED NOV 26, 2014
BLOCK C
NAME: MISTER ZHAI
PARTNER: OBAMA SELF
LAB # 88C DETERMINATION OF A SOLUBILITY PRODUCT CONSTANT
1. PURPOSE
The purpose of this lab is to determine the solubility product constant of PbI
2
at room temperature and higher temperatures.
2. APPARATUS & MATERIALS
Refer to page 220 of Heath lab manual. Bunsen Burner was replaced by a hot plate.
3. PROCEDURE
Refer to page 220 of Heath lab manual.
4. DATA TABLE
Test Tube #
Volume of 0.010M Pb(NO
3
)
2
(mL)
Volume of water added (mL)
Volume of 0.020M KI (mL)
1 2 3 4 5 6
10.0 8.0 6.0 4.0 3.0 2.0
0.0 2.0 4.0 6.0 7.0 8.0
10.0 8.0 6.0 4.0 3.0 2.0
Volume of water added (mL) 0.0 2.0 4.0 6.0 7.0 8.0
Precipitate or no precipitate (at room yes yes yes yes no no temperature)
Temper ature at which precipitate dissolves (°C)
85 75 65 31 - -
5. OBSERVATIONS
Yellow precipitation formed immediately upon combining the two solutions in Test
Tubes A, B and C. Upon further inspection, a very faint yellow precipitate could also be seen in Test Tube D if examined carefully or placed against a dark background.
In A and B, the solution became cloudy, C contained scattered yellow crystals throughout a clear solution and D was similar to C but with much fewer crystals. Test
Tubes E and F did not precipitate even after they were shaken. A hot plate was used instead of a Bunsen Burner and the heat was set to 10. A thermometer was placed in the beaker in a position to ensure that it was measuring the temperature of the water inside the beaker and not the temperature of the hot plate. Test Tube D was completely clear once the temperature reached 31 °C. After about 2 minutes, the precipitate in Test Tubes A, B and C were settling to the bottom so stir rods were used to mix the contents. Different stir rods were used for each test tube to avoid contamination. With periodic stirring, Test Tube C completely dissolved at 65
°C, B at
75 °C and A at 85°C.

6. QUESTIONS AND CALCULATIONS
PAGE 221
1. Pb(NO
3
)
2
(s)  Pb 2+ (aq) + 2NO
3
(aq)
A. Final [Pb 2+ ] = initial [Pb 2+ ] * dilution factor
= 0.010M ∗
10mL
10mL+10mL
= 0.0050M
B. 0.0040M, C. 0.0030M, D. 0.0020M, E. 0.0015M, F. 0.0010M
2. KI (s)  K + (aq) + I (aq)
A. Final [I ] = initial [I ] * dilution factor
= 0.020M ∗
10mL
10mL+10mL
= 0.010M
B. 0.0080M, C. 0.0060M, D. 0.0040M, E. 0.0030M, F. 0.0020M
3. PbI
2
(s)  Pb 2+ (aq) + 2I (aq)
K sp
= [Pb 2+ ][I ] 2
K sp
for test tube A = 0.0050*0.010
2 = 5.0E-7
B. 2.6E-7, C. 1.1E-7, D. 3.2E-8, E. 1.4E-8, F. 4.0E-9
4. The K sp
must be between the trial ion products of Test Tube D and Test Tube E.
Q
E
= [Pb 2+ ][I ] 2 = 0.0015*0.0030
2 = 1.4E-8
Q
D
= [Pb 2+ ][I ] 2 = 0.0020*0.0040
2 = 3.2E-8
Therefore the K sp
should be between 1.4E-8 and 3.2E-8.
5.
Temperature ( °C)
K sp
Tube A
85
5.0E-7
Tube B
75
2.6E-7
Solubility (M) 0.0050 0.0040
6. Solubility increases with temperature.
Tube C
65
1.1E-7
0.0030
Tube D
31
3.2E-8
0.0020

7.
0,006
0,005
0,004
0,003
0,002
0,001
0
0
10 20 30 40 50
Temperature (°C)
60 70 80 90

PAGE 222
1. To determine the K sp
of PbI
2
from its saturated solution, you would first precipitate either Pb 2+ or I . To precipitate Pb 2+ , Cl , Br , SO
4
2, S 2, OH , PO
4
3, CO
3
2, or SO
3
2can be used. To precipitate I , Ag + or Cu + can be used. The precipitate must be separated using a filter. The resulting solid is to be thoroughly dried then weighed.
Using the mass one can calculate the number of moles and therefore the K sp
.
2. PbI
2
will be less soluble in a solution already containing I because of the common ion effect. In accordance with Le Chatelier’s Pinciple, adding products (I ) will shift the equilibrium to the reactant side (PbI
2
solid) which will contribute to PbI
2
to wanting to remain as a solid longer.
3. Based on the experimental results, solubility increases with heat. Therefore washing the test tube with hot water will help dissolve solid lead iodide more easily.
4. K sp at 25C = 1.39E-8
7.
If three significant figures were used for experimental values, then the actual K sp value would lie within the range predicted from by experimental results of 1.35E-8 and 3.2E-8.
SOURCES OF ERROR
There were many possible sources of error that may have occurred during this lab.
First, there was no way of ensuring if the chemicals given to us, Pb(NO
3
)
2
and KI, were at the correct concentrations of 0.010M and 0.020M respectively. If the concentrations were off, then the K sp
values calculated will be completely wrong.
Some solution may also have been lost when being transferred from one container to another. For example, some solution may have left in the pipettes or test tubes.
The lab instructions were also unclear as to whether or not we were supposed to stir the solutions with precipitates while they were being heated. I noticed that stirring seemed to increase the solubility of the precipitates drastically.

8. CONCLUSION
In this lab, the range within which the K sp
of a sample of PbI
2
should lie at room temperature as well as at higher temperatures were determined. The true K sp
value of PbI
2 at 25 °C is 1.39E-8 which lies within the experimental values. This result makes sense because of how little precipitate formed in Test Tube D meaning that the contents of Test
Tube D were barely saturated. The uncertainty of the molarity of reagents used was one possible source of error. Improper solution transfer techniques may also have contributed to a less than ideal K sp for the higher temperatures. Proper placement of the thermometer was important in ensuring the measure of the water of the beaker instead of the glass which may conduct heat more than water. It was also determined in this lab that solubility and K sp
of a substance increase as temperature increases.