Chemistry 11
QUANTITATIVE STUDY of a PRECIPITATION REACTION
In this experiment you will prepare two solutions of an exact concentration and then
investigate the mixing of varying amounts of the two solutions.
Part A (Preparation of the solutions)
(1) Calculate the mass of solid lead nitrate needed to prepare 100 mL of a 0.20 mol L -1
solution of lead nitrate
(2) Calculate the mass of solid potassium iodide needed to prepare 100 mL of a
0.20 mol L-1 solution of potassium iodide.
(3) Now prepare one of the above solutions using the method described below. Your
teacher will tell you which solution you will prepare and then you will share the other
solution with another group.
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Weigh out the calculated mass of the solid into a clean, dry 100 mL beaker
Add 20 to 30 mL of distilled water to the solid and carefully stir until it has all
dissolved.
Carefully transfer the solution to a 100 mL volumetric flask. Rinse the beaker with
about 10 mL of distilled water (do this twice) and transfer the liquid to the volumetric
flask
Carefully add sufficient distilled water to the volumetric flask until the level reaches
the mark on the stem of the flask.
Transfer your solution to a plastic storage bottle and clearly label the bottle.
The diagrams below show you how this may be done.
Part B (Mixing the solutions together)
(1) Collect 9 identical test tubes (label them 1 to 9) and stand them in a test tube rack.
(2) Measure out exactly 1 mL of lead nitrate into the first tube tube, exactly 2 mL of lead
nitrate into the second test tube, 3 mL into the third and so on.
(3) Measure out exactly 9 mL of potassium iodide into the first test tube, 8 mL into the
second test tube, 7 mL into the third and so on.
(4) Gently shake each test tube to ensure complete mixing of the two solutions and then
allow the precipitate to settle for 20 minutes.
(5) After 20 minutes, carefully measure the height of the precipitates in each test tube.
It is essential that you do NOT shake or disturb the precipitate while you are measuring
the height. Record all of your results in the table below.
RESULTS TABLE
Test Tube
Number
Volume of
Pb(NO3)2 (mL)
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
Volume of KI
(mL)
Height of ppt
(mm)
9
8
7
6
5
4
3
2
1
Questions and Conclusions
(1) Give a full description of what happened when the two solutions are mixed together.
(2) Write the net ionic equation to show the formation of the precipitate.
(3) Use your data to plot the following graph.
(4) What is the significance of the highest point of your graph? What does it represent?
(5) What is the volume combination that gave the maximum amount of precipitate?
Use this volume information to work out the actual mass of lead iodide precipitated in this
test tube.
(6) Why didn't you obtain the same amount of lead iodide precipitate for each of the other
test tubes?
(7) The accuracy of this experiment is hampered by a number of factors. Suggest THREE
possible causes of inaccuracy.
(a) __________________________________________________________
(b) _________________________________________________________
(c) _________________________________________________________