Page 3 - Solubility and Temperature
Safety Precautions
Potassium nitrate in solid form is a strong oxidant and a fire and explosion risk when heated or in contact with organic materials. It is also a skin irritant. Avoid contact with skin
and eyes. Wear chemical splash goggles and chemical-resistant gloves and apron. Use caution when working with a hot water bath and a hot plate. Wear heat-resistant gloves or a
heat protector when handling hot glassware. Wash hands thoroughly with soap and water
before leaving the laboratory.
Procedure
1. Form a working group with three other students and divide into two pairs. Each pair of
students will prepare three different solution concentrations (A-C) and measure their
saturation temperatures. One pair of students will use the Series I masses shown in the
reagents table in step 4, the other pair of students will use the Series II masses. Both pairs
of students may share the same hot water bath (step 2).
2. Prepare a hot water bath (80-90 DC)for use in step 10: Fill a 250-mL beaker about twothirds full with hot tap water and place it on a hot plate at a medium-high setting.
3. Obtain three clean and dry test tubes and label them A, B, and C. Measure and record the
mass of each empty test tube in the data table.
4. Using the following table as a guide, add the recommended amount of potassium nitrate
to each test tube A-C. Note that the masses given are ranges-anywhere
in this mass
range is fine, as long the exact mass used in step 5 is recorded.
A
B
c
Mass of KN03, g (Series I)
0.45-0.50 g
0.70-0.80 g
1.20-1.30 g
Mass of KN03, g (Series II)
0.35-0.40 g
0.90-1.00 g
1.50-1.60g
Testtuhe
5. Measure and record the combined mass of each test tube and potassium nitrate.
6. Use a clean, thin-stem pipet to add 20 drops of distilled water to each test tube A-C.
7. Place a 50-mL beaker on the balance pan to support the test tubes. Zero (tare) the balance
with the empty beaker in place, then place test tube A in the beaker and measure the
mass of the test tube and its contents. Record the total mass of the test tube plus solid
plus water in the data table. Note: The mass of water in each test tube should be at least
0.90 g. If not, add one or two more drops of water to the tube and measure the total mass
again.
8. Repeat step 7 for test tubes Band C.
9. Place all of the labeled test tubes in the hot water bath.
10. Immerse the thermometer in test tube C. Gently stir the mixture in test tube C using an
up-and-down motion of the thermometer until the solid dissolves completely. Note: At
this point the solids in the other test tubes should also have dissolved, even without stirring, since they contain less solid.
Solubility and Temperature