Illustrated Guide to Home Chemistry Experiments

154 DIY Science: Illustrated Guide to Home Chemistry Experiments

TABLE 8-2: Freezing point depression—observed and calculated data

dISpoSAL: dispose of the solutions in the test tubes

by flushing them down the drain. Allow the beakers

with the remainder of the six solutions to come to

room temperature. These solutions will be used in the

following laboratory session.

1.f you have not already done so, put on your splash I

goggles, gloves, and protective clothing.

2. Half fill the large beaker with crushed ice, pour a 15 mm
   to 25 mm layer of sodium chloride on top of the ice, and
   stir until the ice and salt are thoroughly mixed.


3. Immerse the thermometer in the ice/salt bath,
   allow a minute or so for it to stabilize, and record the
   temperature of the ice/salt bath in Table 8-2.


4. Half fill a test tube with water and carefully press it down
   into the ice bath until the water is completely below the
   surface of the ice bath. See Figure 8-2.


5. Gently stir the water with the thermometer continuously
   until ice crystals begin to form on the side of the test
   tube. You will probably have to remove the test tube from
   the ice bath periodically to check the status. Ice crystals
   tend to form first near the bottom of the tube.


6. When ice crystals begin to form, record the temperature
   of the water in Table 8-2.

PRTII:A ETERd mINE THE fREEzING poINTS of

SodIUm CHLoRIdE ANd SUCRoSE SoLUTIoNS

In this part of the lab, we determine the freezing points of the

sodium chloride and sucrose solutions.

1. If you have not already done so, put on your splash
   goggles, gloves, and protective clothing.


2. Label six test tubes A through F.


3. Transfer approximately 10 mL (about half a test tube)
   of solution from beaker A to test tube A.


4. Repeat step 3 for the solutions in beakers B through F.


5. Carefully press test tube A down into the ice bath
   until the solution is completely below the surface of
   the ice bath.


6. Gently and continuously stir the solution with the
   thermometer until ice crystals begin to form on the
   side of the test tube. You will probably have to remove
   the test tube from the ice bath periodically to check the
   status. Ice crystals tend to form first near the bottom
   of the tube.


7. When ice crystals begin to form, record the
   temperature of the solution in Table 8-2. If no ice
   crystals appear within a few minutes, note that fact in
   Table 8-2, record the lowest temperature reached for
   that solution, and go on to the next solution.


8. Repeat steps 5 through 7 for test tubes B through F.

FIGURE 8-2: Determining the freezing point of a solution

Test tube/solutionFreezing

point

Calculated formula

weight

Ice/salt bath ______.__°C

Water ______.__°C

A. Sodium chloride,

6 mol/kg ______.__°C_________.___ g/mol

B. Sodium chloride,

3 mol/kg ______.__°C_________.___ g/mol

C. Sodium chloride,

1.5 mol/kg ______.__°C_________.___ g/mol

D. Sucrose, 6 mol/kg ______.__°C_________.___ g/mol

E. Sucrose, 3 mol/kg ______.__°C_________.___ g/mol

F. Sucrose, 1.5 mol/kg ______.__°C_________.___ g/mol