5 Steps to a 5 AP Chemistry

284  Step 4. Review the Knowledge You Need to Score High

Equipment

beaker(s) ice pipet

stirrer stopwatch test tube(s)

thermometer support stand clamp

wire gauze

Measurements

1.the mass of the empty test tube

2.the mass of the test tube plus the solvent

3.the mass of the test tube plus solute plus solvent

The solid solvent or solution is heated above its melting point and then

allowed to cool.

4.repeated measurements of the temperature

5.the times at which the preceding measurements were made

The above series of measurements is done one time for the solvent and one time for the solu-

tion, or the melting point of the solvent may be obtained (not measured) from a table.

Calculations

The mass of the solvent is calculated from the difference between measurements 1 and 2.

The mass of the solute is calculated from the differences between masses 2 and 3. The mass

of the solvent is converted to kilograms.

The temperature and time measurements (4 and 5) are plotted, and a smooth curve is drawn.

The temperature difference between the “level” regions of the solvent plot and the solu-

tion plot (or the difference between the solution plot and the tabulated freezing point of

Thermometer

Stirrer

Solute

+

Solvent

Figure 19.2 Freezing-Point Depression Apparatus.