Passage III

A chemist performed 3 experiments to determine the boiling points and freezing points of purified water (H₂O) and solutions of various types of solids dissolved in H₂O.

Experiment 1

Fifty milliliters (mL) of H₂O was heated in a beaker. The temperature of the H₂O was recorded every 2 minutes (min) until it remained constant, indicating the boiling point. The procedure was repeated with a solution of 5 grams (g) of sodium chloride (NaCl) in 50 mL of H₂O and with 10 g of NaCl in 50 mL of H₂O. The results are shown in Figure 1.

Figure adapted from M. Lesser, C. Constant, and J. Weisler, Contemporary Science — Book 3. ©1978 by Amsco School Publications, Inc.

Experiment 2

A beaker containing 50 mL of H₂O was placed in a dry ice bath (an insulated bowl of solid CO₂, which produces temperatures below -70°C). When the H₂O began to solidify, the temperature was recorded. The procedure was repeated with various amounts of NaCl added to 50 mL of H₂O. The percentages of NaCl by mass, the masses of NaCl, and the freezing points are shown in Table 1.

Experiment 3

The freezing points of various solutions of potassium chloride (KCl) and calcium chloride (CaCl₂ ) were measured using the same method as in Experiment 2. The results are shown in Tables 2 and 3.