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.
17. Based on the results of Experiment 3, a 7.5% solution of CaCl2 in H2O would have a freezing point closest to:
Your Answer is
Correct Answer is B
Explanation
Looking at table 3, 7.5% is between 6% and 9%, so the freezing point of the solution should be between -2.93~-5.04°C, option B meets