Passage IV
Some students were interested in why antifreeze is mixed with the H2O in a car's radiator. They knew that when a substance is dissolved in H2O, the boiling points are elevated and the freezing points are lowered relative to H2O. They performed the following experiments to investigate the effects of the addition of ethylene glycol (C2H6O2), the active ingredient in most types of antifreeze, to H2O.
Experiment 1
Six solutions of various concentrations of C2H6O2 in H2O were prepared. The mass of 10.00 mL of each solution was measured, and the density of each solution was calculated using the following formula:
The densities of 100% H2O and 100% C2H6O2 were also determined. The students found that as the concentration of C2H6O2 increased, the density of the solution increased.
Experiment 2
A 20 mL sample of H2O was placed in a flask containing a thermometer and the flask was heated. The temperature at which the H2O first started to boil was recorded as the boiling point. This procedure was repeated with C2H6O2 and the solutions prepared in Experiment 1 (see Figure 1).
Experiment 3
A 90 g sample of H2O (freezing point = 0℃) and 10 g of C2H6O2 (freezing point = -11. 5°C) were placed in a cup containing a thermometer. The mixture was stirred as it was cooled in a low-temperature bath. The temperature at which ice crystals first began to appear was recorded as the freezing point. The procedure was repeated with different amounts of H2O and C2H6O2 (see Table 1) .
23. Based on the results of Experiment 2, why would it be better to use a mixture of antifreeze and H2O rather than pure H2O in a car radiator during hot weather? The mixture has a:
Your Answer is
Correct Answer is A
Explanation
Look at figure 1, the boiling point of pure water is 100°C, and after mixing C2H6O2 in water, The boiling point increases, which is conducive to cooling