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) .