Passage VII

Students conducted experiments to study the effects of temperature on density.

In the experiments, each flask was filled to the top with either distilled water or salt (NaCl) water at 20°C. A rubber stopper with 2 holes—one fitted with a thermometer and the other fitted with glass tubing—was placed in the neck of the flask (see figure of apparatus).

The initial height of the liquid in the tubing was adjusted to 25 mm above the top of the stopper.

Experiment 1

A flask filled with distilled water was slowly heated. As the temperature of the water increased, the height of the water in the tubing increased. At 100°C, water and steam squirted out the top of the tubing.

Experiments 2

The body of a flask filled with distilled water was submerged in a cold bath at -6°C. As the temperature of the water in the apparatus decreased, the height of the water in the tubing decreased. At 4°C, the height of the water in the tubing stopped decreasing, and then began to increase. At 0°C, water and ice were forced out the top of the tubing. Eventually, the flask cracked in several places.

Experiment 3

Two saltwater solutions were prepared. Solution I had a lower salt concentration (in g/mL) than did Solution II. Two flasks containing Solutions I and II, respectively, were slowly heated. In both flasks, the salt water in the tubing rose and then squirted out the top of the tubing (at 102°C for Solution I and at 104°C for Solution II).

Two flasks containing Solutions I and II, respectively, were cooled as in Experiment 2. In both flasks, the height of the salt water in the tubing decreased until the temperature reached一6°C and then remained level (no freezing occurred).