Question 35 Answer and Explanation _ACT April 2008 Form 65D Science Section

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).

35. Water in the upper part of a hypothetical 2-compartment container is at 10°C, and water in the lower part is at 80°C, as shown in the figure below.

If the barrier separating the 2 compartments could be removed without disturbing the water, what mixing, if any, would occur?

A. No mixing would occur, because the water in the upper part of the container is more dense than the water in the lower part of the container.

B. No mixing would occur, because the water in the upper part of the container is less dense than the water in the lower part of the container.

C. Mixing would occur, because the water in the lower part of the container is more dense than the water in the upper part of the container.

D. Mixing would occur, because the water in the lower part of the container is less dense than the water in the upper part of the container.

Answer and Explanation

Your Answer is

Correct Answer is D

Explanation

From the text part of Experiments 1 & 2, it can be inferred that water has the highest density (smallest volume) at 4°C, and the density of water at 10°C is greater than that of water at 100°C, so there will be mixing, and the denser 10 °C water will sink