Question 11 Answer and Explanation _ACT April 2019 Form Z15 Science Section

Passage II

During a demonstration, a teacher placed 20 mL of water , 10 mL of isopropyl alcohol (IPA), and 1 drop of blue food coloring into a test tube, capped the test tube, and inverted it 6 times. Next, she added 7 g of ammonium sulfate (AS), an ionic solid, to the test tube, capped the test tube, and vigorously shook it for 10 sec. Then, over the 15 sec period immediately following the shaking, the mixture in the test tube completely separated into 2 distinct liquid layers (see figure).

The teacher asked each of 4 students to provide an explanation for what occurred in the test tube over the 15 sec period.

Student 1

Over the 15 sec, the mixture separated into 2 layers because IPA is denser than water. The water layer was on top, and the IPA layer was on the bottom. The AS dissolved in the IPA only, because AS breaks apart into neutral molecules when dissolved in IPA. Blue food coloring is polar, so it dissolved in the water only.

Student 2

Over the 15 sec, the mixture separated into 2 layers because water is denser than IPA. The IPA layer was on top, and the water layer was on the bottom. The AS dissolved in the water only, because AS breaks apart into neutral molecules when dissolved in water. Blue food coloring is polar, so it dissolved in the IPA only.

Student 3

Over the 15 sec, the mixture separated into 2 layers because the AS dissolved in the IPA only, causing the density of the IPA layer to increase . The water layer was on top, and the IPA layer was on the bottom. The AS dissolved m the IPA only, because AS breaks apart into ions when dissolved in IPA. Blue food coloring is polar, so it dissolved in the water only.

Student 4

Over the 15 sec, the mixture separated into 2 layers because the AS dissolved in the water only, causing the density of the water layer to increase. The IPA layer was on top, and the water layer was on the bottom. The AS dissolved in the water only, because AS breaks apart into ions when dissolved in water. Blue food coloring is polar, so it dissolved in the IPA only.

11. Based on the figure, 5 sec after the shaking, would the contents of the test tube have been better classified as a heterogeneous mixture or a homogeneous mixture ?

A. Heterogeneous, because the contents of the test tube varied in composition from one region to another .

B. Heterogeneous, because the contents of the test tube were uniform in composition throughout.

C. Homogeneous, because the contents of the test tube varied in composition from one region to another .

D. Homogeneous, because the contents of the test tube were uniform in composition throughout.

Answer and Explanation

Your Answer is

Correct Answer is A

Explanation

Because there is an obvious phenomenon of separation in the test tube, it means that the density of the substances in the upper and lower layers is completely different; and the solutes dissolved in the solvents of the upper and lower layers are also different, resulting in the color difference between the upper and lower layers, which means that the two layers of substances should be Different in nature, namely heterogeneous