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.

13. The chemical formula of AS is (NH4)2SO4. Based on Student 3's explanation, which of the following chemical equations best represents a process that only occurred in the IPA?

Answer and Explanation

Your Answer is

Correct Answer is A

Explanation

Line 4-6 of Student 3 mentioned that AS will be ionized into ions after being dissolved in IPA, so the correct option should reflect this ionization process, and according to common sense, ammonium ion NH4+ carries a unit of positive charge, while sulfate ion SO42- has two negative units, so option A is reasonable