Question

One student filled two clean jars with hot water. Baking soda was added to water in both the jars and stirred until no more baking soda dissolved in the water. Small weights were tied to two ends of a thread, and the ends were dipped into the two jars as shown below. After two or three weeks, the student observed a white solid material growing down from the middle of the thread between the two jars. The student's experiment demonstrates that:

A. Baking soda can dissolve indefinitely in hot water.
B. Baking soda is not soluble in hot water.
C. A chemical reaction occurred between baking soda and water.
D. The weight of the jars caused the material to form.

Answer 1

The experiment demonstrates crystallization of a saturated solution of baking soda. As the solution cools and water evaporates, baking soda recrystallizes along the thread, forming a solid white material.

Step-by-step explanation:

The student's experiment demonstrates the process of crystallization of a saturated solution. When baking soda (sodium bicarbonate) is added to hot water, it dissolves until the solution becomes saturated, at which point no more solid can dissolve. Over time, as the solution cools and water evaporates, the dissolved baking soda begins to recrystallize along the thread due to the loss of solvent (water) and thus a decrease in solubility. This results in the formation of a solid white material along the thread. This experiment does not show that baking soda can dissolve indefinitely in hot water (A), nor that baking soda is not soluble in hot water (B), nor that there was a chemical reaction between baking soda and water (C), and the weight of the jars had no influence on the formation of the material (D).