Question

predict what will be observed in each experiment below.
a pair of 100 ml samples of water are taken from a well bored into a large underground salt (nacl) deposit. sample #1 is from the top of the well, and is initially at 32°c. sample #2 is from a depth of 50. m, and is initially at 42°c. both samples are allowed to come to room temperature (20.°c) and 1 atm pressure. an nacl precipitate is seen to form in sample #1.
a student sees tiny bubbles clinging to the inside of an unopened plastic bottle full of carbonated soft drink. the student opens the bottle, and hears a loud hiss as gas under pressure escapes from the bottle.

Explanation:

• For the first experiment: The solubility of NaCl in water decreases with decreasing temperature. Sample #2 is initially at a higher temperature ($42^{\circ}C$) compared to sample #1 ($32^{\circ}C$). When both are cooled to room temperature ($20^{\circ}C$), sample #2 was able to dissolve more NaCl at its initial higher temperature. So, more NaCl will precipitate out from sample #2 as it cools (since it had a higher initial solubility at $42^{\circ}C$ compared to sample #1 at $32^{\circ}C$).
• For the second experiment: Carbonated soft - drinks have dissolved carbon dioxide gas under pressure. When the bottle is opened, the pressure is released. According to Henry's law ($C = kP$, where $C$ is the concentration of the dissolved gas, $k$ is the Henry's law constant, and $P$ is the partial pressure of the gas above the solution), the solubility of $CO_2$ in the soft - drink decreases. The dissolved $CO_2$ starts to come out of the solution, causing the bubbles to grow and more bubbles may appear as the gas continues to escape from the supersaturated solution.

Answer:

• First experiment: A bigger mass of NaCl precipitate will form in Sample #2.
• Second experiment: The bubbles will grow, and more may appear.