Question

experiment:
rock candy is formed when excess sugar is dissolved in hot water followed by crystallization. a student wants to make two batches of rock candy. he finds an unopened box of \cane sugar\ in the pantry. he starts preparing batch a by dissolving sugar in 500 ml of hot water (70 °c). he keeps adding sugar until no more sugar dissolves in the hot water. he cools the solution to room temperature. he prepares batch b by dissolving sugar in 500 ml of water at room temperature until no more sugar is dissolved. he lets the solution sit at room temperature.
predicted observation (choose one):

• it is likely that more rock candy will be formed in batch a.
• it is likely that less rock candy will be formed in batch a.
• it is likely that no rock candy will be formed in either batch.
• i need more information to predict which batch is more likely to form rock candy.

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 temperature info partially missing.
predicted observation (choose one):

• a bigger mass of nacl precipitate will form in sample #2.
• a smaller mass of nacl precipitate will form in sample #2.
• the same mass of nacl precipitate will form in sample #2.

Explanation:

First Experiment (Rock Candy)

For the rock candy experiment, solubility of solids (like sugar) generally increases with temperature. Batch A uses hot water (70°C) to dissolve sugar, and batch B uses room - temperature water. Since more sugar can be dissolved in hot water, when the solutions cool, the excess sugar (the amount dissolved beyond the room - temperature solubility) will crystallize to form rock candy. Batch A has more sugar dissolved initially (because hot water can hold more sugar), so when it cools, more sugar will crystallize out, forming more rock candy.

The solubility of salts like NaCl in water can be affected by pressure (and depth in a well is related to pressure). Generally, as pressure increases (with increasing depth), the solubility of NaCl in water can increase slightly, but the change is relatively small. However, the main idea here is that the water from a greater depth (Sample #2, 50m depth) is in a different pressure environment. But in most cases, the solubility of NaCl in water doesn't change drastically with depth - related pressure changes in a well. But if we consider that maybe the water at depth has been in contact with more salt - bearing rock or has a different history, but the most probable answer based on the fact that the solubility change with pressure for NaCl is minimal and if we assume that the initial amount of dissolved NaCl is related to the environment, but the option "The same mass of NaCl precipitate will form in Sample #2" is incorrect. Wait, actually, the solubility of NaCl in water is relatively insensitive to pressure changes in the range of well depths. But if we consider that the two samples are from the same well (just different depths) and the initial dissolved NaCl amount is related to the saturation at their respective conditions. But the key here is that the solubility of NaCl doesn't change much with depth (pressure) in a well. However, if we assume that the water at depth (Sample #2) has a higher pressure, and for some salts, solubility increases with pressure, but for NaCl, the effect is small. But the options given: "A bigger mass of NaCl precipitate will form in Sample #2" - if we consider that maybe at depth, the water was able to dissolve more NaCl (due to pressure) and when it is brought to the surface (where pressure is lower), more NaCl would precipitate. But this is a bit of a stretch. Alternatively, if the two samples have the same initial dissolved NaCl concentration, then the same mass would precipitate. But the problem says "a pair of 100 mL samples of water are taken from a well bored into a large underground salt (NaCl) deposit". So the water is in contact with the salt deposit. At greater depth, the pressure is higher. For a salt like NaCl, the solubility increases slightly with pressure. So the water at 50m depth (Sample #2) can dissolve more NaCl. When both samples are brought to the surface (where pressure is the same, room pressure), the water in Sample #2, which had more dissolved NaCl (due to higher pressure at depth), will have more NaCl precipitate out when the pressure is reduced (and solubility decreases). So a bigger mass of NaCl precipitate will form in Sample #2.

Answer:

It is likely that more rock candy will be formed in batch A.

Second Experiment (Salt Deposition)