Passage
Students grew salt crystals from a solution and studied what makes the crystals larger. In each trial they dissolved salt in warm water, let the solution cool so that crystals formed, and then measured the average width of the crystals in millimeters (mm).
Experiment 1: Starting each time with 20 grams (g) of salt dissolved in 100 mL of water, the students let the solution cool to room temperature over different lengths of time and measured the average crystal size (Table 1).
| Cooling time (min) | Average crystal size (mm) |
|---|
| 5 | 1 |
| 15 | 3 |
| 30 | 6 |
| 60 | 10 |
| 120 | 14 |
Experiment 2: Holding the cooling time at 30 min, the students varied the starting amount of salt dissolved in 100 mL of water and measured the average crystal size (Table 2).
| Salt concentration (g per 100 mL) | Average crystal size (mm) |
|---|
| 10 | 2 |
| 20 | 6 |
| 30 | 9 |
| 40 | 12 |
In every trial the same kind of salt and the same containers were used.
