Passage
Students investigated how a powdered substance, Compound X, dissolves in water. In each trial they used 100 milliliters (mL) of water held at a fixed temperature.
Study 1: The students added Compound X a little at a time, stirring constantly, until no more would dissolve. The greatest mass that dissolved at each temperature (the solubility) is shown in Table 1.
| Water temperature (°C) | Solubility (g per 100 mL) |
|---|
| 10 | 22 |
| 20 | 30 |
| 30 | 39 |
| 40 | 51 |
| 50 | 66 |
Study 2: Using fresh water at each temperature, the students added a fixed 20 grams (g) of Compound X, stirred at a constant rate, and measured the time needed for all 20 g to dissolve. The results are shown in Table 2.
| Water temperature (°C) | Time to dissolve 20 g (seconds) |
|---|
| 10 | 145 |
| 20 | 96 |
| 30 | 61 |
| 40 | 38 |
| 50 | 25 |
In both studies the water was stirred at the same steady rate, and the same batch of Compound X was used throughout.
