why does the fluid level in the osmometer rise, at least at first?
Analysis and Discussion
1. In terms of water molecules and solute concentration gradients, why does the fluid level in the osmometer rise, at least at first? (Hint: Think about the concentration gradient and the net movement of water at the molecular level.)
2. Look at the numbers in Table 2, and at the steepness of the slope of the graph. Why does the rate of rise (the number of mm of rise per 5 min. interval) change as the experiment progresses? (Hint: Again think at the molecular level.) How might the net inward movement of water molecules be affected by the water pressure (or “hydrostatic pressure”) that is building up inside the bag?
3. When the fluid level finally stops rising, what keeps more water from moving in? Warning: The reason is not that the concentration of water is equal on both sides! The concentration of water inside the bag is always going to be lower, because all the sucrose molecules are trapped inside and so are still “diluting” the water.
4. “What If” Questions: What would have happened … … if all the sucrose had been placed in the beaker rather than inside the bag? … if the glass tube had been only 5 cm long?