When a piece of celery is placed in distilled water, it gains mass due to a process called osmosis. Osmosis is the movement of water across a semi-permeable membrane (like the cell walls of the celery) from an area of low solute concentration to an area of high solute concentration. In distilled water, which has a lower concentration of solutes compared to the fluids inside the celery cells, water enters the cells. This influx of water causes the cells to swell, leading to an increase in mass.
On the other hand, when a piece of celery is placed in a NaCl (sodium chloride) solution, the situation is different. The NaCl solution has a higher concentration of solutes compared to the celery’s internal cellular fluids. In this case, water moves out of the celery cells into the surrounding NaCl solution, following the gradient of higher solute concentration. As water leaves the cells, the cells lose turgidity and the overall mass of the celery decreases.
In summary, the celery in distilled water gains mass because water moves in due to osmosis, while the celery in NaCl loses mass because water moves out, resulting in a net loss of mass.