Why is it important to cut the two potato pieces in roughly equal size and measure their initial weight before placing them in different liquids?
It is important to cut the two potato pieces in roughly equal size and measure their initial weight to ensure a fair comparison between the two set-ups. If the pieces are of different sizes or weights, the observed changes cannot be accurately attributed to the effect of the different liquids alone.
Measuring the initial weight allows us to accurately calculate the difference between the initial and final weights. This calculation is essential to clearly observe the effect of osmosis, where the piece in plain water swells and gains weight, while the piece in the concentrated solution shrinks and loses weight.
Explanation
The textbook context explains Activity 2.2, which demonstrates osmosis by placing potato pieces in plain water and a concentrated solution. To reliably compare the outcomes (swelling vs. shrinking), the experiment must control the variables, meaning the potato samples should be as similar as possible initially. Furthermore, the activity explicitly instructs students to calculate the difference between initial and final weights, which is only possible if the initial weight is measured. This ensures the observed weight change is a direct result of osmosis caused by the different liquids.