Question

Data Table 1: Potato Masses Test Tube Solution Initial Mass (9) Final Mass (g) Mass Difference (9) Percent Change in Mass (%) Distilled 1.53 1.60 0.08 1.83 1.89 0.06 1.84 1.86 0.02 water 0.2 M sucrose 0.4 M. sucrose 0.6 M sucrose 0.8 M sucrose 1.0 M sucrose 1.87 1.60 0.27 1.75 1.35 0.40 1.72 1.27 0.45 Hypothesis

in picture one calculate the percentage difference and also form a hypothesis based on the results. then answer questions 1-5 in the second photo

Answer 1

The experiment is performed to understand the concept of osmosis. Osmosis is defined as the movement of water from a region of lower solute concentration (hypotonic) to a region of higher solute concentration (hypertonic) across a semi-permeable membrane. When the concentration of solutions both inside and outside the membrane is equal (isotonic) then there is no net movement of water across the membrane.

The hypothesis here would be to test the above theory in the said experiment. The hypothesis would be that when potato strips are kept in a isotonic solution, there is no net movement of water and therefore the potato strips would weigh the same as before; when kept in a hypotonic solution, then water would move into the potato tissue thereby increasing its weight; when kept in a hypertonic solution then water would move out of the potato tissue into the surrounding solution, leading to a decrease in the weight of the potato strips.

Now look at the data and see whether the results adhere to the hypothesis.

Test tube	Solution	Initial mass (g)	Final mass (g)	Mass difference (g)	Percentage change in mass (%)
a	Distilled water	1.53	1.6	0.08	4.6
b	0.2M Sucrose	1.83	1.89	0.06	3.3
c	0.4M Sucrose	1.84	1.86	0.02	1.1
d	0.6M Sucrose	1.87	1.6	0.27	-14.4
e	0.8M Sucrose	1.75	1.35	0.4	-22.9
f	1.0M Sucrose	1.72	1.27	0.45	-26.2

The percentage change given above is calculated using the formula:

Percentage change = (Final mass - Initial mass) / Initial mass)) * 100

Negative values represent a decrease in percentage weight and positive values represent an increase in percentage weight.

Now let us answer the questions:

2. Here we are asked to list those molar concentrations of sucrose that resulted in water entering the tissue. This means we should look at those values that resulted in percentage weight gain. Looking at the results, we could say that the first three solutions, Distilled water, 0.2 M sucrose and 0.4 M Sucrose resulted in water entering the tissue. These solutions are hypotonic. Potato strips when kept in a solution whose solute concentration is less than that in the tissue, water tends to enter the tissue and the tissue gains weight as a result.  

3. The molar concentrations that resulted in water exiting the tissue would be the last three concentrations of sucrose, 0.6 M, 0.8 M and 1.0 M as there is a percentage loss in mass of the potato strips. These solutions can be termed hypertonic. When potato strips are kept in these, water moved out of the tissue as the solute concentration is higher in the surrounding solution. This resulted in the tissue losing weight in the form of water loss.

4. The hypothesis stated has supported the experimental results. As the sucrose concentration increased, there was a reduction in the mass of potato strips and at low sucrose concentrations the mass of potato strips increased. This clearly proves the concept of osmosis as described in the hypothesis.

5. The potato strips should be kept in an isotonic solution for them to neither lose or gain weight, as there would be no net movement of water when the solute concentrations are the same both inside the tissue as well as the solution outside. We could choose a molarity close to 0.4 M Sucrose, as this resulted in a 1.1% change in weight of potato strips. The net movement of water is minimal at this concentration.