Which salt solution concentration is the most similar to the ion concentration in potato cells?
Aim:
To find which concentration of salt solution is the most similar to the ion concentration in potato cells by measuring changes mass.
Hypothesis:
As the concentration is decreased, the 5 change in mass will increase because according to osmosis, water will move from areas of high solute concentration to areas of low solute concentration. Variables:
Independent- The concentration of the salt solution
Dependent- The final mass of the potato
Controlled- Initial potato size, potato cells (same potato), volume of solution, size of beakers, measuring cylinder, scales, vernier, time left in solution, environment solution and potato is left in.
Materials:
6 x 50ml beakers
1 x 50ml measuring cylinder
150ml 10% salt solution
Rainwater
Bunsen burner barrel
Stirring rod
Labels
Vernier
Scales
Method:
1.
Determine the amount of each solution – 10% salt and rainwater, that is needed to make up the concentrations of 4,2,1,.8 and .4 percent for a volume of 40ml.
2.
Pour each of the solutions into 50ml beakers that are labelled with the concentration.
3.
Use a bunsen burner barrel as a cutter to core pieces of potato. Use a stirring rod to remove the potato from the barrel and then using a vernier and knife cut the cores into 1cm pieces.
Prepare 18 pieces – 3 per beaker.
4.
Weigh and record the first three pieces and put them into the 1st concentration.
5.
Repeat this for all 6 concentrations.
6.
Leave the solutions for approx. 24 hours.
7.
Remove the potato from the 1st concentration and weigh and record their new mass.
8.
Measure the lengths using the vernier.
9.
Repeat for the last 5 concentrations.
Results:
Fig 1. Raw Data
Observations:
As the potato was cored and then cut is lost water and while is was being measured water would have been evaporating resulting in weight loss and a higher than original salt concentration.
Analysis:
The trend shown in the data recorded suggests that as the concentration of the solution is increased the % change in mass steadily increases until it reaches a point where the increase in mass starts to slow down and mass increases only very slightly. The salt concentration of the potato could be approximated at between .85% and .9%
According to osmosis, water will move from areas of high solute concentration to areas of low solute concentration to balance the concentration between the two environments. When the potato is added to distilled water is looses water because it has a higher solute concentration and the potato has been placed in a hypotonic environment. As the concentration is increased, the potato looses less water until is in an isotonic environment which is shown by the graph to be between
0.8% and 1.0% concentration of slat solution. This is where the % change in mass is the smallest or there is no change in mass. As the concentration is increased again after this point, the potato starts to take on more water because it is in a hypertonic environment this continues at a relatively steady rate until the potato has absorbed as much salt solute as possible and the rate of % change in mass slows.
Evaluation:
The experiment successfully demonstrated osmosis by showing the loss, gain and balance of the mass of the potato in salt solution. There were a number of weaknesses in the investigation which have the possibility to alter results.
The first is that the potatoes bleed water while being cut and measured. This will not only change
the
