Raquel Water Potential and Molarity Mixup

The molarities of the different colored solutions are as follows: the red solution is 1.0M, the yellow solution is 0.8M, the blue solution is 0.6M, the purple solution is 0.4M, the orange solution is 0.2M, and the green solution is 0M. For our experiment, we put distilled water into the dialysis bags and weighed them. After we left the dialysis bags in each of the different solutions overnight we weighed them again and calculated the percent difference of the initial weight and final weight.

Bag in Colored Solution	Initial weight (g)	Final weight (g)	Percent Change of Mass
Bag 1, blue	13.68	8.5	-37.9
Bag 2, green	15.37	15.3	-0.46
Bag 3, orange	12.14	8.3	-31.6
Bag 4, red	13.9	6.2	-55.4
Bag 5, purple	11.84	7.4	-37.5
Bag 6, yellow	10.08	5.5	-45.4

Water flows from a high concentration to a low concentration. The lower the concentration in comparison to the higher concentration, the more water is going to flow into it. The red solution had the highest percent change in mass which means that the most water flowed out of the bag and into the solution. It would make sense that the solution therefore had the least amount of water in it to begin with (which indicates that it had the highest concentration of sucrose which was 1.0M). Since the green bag had the least amount of water flow out of it, indicated by the -0.46%, that means that was the solution that had the closest amount of water in it compared to the distilled water. There was less of a flow of water because the concentrations of water were the closest and it was the solution with the least amount of sucrose in it (which was 0M). To figure out the rest of the molarities of the sucrose solutions, we put the percent changes of mass in order from highest to lowest (-55.4%=red, -45.4%=yellow, -37.9%=blue, -37.5%=purple, -31.6%=orange, -0.46%=green).

The water potential of our cucumber sample is -2.21 bars. In order to perform this experiment and calculate this, we cut and weighed six different pieces of cucumber and let them sit in the six different sucrose solutions overnight. We then weighed them again and calculated the percent change of mass just like we did for the first experiment.

Cucumber Samples in Colored Solution	Initial weight (g)	Final weight (g)	Percent Change of Mass
Cucumber 1, blue	10.19	7.04	-30.9
Cucumber 2, green	8.22	10	21.7
Cucumber 3, orange	5.97	4.4	-26.3
Cucumber 4, red	9.81	6.3	-35.8
Cucumber 5, purple	9.68	6.9	-28.7
Cucumber 6, yellow	7.23	4.3	-40.5

Using these numbers, we constructed a graph of the percent change in mass for each solution of a different molarity (based on our results from the first experiment) to show us the molar concentration of the cucumber. This would be the sucrose molarity in which the mass of the cucumber does not change. The point at which the line crosses the x-axis on our graph represents the molar concentration of sucrose with a water potential that is equal to the cucumber tissue water potential.  

We agreed that the line crosses the x-axis at 0.09M. To find the water potential of the cucumber, we then needed to use the equation (Ψs) = −iCRT. The “i” would be the ionization constant and for sucrose that number would be 1. The “C” would be the molar concentration of the solute which we found to be 0.09M. The “R” would be the pressure constant which is 0.0831 liter bars/mole K. The “T” would be the temperature in Kelvin.  

(Ψs) = -(1)(0.09)(0.0831)(295)

(Ψs) = -2.21 bars