Molarity and Water Potential Activity

Molarity and Water Potential Lab

The Goal of this lab was to determine the molarity of each solution

Claim:

Green has a concentration of 0M, orange has .2M, purple has .4M, blue had  .6M, red had .8 M, and yellow had 1M.

Evidence:

My partner and I conducted this experiment over the course of two days in order to get accurate answers. After receiving the six different colored cups we labeled them 1-6, then filled dialysis tubing with water and weighed the bags before placing them in the different solutions and once this was done we placed plastic wrap over the cups. We left the dialysis bags sit in the solutions over night and once we got back to class we weighed them again.

Solution	1 Red	2 Orange	3 Yellow	4 Green	5 Blue	6 Purple
Initial Weight of Dialysis Tube	11.94 grams	13.56 grams	10.85 grams	14.61 grams	13.1 grams	13.7 grams
Final Weight of Dialysis Tube	5.3  grams	8.9 grams	4 grams	14.5 grams	7.9 grams	8.5 grams

Many of the bags decreased greatly in weight which means that they had a higher concentration of sugar/solution than the pure water in the dialysis tubing since water flows from areas of high concentration to low concentration. The Pure water flowed from the dialysis bag to the solution in the cup. All of the bags decreased in weight but some in lost much greater quantities than other which signified they had higher concentrations of sugar than others.

Reasoning:

Since water flows from areas of high concentration to low concentration it was simple to see which ones were more concentrated than others by comparing their percentage change in mass. This was calculated by subtracting the initial weight from the final weight and then dividing that number by the initial weight and multiplying it by 100.

Solution	1 Red	2 Orange	3 Yellow	4 Green	5 Blue	6 Purple
% change in mass	-56%	-34%	-63%	-11%	-39%	-38%

Using the percentage change we were able to place them in order of highest molarity to lowest molarity. The bags that were place in the solutions with  lower concentrations of water lost the greatest amount of weight therefore causing them to have a greater negative percent.

Claim:

In this experiment we also had to find the water potential of a vegetable that we chose and my partner and I chose to study the water potential of a turnip

The Water Potential of the turnip to be -11.03 bars

Evidence:

We did the same thing we did for the dialysis tubing activity but instead of using the tubes we used pieces of turnips. We cut up pieces of turnips and weighed them before and after placing them in the solutions in order to calculate the change in mass and water potential of the turnip.

Solution	1 Red	2 Orange	3 Yellow	4 Green	5 Blue	6 Purple
Initial Weight of Turnip	3.81 grams	4.65 grams	3.42 grams	3.45 grams	2.84 grams	4.99 grams
Final Weight of Turnip	2.8 grams	4.8 grams	2.39 grams	4 grams	2.7 grams	5.1 grams
% change in mass	-27%	3%	-33%	16%	-4%	2%

By finding the molarity of the solution and percentage change in mass, we were able to see estimate the point in which the line crosses the x axis and use this number to determine the water potential.

Reasoning

In order to find the water potential of the turnip needed to use the equation (Ψs) = −iCRT. “I” is the ionization constant and we used 1 because we were dealing with sucrose. “T” is temperature and we used 295 because the temperature in the room was 22 degrees celsius but this needed to be in kelvins so we added 273. For “R” we used .0831 since that number represents the pressure constant. Finally for “C” we used .45 since that is what we thought to be our molar concentration. This gave us -11.03 bars as the water potential.