RP 03 Investigating Water Potential

method

1) use 5 test tubes and fill them up with 20ml of stock solution and distilled water

2) make serial dilutions of 1M sucrose solution: 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 - use x/20 × 1M = conc of sucrose where x is the volume of stock solution that needs to be transferred

3) then place test tubes in water bath to equilibrate

4) use cork borer to cut out 6 potato chips and then use scalpel to make them identical sizes

5) pat dry gently each chip with paper towel then weigh initial mass of each using mass balance

6) place each potato chip into each tube and leave for 20 minutes

7) after remove each chip and pat dry gently each chip with paper towel then weigh final mass

8) then calculate ratio of masses and percentage change in mass for each chip

9) then plot calibration curve with percentage change against concentration

why are bungs placed on the test tubes?

to prevent spillage of solution while in water bath and to stop evaporation of solution which would affect the water potential

why are the potato chips pat dry gently after?

to remove excess liquid on surface which could affect the mass

why are the ratio of masses worked out?

because the potato chips have different initial masses

how would you find the sucrose concentration where it has the same water potential as the potato?

plot the ratio of masses on the y-axis and the concentration on the x-axis on a graph then find the concentration where the ratio is 1

conclusion

-potato chips in lower concentrations of sucrose solution will increase in mass - net movement of water molecules into

-potato chips in higher concentrations of sucrose solution will decrease in mass - net movement of water molecules out