Osmosis - Practical Flashcards
What technique is used to make several solutions of different known concentrations
Serial dilutions
Outline method of serial dilutions: making 5 dilutions starting with 2M sucrose and diluting by a factor of 2
- Have 5 test tubes on test tube rack
- Add 10cm3 of 2M sucrose in the 1st tube
- Add 5cm3 of distilled water to the other 4
- Using pipette take 5cm3 from the 1st test tube and add it to the second
- Mix well
- Repeat down the test tubes
If you wanted to dilute by a factor of 10 each time how would you
Add 10cm3 to the initial conc
Take 1cm3 from each
How do you find the scale factor
Starting known conc / desired conc of sol = sf
How to make a solution of 15cm3 0.4M from 1M
Sf = 1/0.4 = 2.5
15/2.5 = 6cm3 needed of 1M
Top up with distilled water to make 15cm3 = 15 - 6 = 9
Outline method to find water potential of potato cells
- Use cork borer to cut potatoes into identically sized chips
- Divide into groups
- Measure mass of each group using mass balance
- Place 1 group into each conc of sucrose
- Leave for 20mins
- Remove and pat dry with paper towel
- Weigh again
- Calculate % change in mass
- Plot calibration curve
What is on the x axis if a calibration curve
Conc of sucrose
What is on the y axis if a calibration curve
% change in mass
How calculate % change
Difference/orignal x 100
Why will potatoes gain mass
Water has moved into potato
The potato had a lower water potential than the sucrose
Why has a potato lost mass
Water has moved out of potato by osmosis
As the potato had a high water potential than the sucrose solution
At what point on the graph is the potato and sucrose solution isotonic
When the curve crosses the x axis
How do u find the water potential of the isotonic solution
Find conc when the curve crosses the x axis
Look up the conc in a text book
