required practical 3

Question 1

what is the purpose of a calibration curve?

Answer 1

they are used to determine the concentration of an unknown sample by comparing it to a set of standard values with known concentrations

Question 2

method

Answer 2

1. make a dilution series of 1M sucrose solution (0.0, 0.2 - 1) using distilled water
2. measure 5cm3 of dilution into separate test tubes
3. use a cork borer to cut 6 potato chips and dry using a paper towel
4. weigh each potato before start
5. place a potato in each tube and leave for 20 minutes
6. remove each chip, dry and weigh
7. calculate percentage change in mass

Question 3

why are the potatoes left for 20 minutes?

Answer 3

to allow time for osmosis until plant tissue reaches equillibrium with its surrounding solution

Question 4

why is percentage change measured rather than change in mass?

Answer 4

potato chips may not have the same starting mass so percentage allows comparison

Question 5

explain change in mass in chips with concentration lower than sucrose solution

Answer 5

decrease in mass

Question 6

explain change in mass in chips with concentration higher than sucrose solution

Answer 6

increase in mass

Question 7

what are the controlled variables?

Answer 7

volume of sucrose solution
size of potato chips
length of time left in solution