PAG 8.1 Flashcards
1
Q
Equipment
A
- Potato
- Cork borer
- Ruler
- Knife
- White tile
- Sucrose solutions : 1.0 mol dm-3 and 0.8 mol dm-3
- Distilled water
- 2 x 20 cm3 syringes
- 3 x 100 cm3 beakers for serial dilution
- 6 boiling tubes
- 6 bungs to fit the boiling tubes
- Marker pen
- Forceps
- Stopwatch
- Balance
- Paper towel
2
Q
method
A
- Serial Dilution: First you need to prepare these solutions: 0.4 mol dm-3, 0.2 mol dm-3 and 0.1 mol dm-3, by using the 0.8 mol dm-3 sucrose solution and distilled water. Use the following diagram to help you.
- Next, label the six boiling tubes: Water, 0.1 mol dm-3, 0.2 mol dm-3, 0.4 mol dm-3, 0.8 mol dm-3 and 1.0 mol dm-3 and place 20 cm3 of water, or sucrose solution into the corresponding tube using a fresh syringe.
- Construct a results table in which you will record the initial and final masses of each of 6 potato chips incubated in 6 different concentrations of sucrose solution. You will also need to record the percentage change in mass of each chip.
- Use the cork borer, knife and ruler to cut 6 potato chips that are 40 mm long. Remove the skin.
- Carefully dry the potato chips using the paper towel by rolling them 3 times for each chip.
- Use the balance to weigh a chip. Record its mass in your results table against the appropriate sucrose concentration and place it in the corresponding solution.
- Repeat for all six solutions and place the bungs in the tubes.
- Leave the tubes for at least one hour.
- In the same order that they were put into the tubes, remove the chips one at a time, roll them 3 times on the paper towel and re-weigh. Record the masses in the table.
- Use the starting and ending masses to calculate the percentage change in mass of each chip. Record in the table.
- Plot a graph of percentage change in mass against concentration of sucrose solution, show the intercept and work out the water potential of the potato using the following calibration table.
3
Q
- Why was it important to dry the chips and in the same way each time?
A
- So that the mass of water on the outside of the chips does not affect the weighing of the chips.
4
Q
- What was the purpose of placing the bungs in the tubes?
A
- Prevents evaporation of water.
5
Q
- Why did you compare the percentage change in mass rather than simply the change in mass of each chip?
A
- To allow for variations in size of the chips, even though attempts were made to cut them to the same size.
6
Q
- What are the limitations of this practical activity? What improvements could be made?
A
- Candidates ideas e.g. different parts of the potato may have different water potentials
