From the equation, it can be concluded that one mole of glucose reacts with two moles Cu2+ to give one mole of Cu2O. Thus, one can weigh the mass of Cu2O formed and relate it to the amount of glucose present in a solution. This method can be used to study the rate of glucose uptake by yeast cells.
2. Start the timer and add 1.00 mL of yeast suspension with a micropipette into one flask containing the glucose solution. Repeat this until 7 replicates are obtained. Please note that this has to be done very fast (within 1 minute if possible). To the remaining flasks, add 1.00 mL of distilled water into each, and label them as blank.
4. After 30 minutes have elapsed, pour the contents of one flask labelled blank sample and one containing the yeast suspension into two separate beakers containing around 150 mL of boiling distilled water. Cool the mixtures to room temperature and transfer them into two separate 250-mL volumetric flasks. Add distilled water to the flasks to make a final volume of 250.00 mL. Shake the flasks well and let them stand until clear supernatants are obtained (the blank solution should not have a sediment if the experiment has been done properly). Label the one obtained from the blank sample as B60 and the other one as Y60
5. Pipette 25.00 mL of supernatant from B60 and pour it in a 100 mL beaker. Add 25 mL of 0.2500 M Benedict's solution (it is in excess) to the beaker containing the supernatant from B60. Heat the resulting mixture to boiling until a red precipitate is formed. Cool this mixture to room temperature. Repeat to get a replicate.
6. Filter the mixture with a Gooch crucible tared with filter paper using the set up shown in Figure 1. Wash the precipitate several times with cold distilled water.
Figure 1. Set up for filtration apparatus
7. Use a cloth (this would avoid fingerprints on the surface) to remove the crucible containing the precipitate from the filtration apparatus.
8. Dry the sample to constant mass. Ensure that tongs are used to handle the crucible and that the sample is kept/cooled in a dessicator before weighing.
9. Repeat steps 5-8 with Y60.
10. Repeat steps 4-9 to get data at t =120,180,240,300,360,420 mins and label the samples accordingly.
As per Equation 1, one mole of glucose reacts with two moles of Cu2+ to give one mole of Cu2O. In the above experiment, glucose is the limiting reagent and Cu2+ is in excess. Hence the amount (mole) of Cu2O formed of is directly proportional to the amount of glucose in the solution.
Molar mass of Cu2O = (63.55 x 2) + 16 = 143.10
Molar mass of glucose, C6H12O6 = (12.01 x 6) + (1.01 x 12) + (16.00 x 6) = 180.18
No. of moles of Cu2O formed =