17
flasks, a 2 ml pipette, a 10 ml pipette, six 25 ml test tubes, six round or square
cuvettes, and a hot plate.
Procedure:
1.
Fill the burette to the top calibration line (50 ml) with the glucose stock
solution. Deliver 5 ml of the glucose solution from the burette into the
volumetric flask. Dilute the flask to the mark with de-ionized water, cape the
flask, and mix the diluted solution thoroughly. Transfer this first standard to
an Erlenmeyer flask, calculate its concentration, and label the flask. Rinse
the volumetric flask with de-ionized water and repeat step 2 for standards 2,
3, and 4 using 10 ml, 15 ml, and 20 ml of the stock solution.
4.
Pour 10 ml of the soft drink into the 100 ml volumetric flask, swirl it until
bubbling stops, and dilute to the mark. Transfer this solution to an
Erlenmeyer flask. Rinse the volumetric flask, pipette 10 ml of the diluted soft
drink solution into it, dilute and mix. Transfer this solution to another
Erlenmeyer flask. Rinse the pipette and volumetric flask. Pipette 10 ml of the
second dilution into the volumetric flask, dilute and mix. This final unknown
solution is the 1:1000 dilution of the original soft drink.
5.
Label six test tubes. Fill them with 25 ml of water using a pipette, mark the
solution level, and empty them. Pipette 2 ml of water, the unknown and the
four standards into the tubes, respectively. Rinse the pipette after each use.
6.
Using a graduated cylinder, add 2 ml of the alkaline copper titrate solution to
each test tube and stir by swirling the tubes. Rinse the graduated cylinder
well.
7.
Fill half of a 600 ml beaker with water and place it on a hot plate to boil.
Prepare an ice-water bath in a second 600 ml beaker.
8.
Immerse the six tubes into the boiling water for exactly six minutes to oxidize
the glucose. Remove the tubes from the boiling water and immerse them in
the ice water bath for exactly 3 minutes to allow them to cool.
9.
Using a graduated cylinder, add 2 ml to the phosphomolybdic acid solution to
each tube and stir by swirling them. Allow the solution two minutes to react,
and then dilute them to the 25 ml mark with de-ionized water.
10.
Place rubber stopper in each tube and mix by inverting the tubes several
times.
11.
Set the wavelength to 780 nm and put the second order filter lever in the red
position. Fill a cuvette with a blank solution and insert it into the sample
compartment. Blank the instrument according to the procedure in
Basic
Operation
.
12.
Fill another cuvette with the first standard and measure its absorbance on the
spectrophotometer.
Repeat
Step 12
for the other three standards and the unknown solution.
Calculation:
1. On a piece of regular graph paper, label the horizontal axis concentration and
mark it in equal intervals from 0 to the value of standard 4. Label the vertical
