Biology Lab

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DATE: 8th October, 2012
SYLLABUS TOPIC: Food Tests – Semi Quantitative Test
AIM: To determine the concentration of glucose present in an unknown sample, using a semi quantitative glucose test APPARATUS AND MATERIALS: 4% stock solution of glucose, water, 6 test tubes, ruler, water bath, solution of unknown concentration (Sample A), Benedict’s reagent METHOD:

1. Solutions of different concentration were made from the stock solution and placed in test tubes. 2. All test tubes were labeled appropriately, according to table below, and Benedict’s test was carried out on the various dilutions for 5 minutes. 3. The colours of the solution were observed and heights of precipitate formed were recorded. The test tubes were placed in a rack and put aside to be used as a colour standard for comparison. 4. Benedict’s test was carried out on sample A.

5. Solution formed was compared to solutions of known concentrations to find the concentration range in which sample A fell. RESULTS AND OBSERVATIONS:
Test Tube| Concentration / %| Volume of stock / cm3| Volume of water / cm3| Height of precipitate / mm| Colour Change| 1| 4| 5| 0| 10| Blue to Red|
2| 1.5| 7.5| 12.5| 7| Blue to Dark Orange|
3| 1| 2.5| 7.5| 5| Blue to Orange|
4| 0.5| 2.5| 17.5| 4| Blue to Light Orange|
5| 0.25| 2.5| 37.5| 3| Blue to Yellow|
Sample A| Unknown| Unknown| Unknown| 9| Blue to Red|
TABLE SHOWING CONCENTRATIONS OF SOLUTIONS AND HEIGHT OF PRECIPITATE **A multiplication of X2 was used for solutions 3
**A multiplication of X4 was used for solution 2 and 4
**A multiplication of X8 was used for solution 5

CALCULATIONS:
Solution 2
Initial Volume (V1) x Initial Concentration (C2) = Final Volume (V2) x Final Concentration (C2)
4 V = 5 x 1.5
4 V = 7.5
V = 1.875 cm3
Volume of water = 5 -1.875 = 3.125
Using a...
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