Experiment 2
Date: November 23, 2021
Title: A quantitative comparison of reducing sugar present in mango and June plum extract.
Aim: To determine the concentration of the mango and June plum samples via stoichiometric
calculation by titration.
Apparatus/ Materials: Burette, pipette, pipette filler conical flask, Bunsen burner, wire gauze, tripod
stand, retort stand, dropper.
Reagents: Anhydrous sodium carbonate, benedict’s solution, sample extract, water
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
Pipette 25cm3 of Benedict’s solution of a known concentration into a conical flask.
Add 6g of anhydrous sodium carbonate to the conical flask and then heat gently for 30 seconds
Fill the burette with a sample of the extract.
Perform the titration using the relevant technique until the blue color disappeared. (Look for the
precipitate until it is formed).
Record the volume of the extract that completely reduce Cu2+ ions to Cu+ ions.
Repeat this twice for each of the extract (and boil the mixture during titration).
Record the results in a table which outlines, the initial volume, final volume, as well as the
calculation of volume used for each sample.
Repeat the titration using 1% glucose as the standard.
Results:
Mango juice
Initial volume
Final volume
Volume used
Titration
1
0.00
12.00
12.00
2
12.00
23.5
11.5
3
23.5
44.0
20.5
Titration
1
June plum juice
Initial volume
Final volume
Volume used
0.00
50
50
Titration
1
Glucose (1%)
Initial volume
Final volume
Volume used
2
3
0.00
50
50
0.00
50
50
2
3
0.00
17.00
17.00
34.12
34.12
47.00
17.00
17.12
12.88
Calculations:
i.
Calculate average volume of titrant used
Mango
12+11.50 = 11.8m3
34 ÷ 3 = 11.33m3
June Plum
50 +50 +50 = 150m3
150 ÷ 3 = 50m3
Glucose 1%
15 + 15 + 15 = 45m3
45 ÷ 3 = 15m3
ii.
Identify standard solution and use this information to calculate number of moles of the standard
solution used.
CuSO4H2O
Conc x volume
25cm3/1000 x 0.06moldm-3
0.0015mol or 1.5 x 10-3 mol
iii.
Use mole ratio from balanced equation between glucose / sample and Benedicts (CuSO4. 5H2O)
to find out the number of moles of all reactants based on that of standard solution.
2CuSO4+5H2O+C6H12O6  C6H12O7 + Cu2O + 2H2SO4+3H2O
2:1
0.0015: X
=0.00075mol or 7.5 x 10-4 mol
iv.
Use this information to calculate final concentration of mango extract in volume of extract used.
Concentration = moles/volume
=0.00075/ (11.8/1000)
=0.00075/0.0118
=0.064moldm-3
Discussion: Titration is the slow addition of a known concentration (called a titrant) to a known volume
of another solution of unknown concentration until the reaction reaches neutralization, which is often
indicated by a color change. The basic principle of titration is the following: A solution – a so called titrant
or standard solution – is added to sample to be analyzed. The titrant contains a known concentration of
a chemical which reacts with the substance to be determined. The titrant is added by means of a burette.
Benedict’s test is a simple chemistry test used to detect reducing sugars. Reducing sugars are
carbohydrates having free aldehyde or ketone functional group in its molecular structure. These include
monosaccharaides like glucose and fructose and disaccharides like lactose and maltose. Benedict’s
reagent is the solution used in Benedict’s test to detect simple sugars such as glucose. It is a bright blue
solution prepared by mixing copper sulfate pent hydrate (CuSO4 5H2O), sodium citrate (Na3C6H5O7), and
sodium carbonate (Na2CO3) in distilled water.
The test may be qualitative, or it may be quantitative. The qualitative test produces a color change from
blue to green to yellow to orange to brick red. The qualitative test is also regarded as semi-quantitative
as the color obtained correlates to the concentration of reducing sugars in the solution. After three
necessary steps mentioned in the method were followed the juice was then dripped into the freshly
warmed benedict solution. As the juice dropped into the benedict solution there was no change but over
time a flash of green could be noticed. They disappeared quickly as the solution was being mixed. The
flashes of green started to linger longer in the solutions till eventually the once blue benedict solution
turned to a light shade of green.
For each titrant the average volume was calculated. Mango was 11.8cm3, June plum was 50cm3and
glucose 15cm3. The mango juice was observed to have the lowest average volume hence noting it had the
highest concentration. More reducing sugar was present in the mango juice than all the other solutions.
Sources of error: Parallax error in reading instruments
Limitation: Heat was lost from the mixtures to the environment during titration
Precaution: apparatus were washed before the measuring of a different solution.
Conclusion: the concentration of the mango sample is 0.064moldm-3.