Method
- Measure 10cm ³ of glacial acetic acid, 4cm³ of appropriate juice and mix it together with distilled water until it make up of 100cm³.
- Fill a burette with this solution and note the burette reading.
- Use a syringe to transfer 1 cm³ of D.C.P.I.P into a conical flask and titrate.
- Add the juice, one drop at a time until the blue D.C.P.I.P is reduced to a colourless solution.
- Repeat for the other juice samples, then repeat the whole procedure.
- Calculate using the results obtain the concentration of ascorbic acid in each of the juice samples.
- Tabulate and present all data.
Data Collection
- Qualitative data
- 10.0 ± 0.5 ml of acetic acid is used in each experiment.
- 4.0 ± 0.1 ml of lime juice - fresh, boiled (10 minutes, 1 hour)
- 1.0 ± 0.1 ml of DCPIP solution is used in each experiment
- A total of 100 ml of mixture of the following will be used in each titration
- Acetic acid + lime juice + distilled water
- The concentration of DCPIP is 0.1 %
- Quantitative data
* Solution is the mixture of glacial acid, respective lemon juice and distilled water.
Table 1: volume of solution used in the titration
Data Processing
-
The average volume of titrated juice =
- The concentration of ascorbic acid in each juice can be calculated using the following formula;
The mass of ascorbic acid equivalent to 1 cm3 of DCPIP = 0.05 mg
In n cm3 of juice solution = 1 cm3 DCPIP
Hence, the volume of lime juice sample titrated contains 0.05 mg of ascorbic acid
Therefore, the concentration of ascorbic acid in sample = mg ascorbic acid
= X
Therefore, concentration of ascorbic acid in pure juice, =
Concentration of ascorbic acid in pure juice = 25% X
- Uncertainty = % uncertainty of average volume used in titration
Table 2: average volume of juice used and its respective concentration of ascorbic acid
Bar Chart 1 : Concentration of ascorbic acid in pure juice
Evaluation and discussion
-
From the calculation, it is clear that fresh lime juice has the highest concentration of vitamin C which is 0.0476 mg cm-3 followed by the boiled lime juice ( 10 min ) which is 0.0379 mg cm-3. The boiled lime juice ( 1 hour ) has the lowest concentration of vitamin C which is only 0.0362 mg cm-3.
- Vitamin C, one form of ascorbic acid, can be denatured by high temperature breaking it into simpler molecules. The longer the lime juice is boiled, the higher the amount of vitamin C that will be denatured and thus decreasing the concentration of vitamin C in lime juice.
- We can relate this result of experiment in our daily life such as cooking. In order for us to get the maximum benefit of eating fruits and vegetables, we should reduce the time of cooking of the fruit or in some cases, just eat them raw so that the amount of vitamins in them is the highest.
- The function of acetic acid in this experiment is to minimize the acidic effect of ascorbic acid as it can lower the temperature of the solution.
Conclusion
From the result, the longer we boil the juice sample, the lesser is the content of ascorbic acid in the sample. So, we can conclude that the longer we cook our food, the lesser is the content of vitamin C in them.
International Data Standard, July 1980