Variable
Predictions
It is predicted that the blue chemical found in the DCPIP will turn colourless or a pale pink to show the content of the fruit juice with the most Vitamin C. However, if a greater percentage of vitamin C solution is added to an agar gel plate, to test out this hypothesis, the procedure used to carry out the investigation will be less efficient.
Equipment List
- Standard vitamin C solution (1%)
- A wide variety of fruit juices
- Clear rulers (for measuring the length of the pre-prepared wells)
- DCPIP plates with pre-prepared wells
- Pasteur pipettes
- Measuring cylinders
- Clear beakers
- Cork borer
- Dropping pipettes
Method
0.5% of Vitamin C solution is added to an agar plate with pre-prepared wells and is dissolved with 2 drops of fruit juice. It is then left for a short period of time; to enable the concentration of Vitamin C in the fruit juice to diffuse in the gel. This will result in a clear or pinkish circle around the wells. Each student was given an agar gel plate with 5 pre-prepared wells with their different percentages of fruit juice. The agar plates were in turn placed on the laboratory work surfaces and clearly labelled to avoid spillages and confusion when area of the circles were been measured and the results recorded. The averages of all 5 trails were calculated and recorded on a table of results and a graph for comparison.
Risk assessment, Safety precautions, and Ethical considerations
Justifying the validity and reliability of the chosen method
Repeats should be kept at a minimum and only repeated when necessary and students must familiarise themselves with the equipment before the start of every practical. Measurements taken should be accurate and students may cross-check with each other to avoid too many anomalous results. However, anomalous results should be investigated if they occur too frequently. Suitable apparatus and experimental procedures should be followed strictly to ensure valid results and precision and only the most precise equipment should be used to make the test fair and accurate.
Results
A table to show the area of colour change produced by solutions with varying vitamin C concentration %
Discussion of results
Data analysis
It was predicted that the fruit juice with the most Vitamin C concentration would be orange juice. However, this hypothesis was proven to be wrong and Lemon juice was shown to be the fruit juice with the most Vitamin C. Oranges which have a wide range of uses however, lemons expand on theirs all the way down to home remedies. They are used as common food sources and to cure illnesses like: Throat disorders, flu and certain skin conditions (Acne). Lemons are the most commonly used drugs in the world and renowned for their effectiveness. As shown on the graph the experiment results disagree with the prediction that apple and black-currant juices contain the most vitamin C as their contents had additional flavours and sweeteners. Unfortunately, there were no concentrated fruit juices to carry out a thorough investigation. However, when all 3 repeats were carried out on the lemon juice it tended to contain the most vitamin C.
Justifying the validity and reliability of the results collected
The results are valid and accurate because, a trial run was done before the practical was started. This was to ensure that there were no errors. In order to avoid errors in the experiment, the procedure was straight-forward and easy to follow. The results are reliable because they were 3 repeats and the measurements were cross-checked to ensure precision and to make it a fair test. Furthermore, only suitable equipment was used for the practical.
Limitations
One main limitation was lack of time and also the variety of juices, as a few contained less vitamins C so it was difficult to trace the concentration of vitamin C. This also meant the repeats were narrowed down only to 3.
Criticms of the data
Unfortunately more repeats were not possible due to the lack of fruit juices so it was difficult to observe any anomalies in the data. Callipers were not available during the practical so clear rulers were used instead which may have reduced the accuracy of the results recorded.
POTENTIAL ANOMALOUS RESULTS
Looking at the concentration of fruit juice on test two, the area of the circle is 0.5 whilst the repeats are both 1.33.This suggests that the results may be correct as the repeats are closer together which means the results are close to their true value.
Apart from the anomalous results, mentioned above, the results are valid although the orange juice didn’t not react to the concentration solution of Vitamin C there are still some sources of error even through the experiment was carried out carefully.
POSSIBLE SOURCES OF ERRORS
Even though there are no obvious anomalies it is important to consider the possibility of random errors. Although we aimed to cross-check every result due to insufficient time it was impossible.
Other sources of error are lack of concentration and personal bias and lack of callipers meant that the results may not have been as precise and accurate.
LIMITATIONS
One of the most common factors was lack of time and callipers were not available so the numbers of repeats were limited.
REDUCING ERRORS
Extra care should be taken when using Vitamin C solution and callipers should be used when repeating the experiment as it would improve accuracy. ‘Used’ agar gel plate should be labelled clearly so they are not disposed off or used carelessly when a separate group is carrying out the same practical.
CONCLUSION
In conclusion, the overall results disagree with the prediction that orange juice contains the most Vitamin C. This was due to the lemon juice been proven to contain the most vitamin C since it provided the most results when the Vitamin C solution was added to it and also lemon juice is most known for its medicinal purposes.
IMPROVEMENTS
Callipers will improve accuracy and also more repeats carried out in the practical will ensure reliability and the students would have more time to cross-check every measurement.
FUTHERWORK
It would be necessary to carry out the experiment using 2%of Vitamin C solution and also to repeat the 2nd and 3rd trials carried out earlier to produce more accurate results.
RESOURCES
As Salter’s’ Nuffield Biology
C-0003339.htm