Hypothesis
I think that the fresh fruit juices will contain more vitamin C than the fruit juices. I think that the Orange fruit will have the most vitamin C and the lemon juice having the least. The fresh fruits will have more vitamin C content than the juices because Vitamin C can be very easily Oxidised and the fruit juices will have been in contact with Oxygen for longer than the fresh fruits. Other factors such as additional ingredients in the fruit juices may deplete the content of vitamin C.
When the food companies state the contents on the cartons, they will have stated the vitamin C content before the product is finally finished, the older the juice is, the less vitamin C content there is. This could perhaps be why there is actually less vitamin C in fruit juices than stated on the cartons.
Results
This table shows how change in concentration of ascorbic acid affects the volume of the acid required to decolourise 1cm3 of DCPIP
This table shows how much volume of different sources of vitamin C is required to decolourise 1cm3 of DCPIP and using these results we found the concentration of vitamin C in each solution. We used this information to compare the content of vitamin C in fruit juice in relation to fresh juice and what the carton suggests the fruit juice contains.
Analysis
As we increased the concentration of ascorbic acid used, our results show a decrease in the volume required to decolourise 1cm3 of DCPIP. For a concentration of 0.003125% of ascorbic acid, we found an average volume of 13.79cm3 was required to decolourise the DCPIP. As the ascorbic acid volume was increased to twice the concentration, the average volume required decreased to 8.17cm3. As we doubled the concentration of acid again, the average volume required decreased to 2.52cm3. Then, when we doubled the concentration of the acid for a fourth time, the average volume required still decreased but at a much lower rate to 1.04cm3. As we doubled the concentration again, the average volume required decreased at an even lower rate to 0.57cm3. Using the graph from the results, it was possible to find an estimate for the concentration of the unknown solution by following the pattern shown, which was 0.017%.
Our results show a negative correlation because vitamin C the ascorbic acid is an antioxidant and reduces the DCPIP. Therefore, a higher concentration would contain more acid molecules, so a lower volume is required for the same amount of molecules to reduce the DCPIP and make it colourless.
The error bars are relatively small and consistent as most of our results were very similar but for 0.003125%, there is a quite large error bar as there is an anomaly and we also collected less results compared to the other volumes with only two similar, which therefore aren’t very reliable. Our results for 0.0125% aren’t very reliable as the error bar is quite large because, again, there is an anomaly and we collected smaller amounts of results. Again, for the unknown solution we only collected three results, and so they aren’t very reliable either.
Evaluation
My results were fairly reliable as the patterns set a trend that compliments modern theories of vitamin C content in fruit and fruit juices. Although the outliers could have been prevented if there had not been human errors such as misreading measurements, bad equipment and individual measuring systems. Because we were using old and not fresh fruit juices, vitamin C may have been lost due to age, temperature and sunlight on the carton, therefore effecting the vitamin C content. But as we know, all contents on the carton are slightly higher than the true value due to these problems. When testing with the DCPIP, some solutions did not Cleary go colourless so it was hard to interpret whether it had decolourised or not. Most of these errors where systematic errors which lead to human errors. Random errors however were also frequent in this experiment as most variations of temperature, air flow, volumes of solutions did affect the vitamin C content.
To prevent these errors and anomalies appearing next time, I will take more care in measuring the volumes of solutions and I will use the best equipment possible to increase reliability of our results and get as many results as possible to make the possibility to outline anomalies and remove them from the results.
