Safety/Risks:
- During the experiment, make sure that none of the solutions are ingested. Even if the DCPIP hasn’t been added to the fruit juice, there should be no reason to drink the juice, because other toxic chemicals might have accidently poured into it by mistake.
- DCPIP itself is a toxic chemical which will cause death.
- Wear goggles and gloves so that the DCPIP does not touch your eyes/skin etc
- Clean up any DCPIP solution spills immediately.
- All DCPIP solutions, after the experiment, should be poured into a waste bucket. Wash out the test tubes with water thoroughly.
- Be careful not to break any glassware, so that you do not get cut and suffer from an infectious wound.
- Tie back long hair, and remember to wash your hands after the experiment is over.
Variables:
Independent variable:
- The type of fruit juice used.
Dependent variable:
- The time taken for the DCPIP to decolourise.
Controlled variables:
- The volume of Vitamin C solution/fruit juice added.
- The volume of DCPIP poured into the fruit juice.
- The temperature of the equipment used by performing the experiment in a temperature-maintained laboratory.
- The people performing each task are constant: same person operates the stopwatch, same person pours the Vitamin C/fruit juice/DCPIP, same person observes the colour change and stirs glass rod.
To ensure that the experiment was fair, we kept the amount of DCPIP added as 1cm³ per test tube. Furthermore, we made sure that we started the stopwatch as soon as the DCPIP was added to the juice, as to reduce the error of time delay in our results.
The actual chemical reaction that occurs when the DCPIP reacts with the fruit juice:
Results:
As the table clearly shows, the greater the time for the DCPIP to change, the less concentrated the juice is with Vitamin C. Therefore, the DCPIP in Vitamin C takes only a mere 4.67 seconds on average to change colour, thus indicating that the concentration of Vitamin C is very high indeed.
Analysis of results:
I can see that the Vitamin C already acts as the control because it has the highest amount of Vitamin C in it. This is shown in the time taken for the DCPIP to decolourise, and we see that it only took 4.67 seconds on average. Close after it, as I had predicted in my hypothesis, the orange juice had the highest concentration of Vitamin C, because the time taken for DCPIP to decolourise it took 6.13 seconds on average and was the quickest out of the three. After the orange juice came the pineapple juice in 9.48 seconds and lastly, papaya juice in 10.23 seconds.
Conclusion: In conclusion, my hypothesis was proven correct. The orange juice did have the highest concentration of Vitamin C out of the three fruit juices we experimented with. This is because oranges are naturally rich in Vitamin C. However, I cannot say that the experiment was entirely reliable; therefore the results could prove to be invalid.
Evaluation: Our experiment went well, and our hypothesis was proven successful, however I feel that the method could have been improved to get more accurate results. In Step 1, I felt that using a higher volume of Vitamin C solution would be better; there would be more moles of ascorbic acid. This would get a better control value, especially if a larger volume is used. I don’t feel that the other juices will comply and correlate with this control, if a small volume of Vitamin C is used. Therefore, increase the volume of the control, and the fruit juices, especially if the DCPIP happens to be in excess. Furthermore, more DCPIP will mean that the accuracy of the results will be improved, and they will correlate as the amount of DCPIP increases with the amount of fruit juice used. The type of pipettes we used were those plastic versions where we squeezed it to suck up fruit juice into its hollow body. To save time in using a pipette and a measuring cylinder, we could have used an adjustable pipette which allows the user to adjust how much liquid they want to pipette up for their sample.
We could further the experiment by using more types of juice, in greater quantities. We could also analyse whether the season/weather affects the vitamin C content of the juice. Furthermore, we would repeat the experiment many more times to get even more accurate results.
In our experiment, we were very careful about being accurate, even though we repeated the experiment 3 times. The same person was used to do the same task. The person we used to stir and observe the DCPIP solution decolourisation has the fastest reaction time than everyone in our group, and they could manage an even stir method without growing weary. We were careful when we measure out the volumes for each liquid, because we used an accurately detailed measuring cylinder. We judged the volumes by levelling it off at the meniscus. We used standard laboratory pipettes to transport the juice from the carton to the test tube. We used standard stopwatches to time the decolourisation.
On the question on whether any mistakes were made, I would have to say that when doing our third repeat of the experiment, all of the juices were not double-checked with their volumes, and their percentage error is arguably 10-35% inaccurate. The reason for this blunder is due to the fact that we had limited time left, with only a time limit of 1 hour. However, I don’t believe that the results were dramatically corrupted. If we had unlimited time do complete the experiment, I believe that the results produced would be far more satisfactory than the results we have currently. Suffice to say that the general results do support our hypothesis; we still have reason to believe that further experimentation might alter that conclusion.
When we were performing the experiment, we knew that the DCPIP would allow us to find out the vitamin C content easily. Dichlorophenol-indophenol is a redox dye, that when in contact with any isomer of ascorbic acid – Vitamin C is a stereoisomer of ascorbic acid. Naturally DCPIP is a blue compound, but when oxidised, it turns a red colour. Normally we get oxidised DCPIP when we do lab experiments, mainly because the oxygen in the air reacts with it during factory bottling. During the reaction, oxidised DCPIP is reacted with Vitamin C where the Vitamin C becomes oxidised and the DCPIP becomes colourless and reduced.
This is the result we expected, because we suspected from other scientific experiments that oranges/orange juice contained a rich content of Vitamin C.
Our results back up other scientific doctrines, such as advice given by doctors to patients with the common cold, flu that they must drink a lot of orange juice and consume oranges for the next few days.
In our experiment, the equipment/environment we worked did not pose major threats to us, except for the fact that we were, in fact, handling the toxic chemical, DCPIP, and we were using glassware that could potentially cut us, leading to a developing infectious wound. Other than that, no-one was hurt and our experiment was completed on schedule.
[How the did you ensure that the measuring was correct? What mistakes were made? How could this improve? What did you observe? Is the result what you expected? Compare to published information. Were there any hazards?]
During the experiment, there were a few issues concerning the validity of the experimental results. Our set of results did not actually cover the entire “fruit juice” umbrella, meaning that our experiment was in fact exclusive only to the equipment we used that day. For example, we used three different types of juices: orange, pineapple and papaya, which were bought from a supermarket in the middle of December. We do not know whether those fruit juices were squeezed from their fruits as soon as they were picked and put into constant refrigeration, or whether they were picked, left in storage for a few days, squeezed into cartons, left out in a warehouse for a day, and then put into refrigeration for a short while in the supermarket after being shipped from the country of origin.
Furthermore, the results show that the orange juice in the experiment has a higher concentration of Vitamin C than pineapple and papaya juice, but generalising about all oranges, pineapples and papaya fruits cannot be justified. There is a big difference in variation with subspecies of fruit, age and season of fruit.
We also had to make sure that the fruit juices were not heated any point, because heating Vitamin C causes it to be destroyed.
Also, during our experiment, we used our pipettes from a storage box. Some of the other groups working on the same experiment were taking pipettes from there as well. Therefore, there is a chance that the same pipette was used to pipette up two or more of the fruit juices. This means that the samples used were contaminated, and our results could be invalid and effectively unreliable.
There is also a chance that heating the fruit juice will concentrate the Vitamin C, therefore the decolourisation would be inaccurately quick. The results, in the end, would not support the hypothesis.
There is also a reason to believe that the fruit juice companies add extra artificial ascorbic acid to increase its concentration.
Moreover, if the squeezed fruit juice is left out exposed to the air, there could be a considerable difference in the concentration of Vitamin C.
Lastly, due to the fact that other chemicals like sodium sulphite can react with DCPIP, if they are present in the juice, then it will be unfair to accept the results, unless we assume that the only reducing agent is Vitamin C.
