Different concentrations of Vitamin C will be made up as follows:
The concentrations of the solutions were calculated as follows:
Volume of Vitamin C in solution x Original concentration of Vitamin C
Total Volume of solution
Concentration of solution A: 10 x 2 = 2mg/cm³
10
Concentration of solution B: 8 x 2 = 1.6mg/cm³
10
Concentration of solution C: 6 x 2 = 1.2mg/cm³
10
Concentration of solution D: 4 x 2 = 0.8mg/cm³
10
The same experiment will be done for the last three solutions - Vitamin C solution will be added to DCPIP until DCPIP is reduced. This part of the experiment will be called the control.
Then, fresh fruit juices will be used in the place of Vitamin C solution. Orange juice, lemon juice, grapefruit juice and pear juice will be used. These juices will be freshly squeezed. The fresh fruit juice will be added to the DCPIP until the DCPIP turns colourless. The results for this part of the experiment will give us the concentration of Vitamin C in the fresh fruit. The volume of Vitamin C needed to reduce the DCPIP will be recorded. Juices must be freshly squeezed so as a risk assessment, a tile will be used to cut the fruits on. The volume of juice needed for the DCPIP to turn colourless will be compared to the results of the control experiment. This will give the concentration of Vitamin C in the fresh fruit. I.e. if 5cm³ of 2mg/cm³ Vitamin C were needed to reduce
DCPIP and 5.2cm³ of orange juice was needed to turn DCPIP colourless, the concentration of Vitamin C in orange juice would be 2mg/cm³.
Then, carton juice will be used to reduce DCPIP instead of Vitamin C and fresh fruit juice. In order to compare concentrations of Vitamin C, the same carton juices will have to be used as the fresh fruit juices. I.e. if fresh orange juice was used, orange juice in a carton will be used. The same procedures apply to the carton juices as the fresh fruit juices. Results will be noted.
Results will be tabulated in three different tables. Table 1 will consist of the results from the control experiment; table 2 will consist of the results of the fresh fruit juices and table 3 will include the results of the carton juices.
Method:
Taking 4 Vitamin C tablets and dissolving them in 100cm³ of distilled water made up a 2mg/cm³ Vitamin C starting solution. Using a syringe, 1cm³ of DCPIP was taken up and put in a test tube. Another syringe was used to take up some of the Vitamin C solution. Vitamin C was added into the DCPIP drop by drop until the DCPIP turned colourless. The volume of Vitamin C needed for the colour change was recorded.
Different concentrations of Vitamin C were made up using the starting solution. However, the numbers of solutions made up in the plan were not enough as a control. So, more solutions were made up:
The same formula used in the plan was used to calculate the concentrations of the solutions.
The same experiments were done for solutions B to J as were done for solution A – each solution was added to 1cm³ of DCPIP until the DCPIP turned colourless. This was the control of the experiment.
Then fresh fruit juices were made – orange, lemon, pear and grapefruit juices. These juices were made by freshly squeezing the fresh fruits. The same experiment was done, tested with DCPIP. The results were compared to that of the control experiment and the concentration of Vitamin C in the fresh fruit was determined. E.g. the volume of fresh orange juice needed to reduce the DCPIP was 11.6cm³. The control experiment
showed that the volume of 1.6mg/cm³ Vitamin C needed to reduce the DCPIP was 11.4cm³ and the volume of 1.4mg/cm³ Vitamin C needed to reduce DCPIP was 12.4. This shows that the concentration of Vitamin C in the fresh orange must be between 1.6 and 1.4mg/cm³.
Carton juices were then used in the place of Vitamin C and fresh fruit juice. The results were compared to that of the control experiment and the concentration of Vitamin C in the carton juice was determined. The comparisons were done in the same way as the results of the fresh fruit juices were compared to the control experiment results.
Results:
TABLE 1:
Control Experiment
Volume of Vitamin C needed to reduce the DCPIP and turn it colourless
TABLE 2:
Using fresh fruit juice
Volume of fresh fruit juice needed to reduce the DCPIP and turn it colourless
TABLE 3:
Using carton juice
Volume of carton juice needed to reduce the DCPIP and turn it colourless
The results and the graphs of the control experiment show that as the concentration of Vitamin C decreases, the volume of Vitamin C needed to turn the DCPIP colourless increases.
The differences between the results get larger as the concentration of Vitamin C gets smaller. I.e. the difference between the results of 1.6 and 1.4mg/cm³ was 1cm³ and the difference between the results of 0.4 and 0.2mg/cm³ was 6.3cm³.
Tables 2 and 3 also include the expected volumes of Vitamin C present in the juices. Here are the tables summarised:
The table shows that fresh grapefruit and fresh lemon contained more Vitamin C than their carton juices. However, fresh orange juice and carton orange juice contained roughly the same concentration of Vitamin C, which was between 1.4 and 1.6 mg/cm³.
The table above and tables 2 and 3 show that there were no results for the pear juice. There was hardly any trace of Vitamin C in the pear. Over 100cm³ of juice had to be used and there was still no change in the colour of the DCPIP. I would have liked to continue adding juice to the DCPIP until there was a colour change but the juice was hard to obtain by squeezing the pear. This unknown concentration of Vitamin C in the pear shows that I have had anomalies within my results. This could have been because the concentration of DCPIP may have been too high for the pear to reduce.
The citrus fruit showed a high concentration of Vitamin C was present in both fresh fruit and carton juice. This proved my hypothesis saying that citrus fruits will contain a higher concentration of Vitamin C than other fruits.
My results showed that oranges contain the highest concentration of Vitamin C, followed by lemons and finally grapefruit.
The results tables also show that the juices of table 2, fresh fruit juices, needed less juice to reduce the DCPIP than the juices of table 3. This shows that the fresh fruit juices have a higher concentration of Vitamin C than the carton juices. This proves my hypothesis is correct.
The bar chart that shows the volumes of juice needed to turn the DCPIP colourless, which is the blue and orange coloured bar chart, shows the results of the fresh juice and carton juice on one graph. It shows that the volumes of juice needed to turn the DCPIP colourless for grapefruit, orange and lemon juices was higher in carton juices than fresh fruit juices. This means that the concentration of Vitamin C is higher in fresh fruit than carton juice. The bars for the orange juice show that a little bit more carton orange juice was needed to reduce the DCPIP than the fresh orange juice. This goes to show that the fresh orange juice must have a slightly higher concentration of Vitamin C than the carton orange juice.
The concentrations of Vitamin C in the fresh fruit juices and carton juices were worked out simply by comparing the results to the results of the control experiment.
Concentration of Vitamin C in grapefruit: 14.8cm³ fresh juice needed to reduce DCPIP. Looking at the table of results of the control experiment, 14.8 lies between the values 14.4 and 15.9cm³. Going across the table, this shows that the concentration of Vitamin C must lie between 0.8 and 0.6mg/cm³. The comparisons were done for each of the results in tables 2 and 3.
Evaluation
The results may not be as accurate as I would have hoped. This is because of the main experimental limitation being that I may not have known exactly when the DCPIP turned colourless. E.g. with the fresh lemon juice, I read that 13.2cm³ of juice was needed for the DCPIP to turn colourless. It may have needed only 12.9 or 13cm³ to turn colourless.
To remove the anomaly, which was the pear, I could have taken only 0.5cm³ of DCPIP instead of 1cm³. This may have allowed the Vitamin C in the pear to reduce the DCPIP and give me an estimate as to the concentration of Vitamin C in the DCPIP. Another way I could have found out the concentration of Vitamin C in the pear would have been to continue adding juice to the DCPIP in a 250cm³ beaker, so I would have been able to continue adding juice until the beaker was full. If the beaker had filled up to 250cm³, it would have shown that the concentration of the DCPIP was too high.
This investigation could have been improved by doing repeats of the experiments. This would have given more accurate results. The mean of the readings could have been used to plot graphs and explain the results. I only did one reading of each juice, which could have given me inaccurate results. It may be that lemons have a higher concentration of Vitamin C than oranges and grapefruits have a higher concentration of Vitamin C than lemons.
Also, a wider range of concentrations of Vitamin C could have been used in the control experiment. This would have given more accurate results overall. I may have been able to give a more precise result as to the concentration of Vitamin C in the juices. I had expanded the range of the solutions. I had planned to use only 4 different concentrations but then I realised that I needed a wider range and used 10 different solutions.
A wider variety of fruits could have been used as well. I could have used apples, bananas, plums, grapes and other non-citrus fruits to give me a greater number of results to compare the citrus fruits with non-citrus fruits.
