Activity 1.21 Vit C Report of Core Practical Edexcel As

Activity 1.23 The concentration of vitamin C in different fruit juices Aim and Introduction Vitamin C, or ascorbic acid, is essential in the diet to keep our bodies healthy as it helps repair damaged tissues, gives us healthy teeth and bones and enhances our immune system. Vitamin C also has a very important role as an antioxidant - to neutralize free radicals, which are a product of oxidation in the cells and which cause damage to molecules such as DNA. These free radicals can lead to premature aging (not only to the skin but also to the organs and tissues) and diseases (such as heart disease and cancer). It is therefore vital to maintain high levels of Vitamin C in our diet. This can be achieved by eating citrus fruits (e.g. lemons and oranges) or drinking juices made from these citrus fruits. High levels of fresh fruit and vegetables are known to reduce risk of various diseases including cardiovascular disease. This is, in part, because of the antioxidants they contain. Fruit juices are marketed as healthy drinks and part of the marketing is to state that vitamin C (widely perceived by consumers to be favourable) is present in the drink. In this investigation I looked at whether or not juices actually contain the levels of vitamin C that they claim to have. Variables The independent variables in this experiment were the different fruit juices that were used to decolorize the DCPIP solution. The dependent variables were the volume of fruit juices required to decolourise the DCPIP. The control variables were the volume of DCPIP solution was measured as 1cm³ per experiment that took place, and the concentration of the DCPIP was 1% at all times. Method I started off by adding approximately 1cm³ of the DCPIP into a test tube with a 1cm³ measuring syringe. I then measured the initial volume of the juice, before adding it to the DCPIP solution. I added the juice drop by drop to the DCPIP, shaking the test tube gently per drop, until the dark blue/purple colour of the DCPIP disappeared. Once that happened, I stopped adding drops of the juice, and measured the end point volume of the juice, to work out exactly how much of the juice was needed to decolourise the DCPIP solution. I repeated this procedure with the Vitamin C solution and the rest of the juices. Once I had completed the experiment, I gathered the rest of the results and worked out the mean. I then used the mean of Vitamin C (0.51cm³) and then divided it by the mean volume of juice used, then times it by 100 to get the mg/100cm³ so I could compare my results to what the factory had stated on the packaging. Results and Conclusion

Sample 1% Vit C solution

Vol. of solution required to decolourise DCPIP / cm3 1 2 3 4 5 6 7 8 mean 0.3 0.3 0.5 0.7 0.4 0.6 0.5 0.8 0.51

Tropicana Orange

2.8

3.3

2.6

3.1 2.9

3.2

2.4 3.3

2.95

Tropicana Orange & Lime

3.5

4.7

3.7

2.2 3.9

4.8

3.5 4.6

3.86

Tropicana Apple

2.6

3.8

2.8

3.3 3.0

3.4

3.0 3.8

3.21

4.0

5.9

4.9

5.2 5.2

5.0

6.1 4.8

5.14

Tropicana Grapefruit

The vitamin C concentration for each juice can be calculated by relating the volume needed to decolourise the DCPIP to the volume needed of the vitamin C of known concentration. For example, for the known 1% [1mg cm-3] Vitamin C solution: 0.51cm3 of 1% Vitamin C solution is needed to decolourise 1cm3 DCPIP. So for the Tropicana Orange Juice: Mean volume needed to decolourise DCPIP = 2.95 cm3 Therefore, 1mg/cm-3 x 0.51 cm3 ÷ 2.95 cm3 = 0.17mg/cm3 x 100 = 17mg/100cm3 of Vitamin C in the Tropicana Orange Juice On the cartons the Vitamin C value stated is per 100mg/cm³, therefore the calculation must include *100 in order to state 100mg/cm³ rather than 1mg/cm³ of Vitamin C.

vitamin C concentration 100mg/cm³, Stated Measured Value Mean 100mg/cm³, 100mg/cm³, S.D 33 17 0.33

Tropicana Orange Tropicana Orange & Lime

29

13

0.86

Tropicana Apple

41

16

0.44

25

10.0

0.65

Tropicana Grapefruit

Vitamin C Content of Fruit Juices 45 40 35 30 25

Stated value

20

mean

15 10 5 0 1

2

3

4

As you can see from the graph, the concentration of vitamin C in each fruit juice tested about half of what was stated on the cartons. This is primarily because the juice was not fresh, and appears that half of the Vitamin C had been oxidised since the opening of the cartons (we experimented after 5 days of the cartons being opened). Interpretation It seems that the supermarket has been conservative in the levels of vitamin C stated on the packaging for each of the juices tested. This may be so that even when the juice varies, it will still contain at least as much vitamin C as stated. Evaluation According to the standard deviation, the results contain no anomalies as the standard deviation is small (below 1), meaning results are closer to the mean, therefore more reliable. Further reliability is presented as there were 8 experiments on each juice, rather than 3. However, the accuracy was not able to be measured properly as the experiment was carried out only once per juice per group, as there wasn’t enough time to repeat the experiment with the same juice per group. When we put all results together, this could have affected the overall outcome of the results, as the results were all from different people for each “repeat” of the juice experiment. Due to all results being fairly similar per juice, though, it doesn’t seem to have had as much as an impact as expected, even though everyone tried to be as precise as possible for this overall experiment. The burette drops were of different sizes, and the drops were rapid, so the test tube was in continuous movement, and when the end point was noticed, a few more drops had been able to get into the solution before the burette was shut. This could have made the volume of juice taken to decolourize the DCPIP a little bit more than what it would actually take to decolourize it. Another precision error that could have taken place is when measuring the initial and final volume of the juice as the meniscus wasn’t always too clear as it was taller than my height. This may have led me to slightly overestimate or underestimate the volume of juice used (by 0.1-0.2cm3)The data wasn’t as precise as the juice cartons weren’t opened on the same day as the experiment, therefore some of the vitamin C (in our case about half) could of oxidised, meaning not all Vitamin C could have been detected. The errors I have identified were all random errors, as no instrument was improperly used or had any issue with it. The random errors were there because errors took place through unpredictable stages. If we were able to control when the cartons were opened, I think we could have a closer result to how much vitamin C was stated on the carton, as barely any of the Vitamin C would have oxidised. But as mentioned earlier, since the carton was opened 5 days before the experiment, it appears that around half of the Vitamin C expected was tested and found during the experiment.