Measurement of the vitamin C content of fruit juices

2. Fill a syringe fitted with a needle with 1 cm³ of 0.1% solution of vitamin C.

3. Add the vitamin C slowly to the DCPIP solution stirring gently with the syringe needle. As the DCPIP starts to loose its colour add the fruit juice drop by drop until the DCPIP just goes colourless. If necessary fill the syringe more than once. Record the volume of vitamin C added. Repeat this at least once so that you can work out an average volume of vitamin C needed to decolourise the DCPIP.

4. Repeat the experiment using each of the fruit juice solutions instead of the vitamin C and work out an average volume for each fruit juice.

5. Calculate the percentage of vitamin C in each fruit juice solution using the following equation.

Percentage of Vitamin C        =        Average volume of vitamin C used x 0.1

in fruit juice                              Average volume of fruit juice used

Each of the fruit juices was heated at their boiling points (100°C) for different periods or time before the experiment. Below shows the time they were left for:

Fruit juice A         - Fresh

Fruit juice B         - ½ hour

Fruit juice C         - 1 hour

Fruit juice D         - 2 hours

Fruit juice E         - 5 hours

Diagram:

Apparatus:

• Test tubes
• Syringe with needle on it
• DCPIP solution
• 5 samples of fruit juice
• Safety goggles

Fair test:

        Make sure when reading the syringe that you read it the correct way up each time. If it reads 0.4 when you have finished than this is now much liquid is left. I.e. you have added 0.6 cm³.

Safe Test:

        Do not carry the syringe around the room. Hold the syringe with the needle pointing down. Wear safety goggles at all times. If the syringe appears blocked, do not force it.

Prediction:

        I thick that the longer the vitamin C is heated the more solution it will take for the DCPIP to decolourise.

Observing

Analysis

        

        I took the averages of my results and used them in the equation mentioned earlier.

Percentage of Vitamin C        =        Average volume of vitamin C used x 0.1

in fruit juice                             Average volume of fruit juice used

Percentage of Vitamin C        =        0.92 x 0.1

in fruit juice A                             1.0

                        =        0.092                =        0.09%

        

Percentage of Vitamin C        =        0.92 x 0.1

in fruit juice B                                 1.09

                        =        0.084403669        =        0.08%

Percentage of Vitamin C        =        0.92 x 0.1

in fruit juice C                                  1.14

                        =        0.080701754        =        0.08%

Percentage of Vitamin C        =        0.92 x 0.1

in fruit juice D                                  1.45

                        =        0.063448275        =        0.06%

Percentage of Vitamin C        =        0.92 x 0.1

in fruit juice E                                   2.23

                        =        0.041255605        =        0.04%

I have come to the following conclusions based on my results:

• The longer the vitamin C is boiled, the less the vitamin C content
• The content of vitamin C in fruit juice is very low

The prediction I made was correct and I used the results to make a graph.

Evaluation

        

        I think the experiment went well because I achieved a good set of results. I think the results were quite accurate because when we repeated the experiment the results were almost exactly the same.

        If were to do the experiment again I would change the method by using syringes that were a bit more accurate so that I could measure to two decimal places instead of just one, which would make my results more accurate. My method may not have given results that were reliable because I could have made human errors, such as miss reading the syringe, dropping too many drops at once, not leaving the solution long enough before adding more fruit juice as it may have been enough fruit juice in the solution already. Also there could have been mistakes when measuring the standard solution, which would have made all of the results of vitamin C % in the juice, inaccurate.

         I think there were enough results, however if I had of repeated the experiment once more, it would have given more accurate results. But the results I did get allowed me to form a good conclusion because there was a visible pattern, showing that the content of vitamin C got less as the time it was boiled for got more. So there is an inverse relationship between vitamin C content and time it was boiled for. There was also the visible trend that showed you that the longer the juice had been boiled for the more was needed to decolourise the DCPIP as there is a lower content of vitamin C in the juice.

        I had one anomalous result, the test of fruit juice B. The amount of vitamin C added should have been about 0.12 cm³ instead of the 0.09 cm³ that I got. This means I did not put enough fruit juice into the DCPIP, which shows a human error as I said before. This was the only anomaly, which shows the results were quite accurate, but also points out the importance of repeating the experiment three times, so that you can see any anomalies.

        As I said before, you could use a more precise syringe to get more accurate results. Also the more times you repeat the experiment the more accurate the experiment, which means the more accurate the results. Ensure that the Standard solution is tested well as that result effects the end overall results.

        Another experiment, which could be done, is; to compare the vitamin C contents of Oranges, Lemons and grapefruits, to see which one had the highest amount of vitamin C. The method would be:

• Draw up 2 cm³ fresh orange juice into a syringe. Add this drop by drop to 1 cm³ of DCPIP solution.
• Record how much was added and repeat the experiment to obtain averages.
• Repeat the experiment with orange and grape fruit juices
• Compare the results of all three samples. The one, which uses the least amount of juice, contains the most vitamin C in the juice.