Variables such as temperature could affect the results that are collected, as much as can be done to control the temperature to make the results accurate will be done, holding samples with hands can increase the temperature slightly so they will be handled by the lip of the vial and placed into a rack.
When testing samples multiple times I will ensure that the equipment cleaned and dried or if possible new as the pH of water might affect the reaction of DCPIP and ascorbic acid, water can also affect the results depending on whether it is 'hard water' or 'soft water', hard water contains more mineral and more chlorine is present.
Measuring will be as close to as possible accurate, this will include re-measuring samples.
I will be measuring the amount of juice sample solution it takes to decolourise 1cm of DCPIP, first I will use a controlled sample of 1% vitamin C to decolourise the DCPIP, and with this I can compare results from the other juice samples. The measurements will be taken with a pipette and released into the DCPIP 1ml at a time, each time 1ml is released it will be shaken to allow a fair mix of solution, and this will be repeated on till decolourisation.
Vitamin C (Ascorbic Acid) has a pH of under 4-5 when diluted with water
DCPIP, 2,6-dichlorophenolindophenol, which is a dye used to monitor light reaction in photosynthesis
Apparatus & Chemicals;
Fruit Juice Samples
DCPIP 1% Solution
Test tube rack
Glass Rod (Possibly)
I have decided to use test tubes because they provide a clear sight into the experiment at hand, they are also smaller then Pyrex beakers which would spread the solution over a large surface where as a test tube would make it easier to establish decolourisation.
Pipettes are a fast way to measure the solution with a limited amount of time, it is a suitable and vital piece of apparatus however there might be a probably with used pipettes as they can have dents from previous experiments and would only be accurate to around 0.0ml-0.2ml when measuring solutions.
A burette would allow an accurate measure of how much solution has been added into the DCPIP, probably a greater accuracy then using a pipette.
A glass rod would allow a fair mixing of the solution but the effects on the results are unknown.
Take care of glassware.
Sanitise experimental area after.
Wear eye protection at all times..
Care when handling juice samples or chemicals as they may stain.
Do not drink juice samples as dangerous chemicals may be present after experimentation.
The method I will be conducting is simple. I will measure 1% DCPIP 1cm(3) from a beaker to a pipette, with another pipette I will add the 1% vitamin C solution which is the control of the experiment 1cm(3) at a time to a test tube, each time 1cm(3) is added, I will gently stir the test tube to make sure then the reaction takes place. I will repeat this on till the DCPIP solution is decolourised. To get a fair and accurate result I will repeat this 3 times and then average the results. Outliers will be excluded to keep the test accurate. The samples will be kept in a test tube rack to compare different colours.
The next juice two sample will be tested with the same amount of DCPIP, first placed into a test tube via pipette then another unused Pipette will extract the juice sample and will be added into the DCPIP 1ml at a time then stirred gently and this will continue on till the DCPIP is decolourised. The time allocated during this experiment is 1/2 hour. Accuracy could be improved but due to this some apparatus and time will be put aside in order to complete the experiment
There are some ethical issues with testing these chemicals and releasing them into the sewer as they are not helpful to the environment due to their pH, care will be taken so that any DCPIP and Vitamin C is not wasted and only what is needed is used.
Once all of the data was collected, It was input into the table below, It shows the amount of juice required to decolourise the DCPIP, 3 tests were conducted and from that you can then work out the average with a formula to get the average, the average can be used to conclude a fair result from all 3 of the trials.
Vol. Of Juice Required to Decolourise 1cm(3) of 1% DCPIP Test 1 Test 2 Test 3
Vitamin C. Content
Vitamin C Solution
Pure Orange Juice
These results show that the juice sample that contains the most Vitamin C was the Jiff, with an average of 5.5ml to turn the DCPIP decolourised compared to the 15.6ml of pure orange Juice. The Vitamin C. Solution took 7.3ml to decolourise the DCPIP which was 1.8ml more than Jiff, This suggests to me that Jiff contains less water than the Vitamin C. 1% Solution did.
With the average, I then calculated the Content of Vitamin C in each of the samples by Dividing them by the 1ml of 1% DCPIP Solution which gave the sum then converted to grams.
These results prove my hypothesis in that freshly squeezed fruit will contain more vitamin C, this is because it will not have been watered down by manufacturers for a higher quantity. The results also prove my hypothesis is right that lemons contain more Vitamin C. Due to their acidity which is the sign of ascorbic acid (Vitamin C) and their low pH levels.
This line graph shows the plot of the tests carried out. From this we can see that for pure orange juice and Vitamin C samples that there is a steady rise from test 1 to test 3, this could be due to a number of factors that I will include in my limitations, However the Jiff tests shows to be accurate and consistent from test 1 to test 3. There is a 4ml difference from test 1 to test 3 in the pure orange juice tests. There is a 2ml difference from test 1 to test 2 in the Vitamin C 1% Solution Test.
This graph also shows standard deviation, from the bars we can see the average of the test, it measures the spread of data from the mean. The results conclude that the deviation is a Low standard deviation because the valves are not spread out so much.
The equation for the standard deviation used is;
The graph shows that on all samples tested,
Post-Experiment Method, Limitations and Variables;
As planned the measurements of the juice solutions were accurately measured and did not obscure sight in the pipette, However the DCPIP was to a degree harder to measure due to the darkness of the solution, it covered the pipette in a dark blue colour and was hard to tell where and how much solution was being measured. The experiment took slightly longer due to this as I had to wait for the solution to settle into the solution.
As this was the first time carrying out an experiment like this, it was unknown that the 1% Vitamin C solution Control would turn into a brown colour when decolourised, Although this happened I still recorded the results and then continue to see if any difference would appear but after 5 minutes of no change they were placed into a test tube rack to be observed later on and compared with the other trials, the result was that they did turn brown and that was expected to be the end of the trial.
The Pure Orange Juice also produced different than expected appearance, the solution did decolourise the solution but it turned to a yellow colour which was the original of the juice sample.
One problem that I was faced with was the limited amount of apparatus, I ended up having to clean them with tap water, they were dried but to a certain extent, the pH of the water could affect the experiments outcome, however all the of solutions would have had some water in them so this shouldn't affect the results in a significant way.
Post-Experiment Method, Limitations and Variables-Continued;
Other problem in the experiment that I later picked up on from observation was that the DCPIP and Juice solutions' were left open meaning that oxidation could affect the results which is a loss of electrons and a gain in hydrogen, this will cause the DCPIP to turn blue again, as Vitamin C is a reducing agent it adds electrons therefore its used in this experiment because it will change colour.
The limitation of this experiment is that it was only repeated three times due to the amount of time available, more results would have given better accuracy in results and given me the chance to spot outliers in the experiment.
We also do not know if Vitamin C is lost during ageing or through heat treatment which often products go through to ensure that it's free from harmful bacteria.
One improvement that could be made to the experiment is the equipment, having a larger choice to use from, and enough so that other factors like water don't come into play.
One modification that could used is that now we know that after a certain colour in the process of decolourisation we know that the trial is finished therefore saving us time for something else.
Another Improvement is to be more careful with the juice samples and to keep them contained so that they are not affected by the elements.
In this experiment, I learned that freshly squeezed orange juice will contain more vitamin C then juices from concentrate and that lemon contain more vitamin C then oranges.
The experiment carried out was to measure the content of Vitamin C in the selected fruit samples, from the results I can conclude that the results were accurate, reliable and precise therefore allowing me to state this conclusion and to prove my hypothesis right!