How does varying the temperature of freshly squeezed orange juice affect the concentration of Vitamin C within it, which can be tested using a titration method with iodine solution. Iodine + Ascorbic Acid Dehydroascorbic acid + Iodide ions + Hydrogen ionsI2 + C6H8O6 C6H6O6 + 2I- + 2H
When deciding the topic on which to base my experiment, I wanted to do something outside of the standard syllabus, in which I would be fully interested and immersed whilst enjoying collecting data and taking further action once I had completed the experiment. The idea came to me within a discussion amongst a group of friends about what temperature we all prefer to drink orange juice at, and whether the taste varies at different temperatures. One of my personal favourite topics in science, is about the denaturing of enzymes, and how this process occurs at higher temperatures. Therefore, from a scientific point of view, after gaining my initial idea, I was thoroughly intrigued in order to see the correlation between temperature and Vitamin C content, and if it essentially ‘denatures’ like enzymes do at higher temperatures. Initially I was going to use packed juice at six different temperatures, but then decided that using freshly squeezed orange juice would be more interesting as it is not processed and each orange differs. Having chosen and planned out my experiment, I did a trial run through and came to the conclusion that five varying temperatures was more feasible and would allow me to do be more accurate with repeats hence allowing a more in depth analysis in the long run.
Vitamin C was discovered in 1912, then isolated in 1928 – before being the first vitamin chemically produced in 1933. As we know, all fruits have a high content of vitamins and fibre whilst being low in calories and fats. Certain beneficial properties of fruits, more specifically orange juice, are due to their content in vitamins, minerals, nutrients and anti-oxidants which help to extend lives by replenishing and protecting tissues, organs and cells. It protects from skin-wrinkling, memory loss and other age-related changes within humans. A key source of Vitamin C is oranges, with a Vitamin C content of around 70 milligrams per segment. Vitamin C – also known as ascorbic acid – is soluble in water so that we can take it into our bodies easily in a drink, and is also found in food and is used as a dietary supplement – and additionally scurvy is treated with predominantly Vitamin C-containing foods or supplements. Vitamin C is also required for the functioning of several enzymes and is also important for the functions of the immune system. Prior to the experiment, having already been interested in the denaturing of Vitamin C, my research stated that in fact Vitamin C denatures very easily at high temperatures.
In the following experiment, the Vitamin C in the orange juice reacts with the Iodine Solution, using a titration method for collecting relevant data.
Having researched the information regarding the solutions and materials I would be using when carrying out my experiment, I formulated my original hypothesis which was that as the temperature of the juice increases, the concentration of Vitamin C in the within would decrease indirectly proportionally because Vitamin C becomes denatured at these higher temperatures.
Independent variable: The independent variable is the temperature of the freshly squeezed orange juice used. The temperatures will be one of 20ºC, 30ºC, 40ºC, 50ºC or 60ºC. Dependent variable: The dependent variable is the 0.005M Iodine Solution which is used in the titration in order to react with the orange juice solution, which will have previously been mixed with 0.5% Starch Indicator Solution and distilled water. Controlled Variables: The concentration and volume of starch indicator solution used to mix with the juice. The concentration and volume of distilled eater used to mix with the juice. The same thermometer to check the temperature of each of the orange juices. The end colour reached at the end of each titration was kept as constant as possible by establishing a set colour in the first titration, and then matching each consecutive titration to that original first colour in order to ensure that the values were accurate. The environment in which the experiment was done in, and therefore each experiment at the same room temperature. The oranges were all bought in the same batch at the same time – therefore were all in roughly the same state of ripeness.
Setting Up the Apparatus
The titration is set up as shown in this diagram. The burette is filled with the 0.005M Iodine Solution and the conical flask should contain the 150ml of distilled water, 20ml of orange juice at a certain temperature and 1ml of the starch indicator solution.
Firstly, take the oranges out of the refrigerator, and cut each of them in half using the knife and a chopping board. Using one half of each orange at one time, use the juice extractor, by placing the centre of the cut orange on the tip of the extractor, and doing this will extract as much smooth orange juice from each orange as possible. Pour 5 lots of 100ml of this smooth fresh orange juice into five separate beakers. Having set up each of the water baths at 20ºC, 30ºC, 40ºC, 50ºC and 60ºC, place each of the beakers of orange juice into their corresponding bath – labelling each beaker with the temperature to avoid confusion and mixing them up. Keep a thermometer handy in order to keep checking the temperatures, and remove them when they reach the desired temperature. Pipette 20ml of the 20ºC orange juice, using the 20ml pipette listed within the apparatus, into a conical flask and add 150ml of distilled water and 1ml of starch indicator solution. Having set up the titration as displayed in the diagram above, titrate the orange juice sample with the 0.005M iodine solution in the burette. Carry on dripping the iodine into the orange juice sample, and the endpoint of the titration can be identified at the sight of the first permanent trace of a dark black/blue solution. Repeat the titration (steps 5-6) with the other orange juices at varying temperatures until the rest of the results are obtained. Repeat each of the experiments for each varying temperature three times in order to calculate an average accurate result. Having obtained the result for the average amount of Iodine Solution used, I was then able to do the following three calculations: Calculate the average volume of the iodine solution which was used. Calculate the amount of moles of iodine reacting. Determine the number of moles of vitamin c reacting. Calculate the concentration of vitamin c in the solution which was obtained from the juice.
Due to glassware being easily smashed and broken – this can be a dangerous hazard to other students as well as yourself. In order to solve this issue, all glassware should be handled very delicately and you should be very cautious always. All chemical substances and solutions, including the Iodine Solution, the Starch Indicator Solution and the extremely hot water, should all be used very carefully and diligently to avoid any spillages or harm to other people in and around the lab. Safety goggles should be worn at all times to protect your eyes from any chemicals. Lab coats should be worn at all times to protect yourself and your clothes from any spillages. The Iodine Solution must not be poured away down a sink when disposing it because it is extremely harmful, so therefore it must be reacted with a reducing agent, such as sulphuric acid first.
RAW DATA: 1) 20ºC Orange Juice – Average volume of Iodine used at 20ºC: 1.4ml 2) 30ºC Orange Juice – Average volume of Iodine used at 30ºC: 1.6ml 3) 40ºC Orange Juice – Average volume of Iodine used at 40ºC: 1.9ml 4) 50ºC Orange Juice – Average volume of Iodine used at 40ºC: 2.2ml 5) 60ºC Orange Juice – Average volume of Iodine used at 60ºC: 2.7ml
As soon as the Iodine Solution was being added to the mixture of orange juice, starch indicator solution and distilled water, it would periodically go more and more grey until the whole solution turned a permanent blue/black colour, and this process evidently took longer in the higher temperature Orange Juice.
UNCERTAINTIES (examples for 20ºC Orange Juice) Uncertainty for average volume of Iodine used in the titration: (1.4±0.5 cm3) + (±0.5 cm3) = (±1.0 cm3) 2) Uncertainty for the number of moles of vitamin C reacting: 3) Pipette uncertainty: (±0.03 ml / 20) x 100 = 0.15% uncertainty 4) Burette uncertainty: ( ±(0.025 + 0.025) / 1.4 ) = 0.035% uncertainty This can be turned into an absolute uncertainty PROCESSING THE QUANTITATIVE DATA Having gathered my average titration values and averages, I firstly will use them in order to work out the number of moles of iodine reacting. For example, this is how I calculate the consecutive results from the results of the 20ºC Orange Juice. Firstly, I calculated the number of moles of iodine reacting in the experiment: Moles of Iodine (reacting with 20ºC Orange Juice) = 0.0014 x 0.005 = 7×10-6 Moles 2. Secondly, I determined the number of moles of vitamin C reacting due to one mole of iodine reacting with one mole of vitamin C. (as shown in the table above) e.g. 1:1 ratio so 7×10-6 moles of iodine is equal to 7×10-6 moles of vitamin c reacting. This ratio can be extracted from the initial equation for the experiment: I2 + C6H8O6 C6H6O6 + 2I- + 2H 3. Finally, I calculated the concentration of Vitamin C in the solution which was obtained from the juice. The volume is the 20ml orange juice, and the number of moles of Iodine which has previously been calculated. This can all be calculated using the following equation: Concentration = number of moles / volume Concentration = 7×10-6 / 20 = 3.5×10-7 mol/dm3 This above data can also be shown one a scatter graph:
Graph Analysis and Conclusion
As previously mentioned, my initial hypothesis was that as the temperature increased, the concentration of Vitamin C in the final solution would decrease. However, having carried out the experiment and worked out all of the necessary results, I have found that as the temperature increases, the concentration of Vitamin C also increases. The results from my experiment can be shown in the graph above. The graph shows and states this unexpected linear relationship between the temperature of the orange juice and the effect that the temperature has on the concentration of its vitamin c content in the orange juice. Vitamin C has proven to be in such small quantities within the oranges used for my experiment, and this will be evaluated below. As previously mentioned, my initial hypothesis was that as the temperature increased, the concentration of Vitamin C in the final solution would decrease. However, having carried out the experiment and worked out all of the necessary results, I have found that as the temperature increases, the concentration of Vitamin C also increases.
Throughout this experiment, I controlled all of my listed controlled variables which could have affected my results or altered my original hypothesis. However, my experiment lead to me receiving an unexpected set of results, as I had hypothesised that the Vitamin C content of the orange juice would decrease as the temperature increased. I would have liked to have repeated the whole experiment – and altering it by either getting my oranges from a different place, or by making sure that the whole solution was the same temperature having added in the starch solution and distilled water which had been kept at room temperature. The fact that I got opposing results could be down to a few certain reasons; keeping the oranges refrigerated for a long period of time before carrying out the experiments could have potentially caused the vitamin c content within them to decrease. Additionally, when adding the room temperature distilled water and starch indictor solution to the mixture before titrating, the temperature of the orange juice solution would have decreased.
However, on the contrary each freshly squeezed orange will not contain an identical content of vitamin c, and so varying results were expected in that sense. Moreover, if I could do this experiment again, I would have firstly used a wider range of temperatures of the orange juice in order to gain more accurate results. Also, I would have used a more precise method when it came to the titration – perhaps the dropping process took such a length of time that the orange juice had time to cool down, or perhaps my method of trying to mach up colours to mark the finish point of the titration was not accurate either. Therefore, in order to absolve this issue I would put a piece of paper with a cross on it underneath the conical flask and I would record the point at which it was non longer visible.