Baking Bell Peppers – Determining Vitamin C ContentShruthi SundararamanSCH3U7 – AMr.
AshworthMonday, January 29, 2017Introduction:Vitamin C, or ascorbic acid, is an essential vitamin needed for the body to survive. It aids in maintaining our connective tissue and it also serves as a powerful antioxidant. When I first heard of the topic of determining the Vitamin C content in foods, I was instantly drawn to it as it connected two of my favourite sciences, biology and chemistry. So, I started doing some research and found that there were lots of fruits that contain high amounts of Vitamin C. This wasn’t appealing to me, since I am not a fan of fruits, so I dug deeper and found that the food with one of the highest amounts of Vitamin C, is actually a vegetable: Bell Peppers.
This was interesting, since I never thought of Bell Peppers as something that would have a lot of Vitamin C. This is when I decided that I want to determine the Vitamin C content in Bell Peppers. I typically like eating bell peppers in my salad, or as a pizza topping.
However I realized that the bell peppers I eat are usually roasted (baked) beforehand, and this cooking might have an impact on its nutritional benefits. This was what had led me to my research question: How does the Vitamin C content in Bell Peppers change as it gets baked?From prior knowledge and some research done, I hypothesize that the amount of vitamin C in the Bell Pepper will decrease as it is cooked for a longer period of time. This is because when heat is added to the Bell Pepper, the tough outer membrane will break down, allowing for a lot of the nutrients and vitamins to escape.
Therefore, as the pepper is cooked for a longer period of time, the vitamin C content will continue to decrease. Background InformationI will be determining the answer to this question by doing a redox titration. A titration occurs when a solution of a known concentration is slowly added to another solution of unknown concentration, until the chemical reaction between the two are complete. In this scenario, an Iodine solution of known concentration will be added drop by drop to a vitamin C solution (bell pepper juice) to determine its concentration and thus determine the mass of Vitamin C in the sample. Redox, or reduction-oxidation reactions involve the transfer of electrons between different molecules. Oxidation refers to the loss of electrons, and reduction refers to the gain of electrons. Specifically in organic chemistry, oxidation refers to the loss of hydrogen, and reduction refers to the gain of hydrogen.
The chemical formula for the titration reaction is: C6H8O6 + I2 C6H6O6 + 2I- + 2H+(ascorbic acid / vitamin C) (iodine) (dehydroascorbic acid) (iodide) (hydrogen proton)In this reaction, the ascorbic acid gets oxidized to form dehydroascorbic acid, and the iodine gets reduced to form iodide ions. The iodine will only get reduced in the presence of ascorbic acid, so when all the Vitamin C in the sample has been reduced, the excess iodine will immediately react with a starch indicator to form a blue-brown endpoint. This endpoint is a qualitative change that allows us to determine when the reaction is complete. By using this method, we can find out how much iodine was required to react with the ascorbic acid, and using some stoichiometric operations, we can determine the amount of Vitamin C in the original sample.
I decided to use this redox titration method to determine the amount of vitamin C in the sample, rather than a simple acid-base reaction with NaOH, because fruits and vegetables – like Bell Peppers – not only contain ascorbic acid, but also multiple other acids like citric acids. Therefore, an acid-base titration will determine the total acid content in the vegetable, but the redox titration will only find the vitamin c content, which is what I need. In order to truly determine how the Vitamin C content changes over the time it is baked for, I decided to use a constant mass of 100g for each independant step, and then diluted its juice to 200 mL. This procedure would avoid any confusions related to dilution, since the same quantity of bell peppers would be diluted to the same volume. During the titration process, it is possible for some human errors to occur when determining the end point, so I decided to conduct 4 trials for each different bell pepper and average that to calculate a more accurate result.
Figure 1: VariablesType of VariableHow will it be measured / controlled / manipulated?Independant:The amount of time the bell peppers are baked forManipulated by conducting independent trials for different baked times: raw, 10 mins, 20 mins, 30 mins, 40 mins (measured with a timer)Dependant: The amount of Vitamin C in each sampleCalculated using mole ratios and other stoichiometric operationsControl:The amount of bell pepper used for each set of trialsThe baking specificationsThe concentration of the bell pepper juiceThe volume of the titrate in each trialThe concentration of the Iodine SolutionThe freshness of the bell pepperControlled by using 100 g of Bell Peppers for each independant stepThe oven was preheated at 350ofor 20 minutes for all independant bell pepper trialsControlled by using 50 mL of actual juice in 150 mL of distilled waterControlled by measuring 50 mL of juice in a graduated cylinder for each trialControlled by using the same Iodine solution throughout all trialsControlled by sealing the bell pepper with plastic wrap, stored in a ziploc bag inside an airtight container in the fridge. A new bell pepper was used every 3 days.MethodologyPreparing the Bell Pepper Juice100g of Bell peppers were measured, ensuring that most of the membrane and seeds have already been removed.
The bell peppers were cut and blended. The juice was strained using a strainer. Then, this juice was diluted to 200 mL with distilled water.Steps 1-3 were repeated for each set of bell pepper trials: being baked for 10 mins, 20 mins, 30 mins, and 40 mins. (baked after step 1)Preparing the 1% Starch Solution (Indicator)300 mL of distilled water was boiled on a hotplate3g of starch was added to the water and stirred until dissolvedPreparing the Iodine Solution200 mL of distilled water was measured. 10.
00g of Potassium Iodate and 0.54g of Potassium Iodide were added to the waterOnce completely dissolved, 60.0 mL of 3M sulfuric acid was added to the solutionThe solution was then diluted to 1000 mL with more distilled waterThe Titration Process50 mL of the Bell Pepper juice sample was measured in a graduated cylinder and transferred into an erlenmeyer flask1-3 mL of the starch indicator solution was added to the juiceA burette was filled with the iodine solution and placed on the burette stand, with the erlenmeyer flask placed underneath it. The initial volume of iodine solution in the burette was recorded. The titration was started by opening the burette to allow the iodine solution to fall into the erlenmeyer flask drop by drop. The flask was constantly swirled to ensure that the iodine mixes with the solution. Once the bluish-black endpoint had been reached, the burette was quickly closed, and the final volume of iodine solution was recorded.Steps 1-6 were repeated to obtain 4 valuable trialsSteps 1-7 were repeated for all 5 independent bell pepper trialsSafetySince we are dealing with chemicals, specifically strong acids, goggles should always be worn to avoid eye splashes.
Iodine can easily stain clothes and the skin, so gloves should always be work to prevent any splash or spill on the skin. Hair should be tied back, and loose clothes should be avoided. If any of the chemicals do happen to touch skin, it should immediately be put under running water for at least 1 minute, and then it should be washed off. In the end, after the Bell Pepper juice has been titrated with the iodine solution, it should be disposed into the organic waste bin.
The iodine solution must then be tightly closed in a container and stored in a well ventilated area. There were no apparent ethical concerns or environmental concerns involved in this experiment. Qualitative Observations After baking the bell peppers, the skin appeared to shrivel up and it was charred. (Figure 7) The cooked bell peppers had less pulp than the raw bell pepperWhen drops of the Iodine solution were added to the bell pepper juice, there was a quick colour change near the top where the juice appeared blackish, but after swirling it for a few seconds it went awayNear the end of the titration, the iodine had to be dropped in at a slower rate because a single drop could lead the titration to its end point.
At its end point, the juice turned to a brown-black colourQuantitative Data Analysis:Finding the Concentration of the Iodine SolutionUsed: 10.00g 0.01g KI, 0.54g 0.
01g KIO3, 60.0 mL 0.05mL of 3M of H2SO4. Solution was diluted to 1000 mL 25 mLBalanced Chemical Equation: 5KI + KIO3 + 3H2SO4 ? 3I2 + 3K2SO4 +3H2OMoles of KIn=mM=10.001660.0602 molKIMoles of KIO3n=mM=0.542140.0025 mol KIO3Moles of H2SO4c=nv3=n0.
06000.180 molH2SO4Relative Uncertainty:0.0110.000.
0602 610-5 Relative Uncertainty:0.010.540.0025 510-5 Relative Uncertainty:0.0560.00.18 210-4 Finding the Limiting Reagent: Assume 0.
0025 mol KIO35 mol KI1 mol KIO3= x mol KI0.0025 mol KIO3 0.013 510-5 mol KI needed? KI was used in excess3 mol H2SO41 mol KIO3= x mol H2SO40.0025 mol KIO3 0.0076 510-5 mol H2SO4 needed? H2SO4 was used in excess? KIO3 is the limiting reagentMoles of Iodine Created3 mol I21 mol KIO3= x mol I20.0025 mol KIO3 0.
00757 510-5 mol I2 createdConcentration of Solutionc=nv 0.00757 mol1.00 dm3c0.0076 mol dm-3I2Percent Uncertainty:=(AA)2 (510-5)2 + (251000)20.025? The concentration of the Iodine solution we created was 0.0076 0.025 mol dm-3Figure 8: Amount of Iodine Used for Each Sample of Vitamin CType of Bell Pepper Trial #Volume of Juice Used ( 0.05 mL)Initial Volume of Iodine Solution ( 0.
05 mL)Final Volume of Iodine Solution ( 0.05 mL)Total Volume of Iodine used ( 0.07 mL)Raw 1501.623.
5 21.9250 23.5 45.5 22.03501.9 24.1 22.245024.
1 46.5 22.4Baked for 10 mins 1507.828.120.325028.
147.320.2Baked for 20 mins 1503.019.716.
8Baked for 30 mins15014.432.217.
137.817.7Baked for 40 mins1501.515.313.825015.329.
914.3Sample Calculation for Total Volume of Iodine Used, Figure 8, Raw Sample, Trial 1Total Volume = Final Volume – Initial Volume= 23.5-1.6=21.9 mLUncertainty: =A2=0.
052+0.0520.07mLFigure 9: Mass of Vitamin C in Each TrialType of Bell PepperTrial 1 (g)Trial 2 (g)Trial 3 (g)Trial 4 (g)Average (g)Raw0.029 6000.029 6000.030 600 0.030 6000.
030 600Baked for 10 mins0.027 6000.026 6000.026 6000.027 6000.027 600Baked for 20 mins0.022 6000.021 6000.
022 6000.022 6000.023 600Baked for 30 mins0.024 6000.023 6000.023 6000.
024 6000.024 600Baked for 40 mins0.018 5000.019 5000.
019 5000.019 5000.019 500Sample Calculation for Mass of Vitamin C, Figure 9, Raw sample, Trial 1Balanced Chemical Equation: C6H8O6 + I2 C6H6O6 +2I- + 2H+Moles of Iodine Usedn=cv= (0.0076 mol dm 3 )(0.0219)=1.
7 10-4 mol I2Uncertainty:=(AA)2(0.0250.0076)2+(0.0721.9)2 3Moles of Vitamin C in Sample1 mol C6H8O61 mol I2=x mol C6H8O81.710-4 mol I21.7 10-4 3 mol C6H8O6 Mass of Vitamin Cn = mMm(1.710-4 mol)(176.
14 g/mol)m0.029 g C6H8O6Uncertainty31.710-4 0.029600Sample Calculation for Average Vitamin C, Figure 9, Raw SampleAvg 0.029 + 0.029 + 0.030 + 0.
0304 0.030gUncertainty: =4(600) 4= 600Figure 11: Change in Vitamin C content between each time interval of bakingTime IntervalChange in Vitamin C (g)Raw to 10 mins-0.0030 80010 mins to 20 mins-0.0040 80020 mins to 30 mins0.001 80030 mins to 40 mins-0.005 800Sample Calculation for Change in Vitamin C, Figure 11, Raw to 10 minsChange in Vitamin C 0.
027g-0.030g -0.0030gUncertainty: =A26002+6002800Average Change:=-0.003-0.
004+0.001-0.0054-0.0028 800g vitamin C per 10 minutes?-0.
00028 80g vitamin C per minute?On average, the vitamin C content in this diluted bell pepper sample decreases by 0.00028 80 gper minute baked. EvaluationTherefore, this diluted bell pepper sample had lost 0.00028 80g of Vitamin C for every minute that it was baked for. My hypothesis was proven right, since the vitamin C content decreases after the Bell Pepper gets baked.
This is because when heat is added to the vegetable, it causes the nutrients and vitamins to escape. Although the overall trend is decreasing, the change is actually initially gradual, but it starts becoming larger and larger. This occured due to the fact that with longer exposure to heat, the bell pepper breaks down faster and thus much more vitamin C escapes from the Bell Pepper after 40 mins of baking rather than 10 mins of baking.
This can also be seen in the lab, “Effects of Cooking Methods on Vitamin C,” where the scientist explains that cooking for longer periods of time will result in a drastic decrease in vitamin C whereas less time spent cooking will have a significantly lower decrease. There were multiple strengths to this lab that allowed me to achieve the best results possible. The measurements made for the volume of the bell pepper juice were very accurate since they were measured using a graduated cylinder of only 0.
05 mL uncertainty. Even this is minimal in relation to the 50 mL of juice I used for each sample. So, it can be noted that all of the trials were carried out almost identically, which avoids error in the calculations. Also, when I was allowing for the titration to happen by letting the iodine solution drop into the juice, I slowed down its rate of dropping when I saw that it was nearing its endpoint so that I could make sure that no extra drops fell in past the endpoint. In addition, when measuring the volume of all solutions, I ensured that I measured from eye-level and that I measured from the lower meniscus. This further increased the accuracy of all my trials, resulting in my lab to be a better success.However, like all experiments, there were a couple of weaknesses to this lab, specifically related to the apparatus.
Firstly, a single bell pepper could not be used for all 5 independent steps since there just wasn’t enough mass within a single bell pepper. So, I used one bell pepper for my raw, baked 10 mins, and baked 20 mins trials, and another bell pepper for the remaining trials. As can be seen in the graph, the vitamin C content actually increases from 30 minutes to 40 minutes. This was merely a limitation to this lab since both the bell peppers would have had a different vitamin C content to begin with, resulting in different values after baked.
However, the overall trend shows that the vitamin C content decreases, so this small anomaly can be taken out of consideration. To improve upon this weakness, a smaller mass from a single bell pepper could be used for each independant step so that all trials could be completed using the same pepper. We were given only 75 mins per day to conduct the lab, however more time would be required with this method in order to be able to complete all trials in the same day/over two days to maintain the freshness of the pepper. Another weakness to this lab was the fact that the erlenmeyer flask had to be swirled by hand to mix the iodine with the juice. This may have resulted in some variations in the endpoint, and a more effective way to approach this would be to use a magnetic stirrer to automatically stir the content in the flask. In addition, since the bell pepper was already fairly dark in colour, it made the determination of the endpoint a bit harder.
To improve this next time, I would dilute the juice even further so that the colour was very faint, and this would allow me to better see the end point. Another major limitation to this lab was the high uncertainty of the beaker that was used to dilute the iodine solution. Since the beaker had high uncertainty, it resulted in the concentration of the iodine to have a high uncertainty and all of my calculations ended up with an extremely high uncertainty. Although a 1000mL beaker with low uncertainty wasn’t available in our lab, one with lower uncertainty would have allowed for all my calculations to have a low uncertainty. ReferencesClark, Jim.
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