Titration Of Ascorbic Acid

Introduction

My parents make orange juice every day, they inform me that is good for me since it contains vitamin C.Vitamin C which is scientifically called ascorbic acid, due to it being an acid, it can easily be oxidized in neutral or basic concentrations by dissolved oxygen, leading to a loss of two hydrogens, since it lost two electrons(“Vitamin C”) . I chose to investigate what could impact in the content of vitamin C in an orange juice sample, and the factor that will be tested is temperature, the reason I chose temperature is because orange juice should be left in the fridge at low temperatures, so I'm interested in looking at how temperature would affect the Vitamin C content in orange juice. This will be experimentally determined through a titration method between Iodine and ascorbic acid, since iodine would oxidize ascorbic acid.

The purpose of this experiment is to determine how temperature affects the vitamin C concentration in orange juice. This will be determined through a redox titration between Iodine and ascorbic acid. Iodine will be produced by reacting potassium iodide and potassium iodate with each other, iodate ions would react with the iodide ions to produce iodine. Iodine oxidized ascorbic acid, and once the ascorbic acid is oxidized, the excess iodine will react with starch to form a black-blue color.

Theoretical Background

Vitamin C chemical formula also known as ascorbic acid, is a natural water-soluble vitamin, this because it is a polar molecule, it has partially positive and negative charges, so it will form hydrogen bonds with water. The benefits of intaking Vitamin C is that it synthesis the collagen fibers in our body like skin, and it increases the absorption of iron in our body. Our body cannot synthesize Vitamin C, thus it must be diets or supplements such as citrus juices and fruits,orange juice is known for being rich in vitamin C.Vitamin C deficiency can lead to scurvy symptoms to develop(Editors of encyclopedia, britannica,2018). Investigating the effect of temperature on vitamin C content, would allow a better understanding of why orange must be in low-temperature conditions. The orange juice that is going to be tested is the maccaw brand store orange juice. As mentioned before ascorbic acid is oxidized in the presence of oxygen to form dehydroascorbic acid, increase in tempereature will increase the rate at which ascorbic acid is oxidized, thus more dehydroascorbic acid is formed. The way the ascorbic acid content in orange juice will be quantitatively measured is through a titration method. This method uses a known solution which in this case potassium Iodide solution 0.1M and this is used to determine an unknown concentration, which is vitamin C. When potassium iodate is titrated into the solution of orange juice, which contains potassium iodide, the Iodate ions would react with the iodide ions to produce iodine. Iodine is what oxidizes the all ascorbic acid in orange juice into dehydroascorbic acid, and the excess iodine will react with the starch indicator solution to form a blue-black color. This change in the volume of potassium iodate will be recorded to determine the vitamin C concentration.

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Evaluation of results

We can conclude from our results that an increase in temperature leads to a decrease in the ascorbic concentration in orange juices, since from the results the lowest temperature at 30had an ascorbic acid concentration of 0.012mol/L and the highest temperature at 90is 0.010mol/L, and this is seen from the graph.Thus from the data found my hypothesis is true, reason behind this temperature increase causing the ascorbic acid concentration to decrease is because ascorbic acid is vulnerable towards heats, this is because in the (OH) atom the bond between oxygen and hydrogen is weak, this is due to the high electronegativity in oxygen,so oxygen will have a stronger attraction of the electrons from hydrogen, leaving hydrogen to be positively charged. This type of bond is called a hydrogen bond, which is not considered to be strong compared to a covalent and ionic bond,so energy from heat can break the bond between OH in the ascorbic acid, leading to the molecule to denature with heat. Therefore heat can help in oxidizing ascorbic acid in orange juice, thus the concentration of ascorbic acid would decrease, and there would be an increase in the concentration of dehydroascorbic acid.

Evaluation of errors/Improvements

Errors that were encountered in the methodology were random and systematic, the one of the random errors is when transferring the orange juice from the graduated cylinder to the conical flask, there were remains of orange juice in the conical flask, that could not be released into the conical flask. Same applied when adding hydrochloric acid and potassium iodide. This would affect the volume of the solutions used for titration. A solution for this would be using an electronic pipette that can be used to give the exact volume transferred into the conical flask.Another random error is when near the rough titration endpoint, the potassium iodate was titrated in drops from the burette, some of the drops stuck to the sides of the conical flask, therefore they did not react with the solution in the flask, this would affect the titre volume required oxidize ascorbic acid, so the ascorbic acid concentration is inaccurate. Lowering the burette would help in allowing the drops to drop into the solution. Another random error could be from the misjudgement of the endpoint, so misjudging when there is a permanent change in color of the solution, this would lead to inaccuracy of the volume of the titrant. Bubbles formed in the burette would affect the volume of the titrant, it can block the flow of the titrant or flow with it,. Systematic errors that could have occurred in this lab would be from the uncertainty with the burette measurement which ±0.1, the uncertainty from the graduated cylinder which is ±0.05, and the uncertainty from the weighing device ±0.001,all could lead to an inaccuracy of the ascorbic acid concentration determined. There could have been human error which cannot be avoided, our eyesight could lead us to misread the volume accurately which would affect the final ascorbic acid concentration. This had a minimal impact on the accuracy since the % uncertainty calculated for the final values of the ascorbic acid concentration are all less than 2%.

An crucial error would be that I only have 4 data points, I need to have 5 data points to prove my hypothesis, since I do not have 5 data points, then my hypothesis has not been proven, leaving error in my data.Limitations in this lab would be that only 3 trials were made for each temperature, more trials would increase the accuracy of the results. Assumptions made in this investigation is that maccaw orange juice being used has 100% ascorbic acid.Assuming that the solutions are standardized, there could have been contamination, chemicals may undergo decomposition or evaporation, another assumption is that the electric balance had been calibrated, miscalibration would lead to an inaccurate measurement.

Conclusion

We can conclude from the data found that an increase in temperature leads to a decrease in the ascorbic acid concentration. An extension for this lab would be looking into the ascorbic acid concentration in fresh orange juice and in a juicebox, seeing if tempereature affects one more than the other.

Bibliography

1. Helmenstine, Anne Marie, and Anne Marie Helmenstine. “Use Iodine Titration to Determine the Amount of Vitamin C in Food.” Thoughtco., Dotdash, 2018, www.thoughtco.com/vitamin-c-determination-by-iodine-titration-606322.
2. Britannica, The Editors of Encyclopaedia. “Vitamin C.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 28 Dec. 2018, www.britannica.com/science/vitamin-C.
3. Determination of Vitamin C Concentration by Titration. University of CanterBury, www.canterbury.ac.nz/media/documents/science-outreach/vitaminc_iodate.pdf.
4. Volumetric Glassware, www.webassign.net/question_assets/ncsugenchem102labv1/lab_9/manual.html.