Lab # 8 Name: Cleve Hines 27120280 Course: CHEM211 Organic Chemistry 1 Instructor: Maureen R. Wilson Lab section: 1 Lab assistants: Donald Smith and Nicola Clark Date: November 11, 2013 Title: Quantitative analysis of Vitamin C contained in foods Aim: To determine the amount of vitamin C that is present in certain commercial food products by the titration method. Abstract: In this experiment, we use titration method to determine the concentration of Vitamin C in freshly prepared and packaged fruit juice samples. Titration (or volumetric analysis) is a common laboratory method of quantitative analysis that can be used to determine the concentration of a known analyte (or called reactant). A titrant (or called reagent) of known concentration is used to react with a solution of the analyte of unknown concentration. Using a calibrated burette, it is possible to determine the exact amount of titrant that has been consumed when the endpoint is reached. The endpoint is the point at which the titration is complete, as determined by the color change of an indicator. In this experiment, the titration method to determine the concentration of Vitamin C in freshly prepared and packaged fruit juice samples. Titration (or called as volumetric analysis) is a common laboratory method of quantitative analysis that can be used to determine the concentration of a known analyte (or called reactant). A titrant (or called reagent) of known concentration is used to react with a solution of the analyte of unknown concentration. Using a calibrated burette, it is possible to determine the exact amount of titrant that has been consumed when the endpoint is reached. The endpoint is the point at which the titration is complete, as determined by the color change of an indicator.
Introduction Vitamin C is an antioxidant, along with vitamin E, beta-carotene, and many other plant-based nutrients. Antioxidants block some of the damage caused by free radicals, substances that damage DNA. The build-up of free radicals over time may contribute to the aging process and the development of health conditions such as cancer, heart disease, and arthritis. Vitamins are a group of small molecular compounds that are essential nutrients in many multicellular organisms, and humans in particular. The name “vitamin” is a contraction of “vital amine”, and came about because many of the first vitamins to be discovered were members of this class of organic compounds. And although many of the subsequently discovered vitamins were not amines, the name was retained. In this exercise you will be studying vitamin C, also known as ascorbic
acid.
Vitamin C is a highly water-soluble compound that has both acidic and strong reducing properties. It naturally occurs in many plants and animals except in humans. The natural vitamin exists in L-ascorbic acid form. The D-isomer (i.e., D-ascorbic acid), which is the mirror image of the same
molecular structure, has only about 10% of the activity of the
L-
isomer. L-ascorbic acid is a weak sugar acid which is structurally related to glucose attached to a hydrogen ion. It is
a strong
reducing agent, which carries out its reducing function and
easily
converts to its oxidized form, the L-dehydroascorbic acid,
when
oxidative stress is present. Due to this characteristic, L-ascorbic acid is commonly
applied in food industry as a food additive functioning as a versatile antioxidant to protect foods from deterioration by oxidation. Vitamin C is an essential nutrient in humans as it functions as a cofactor in several vital enzymatic reactions. It is widely known that deficiency of Vitamin C would lead to scurvy in humans. Vitamin C also has other beneficial effects to our body, such as preventing
common cold/heart diseases and strengthening human immune system. However, human beings cannot synthesis Vitamin C by themselves and should obtain it from other sources. The richest natural sources of Vitamin C are fruits and vegetables, for example, blackcurrant, blueberry, orange, lime, lemon, strawberry, cabbage and malt. It is noted that Vitamin C can be chemically decomposed under certain conditions, such as heating and oxidation, many of which may occur during the cooking of food. In general, the recommendation for vitamin C intake in humans is around 60–95 milligrams per day and the maximum upper intake level is 2000 milligrams per day. Vitamin C exhibits remarkably low acute toxicity. However, it is reported that a long-term overdose of this vitamin may cause diarrhea, iron overload disorders and kidney stone formation.
Reagents
Apparatus
Crushed vitamin c pills
50ml burette
KIO3
Pestle
HCL
Clamp stand
Distilled water
Scale 10-mL volumetric pipet Erlenmeyer flask
Methodology The methodology was followed as outline in the lab manual
Observations: Results: Mass of crushed pills- 1.22+1.24 Titration1
Titration2
Titration 3
Vol. of HCL – 5.1ml
Vol of HCL- 5.1ml
Vol of Hcl- 5.1ml
Mass of KI-0.59g
Mass of KI- 0.58g
Mass of KI- 0.59g
Initial vol- 0ml
Initial vol- 3.21ml
Initial vol- 6.1ml
Final vol – 3.21ml
Final vol – 6.1ml
Final vol – 9.1ml
Calculations: Average: (3.2+2.9+3.0)/3 Avg= 3.03ml 1
2
3
Initial
0.5
0.5
0.5
final
49
46.5
47
KIO3(aq) + 6 H+(aq) + 5 I(aq) Æ 3 I2(aq) + 3 H2O(l) + K+(aq) Calculations: Average titration= 48.5+46+46.5/3 = 47
Moles of vitamin c = mass/Rmm 0.25g/176
= 0.0014mols
Conc of Kio3 = moles/avg.vol of KiO3 Moles = mass/Rmm = 0.59g/214 = 0.0027mols Conc =0.0027/47 = 0.000057M
Moles of kio3= MX AVERAGE 0.000057X47 = 0.0027 moles
Therefore there is 0.0027 moles KIO3:0.0014MOL C6H8O6 HENCE IT TAKES 0.0014mols ascorbic acid to standardize 0.027mols Kio3
Discussion: Titration is a tool used in the laboratory for quantitative chemical analysis of a chemical. It helps chemists to determine the concentration of a particular compound. Since the measurement of volume plays a key role in titration it is also referred to as volumetric analysis. The basics of food titration involve determining the concentrations of different compounds in foods such as vitamins, minerals and trace elements. It plays a major role in both the food and the pharmaceutical industry. All those labels on food packets and in dietary supplements contain the precise quantity of the different compounds contained within. These precise amounts are determined in the laboratory using the process of titration. Titration uses a reagent, also known as a titrator or titrant, of a standard concentration. This titrant is used to react with the solution being analyzed, also known as the analyte. Since the volume and concentration of the titrant are known, the concentration in the analyte can be determined after the reaction. Let us consider how to determine the concentration of vitamin C in
a solution. One way of determining vitamin C concentration is performing a redox titration using iodine. Vitamin C is also known as ascorbic acid and is an essential vitamin required by the body for its proper functioning. Additionally, it is a powerful antioxidant and helps protect the body from the damaging effects of free radicals. During a redox titration, iodine is added, drop by drop, to a solution of vitamin C. This causes a chemical reaction, in the process oxidizing ascorbic acid into dehydroascorbic acid and reducing the iodine to iodide ions. Iodine will continue to be reduced into iodide ions as long as ascorbic acid is still present in the solution. Once all the ascorbic acid has been oxidized, the excess iodine reacts with a starch solution which was premixed with the ascorbic acid solution. The reaction between iodine and starch produces a typical blue-black color due to the formation of a starch-iodine complex. This change in color is the end of the experiment. The volume of iodine required to completely oxidize the ascorbic acid and bring about the change in color can now be used to determine the concentration of ascorbic acid in the solution. This method can be used to determine vitamin C concentrations in vitamin C supplements, fresh or packaged fruit juices and other foods such as vegetables and fruits. The method of redox titration is easier to perform than alternate methods of titration using potassium iodate but is not as reliable as the latter. This stems from the fact that potassium iodate solution is a lot more stable than iodine and makes for a much more reliable standard. In a redox titration with potassium iodate, an additional reagent, potassium iodide is needed. When iodate ions (IO3ˉ) react with iodide ions (Iˉ) in the presence of an acid such as vitamin C, an oxidation-reduction reaction takes place. The iodate ions are reduced to iodine and the iodide ions are oxidized to form iodine. It is this iodine, formed by the oxidation and reduction of iodide and iodate ions respectively, that oxidizes the ascorbic acid. Once all the ascorbic acid has been oxidized, the iodine formed reacts with the starch solution to form the blue-black color that indicates the end of the experiment. Since this method used the oxidation-reduction reaction of iodide and iodate ions to produce iodine, which then reacts immediately with the ascorbic acid and starch, the stability of iodine is not a factor. This is also why this method is accepted as being the more accurate one.
Conclusion Vitamin C is required for the optimal activity of several important biosynthetic enzymes and it is therefore essential for various metabolic pathways in the body. However, according to RDA for vitamin C, 75mg/day and 90mg/day are required for normal women and men respectively. This level is believed sufficient enough to prevent deficiency disease but not chronic disease. Owing to this, vitamin C should be taken each day to prevent chronic disease and the effective doses are still remained unclear today. On the other hand, the Tolerable Upper Intake Level (UL) is 2000mg/day where too much of vitamin C may be dangerous due to the adverse effects such as kidney stone formation, increase of uric acid excretion and overload iron. There are few factors that will affect the stability of vitamin C which are vitamin E, pH, amount of hydrogen peroxide and temperature. Additionally, freshly prepared orange juice should be taken in as soon as possible. This because vitamin C may be oxidized during storage even we store it in refrigerator. It was found that vitamin C loss is the most when the orange juice was stored at room temperature. Well-pasteurized package juice from market can lose its vitamin C as well due to long storage time even if it is not opened. The highest loss of vitamin C occurred with conventional boiling. The research also shows that orange juice with vitamin E can delay the degradation rate of vitamin C. Besides that, high concentration of hydrogen peroxide will cause greater loss of vitamin C. Finally, lower pH value was preferred to prolong the shelf life of orange juice.
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