Experiment #2 - Vitamin C Lab Report

1 Abstract The main objective of the lab was to experimentally determine the amount of ascorbic acid, also referred as Vitamin C, in three different supplements. Through volumetric analysis, the three various brands; Life Brand, Webber & Jamieson were examined to see if it contained the labelled mass of 500 mg as vitamin C. Each group conducted the experiment using a different tablet from the listed brands. Based on the titration experiment, 0.0037 M iodine solution (titrant) was gradually added to the unknown concentration of substance. The stock solution containing Life Brand and 10 drops of starch indicator was titrated with the iodine solution for 3 trials to determine the average value. The starch indicator caused a slight color change because all of the ascorbic acid had been oxidized. The 1st trial results concluded that there was 485 mg of ascorbic acid, the 2nd trial showed there was 495 mg ascorbic acid, while the 3rd trial concluded to have 493 mg ascorbic acid. The average mass of ascorbic acid was 491 mg, proving to be lower than the expected value of 500 mg. The lab method was deemed as ineffective since the percentage error was 9.56%, which is associated with experimental error as it is a high value. Procedure For the procedure, see lab manual (CH110 Lab Manual, Fall 2023) pages 75-77. No deviations were made to this vitamin C experiment. Wilfrid Laurier University Chemistry Department. Fall 2023. Pages 71-77 in the Chemistry 110 Lab Manual. Wilfrid Laurier University, ON, Canada Observations/Results Table 1: Qualitative observations throughout experiment Before observations During observations After observations Life Brand vitamin C tablet 1st trial - Vitamin C tablet is in solid form - white in colour - Iodine - dark orange, liquid - Cloudy solution - Sparks of blue colour - Clear liquid form - Mixture of vitamin c and iodine tuned into slight blue colour - Liquid form - Fully dissolved 2nd trial - Vitamin C tablet is in - Sparks of blue colour - Light blue color change

2 Table 2: volumized burette readings for Life Brand ascorbic acid titrations with iodine Trial 1 Trial 2 Trial 3 Final burette reading (mL) 20.5 21.2 20.7 Initial burette reading (mL) 0.00 0.20 0.10 Volume of iodine used (mL) 0.5 21.0 20.6 Table 3: Ascorbic Acid Analysis Through Titrations solid form - white in colour - Iodine - dark orange, liquid - Iodine was in dark orange colour - Dissolved in solution - Transparent - Liquid - Fully dissolved 3rd trial - Tablet was in solid form - White in colour - Iodine - dark orange, liquid - Clear liquid - Cloudy solution - Sparks of blue - Liquid form - Transparent - Light blue colour appeared - Fully dissolved Iodine - Thin consistency - Transparent - Liquid form - Red-orange colour - Distinct odour - Clear liquid - Transparent - Homogeneous - Slight blue colour Deionized water - Clear liquid - colourless - no smell - Transparent - Liquid form - Slight odour - Dark blue colour - Transparent - Liquid form

4 2 . Sample calculation #1: calculation of percent error using average sample and reported value 3a.

5 Table 4: Mean class value and standard deviation for the amount of ascorbic acid found in the three supplements Mean Class Value Standard Deviation Life Brand 547.8 53.8 Jamieson 519.2 25.9 Webber 538.4 59.8 Appendix A : Class data of the 3 supplements 3b . Sample calculation #2: calculation of percentage error between mean class data and reported mg of vitamin C for Life Brand tablet

7 Discussion The titration of ascorbic acid with iodine solution was found to calculate greater masses of vitamin C than expected value of 500 mg, resulting in ineffective titration of vitamin C. The average mass was found to be 484.3 mg with a percent error of 9.6%. According to table 3, Life brand had an average mass of 547.8 mg, Weber had an average mass of 538.4 mg and Jamieson had an average mass of 519.2 mg. The titration using Jamieson tablet had produced the least percent error of 3.84% (table 4). The percent error when comparing the mass calculated for the Webber tablet and the expected was 7.68% (table 4). Any set of data with a percent of error greater than 5%, results in invalid data as the value is too high to be considered as effective results. Hence, the data using Webber and Life Brand tablets would be seen as invalid results. Standard deviation is the measure of accuracy based on method used to experimentally perform the lab. Based on table 4, the increase in standard deviation represents a high value of inaccuracy of method and/or procedure. A potential source of human error would be overtitrating. The titration would have continued beyond the end point since the colour change was not observed quickly, this could have resulted in greater mass calculated for ascorbic acid in each trial. Therefore, it would explain the increased percentage error as the mass of ascorbic acid was higher than expected value. A potential source of non-human error could be the movement of air around the room. As the room contains oxygen, nitrogen and small traces of carbon dioxide, this could have an oxidizing impact on the solution and titrant used in the experiment. The rate of oxidation would be greater than what is expected at normal STP, resulting in different final burette readings and calculated mass of ascorbic mass to be greater than expected value. To improve this non-human error, the

8 oxidation rate can not change. This can be done by using STP calibrated equipment where temperature is at STP. Conclusion In conclusion, the objective to determine the actual mass of ascorbic acid using 0.0037 M iodine solution was achieved. Due to experimental error, the mass calculated was noted to be lower than mass expected and two out of three tablets (Life Brand and Webber) had a percent error higher than 5%. Hence, the two tablets' data were not scientifically correct. The Jamieson tablet had a percent error less than 5% and the calculated mass to be roughly close to expected value. Therefore, the lab was ineffective but the criteria for this experiment have been met.

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11 References Refer to page 71-77 in the lab manual