Lab Report - Vitamin C
Lab report regarding the concentration of Vitamin C in food samples...
Mohamad Syahmi bin Mohd Hothzani M13F
TOPIC 6.1 – DIGESTION EXPERIMENT – ANALYSIS OF VITAMIN C IN FRUITS / VEGETABLES BY USING THE DCPIP TEST Introduction: Vitamins are micronutrients, which means that they only required in only small amounts by the body. It is to maintain health and well-being. An example of vitamins is Vitamin C. It is also known as ascorbic acid. It plays role in cell division, in in cell wall synthesis an in inhibition of dangerous compounds like hydrogen peroxide. This experiment is done to analyse samples of materials for the amount of ascorbic acid in each of those samples. The indicator used will be the dichlorophenolindophenol (DCPIP) solution. The reaction between DCPIP solution and the solution containing the sample extract will determine the amount of Vitamin C available in that particular sample.
Aim: To investigate the relationship between the types of food sample, which are cabbage, onion and pineapple, and also the concentration of Vitamin C in the food sample.
Hypothesis: If a food sample requires less volume of solution to cause a permanent colour change of DCPIP solution, then the food sample has a greater concentration of Vitamin C.
The type of food sample
The concentration of Vitamin C in the food sample
The type of indicator used
The volume of DCPIP solution used
The concentration of DCPIP solution
The mass of food sample taken
The initial volume of extract taken
Method to control For a sample of ascorbic acid solution, prepare it by taking a certain volume from its container and put it in a clean burette. For sample of cabbage, grind 10 g of its flesh and mix it with distilled water, then filter the mixture to get 50 cm3 of a clear solution. For sample of onion, grind 10 g of its flesh and mix it with distilled water, then filter the mixture to get 50 cm3 of a clear solution. For sample of pineapple, grind 10 g of its flesh and mix it with distilled water, then filter the mixture to get 50 cm3 of a clear solution. Calculate and record the concentration of Vitamin C in the food sample by using the formula: 0.05 50 n 10 , 50 where n is the average volume of the food sample solution needed to decolourise DCPIP solution. Use the same type of indicator to detect the presence of Vitamin C in the food samples, which is DCPIP solution. Fix the same volume of the DCPIP solution used, which is 1 cm3. Fix the same concentration of DCPIP solution for all sets, which is 1%. Use the same mass of 10 g for all food samples by using a balance. Ensure that all volumes of extract are fixed to 50 cm3 by using filter funnel.
Materials: Material DCPIP solution Vitamin C solution (Ascorbic acid) Distilled water Pineapple Cabbage Yellow onion
Volume 100 cm3
10 g 10 g 10 g
Apparatus: Apparatus 50 cm burette with stand 50 cm3 conical flask 400 cm3 beaker 100 cm3 beaker Tissue paper 10 cm3 measuring cylinder Analytical balance Mortar and pestle Glass rod Filter funnel Filter paper Knife Dropper Chopping board Forceps 3
Quantity 1 5 1 5 1 roll 1 1 1 1 1 3 1 1 1 1
Uncertainty ± 0.5 cm3 ± 0.1 cm3 ± 0.01 g -
Procedure: 1. Grind up 10 g of fruit and mix it with 50 cm3 of water. 2. Filter the plant macerate to provide 50 cm3 of a clear solution, then use this plant extract solution for titration. 3. Clean, rinse, and fill a burette with 1% Vitamin C solution and take an initial burette reading. 4. Transfer 1 cm3 of 1% DCPIP solution into a conical flask, and place the flask beneath the burette. 5. Add Vitamin C solution drop by drop to the DCPIP solution, and shake the conical flask gently after adding each drop, until the DCPIP solution changes to colourless. 6. Record the volume of the Vitamin C solution used. 7. Repeat steps 4 to 6 and calculate the average volume used. 8. Repeat steps 4 to 7 with the plant extract solution. 9. Calculate the concentration of Vitamin C in each of the plant extract solution.
Data collection: Qualitative data 1. For cabbage extract, the DCPIP solution changes its colour from dark blue to colourless. 2. For onion extract, the DCPIP solution changes colour from dark blue to light purple. 3. For pineapple extract, the DCPIP solution changes colour from dark blue to light red.
Quantitative data Reading of burette / cm3 (±0.05) Sample name
0.00 11.00 11.00 25.00 25.00 36.90 38.90 49.80 0.00 14.00 Table 1: The Final and Initial Burette Reading for Different Food Samples in Six Trials
Sample name Ascorbic acid Cabbage Onion Pineapple
Trial 1 1.00 4.50 2.00 11.00
Volume of extract solution used / cm3 Trial 2 Trial 3 Trial 4 Trial 5 Trial 6 0.70 1.00 0.60 0.10 0.20 4.50 3.50 6.90 6.80 6.50 3.10 2.40 5.10 3.70 4.30 14.00 11.90 10.90 14.00 11.50
Table 2: The Volume of Extract Solution Used in Six Trials for Different Food Samples
Sample name Ascorbic acid Cabbage Onion Pineapple
Average volume / cm3 0.60 5.45 3.43 12.22
Standard deviation 0.3847 1.4584 1.1690 1.4275
Concentration of Vitamin C / mg cm-3 0.008333 0.000917 0.001456 0.000409
Standard error 0.0053432 0.0002455 0.0004959 0.0000478
Table 3: The Average Volume of Extract Solution, Concentrations of Vitamin C in Different Food Samples and their Standard Deviations
Sample calculations For onion extract, Volume of extract used (Trial 1) = Final burette volume – Initial burette volume = 25.50 – 23.50 = 2.00 cm3
Average volume of extract used =
Total volume of extract used Number of trials
2.00 3.10 2.40 5.10 3.70 4.30 6
= 3.43 cm3
Standard deviation of average volume of extract used =
Volume used - Mean volume
Number of trials - 1
2.00 3.43 2 3.10 3.43 2 2.40 3.43 2 5.10 3.43 2 3.70 3.43 2 4.30 3.43 2 6 1
For calculating the concentration of Vitamin C in the sample, the following steps are used: 1. 1 cm3 of DCPIP solution is equivalent to 0.05 mg of Vitamin C. 2. So, n cm3 of sample = 1 cm3 of DCPIP solution = 0.05 mg of Vitamin C. 0.05 3. Hence, 1 cm3 of the solution = mg of Vitamin C. n 0.05 50 4. 1 cm3 of the original juice will be mg of Vitamin C. n 10 0.05 50 5. Therefore, concentration of Vitamin C in the juice = n 10 mg cm-3. 50
∴ Concentration of Vitamin C in onion
0.05 50 3.43 10 = 50 = 0.001456 mg cm-3
Standard error of concentration of Vitamin C in the sample =
Standard deviation of average volume of extract used Average volume of extract used
1.1690 0.001456 3.43
Concentration of Vitamin C in extract
Chart of Concentration of Vitamin C against Sample Type 1.6E-02
Concentration of Vitamin C / mg cm-3
0.0E+00 Ascorbic acid
Discussion: 1. Since the graph is a kind of bar chart, there are no obvious trends which can be seen. 2. From this experiment, a bar chart is made because the independent variable, which is the type of sample, has discrete data. 3. Also, due to this conditions, no scatter plots can be made. 4. Excluding the ascorbic acid, the highest value of Vitamin C concentration from the bar chart is 0.001456 mg cm-3, which comes from onion. 5. The lowest value of concentration of Vitamin C is from pineapple, which has a value of 0.000409 mg cm-3. 6. No constant values exist in the bar chart. 7. Experimentally, in ascending order, the concentrations of Vitamin C arrangements are Pineapple < Cabbage < Onion. 8. However, theoretically, this arrangement is wrong. 9. The actual arrangement, in ascending order, is Onion < Cabbage < Pineapple. 10. Theoretically explained, since Vitamin C is a type of acid, which is ascorbic acid, the food containing Vitamin C should have a sour taste. 11. Therefore, food with low content of Vitamin C should have a less sour taste, due to low acidity in the food itself. 12. On the other hand, food containing high Vitamin C content should have a more sour taste due to high acidity in it. 13. Also, in terms of the DCPIP solution, it can be decolourised when the solution titrated to it has Vitamin C present in it. 14. The more the concentration of Vitamin C in the food, the less the volume of the solution needed to decolourise the DCPIP solution. 15. Hence, with high concentration of Vitamin C, DCPIP solution can be decolourised faster. 16. In this context, the pineapple extract should be the solution which can change the colour of DCPIP solution with the least volume. 17. This is because the pineapple extract has a higher concentration of Vitamin C in it. 18. Also, since the pineapple extract has the most concentrated Vitamin C compared to the two other extracts, the extract will be the most acidic. 19. Therefore, it does not decolourise the DCPIP solution, but it only changes its colour from dark blue to red. 20. The cabbage should be the extract which can decolourise DCPIP solution at a volume greater than the pineapple extract, but it is still less compared to the onion extract. 21. This is because the Vitamin C concentration in cabbage extract is lower than that of pineapple, but still, it is still has higher concentration than the onion extract. 22. Likewise, since onion extract is the extract which require the most volume to decolourise DCPIP solution, the onion extract should be the one which has the lowest concentration of Vitamin C. 23. In terms of the experimental values, the data obtained in this experiment for the three extracts are not parallel with the theoretical values.
24. From the experiment, the Vitamin C concentration in onion is the highest, while the Vitamin C concentration in pineapple is the lowest, which do not satisfy the theoretical values. 25. One of the possible cause of this occurrence is that, there might be any of the three extracts whereby during titration, the extract is not titrated enough until the DCPIP solution completely changes colour from blue to colourless. 26. For example, when titrating DCPIP solution with the onion extract, the reaction is assumed ‘stopped’ when DCPIP solution changes colour to light purple. 27. The actual situation is, even though there is a light purple colour in DCPIP solution, the titration still can be continued because DCPIP solution will eventually turn to colourless, no matter what. 28. The 1% ascorbic acid solution acts as a control experiment. 29. The value of concentration of Vitamin C in 1% ascorbic acid solution is also taken, together with the three food extract. 30. This control experiment is present so that its concentration value can be a standard, thus can be compared to the other values obtained from the other independent variables. 31. In terms of the error bar, it represents the standard errors for each of the concentrations of Vitamin C present in each of the sample extracts. 32. From the bar chart, all the error bars of the three extracts, which are cabbage, onion and pineapple, are relatively small. 33. This means that the data obtained for those three extracts have only small ranges. 34. Therefore, less deviation is present for the three data. 35. However, the error bar for the sample of 1% ascorbic acid solution has the greatest length compared to the others. 36. This shows that the value of concentration for 1% ascorbic acid has a wider range. 37. Hence, in terms of reliability, the data for concentration of Vitamin C in 1% ascorbic acid seems to be less reliable.
Evaluation: Limitation / Weakness The food macerate is mixed with water, which may not take all of the juices from the samples. The food macerate is filtered by using filter funnel and filter paper, which consumes a lot of time. The filter paper is folded in a typical way, which actually has less surface area to filter the macerate. The titration is assumed ‘ended’ when the DCPIP solution has turned light purple, which leads to a wrong result. During filtration, not all of the macerate is used, which may affect the concentration of the solution from the macerate.
Suggestion to improve The juices from the macerate can be taken thoroughly by not mixing it with water at all. The time taken to extract the juices can be reduced by squeezing the food in a cloth in order to get the filtered juices. The filter paper can be folded in a way such that it is fluted, so that it has a greater surface area for filtering the macerate. For non-acidic solutions, the titration should be done until DCPIP solution changes colour from dark blue to completely colourless. Ensure that all of the macerate is used for filtration so that it is proportional to the concentration of the extract solution.
Conclusion: Based on all of the data obtained and all of the researches, the less the volume of a solution required to decolourise the DCPIP solution, the greater the concentration of Vitamin C contained in that particular extract solution. Although not all of the data obeyed the hypothesis stated, but the hypothesis itself obey the actual theoretical explanations regarding to the Vitamin C content in food.
References: 1. UKEssays.com. (n.d.) Measuring the Concentrations of Vitamin C Biology Essay. Retrieved July 15, 2014, from http://www.ukessays.com/essays/biology/measuringthe-concentrations-of-vitamin-c-biology-essay.php 2. Metro Richmond STEM Fair. (n.d.). Parts of an Experiment. Retrieved July 17, 2014, from http://sciencefair.msinnovation.info/handbook/parts_of_exp.htm.