Miina Härma Gümnaasium

Transcription

1 Miina Härma Gümnaasium Pille-Riin Hunt Chemistry How does the concentration of vitamin C differ among homemade juices made of apples and pears available in Estonia at the beginning of the school year? Extended Essay Supervisor: Erkki Tempel Candidate Session Number: Number of words: 2395 Tartu 2013

2 Table of Contents Candidate s Name: Pille-Riin Hunt Abstract... 3 Introduction... 4 Vitamin C... 5 Methods... 5 Production of Juice... 5 DCPIP titration... 6 KIO 3 titration... 7 Data from experiments... 8 Processed data Conclusions Evaluations Bibliography

3 Abstract This work investigates the concentration of vitamin C in homemade pear and apple juices, more specifically the question of the work is How does vitamin C concentration differ in pears and apples available in Estonia at the beginning of the school year?. Since vitamin C, also known as ascorbic acid is vital nutrient that is not stored in humans bodies, daily consumption of it is necessary. Two methods of titration were used to determine the amount of vitamiin 3nder consideration in those juices. Two methods were used to get more accurate value of vitamiin C concentrations in every fruit juice examined. One of them was with DCPIP a purple/blue coloured substance and the other method was with KIO 3 which requires more solutions in the process to be able to identify the end point of titration and therefore to get data to be able to calculate the amount of vitamiin C in juices. The juices were made with a juices and 3 sorts of both type of fruit were used to get more accurate results. In the results, the concentration of vitamin C was higher in apple juices than in pear ones, 3.9*10 and 2.7*10 respectively. However in both type of fruit juices the concentration was rather low when taking into consideration the human s daily need of given vitamin. To get the lowest needed amount of vitamin C, over one litre of pear juice or approximately 0.8 litres of apple juice should be consumed on daily basis. Words: 246 3

4 Introduction Candidate s Name: Pille-Riin Hunt The given extended essay investigates the amount of vitamin C in homemade pear and apple juices at the beginning of the school year, more specifically the first week of September in Three sorts of pears and three sorts of apples are chosen to make the juice and two different methods of titration were carried out to determine the concentration of vitamin C. Vitamin C, also known as ascorbic acid, was chosen to be investigated for this work because it is essential nutrient for human body and since humans are not able to store ascorbic acid in their body (4), it is important to consume enough vitamin C on daily basis. Fruit and vegetables, especially fresh ones, are claimed to be the best sources of given nutrient. Since fruit were named as one of the best sources of vitamin C, for example one average orange consists of 70mg(2) of ascorbic acid while daily need of it is 60 to 95 mg(3), fruit were chosen to be investigated as homemade juices for this work. Pears and apples, however, were chosen due to my personal interest since I consume them the most often and also because they are available in supermarkets all year round unlike most of the other fruits. Even though September is that time of the year in Estonia when pears and apples become ripe in home gardens, imported fruit available in bigger supermarkets were used for this work. One reason for it is the reflection by media of the situation in Estonia where people tend to move from the countryside to bigger towns and cities. However, in towns and cities growing own fruit is not very common due to less space and because people living in apartments might not even have a garden. As mentioned, three sorts of apples : Geneva, Jonagored and Paulared and three sorts of pears : Conference, Guyot and Red Bartlett were chosen for this extended essay. All apples were from Poland and all pears from France. Three sorts of each fruit were used to get more accurate results for both types of fruit since one sort of apple might have different concentration of vitamin C than the other sort of apple from the same area, same goes for pears. Fruit were chosen to be from same continent to avoid drastic differences of environment they had grown and therefore to avoid bigger difference in the results of the experiment. To find the concentration of ascorbic acid in the homemade juices, two different methods of titration were used. Both titrations base on redox reaction with vitamin C. One of the titrations was with the substance called DCPIP. This method is very straightforward and includes only the investigated fruit juice and the given substance. The titration method with KIO 3, on the 4

5 contrary, requires also other solutions to carry out the the redox reaction. Two methods were chosen to be used instead of one to get more accurate results. Vitamin C Vitamin C is an acid known as an ascorbic acid. It has polar structure which means it is soluble in water. The chemical formula of the ascorbic acid is C 6 H 8 O 6. Vitamin C is an important and also necessary nutrient in human s diet because it has a role in many essential processes in human body. For example it is needed for the body to be able to repair different tissues, including the scar tissue. It also plays role in the growth of teeth and bones. (4) Also, vitamin C strengthens the immune system and can reduce the risk of many medical conditions like cardiovascular diseases and gall bladder diseases. And since ascorbic acid is an antioxidant, it blocks the damage made to DNA and therefore can prevent cancer or at least reduce the risk of it. (4) Therefore, vitamin C is very important or even inevitable nutrient in human s diet. Since human body is unable to store ascorbic acid (4), daily consumption of it is very important to keep the body healthy. Approximate daily need of ascorbic acid is 60 to 95 mg(3) and best sources of it are fruit and vegetables, however since ascorbic acid can be destructed very easily by air, light and/or heat, it is more beneficial to consume the fresh or only slightly processed fruit and vegetables.(4) Methods Production of Juice All juices used were made one day before the experiment, using a juicer. Pear sorts used were Conference, Guyot and Red Bartlett while apple sorts used were Geneva, Jonagored and Paulared. Fruit were cut into pieces and put into a juicer to get the fresh juice. After pouring juices into bottles, the bottles were closed very carefully to prevent juice being exposed to air and stored away from the sunlight until the next day. 5

6 DCPIP titration One of the methods of titration was to do it with a substance called DCPIP. The method by Richard Walding (5) was adapted for this work. DCPIP, also known as dichlorophenolindophenol, has a blue/purple colour and is with chemical formula of C 12 H 7 NCl 2 O 2. Redox reaction between ascorbic acid and DCPIP takes place when fruit juice is titrated against the DCPIP. After all vitamin C has reacted with DCPIP, the substance works as an indicator and changes the colour of the juice. The concentration of vitamin C can therefore be calculated knowing the amount of DCPIP. Substances used for this method: DCPIP solution with concentarion of M Equipment used for this method: Support stand Iron support ring Conical flasks 50 ml burette (±0.05 ml) 25 ml graduated cylinder (±0.25 ml) Variables: 3 different apple juices 3 different pear juices Procedure: Burette is set up to the support stand using iron support ring and filled with DCPIP solution. 10 ml of fruit juice is measured with graduated cylinder and poured into a conical flask which is placed under the burette. The juice is titrated against the DCPIP until the endpoint which 6

7 means that DCPIP solution is added drop by drop to the juice until the juice changes its colour. Concentration of vitamin C is calculated. KIO 3 titration : The other method is titration with KIO 3, adapted from research published in Journal of Pharmaceutical and Biomedical Analysis (1). This method is more complicated than the one described above since many reactions have to occur to get the final result. For the redox reaction to take place to determine the concentration of vitamin C, the solutions of KI, HCl and C 6 H 10 O 5 have to be added to the fruit juice. I - ions from KI solution and IO - 3 ions from KIO 3 solution react to produce I 2, shown in the following equation : IO I - +6H + = 3I 2 + 3H 2 O Redox reaction between I 2 and ascorbic acid takes place during what the ascorbic acid is being oxidized as shown in an equation below: C 6 H 8 O 6 + I 2 = C 6 H 6 O 6 + 2H + Therefore, the amount of the ascorbic acid can be calculated when it is known that all of it has been reacted and the solution has I 2 molecules in it. To determine whether the I 2 molecules are present, the starch (C 6 H 10 O 5 ) solution is needed since it reacts with I 2 to produce a deep blue colour and, hence, changes the colour of the juice examined, shown in the following equation: C 6 H 10 O 5 (transparent) + I 2 (transparent) = C 6 H 10 O 4 I(deep blue) + IO Substances used for this method: 0.1 M HCl solution M starch solution M KIO 3 solution 0.1 M KI solution 7

8 Equipment used for this method: Support stand Iron support ring Conical flasks 50 ml burette (±0.05ml) 25 ml graduated cylinder (±0.25 ml) 2.5 ml pipette (±0.25 ml) Variables: 3 different apple juices 3 different pear juices Procedure: Burette is set up on the support stand with iron support ring. Burette is being washed with KIO 3 solution and then filled with it. 25 ml of examined fruit juice is measured with graduated cylinder and poured into a conical flask. 50 ml of HCl solution is measured with another graduated cylinder and added to the fruit juice. The addition of 5 ml of KI solution and 3 ml of starch solution, both measured with pipette, to the fruit juice follows. Examined juice is titrated against KIO 3 until the colour of the juice changes. Amount of vitamin C is calculated. 8

9 Data from experiments: Table 1. Collected Data for Apple Geneva Number of Amount of KIO 3 used (±0.05 ml) Amount of DCPIP used (±0.05 ml) trial Table 2. Collected Data for Apple Jonagored Number of Amount of KIO 3 used (±0.05 ml) Amount of DCPIP used (±0.05 ml) trial Table 3. Collected Data for Apple Paulared Number of Amount of KIO 3 used (±0.05 ml) Amount of DCPIP used (±0.05 ml) trial Table 4. Collected Data for Pear Conference 9

10 Number of Amount of KIO 3 used (±0.05 ml) Amount of DCPIP used (±0.05 ml) trial Table 5. Collected Data for Pear Guyot Number of Amount of KIO 3 used(±0.05 ml) Amount of DCPIP used(±0.05 ml) trial Table 6. Collected Data for Pear Bartlett Number of Amount of KIO 3 used(±0.05 ml) Amount of DCPIP used(±0.05 ml) trial Processed data : The mass of vitamin C using data from experiments with DCPIP can be calculated using the following formula : mass of ascorbic acid = molar mass of ascorbic acid*concentration of DCPIP*volume of DCPIP Example calculation: m(c 6 H 8 O 6 ) = (g/mol)* (M)*4.7/1000(l) 7.4*10 (g) 10

11 To calculate the mass of vitamin C using data from experiments using titration with KIO 3, an equation that was introduced before have to be considered : IO I - +6H + = 3I 2 + 3H 2 O It can be seen that one IO 3 - ion in the reaction produces 3I 2 molecules which reacts to the ascorbic acid, one to one as shown in the following equation: C 6 H 8 O 6 + I 2 = C 6 H 6 O 6 + 2H Firstly, the moles of KIO 3 have to be calculated using experimental data to be able to calculate the moles of I 2. The mass of vitamin C can be now calculated by using following formula: mass of ascorbic acid= moles of I 2 * molar mass of ascorbic acid Example calculation: n(kio 3 ) = 0.002(M)*1.7/1000(l) = 3.4*10-6 mol n(i 2 ) = 3.4*10-6 * 3 = 1.02*10-5 mol m(c 6 H 8 O 6 ) = 1.02*10-5 * *10-3 g To calculate the concentration of ascorbic acid, next formula is used : concentration= moles/volume Since during titration with DCPIP method 10 ml of juice were examined while during titration with KIO 3 25 ml of juice were examined, the concentration of vitamin C will be calculated for 100 ml which requires the mass calculated from DCPIP method to be multiplied by 10 and the mass calculated from KIO 3 method to be multiplied by 4. Example calculation for DCPIP method: Mass(C 6 H 8 O 6 ) *10=7.4*10 *10=7.4*10-3 (g) n(c 6 H 8 O 6 ) =7.4*10-3 (g)/176.12(g/mol) 4.2*10-5 (mol) concentration(c 6 H 8 O 6 )= 4.2*10-5 /0.1=4.2*10 (M) Example calculation for KIO 3 method: Mass(C 6 H 8 O 6 ) *4 = 1.8*10-3 *4 = 7.2*10-3 (g) 11

12 Candidate s Name: Pille-Riin Hunt n(c6h8o6) = 7.2*10-3(g)/176.12(g/mol)= 4.09*10-5 (mol) concentration(c6h8o6)= 4.09*10-5/ 0.1 = 4.09*10 (M) Since in some cases, the different methods gave slightly different results in concentration, the average of each sort of fruit is calculated before calculating the average concentration of vitamin C for pears and apples. *Titration with DCPIP in the following tables is marked as method 2 and titration with KIO3 marked as method 1 *Total average in following tables stands for the average calculated using the results of both methods Table 7 Calculated Data for Apple Geneva No.of trial Average Total average Concentration of vitamin C per 100 Concentration of vitamin C per 100 ml ml from method 1 (M) from method 2 (M) 4.1*10 4.1*10 4.1*10 4.1*10 4.3*10 4.2*10 4.8*10 4.2*10 4.8*10 4.4*10 4.4*10 4.2*10 4.3*10 Table 8 Calculated Data for Apple Jonagored No.of trial Average Total average Concentration of vitamin C per 100 Concentration of vitamin C per 100 ml ml from method 1 from method 2 4.1*10 3.7*10 3.8*10 3.7*10 3.8*10 3.8*10 3.8*10 3.8*10 3.8*10 3.7*10 3.9*10 3.7*10 3.8*10 Table 9 Calculated Data for Apple Paulared No.of trial 1 Concentration of vitamin C per 100 ml from method 1 4.1*10 Concentration of vitamin C per 100 ml from method 2 4.0*10 12

13 Candidate s Name: Pille-Riin Hunt Average Total average 3.8*10 3.8*10 3.4*10 3.4*10 3.7*10 3.7*10 3.7*10 3.6*10 3.6*10 3.8*10 3.7*10 Table 10 Calculated Data for Pear Conference No.of trial Average Total average Concentration of vitamin C per 100 Concentration of vitamin C per 100 ml ml from method 1 from method 2 2.6*10 2.4*10 2.8*10 2.3*10 2.2*10 2.4*10 2.4*10 2.2*10 2.4*10 2.2*10 2.5*10 2.3*10 2.4*10 Table 11 Calculated Data for Pear Guyot No.of trial Average Total average Concentration of vitamin C per 100 Concentration of vitamin C per 100 ml ml from method 1 from method 2 2.9*10 2.8*10 2.9*10 2.9*10 3.6*10 2.9*10 2.9*10 3.0*10 3.4*10 3.0*10 3.1*10 2.9*10 3.0*10 Table 12 Calculated Data for Pear Red Bartlett No.of trial Average Total average Concentration of vitamin C per 100 Concentration of vitamin C per 100 ml ml from method 1 from method 2 2.6*10 2.5*10 2.6*10 2.6*10 2.9*10 2.9*10 2.6*10 2.5*10 2.9*10 2.6*10 2.7*10 2.6*10 2.7*10 13

14 Average of vitamin C concentration in all apple juices: (4.3* * *10 ) /3 3.9*10 (M) Average of vitamin C concentration in all pear juices: (2.4* * *10 )/3 = 2.7*10 (M) Since 60mg is the minimum amount of vitamin C needed each day, the concentration of it in 100 ml would be : C=(60/1000/176.14) / *10-3 (M) To get minimum needed daily amount of ascorbic acid only from the homemade pear juice, following amount should be consumed daily: (3.0*10-3 /2.7*10 )M*100 ml 1.1(l) To get minimum needed daily amount of ascorbic acid only from the homemade apple juice, following amount should be consumed daily: (3.0*10-3 /3.9*10 )M*100 ml 0.8 (l) Figure 1. Comparison of Vitamin C Concentration in All Apple Juices Concentration of vitamin C (M) Apple Geneva Apple Jonagored Apple Paulared 14

15 Figure 2. Comparison of Vitamin C Concentration in All Pear Juices Candidate s Name: Pille-Riin Hunt Concentration of vitamin C (M) Pear Conference Pear Guyot Pear Red BartleC Figure3. Comparison of the Average Vitamin C Concentration in Apple and Pear Juices Concentration of vitamin C (M) Average of pear juices Average of apple juices Figure 4. Comparison of the average concentration investigated fruit juices with the minimum daily amount needed Concentration of vitamin C (M) Average of pear juices Average of apple juices Minimum daily needed amount 15

16 Conclusions Candidate s Name: Pille-Riin Hunt The results calculated from DCPIP experiments data is lower in all investigated juices when compared to the results calculated from KIO 3 experminents data. However, the difference in the results seems to be practically at the same constant as the difference in the average results for both methods can be seen in tables 7 to 12. The results of average concentration of ascorbic acid in the juice of apple Geneva is noticeably higher than the concentration in the juices of apple Jonagored or Paulared as it can be seen in figure 1. Figure 2, on the other hand shows that the fluctuations between the results of average concentration of vitamin C are not big and intelligibly smaller when compared to results of apple juices According to the experimental data, as seen on figure 3, the average concentration of vitamin C was higher in investigated apple juices. However, since the average concentration in apple juices was 3.9*10 and average concentration in pear juices was 2.7*10 it can be said that both types of fruit had rather low concentrations of vitamin C. That is also supported by the figure 4, where the concentrations of investigated fruit juice were compared with the minimum daily amount of ascorbic acid needed and, even though, apple juices have higher average concentration of ascorbic acid than pear juices, both are significantly lower than the lowest daily amount needed. In fact, approcimately 1.1 litres of homemade pear juice and 0.8 litres of homemade apple juice should be consumed to get the minimum amount of ascorbic acid needed. Since the amount of the juice to get the needed amount of vitamin C is unreasonably high, it can be concluded that, even though homemade juice made of apples available in Estonia at the beginning of the school year has greater amount of ascorbic acid than homemade pear juices, both of them are poor and insuffisient sources of vitamin C. Evaluations Since experimental methods are never 100% certain, using two different methods for this work and calculating the average based on the data from both methods, the results of this work are more accurate. Nevertheless, because both methods were titrations they had the same weakness. Since for 16

17 both methods the end-point was determined by the change of colour, there was a chance to have a human error during the experiment and simply miss the exact point when the juice changed the colour. Also, as it can be seen from tables 1 to 6 that considerably little amounts of KIO 3 was used to achieve end-point of titration which added the difficulty to spot the colour change and therefore it can be a reason for errors in the final results. Using three different sorts for both types of fruit juices investigated can also be considered to give the results more accuracy. Because if only one sort of pear and one sort of apple would have been chosen, there would not have been data of fluctuations between the concentration if vitamin C in the same type of fruit juices. But knowing the amount of ascorbic acid in more than one sort of each type of fruit gives the opportunity to make the generalisations about the vitamin C content in the investigated fruits. However, the results of this work are limited to make the generalisations only for very little amount of fruit since, even though pears used were the only ones available in the bigger supermarkets at that time, there were a lot more apple sorts which might have different kind of vitamin C content due to what the results made in this work can not be used for them. The result that apple juices had overall higher concentration of vitamin C can be also affected by the fact that France and Poland are on slightly different lattitudes due to what the grown environment might have been different which could have affected the results. However, the aim of this extended essay was to find out how the vitamin C concentration differs in juices made of the pears and apples that are available the the first week of September in supermarkets in Estonia. And the result can be justified because no apples were available from the same lattitude with the pears used. Lastly, during processing the fruit, including cutting them and making juice of them with juicer, the vitamin C in juice was exposed to the air which might have caused the destruction of some vitamin. The same might have been caused by making the juices the day before experiments. Even though, the juices were stored in carefully closed bottles, during the transport to school the vitamin C could have been destroyed because of the light. 17

18 Bibliography Candidate s Name: Pille-Riin Hunt 1. Gritsanapun.W, Nilkamhank.S, Paocham.A, Suntornsuk.L (2001, October 30th) Quantitation of vitamin C content in herbal juice using direct titration Journal of Pharmaceutical and Biomedical Analysis 2. Muzaurieta.B Top 10 Sources of Vitamin C (Including 3 Foods With more than Oranges) Retrieved: March 30th, 2013 from website The Daily Green : #slide-5 3. Office of Dietary Supplements Vitamin C Retrieved: August 21st, 2013 from website Office of Dietary Supplements: HealthProfessional/ 4. University of Maryland Medical Centre (2011, July 7th) Vitamin C (Ascorbic acid) Retrieved: March 30th, 2013, from website: 5. Walding. R Vitamin C in fruit juice using DCPIP titration Retrieved: August 21st, 2013 from: 18