EE Pille-Riin Hunt...rather low when taking into consideration the human’s daily need of given...

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: 006552-0013

Number of words: 2395

Tartu 2013

Candidate’s Name: Pille-Riin Hunt Candidate’s Session Number: 006552-0013

2

Table of Contents

Abstract ................................................................................................................................................... 3

Introduction ............................................................................................................................................. 4

Vitamin C ................................................................................................................................................ 5

Methods .................................................................................................................................................. 5

Production of Juice .............................................................................................................................. 5

DCPIP titration .................................................................................................................................... 6

KIO3 titration ....................................................................................................................................... 7

Data from experiments ............................................................................................................................ 8

Processed data ....................................................................................................................................... 10

Conclusions ........................................................................................................................................... 16

Evaluations ............................................................................................................................................ 16

Bibliography ......................................................................................................................................... 18


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 KIO3 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*10-4 and 2.7*10-4 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


4

Introduction 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

2013. 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 KIO3 , on the


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 C6H8O6.

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.


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

C12H7NCl2O2. 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 0.000895 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


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.

KIO3 titration :

The other method is titration with KIO3 , 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 C6H10O5 have to be added to the fruit juice. I- ions from KI solution and IO3- ions from

KIO3 solution react to produce I2, shown in the following equation :

IO3- + 5I- +6H+ = 3I2 + 3H2O

Redox reaction between I2 and ascorbic acid takes place during what the ascorbic acid is being

oxidized as shown in an equation below:

C6H8O6 + I2 = C6H6O6 + 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 I2 molecules in it. To determine whether the I2

molecules are present, the starch (C6H10O5) solution is needed since it reacts with I2 to

produce a deep blue colour and, hence, changes the colour of the juice examined, shown in

the following equation:

C6H10O5(transparent) + I2(transparent) = C6H10O4I(deep blue) + IO

Substances used for this method:

• 0.1 M HCl solution

• 0.005 M starch solution

• 0.002 M KIO3 solution

• 0.1 M KI solution


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

KIO3 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 KIO3 until the colour of the juice changes. Amount of vitamin C is

calculated.


9

Data from experiments: Table 1. Collected Data for Apple Geneva

Number of trial

Amount of KIO3 used (±0.05 ml) Amount of DCPIP used (±0.05 ml)

1 1.7 4.6 2 1.7 4.6 3 1.8 4.7 4 2 4.7 5 2 4.9

Table 2. Collected Data for Apple Jonagored

Number of trial


1 1.7 4.1 2 1.5 4.1 3 1.5 4.2 4 1.6 4.3 5 1.5 4.1

Table 3. Collected Data for Apple Paulared

Number of trial


1 1.7 4.5 2 1.5 4.1 3 1.5 4 4 1.4 4 5 1.4 4.2

Table 4. Collected Data for Pear Conference


10

Number of trial


1 1.1 2.7 2 1.2 2.6 3 0.9 2.7 4 1 2.5 5 1 2.5

Table 5. Collected Data for Pear Guyot

Number of trial

Amount of KIO3 used(±0.05 ml) Amount of DCPIP used(±0.05 ml)

1 1.2 3.1 2 1.2 3.2 3 1.5 3.2 4 1.2 3.3 5 1.4 3.3

Table 6. Collected Data for Pear Bartlett

Number of trial

Amount of KIO3 used(±0.05 ml) Amount of DCPIP used(±0.05 ml)

1 1.1 2.8 2 1.1 2.9 3 1.2 3.2 4 1.1 2.8 5 1.2 2.9

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(C6H8O6) =176.14 (g/mol)*0.000895 (M)*4.7/1000(l) ≈7.4*10-4 (g)


11

To calculate the mass of vitamin C using data from experiments using titration with KIO3 , an

equation that was introduced before have to be considered :

IO3- + 5I- +6H+ = 3I2 + 3H2O

It can be seen that one IO3- ion in the reaction produces 3I2 molecules which reacts to the

ascorbic acid , one to one as shown in the following equation:

C6H8O6 + I2 = C6H6O6 + 2H

Firstly, the moles of KIO3 have to be calculated using experimental data to be able to

calculate the moles of I2.

The mass of vitamin C can be now calculated by using following formula:

mass of ascorbic acid= moles of I2 * molar mass of ascorbic acid

Example calculation:

n(KIO3) = 0.002(M)*1.7/1000(l) = 3.4*10-6 mol

n(I2) = 3.4*10-6 * 3 = 1.02*10-5 mol

m(C6H8O6) = 1.02*10-5 *176.14 ≈ 1.8*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 KIO3 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 KIO3 method to be multiplied by 4.

Example calculation for DCPIP method:

Mass(C6H8O6) *10=7.4*10-4*10=7.4*10-3 (g)

n(C6H8O6) =7.4*10-3 (g)/176.12(g/mol)≈ 4.2*10-5 (mol)

concentration(C6H8O6)= 4.2*10-5 /0.1=4.2*10-4 (M)

Example calculation for KIO3 method:

Mass(C6H8O6) *4 = 1.8*10-3 *4 = 7.2*10-3 (g)


12

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*10-4 (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 Concentration of vitamin C per 100 ml from method 1 (M)

Concentration of vitamin C per 100 ml from method 2 (M)

1 4.1*10-4 4.1*10-4 2 4.1*10-4 4.1*10-4 3 4.3*10-4 4.2*10-4 4 4.8*10-4 4.2*10-4 5 4.8*10-4 4.4*10-4

Average 4.4*10-4 4.2*10-4 Total average

4.3*10-4

Table 8 Calculated Data for Apple Jonagored

No.of trial Concentration of vitamin C per 100 ml from method 1

Concentration of vitamin C per 100 ml from method 2

1 4.1*10-4 3.7*10-4 2 3.8*10-4 3.7*10-4 3 3.8*10-4 3.8*10-4 4 3.8*10-4 3.8*10-4 5 3.8*10-4 3.7*10-4


3.8*10-4

Table 9 Calculated Data for Apple Paulared



1 4.1*10-4 4.0*10-4


13

2 3.8*10-4 3.7*10-4 3 3.8*10-4 3.6*10-4 4 3.4*10-4 3.6*10-4 5 3.4*10-4 3.8*10-4


3.7*10-4

Table 10 Calculated Data for Pear Conference



1 2.6*10-4 2.4*10-4 2 2.8*10-4 2.3*10-4 3 2.2*10-4 2.4*10-4 4 2.4*10-4 2.2*10-4 5 2.4*10-4 2.2*10-4


2.4*10-4

Table 11 Calculated Data for Pear Guyot



1 2.9*10-4 2.8*10-4 2 2.9*10-4 2.9*10-4 3 3.6*10-4 2.9*10-4 4 2.9*10-4 3.0*10-4 5 3.4*10-4 3.0*10-4


3.0*10-4

Table 12 Calculated Data for Pear Red Bartlett



1 2.6*10-4 2.5*10-4 2 2.6*10-4 2.6*10-4 3 2.9*10-4 2.9*10-4 4 2.6*10-4 2.5*10-4 5 2.9*10-4 2.6*10-4


2.7*10-4


14

Average of vitamin C concentration in all apple juices:

(4.3*10-4+3.8*10-4+3.7*10-4) /3 ≈ 3.9*10-4 (M)

Average of vitamin C concentration in all pear juices:

(2.4*10-4+3.0*10-4+2.7*10-4)/3 = 2.7*10-4 (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) /0.1 ≈ 3.0*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*10-4 )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*10-4 )M*100 ml ≈ 0.8 (l)

Figure 1. Comparison of Vitamin C Concentration in All Apple Juices

0.00034

0.00035

0.00036

0.00037

0.00038

0.00039

0.0004

0.00041

0.00042

0.00043

0.00044

Apple Geneva Apple Jonagored Apple Paulared

Con

cent

ratio

n of

vita

min

C

(M)


15

Figure 2. Comparison of Vitamin C Concentration in All Pear Juices

Figure3. Comparison of the Average Vitamin C Concentration in Apple and Pear Juices

Figure 4. Comparison of the average concentration investigated fruit juices with the minimum daily amount needed

0

0.00005

0.0001

0.00015

0.0002

0.00025

0.0003

0.00035

Pear Conference Pear Guyot Pear Red BartleC

Con

cent

ratio

n of

vita

min

C

(M)

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

Con

cent

ratio

n of

vita

min

C (M

)

Average of pear juices Average of apple juices Minimum daily needed amount

0

0.00005

0.0001

0.00015

0.0002

0.00025

0.0003

0.00035

0.0004

0.00045

Con

cent

ratio

n of

vita

min

C

(M)

Average of pear juices Average of apple juices


16

Conclusions The results calculated from DCPIP experiments’ data is lower in all investigated juices when

compared to the results calculated from KIO3 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*10-4 and average concentration in pear juices was 2.7*10-4 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


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 KIO3 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.


18

Bibliography 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 :

http://www.thedailygreen.com/healthy-eating/eat-safe/top-sources-vitamin-C-

44102808#slide-5

3. Office of Dietary Supplements “Vitamin C“ Retrieved: August 21st, 2013 from

website Office of Dietary Supplements: http://ods.od.nih.gov/factsheets/VitaminC-‐

HealthProfessional/

4. University of Maryland Medical Centre (2011, July 7th) “ Vitamin C (Ascorbic acid)“

Retrieved: March 30th, 2013, from website:

http://umm.edu/health/medical/altmed/supplement/vitamin-c-ascorbic-acid

5. Walding. R “Vitamin C in fruit juice using DCPIP titration“ Retrieved: August 21st,

2013 from: http://seniorchem.com/vitaminC_DCPIP.doc

EE Pille-Riin Hunt...rather low when taking into consideration the human’s daily need of given...

Documents

Transcript of EE Pille-Riin Hunt...rather low when taking into consideration the human’s daily need of given...