THEME: ANALYSIS ON CONTAMINANTS AND ADDITIVES IN CONSUMER PRODUCTS Determination of the concentration of citric acid in soft drinks using acid/base titration NAME:
I/C NUMBER:
INDEX NUMBER:
ABSTRACT Citric acid is often added to food and beverages to improve the flavor. The purpose of this project is to determine the concentration of citric acid in soft drinks by using acid/base titration. In this project, the technique of titration is adopted by reacting the soft drinks that contain citric acid with sodium hydroxide solution. Six types of soft drinks are used in this project, which are 7-UP, Revive, IceCream Soda, Mountain Dew, Pop and 100 Plus. 25.00cm3 of soft drink with unknown molarity of citric acid is titrated with a standard 0.1mol dm-3 NaOH solution. Phenolphthalein is used as an indicator to determine the endpoint of the titration. The results obtained are used to calculate the molarity of citric acid in the soft drinks and thus the number of moles, the average number of moles, and the average grams of moles of citric acid per can or bottle can be calculated. Based on the result, it is found that Revive has the highest concentration of citric acid while Pop has the lowest concentration of citric acid.
1.0 INTRODUCTION 1.1 THEORY Acids are added to a variety of food and beverages and contribute significantly to their taste. Soft drinks often contain varying quantities of several acids, giving sodas their tart flavor. Examples of these acids added are citric acid and carbonic acid, which are found in sodas such as 7-UP and 100 Plus. Citric acid is weak, polyprotic acid. It is both a natural and artificially obtained acid. It is found naturally in living being as a key component of the natural aerobic process of respiration. Citric acid was first artificially produced in 1784 from lemon juice, by Karl Wilhelm Scheele. It can also be obtained through bio-technology processes for industrial purposes by fermenting the citrus glucose, sucrose or molasses in
combination
with
the
fungus
called
“Aspergillus
niger.”
(http://www.veria.com/wellness/healing/citric-acid-benefits-uses-sideeffects/?id=900) 1.2 LITERATURE REVIEW Based on European Citric Acid Manufacturers Association’s (ECAMA's) experience, the use of citric acid and citrates in beverage and soft drink applications reflects levels commonly found in natural fruits. Typical additions of 0.25 to 0.4% of CITRIC ACID are used to enhance or impart tangy flavours and chelate metal ions to improve product storage together with flavour and colour stabilizations. Likewise sodium citrate at 0.1% can offer a cooling saline taste as well as providing buffering 1
capacity to stabilize pH hence aiding Carbon Dioxide retention. (http://www.ecama.org/Reports/Softdrinks.doc\) 1.3 PROBLEM STATEMENT Citric acid is the most frequently used preservative and additive in the world today. It creates an acidic environment that is not favorable for bacterial and microbes to carry out essential living processes. Besides, citric acid contributes to many health benefits, such as preventing kidney stones, accelerating mineral absorption into the body, treating sore throat and nausea, helping in the regeneration of skin tissue and as an antioxidant. However, there are some potential health effects in the consumption of citric acid, which may cause allergic reaction, eye irritation, gastrointestinal tract irritation with nausea, vomiting and diarrhea. Furthermore, frequent intake of citrated beverages may cause erosion of dental enamel and irritation of mucous membranes (http://www.sciencelab.com/msds.php?msdsId=9923494). A study at the University of Bristol, UK, has found that the increasing incidence of enamel erosion was causally connected to the high amounts of citric acid added
to
drinks
and
food
(http://www.alive.com/articles/view/
17903/is_citric_acid_truly_safe). Therefore, it comes to our concern whether the food and beverage we consume contain a high concentration of citric acid. 1.4 OBJECTIVE The objective of this project is to determine the concentration of citric acid in soft drinks. 2
2.0 METHODOLOGY In this project, samples of soft drinks are titrated against a standard sodium hydroxide solution. Careful technique is adopted to detect the endpoint when the reaction is complete. With the aid of an indicator, the endpoint can be observed easily. The method used to carry out titration between citric acid in soft drinks and sodium hydroxide solution can be divided to two parts: preparation of a standard NaOH solution and titration of the soft drinks. (A) Preparation of a standard NaOH solution 1. 1.0g of NaOH is weighed and dissolved in beaker by using distilled water. After that, the solution is made up to 250ml of 0.1mol dm-3 NaOH solution. (B) Titration of soft drinks 1. The soft drink samples have been left flat for several days in advance to assure it is decarbonized. 2. 10.00cm3 of the soft drink is pipetted into 250ml conical flask and 2 to 3 drops of phenolphthalein are added into the soft drink. 3. The buret is filled with standard NaOH solution. The initial volume of NaOH solution in the buret is recorded. NaOH solution is slowly added to the soft drink until the first faint lasting pink colour appears. Once a lasting pink colour has been reached, the final volume of NaOH from the buret is recorded. 5. The molarity of the citric acid in the soft drink is calculated. 3
6. Steps 3 to 5 are repeated three more times and the average molarity is calculated. 7. From the average molarity of citric acid, the number of moles of citric acid per can or bottle of soft drink is calculated. 8. Finally, the number of grams of citric acid per can or bottle of soft drink is calculated. 9. Steps 1 to 8 are repeated for others soft drink samples.
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3.0 RESULTS 3.1 TABULATION OF DATA Table 1: Titration of soft drink 1 (7-UP) Rough
1
2
3
Volume of soft drink (cm3)
25.00
25.00
25.00
25.00
Final burette reading, NaOH (cm3)
21.00
31.10
41.25
40.00
Initial burette reading, NaOH (cm3)
10.70
21.00
31.10
29.80
Total volume, NaOH (cm3)
10.30
10.10
10.15
10.20
Average volume, NaOH (cm3) Molarity of citric acid (mol dm-3) Average molarity of citric acid (mol dm-3)
10.15
0.0135
0.0135
0.0136
0.0135
Average moles of citric acid per can/bottle (mol)
4.39 × 10-3
Average grams of citric acid per can/bottle (g)
8.42 × 10-1
All data are tabulated in the same way as shown in Table 1.
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3.2 CALCULATION 3.2.1 THEORY OF CALCULATION Citric acid is a weak, polyprotic acid that can undergo neutralization reaction with sodium hydroxide solution. The reaction between citric acid and sodium hydroxide solution is shown below: H3C6H5O7 (aq) + 3 NaOH (aq)
3 H2O (l) + Na3C6H5O7 (aq)
The molarity of citric acid in a soft drink can be calculated by using the formula: , where M is molarity and V is volume.
The average number of moles of citric acid per can or bottle can be calculated by using the formula:
The average grams of citric acid per can or bottle can be calculated by using the formula:
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3.2.2 EXAMPLE OF CALCULATION Calculation on soft drink 1 (7-UP):
Similar calculations are carried out for the other soft drinks.
Calculation on the consecutive difference of citric acid per can or bottle of soft drinks: (Between Pop and Mountain Dew)
Similar calculations are carried out for the other consecutive soft drinks.
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3.2.3 SUMMARY OF CALCULATION Table 2: Ascending concentration of citric acid per can or bottle Average number of moles
Average grams
(mol)
(g)
Pop
3.45 × 10-3
6.61 × 10-1
Mountain Dew
3.80 × 10-3
7.30 × 10-1
Soda
4.03 × 10-3
7.74 × 10-1
7-UP
4.39 × 10-3
8.42 × 10-1
100 Plus
5.00 × 10-3
9.60 × 10-1
Revive
5.20 × 10-3
9.98 × 10-1
Soft drinks
Ice-Cream
Higher average number of moles and average number of grams of citric acid per can or bottle indicates that the soft drink has higher concentration of citric acid. Based on the results, Revive has the highest concentration of citric acid, followed by 100 Plus, 7-UP, Ice-Cream Soda, Mountain Dew and Pop.
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Table 3: Consecutive difference in concentration of citric acid per can/bottle of soft drinks Difference Soft drinks
Number of moles Grams (g) (mol)
Pop 0.35 × 10-3
0.69 × 10-1
0.23 × 10-3
0.44 × 10-1
0.36 × 10-3
0.68 × 10-1
0.61 × 10-3
1.18 × 10-1
0.20 × 10-3
0.38 × 10-1
1.75 × 10-3
3.37 × 10-1
3.50 × 10-4
6.74 × 10-1
Mountain Dew Mountain Dew Ice-Cream Soda Ice-Cream Soda 7-UP 7-UP 100 Plus 100 Plus Revive Revive Pop Average
The average difference in number of mols and grams between consecutive soft drinks is small, thus indicating that all the soft drinks have almost the same concentration of citric acid per can or bottle.
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3.3 DISCUSSION In this project, the volume of sample of soft drinks used is same, that is one can or bottle, which is 325cm3. It is assumed that only citric acid and carbonic acid are present in the soft drinks chosen. Since carbonic acid can be removed by releasing all carbon dioxide from the soft drinks, the only acid present in the soft drinks chosen is assumed to be citric acid. Phenolphthalein is used as an indicator to determine the endpoint of the titration. Phenolphthalein is pink in acidic solution and is colourless in basic solution. Therefore, when the solution changes from colourless to pink, the acid-base reaction is said to be complete. The readings of each titration are prone to random errors such as observational errors of determining the endpoint of titration which will result in the addition excess base to the acid. This causes inaccuracy of result that might not be the true value of the volume of base that has reacted. The mistakes can be reduced by titrating slowly and shaking the conical flask to ensure that no excess base is added. Furthermore, error might have occurred when reading the meniscus level of titre. The titration for each sample is repeated a few times to improve the accuracy of results by taking the average value. Based on the results, it is found that all the soft drinks chosen have almost the same concentration of citric acid per can or bottle. Revive has the highest concentration of citric acid per can or bottle while Pop has the lowest concentration of citric acid per can or bottle. 10
4.0 CONCLUSION The concentration of citric acid in soft drinks can be determined by using acid-base titration. Revive has the highest concentration of citric acid per can or bottle, followed by 100 Plus, 7-UP, Ice-Cream Soda and Mountain Dew. Pop has the lowest concentration of citric acid per can or bottle. The difference between the highest concentration of citric acid per can or bottle, Revive, and the lowest concentration of citric acid per can or bottle, Pop, is 1.75 × 10-3mol or 3.37 × 10-1g, which is not significant in comparison. There is a small difference in the concentration of citric acid between the other types of soft drink, which has the average difference of 3.5 × 10-4 mol or 6.74 × 10-1g, indicating that all these soft drinks have almost the same concentration of citric acid per can or bottle. 4.1 SUGGESTION Studies have found that over dosage of citric acid will cause side effects. (http://www.livestrong.com/article/152574-effects-of-citric-acid-onpeople/) However, there is limited study on the recommended daily allowance of citric acid and the amount of citric acid that will cause side effects. Therefore, further investigation on the recommended daily allowance of citric acid and the amount of citric acid that is safe to be consumed should be carried out in the future research. This is to ensure that the consumption of citric acid will not bring side effects to the consumer.
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5.0 REFERENCES/BIBLIOGRAPHY http://www.alive.com/articles/view/17903/is_citric_acid_truly_safe http://www.sciencelab.com/msds.php?msdsId=9923494 http://www.livestrong.com/article/152574-effects-of-citric-acid-on-people/ http://www.veria.com/healing/citric-acid-benefits-uses/?id=900 http://www.flavours.asia/uploads/7/9/8/9/7989988/titration.pdf http://www.ecama.org/Reports/Softdrinks.doc Tan Yin Toon, Loh Wai Leng, Lim Ming Hui, Ho Sook Chee, Ace Ahead STPM Text Chemistry First Term, Oxfod Fajar Sdn. Bhd., 2012.
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