Determination of Citric Acid in Fruit Juice, Lab Reports of Chemistry

Download Determination of Citric Acid in Fruit Juice and more Lab Reports Chemistry in PDF only on Docsity! UNIVERSITI TUNKU ABDUL RAHMAN FACULTY OF SCIENCE BACHELOR OF SCIENCE (HONS) CHEMISTRY YEAR 1 TRIMESTER 1 UDEC1224 CHEMISTRY LABORATORY II Name Chan Yong Li Student ID No. 19ADB04214 Name of Lab Partners 1. Foo Yu Cheng (18ADB02613) 2. Loo Xin Tong (19ADB02955) Practical Group P3 Practical Sub-group G3 No. of Experiment Experiment 3 Title of Experiment Determination of Citric Acid in Fruit Juice Date of Experiment 17th June 2019 Date of Submission 1st July 2019 Name of Lecturer Dr Ooi Zhong Xian 1.0 Title Determination of Citric Acid in Fruit Juice 2.0 Objectives 1. To standardize sodium hydroxide solution by hydrochloric acid solution. 2. To determine citric acid in fruit juice by calculating the concentration of the acid by titrating with a standard sodium hydroxide solution. 3.0 Introduction The sour taste of many fruit juices is due to the presence of organic acids. One of the acids present in juices is citric acid, C3H5O(COOH)3. Citric acid is a naturally occurring acid which, as implied in the name, is found in all citrus fruits (Brima and Abbas, 2014). It contains three carboxylic acid groups and reacts with OH- ions as shown in reaction two. The ionization of sodium hydroxide when dissolved in water is shown in reaction one. From reaction two, we know that it is a neutralization reaction where an acid reacts with a base to form salt and water. The overall reaction in this experiment is shown in reaction three. NaOH (s) → Na+ (aq) + OH- (aq) (1) C3H5O(COOH)3 (aq) + 3 OH- (aq) → C3H5O(COO)3 3- (aq) + 3 H2O (ℓ) (2) C3H5O(COOH)3 (aq) + 3 NaOH (aq) → C3H5O(COONa)3 (aq) + 3 H2O (ℓ) (3) In this experiment, we will assume that citric acid is the sole acid found in fruit juice for the purpose of this experiment. The concentration of citric acid in a given volume can be determined by titrating the lime juice with a standard sodium hydroxide solution. A standard solution is a solution with a known concentration. The standard sodium hydroxide solution is added to the lime juice in a process called titration. Titration is a method of quantitative analysis in which the substance with unknown concentration (to be measured) is reacted stoichiometrically with another reagent (titrant) until it has reacted completely. The change in the appearance of colour from another non- interfering substance (an indicator) indicates the end point of the reaction (Brima and Abbas, 2014). using a dropper. The flask was stopper and shaken well again by repeatedly inverting the flask. Part B: Standardization of NaOH About 50 mL of standardized hydrochloric acid was obtained and the concentration of the standardized hydrochloric acid was recorded. A 10 mL volumetric pipette was rinsed with two small portions of the hydrochloric acid and 10 mL of the hydrochloric acid was pipetted into a clean Erlenmeyer flask. Then, approximately 20 mL of deionized (DI) water and three drops of phenolphthalein were added into the flask. When a pale pink colour was persisted for thirty seconds, the endpoint was reached. The volume of the burette was recorded and the titration was repeated twice. Part C: Titration of the Fruit Juice About 50 mL of fruit juice was obtained. A 10 mL volumetric pipette was rinsed with two small portions of the fruit juice and 10 mL of the fruit juice was pipetted into a clean Erlenmeyer flask. Then, approximately 20 mL of deionized (DI) water and three drops of phenolphthalein were added to the flask. When a pale pink colour was persisted for thirty seconds, the endpoint was reached. The volume of the burette was recorded and the titration was repeated twice. 7.0 Results Part A: Preparation of a Standard NaOH Solution (0.1M) Number of moles of sodium hydroxide = MV 1000 = (0.1M )(100 mL) 1000 = 0.01 mol Mass of sodium hydroxide required = Number of moles× Molar mass = 0.01 mol × 40.00 g /mol = 0.4 g Part B: Standardization of NaOH Titration number 1 2 3 Initial volume of burette (cm3) 0.00 10.10 20.10 Final volume of burette (cm3) 10.10 20.10 30.10 Total volume of NaOH used (cm3) 10.10 10.00 10.00 Average volume of NaOH required for titration = (10.10+10.00+10.00 ) cm3 3 = 10.03 cm3 Before titration After titration Part C: Titration of the Fruit Juice Titration number 1 2 3 Initial volume of burette (cm3) 0.00 9.10 18.00 Final volume of burette (cm3) 9.10 18.00 27.00 Total volume of NaOH used (cm3) 9.10 8.90 9.00 Average volume of NaOH required for titration = (9.10+8.90+9.00 ) cm3 3 = 9.00 cm3 Before titration After titration 8.0 Calculations Part A: Preparation of a Standard NaOH Solution (0.1M) Number of moles of sodium hydroxide = MV 1000 = (0.1 M )(100 mL) 1000 = 0.01 mol Mass of sodium hydroxide required = Number of moles× Molar mass = 0.01 mol × 40.00g /mol Statistical Analysis Let: x = Data of the molarity of sodium hydroxide solution n = No. of data values in this experiment x x−x (x−x )2 0.0990 M 0.0990 M−0.0997 M ¿−0.0007 M (−0.0007 M )2 ¿4.9000 × 10−7 M 2 0.1000 M 0.1000 M−0.0997 M ¿0.0003 M (0.0003 M )2 ¿9.0000 ×10−8 M 2 0.1000 M 0.1000 M−0.0997 M ¿0.0003 M (0.0003 M )2 ¿9.0000 ×10−8 M 2 ∑ x=0.2990 M ∑ (x−x )2=¿ 6.7000 ×10−7 M 2 Mean, x = ∑ x n = 0.2990 M 3 = 0.0997 M Standard deviation, s = √∑ (x−x )2 n−1 = √ 6.7000 × 10−7 M 2 3−1 = 0.0005788 M ≈ 0.0006 M Part C: Titration of the Fruit Juice Considering the equation of the reaction: C3H5O(COOH)3 (aq) + 3 NaOH (aq) → C3H5O(COONa)3 (aq) + 3 H2O (ℓ) From this equation, 1 mole of C3H5O(COOH)3 reacts with 3 moles of NaOH. Using the formula: M1 V 1 n1 = M 2 V 2 n2 , Let: M 1=¿ Molarity of citric acid V 1=¿ Volume of citric acid used n1=¿ Number of moles of citric acid react M 2=¿ Molarity of sodium hydroxide solution obtained from Part B V 2=¿ Average volume of sodium hydroxide solution used n2=¿ Number of moles of sodium hydroxide solution react M1 V 1 n1 = M 2 V 2 n2 M1 V 1 M2 V 2 = n1 n2 M 1 (10.00 mL ) (0.0997 M )(9.00mL ) =1 3 M 1= (0.0997 M )(9.00 mL ) (3) (10.00 mL ) ¿0.02991 M As the citric acid is being diluted by the factor of 10, M 1=0.02991 M ×10 ¿0.2991 M ≈ 0.3 M ∴ The molarity of citric acid is 0.2991 M . Using the formula: M1 V 1 n1 = M 2 V 2 n2 , Let: M 1=¿ Molarity of citric acid V 1=¿ Volume of citric acid used n1=¿ Number of moles of citric acid react M 2=¿ Molarity of sodium hydroxide solution obtained from Part B V 2=¿ Volume of sodium hydroxide solution used in each titration n2=¿ Number of moles of sodium hydroxide solution react Titration number Molarity of citric acid, M 1 1 M1 V 1 n1 = M 2 V 2 n2 M1 V 1 M2 V 2 = n1 n2 M 1 (10.00 mL ) (0.0997 M )(9.10 mL ) = 1 3 M 1= (0.0997 M )(9.10 mL ) (3) (10.00 mL ) ×10 ¿0.03024 M ×10 ¿0.3024 M 2 M1 V 1 n1 = M 2 V 2 n2 M1 V 1 M2 V 2 = n1 n2 M 1 (10.00 mL ) (0.0997 M )(8.90 mL ) =1 3 M 1= (0.0997 M )(8.90 mL ) (3) (10.00 mL ) ×10 ¿0.02958 M × 10 ¿0.2958 M 3 M1 V 1 n1 = M 2 V 2 n2 M1 V 1 M2 V 2 = n1 n2 M 1 (10.00 mL ) (0.0997 M )(9.00 mL ) = 1 3 M 1= (0.0997 M )(9.00 mL ) (3) (10.00 mL ) ×10 ¿0.02991 M ×10 In Part C, 0.0997 M of sodium hydroxide solution was used to titrate with the lime juice prepared in order to determine its citric acid concentration. The procedures for this part were same as the Part B but replacing the hydrochloric acid with the lime juice. Citric acid is a weak triprotic acid and it has three carboxylic acid groups. It donates three protons (H+) when dissolved in water while sodium hydroxide ionizes completely in water to form hydroxide ion (OH-). In this case, when sodium hydroxide is added to citric acid, a salt which is the sodium citrate and water are formed. This is a neutralization reaction where an acid reacts with a base to form salt and water. Each of the hydrogen ion from each carboxylic acid group of citric acid will react with one hydroxide ion from the sodium hydroxide solution to form water. The sodium ion from the dissociated sodium hydroxide will take the place of each hydrogen of the carboxylic acid groups (Truman State University, 2014). The mechanism is shown as below: The colour change of the solution which is from colourless to pink signalled the end point of the reaction. The concentration of citric acid in the fruit juice obtained from this experiment was 0.2991 M and was approximate to 0.3 M . In both Part A and Part B, descriptive statistics such as mean and standard deviation were calculated as they portrayed the basic features of the data in the experiment (Trochim, 2006). In this experiment, mean represented the expected values whereas the standard deviation portrayed how the measurements are spread out from the mean. The concentration of sodium hydroxide solution has a mean of 0.0997 M and a standard deviation of 0.0005788 M and was approximate to 0.0006 M ; while the concentration of citric acid has a mean of 0.2991 M and a standard deviation of 0.0033 M . The low values of standard deviation represented that the data points tend to be very close to the mean. Using the standard deviation as an estimate of uncertainty, the uncertainty of the concentration of sodium hydroxide was (0.0997 ± 0.0006)M while the uncertainty of the concentration of citric acid was (0.2991 ± 0.0033) M . 10.0 Precaution Steps There are a few precaution steps that have to be taken in this experiment. Firstly, safety goggles, gloves and lab coat must be worn whenever one enters the laboratory to provide protection for the arms and the body from any harmful substances and to prevent liquid splashes to the eyes. Besides, glassware must always be handled carefully as glass tubing can easily be broken and can cause severe damage to hands. Next, fill in the burette with distilled water and test for absence of leaks from the tip and stopcock. After that, rinse the burette with small portions of the sodium hydroxide solution before the experiment to prevent dilution of the sodium hydroxide solution. Also, ensure that there are no air bubbles in the solution between the tip and stopcock or in the solution in the burette as it may affect the accuracy of the results. In addition, when reading the meniscus in the burette, use a piece of white paper and place it behind to avoid parallax error. The line of sight must be level with the bottom of the meniscus. Make sure to repeat the titration process at least twice to get the average volume of sodium hydroxide solution used and to get a more accurate and precise result. Moreover, the key of the burette must be operated carefully to ensure that one drop of sodium hydroxide solution falls into the conical flask that containing hydrochloric acid or lime juice at a time upon reaching the endpoint, where pink colouration will be observed. Lastly, avoid contact of acid with skin and clothing. If hydrochloric acid is spilled on the skin or clothes, use cold water to rinse the skin and remove clothing immediately. 11.0 Conclusion The type of titration used in this experiment was acid-base titration, in order to find out the concentration of the sodium hydroxide solution and that of the citric acid in the lime juice prepared. The concentration of sodium hydroxide solution obtained from this experiment was 0.0997 M and was approximate to 0.1 M with a mean of 0.0997 M , and a standard deviation of 0.0005788 M and was approximate to 0.0006 M ; while the concentration of citric acid in the lime juice obtained from this experiment was 0.2991 M and was approximate to 0.3 M with a mean of 0.2991 M , and a standard deviation of 0.0033 M . 12.0 References Brima, E.I. and Abbas, A.M., 2014. Determination of Citric acid in Soft drinks, Juice drinks and Energy drinks using Titration. International Journal of Chemical Studies. [online] Available at: <https://www.academia.edu/31574738/Determination_of_Citric_acid_in_Soft_ drinks_Juice_drinks_and_Energy_drinks_using_Titration> [Accessed 22 June 2019]. Louisiana Tech University, n.d. Chemistry 104: Standardization of Acid and Base Solutions. [online] Available at: <http://www.chem.latech.edu/~deddy/chem104/104Standard.htm> [Accessed 22 June 2019]. Penniston, K.L., Nakada, S.Y., Holmes, R.P. and Assimos, D.G., 2008. Quantitative Assessment of Citric Acid in Lemon Juice, Lime Juice, and Commercially-Available Fruit Juice Products. J Endourol. [online] Available at: <https://www.ncbi.nlm.nih.gov/pubmed/ 18290732> [Accessed 22 June 2019]. Trochim, W.M.K., 2006. Descriptive Statistics. [online] Available at: <https://socialresearch methods.net/kb/statdesc.php> [Accessed 22 June 2019]. Truman State University, 2014. The Determination Of Citric Acid In Fruit Juices. [online] Available at: <http://chemlab.truman.edu/files/2015/07/THE-DETERMINATION-OF-CITRI C-ACID.pdf> [Accessed 22 June 2019].