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ANALYTICAL CHEMISTRY

EXPERIMENT 3 ACID – BASED TITRATION II (BACK TITRATION) DETERMINATION THE PERCENT (W/W) OF THE ACTIVE INGREDIENT IN ASPIRIN TABLET

SUGGESTED

VIDEO

LINK

(technique

titration

of

aspirin

with

NaOH)

https://www.youtube.com/watch?v=_0hzZjVZcQ8 https://www.youtube.com/watch?v=PTH7xOKY_Co

Purpose To determine the percent (w/w) of the active ingredient, acetylsalicylic acid (C9H8O4) in aspirin tablet. Introduction Acetylsalicylic acid (ASA) is an active ingredient in an aspirin tablet. Aspirin can be hydrolyzed by the excess amount of sodium hydroxide to give sodium salts of two weak acids, ethanoic acid and salicylic acid (equation 1). The unreacted NaOH can then be neutralized by HCl (equation 2). CH3COO-C6H4-COOH + 2NaOH → CH3COO- Na+ + HO-C6H4-COO- Na+ (1) (reacted) (reacted) NaOH + HCl → NaCl + H2O (2) (excess/unreacted) (standard)

In this experiment the principle of back titration is being used to determine the excess mole of NaOH and hence the mole of NaOH is consumed by acetylsalicylic acid in the reaction.

Calculations (Students may refer to Chapter 5 on topic back titration) Initial mole of NaOH used in hydrolysis = a Mole of unreacted NaOH (from Eqn. 2) = mole of HCl used in titration = b Mole of NaOH that reacted with acethylsalicyclic acid (initial mol - excess mol) = a-b = c Mole of acethylsalicyclic acid (from Eqn. 1) = ½ c Mass of acethylsalicyclic acid = ½ c x MW % w/w = mass of acethylsalicyclic acid x 100 mass of aspirin

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Apparatus Volumetric flasks: 250 mL(1) 100 mL (2) Retort stand 250 mL conical flask (x3) 20, 25 mL pipette Burette Weighing boat/bottle/paper Filter tunnel Dropper

Chemical Reagents 1 M NaOH –100 mL Indicator : Phenol red or phenolphthalein Aspirin tablet 0.05 M Na2 CO3

Procedure A. Standardization of HCl solution with Na2CO3 1. Follow the procedure as in Experiment 1 to standardize or your HCl solution. The solution is titrated with primary standard of Na2CO3. Record the data in Table 2. Equation: Na2CO3 + 2HCl → 2NaCl + H2O + CO2 B. Preparation of 1.0 M NaOH (Standardization of NaOH solution with HCl) 1. 2. 3.

Fill the burette with NaOH solution. Pipette solution of HCl into 250 mL conical flask. Add 2 - 3 drops of phenolphthalein as indicator. Titrate the HCl in the conical flask with the NaOH from the burette slowly while shaking the flask until the indicator color change. From titration and calculation in lab, you prepare 1.0 M NaOH from HCl as secondary standard solution.

C. Hydrolysis of aspirin 1. 2. 3. 4.

Collect one commercial aspirin tablet. Record the brand name and calculate % content (mass) of the active ingredient in the tablet Weigh the aspirin tablet accurately in a weighing paper and transfer the tablet into a 250 mL conical flask. Add 25 mL (use pipette) of 1.0 M NaOH solution and 25 mL of water to the tablet. Heat this mixture until it boils for about 10 minutes in order to hydrolyze the aspirin. Cool the solution at room temperature then transfer quantitatively into 250 mL volumetric flask. Dilute the solution to the mark carefully using dropper when the level is close to the calibration mark.

D. Back titration

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1. 2. 3.

4. 5.

Pipette 25 mL of aspirin solution into a 250 mL conical flask. Add 1-2 drops of phenol red or phenolphthalein indicator Titrate the aspirin solution in the 250 mL conical flask with the HCI solution prepared in (A) from the burette slowly while shaking the flask until the indicator changes color (phenol red: light red to light yellow; phenolphthalein: pink to colorless). Record your reading at the end point of the titration. Repeat 2 – 3 times and record all readings in Table 3. Calculate the % w/w of acetylsalicylic in aspirin tablet.

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ANALYTICAL CHEMISTRY REPORT SHEET

Experiment No

3

Title

ACID – BASED TITRATION II (BACK TITRATION) DETERMINATION THE PERCENT (W/W) OF THE ACTIVE INGREDIENT IN ASPIRIN TABLET

Name and Student ID

FATIN NUR NAJWA BINTI SHUBRI (2019272158) NUR FATIHIE BINTI MOHD NOOR (2019432392)

Course

FACULTY OF APPLIED SCIENCES

Group

A4AS1204_5

Date of Experiment

19TH APRIL 2021

Date of Submission

30TH APRIL 2021

Lecturer’s Name

MADAM UMI KALSUM ABDUL KARIM

ANALYTICAL CHEMISTRY

EXPERIMENT 3 ACID – BASED TITRATION II (BACK TITRATION)

1. State the objective of the experiment. To determine the percent (w/w) of the active ingredient, acetylsalicylic acid (C9H8O4) in aspirin tablet. 2. Describe the procedure (use schematic diagram if necessary). A. Standardization of HCl solution with Na2CO3 1. HCl solution was standardized by follow the procedure as in Experiment 1. The solution is titrated with primary standard of Na2CO3. The data was recorded in Table 2. Equation: Na2CO3 + 2HCl

2NaCl + H2O + CO2

B. Preparation of 1.0 M NaOH (Standardization of NaOH solution with HCl) 1. The burette was filled with NaOH solution. Solution of HCl was pipetted into 250 mL conical flask. Then, 2-3 drops of phenolphthalein were added as indicator. 2. HCl in the conical flask was titrated with NaOH from the burette slowly while shaking the flask until the indicator color change. 3. From titration and calculation in lab, 1.0 M NaOH was prepared from HCl as secondary standard solution. C. Hydrolysis of aspirin 1. Firstly, one commercial aspirin tablet was collected. The brand name was recorded and the % content (mass) of the active ingredient in the tablet was calculated. 2. The aspirin tablet weighed accurately in a weighing paper and the tablet transferred into 250 mL conical flask. 3. 25 mL (use pipette) of 1.0 M NaOH solution and 25 mL of water were added to the tablet. The mixture was heated until it boils for about 10 minutes in order to hydrolyze the aspirin. 4. The solution was cooled at room temperature then transferred quantitatively into 250 mL volumetric flask. The solution was diluted to the mark carefully using dropper when the level is close to the calibration mark. D. Back titration 1. 25 mL of aspirin solution was pipetted into a 250 mL conical flask. 2. 1-2 drops of phenol red or phenolphthalein were added as indicator 3. The aspirin solution was titrated in the 250 mL conical flask with the HCI solution prepared in (A) from the burette slowly while shaking the flask until the indicator

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changes color (phenol red: light red to light yellow; phenolphthalein: pink to colorless). The reading was recorded at the end point of the titration. 4. It was repeated for 2 – 3 times and all readings were recorded in Table 3. 5. The % w/w of acetylsalicylic in aspirin tablet was calculated.

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RESULT/DATA ANALYSIS Table 1 Commercial/brand name of aspirin tablet

Millisprin

Name of manufacturer

KCK Pharmaceutical

Mass per tablet of active ingredient (acetylsalicylic acid) stated on the label

900 mg

Mass of aspirin tablet

1.1567 g Calculated % w/w

Table 2 Standardization of HCl solution. Titration Rough Final burette reading Initial burette reading Volume of HCl used

77.81 %

1

2

3

23.70 0.00 23.70

23.70 0.00 23.70

23.80 0.00 23.80

1

2

3

13.90 0.00 13.90

13.10 0.00 13.10

13.10 0.00 13.10

a) Average volume of HCl: 23.73 mL b) Volume of Na2CO3 used: 25.00 mL c) Molarity of Na2CO3: 0.05 M Standardization of NaOH solution with HCl Molarity of NaOH: 1.0 M Table 3 Titration of aspirin solution with HCl Titration Rough Final burette reading Initial burette reading Volume of HCl used

a) Average volume of HCl: 13.37 mL b) Initial volume of NaOH used to hydrolyze aspirin: 25.00 mL CALCULATIONS 1a) Based on the data obtained in Table 2 calculate the exact molarity of HCl. Use (M aVa / MbVb) = a/b Na2CO3 + 2HCl 2NaCl + H2O + CO2 𝑀𝑎𝑉𝑎 𝑀𝑏𝑉𝑏

=

𝑎 𝑏

𝑀𝑎(23.73) (0.05)(25.00)

𝑀𝑎

=

=

2 1

2(0.05)(25.00) 1(23.73)

𝑀𝑎 = 0.1054 M

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a) Using back titration method, calculate the % (w/w) ASA in the aspirin tablet. i)

Calculate the initial mole of NaOH used for hydrolysis.

ii) Based on Equation (2), calculate the mole of excess (unreacted) NaOH. (Remember in C: Hydrolysis of aspirin, solution mix with NaOH is diluted 10 x [25 mL into 250 mL]. Need to find mol NaOH before dilution)

iii) Calculate the mole of NaOH that has actually reacted with acetylsalicylic acid.

iv) Based on Equation (1), calculate the mole of reacted acetylsalicylic acid (ASA) in the solution.

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v)

Calculate the mass then the % w/w of acetylsalicylic acid in the tablet. Molar mass of acetylsalicylic acid, C9H8O4

12(9) + 1(8) + 16(4) = 180 g/mol Mass of acetylsalicylic acid, C9H8O4 = mole x molar mass Mass of acetylsalicylic acid, C9H8O4 = 0.0118 mol x 180 g/mol Mass of acetylsalicylic acid, C9H8O4 = 2.124 g % w/w of acetylsalicylic acid =

% w/w of acetylsalicylic acid =

𝑚𝑎𝑠𝑠 𝑜𝑓 𝑎𝑐𝑒𝑡𝑦𝑙𝑠𝑎𝑙𝑖𝑐𝑦𝑙𝑖𝑐 𝑎𝑐𝑖𝑑 𝑚𝑎𝑠𝑠 𝑠𝑎𝑚𝑝𝑙𝑒 2.124 𝑔 1.1567 𝑔

𝑥 100%

𝑥 100%

% w/w of acetylsalicylic acid = 183.63 % vi) Compare the % w/w calculated in Table 1 and the result obtained in (v). Calculate the % error. (% Error = % Error =

183.63−77.81 77.81

𝑥 100%

% Error = 136 %

Conclusion: In this experiment, as the conclusion, the measured value obtained was greater than true value which is 183.63% while true value is 77.81%. Then, the percent value obtained is greater than 100% because the measured value is twice the value of the true value. So, the percent error obtained is 136% due to measurement error.

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