Chemistry Full Investigation

TED ANKARA COLLEGE FOUNDATION HIGH

SCHOOL

CHEMISTRY

ACID - BASE REACTIONS

AMOUNT OF ACETY SALICYCLIC ACID FOUND IN A TABLET OFASPIRIN, CORASPIN & BABY

ASPIRIN

Instructor : Okan GüzelStudent : Umay Atay

FULL INVESTIGATION

ACID – BASE REACTIONSACETYL

Umay Atay

SALIYCLIC ACID (C9H8O4) (Weak Acid) & NaOH (Strong Base) TITRATION

Research Question

What is the amount of acetyl salicylic acid (C9H8O4) in a tablet of Coraspin, Aspirin and Baby Aspirin through the process of ‘weak acid and strong base’ titration between the main ingredient of these tablets and a weak acid Acetyl salicylic acid, dissolved in 30.0 mL ± 0.1 mL water and 20.0 mL ± 0.1 mL Ethyl Alcohol solution, and 0.1 moldm-3 NaOH(aq) as strong base, by adding 3 drops of Phenolphthalein indicator to the 50.0 mL ± 0.2 mL solution of ethyl alcohol, water and dissolved ASA, to determine the equivalence point of the reaction between NaOH and ASA by color change from colorless to pink, under the same pressure and temperature?

Background Information

Titration 1

Titration is the slow addition of one solution of a known concentration (called a titrant) to a known volume of another solution of unknown concentration until the reaction reaches neutralization, which is often indicated by a color change. The solution called the titrant must satisfy the necessary requirements to be a primary or secondary standard. In a broad sense, titration is a technique to determine the concentration of an unknown solution.

Introduction

For acid base titrations, a pH indicator or pH meter is used in order to determine whether neutralization has been reached and titration is complete. The information obtained from the process of titration can then be inserted into the equation, MiVi=MfVf, to determine the concentration of the unknown solution. Mi and Mf are the initial and final molarities, and Vi and Vf are the initial and final volumes.

Elements of Titration

• The standard solution is the solution of known concentration. An accurately measured amount of standard solution is added during titration to the solution of unkown concentration until the equivalence or endpoint is reached. The equivalence point is when the reactants are done reacting.

• The solution of unknown concentration is otherwise known as the analyte. During titration the titrant is added to the analyte in order to achieve the equivalence point and determine the concentration of the analyte.

• The equivalence point is the ideal point for the completion of titration. In order to obtain accurate results the equivalence point must be attained precisely and accurately. The solution of known concentration, or titrant, must be added to the solution of unknown concentration, or analyte, very

1 http://chemwiki.ucdavis.edu/Analytical_Chemistry/Quantitative_Analysis/Titration Retrieved Date : 01.05.2014

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slowly in order to obtain a good result. At the equivalence point the correct amount of standard solution must be added to fully react with the unknown concentration.

• The end point of a titration indicates once the equivalence point has been reached. It is indicated by some form of indicator which varies depending on what type of titration being done. For example, if a color indicator is used, the solution will change color when the titration is at its end point.To clear confusion, the endpoint and equivalence point are not

necessarily equal, but they do represent the same idea. An endpoint is indicated by some form of indicator at the end of a titration. An equivalence point is when the moles of a standard solution (titrant) equal the moles of a solution of unknown concentration (analyte).

Indicators

The use of an indicator is key in performing a successful titration reaction. The purpose of the indicator is to show when enough standard solution has been added to fully react with the unknown concentration. However, an indicator should only be added when necessary and is dependent upon the solution that is being titrated. Therefore, indicators must only be added to the solution of unknown concentration when no visible reaction will occur. Depending on the solution being titrated, the choice of indicator can become key for the success of the titration.

 2

Acid-Base Titration Reactions

Titration of acid/base reactions involve the process of neutralization in

2 http://chemwiki.ucdavis.edu/Analytical_Chemistry/Quantitative_Analysis/Titration Retrieved Date : 01.05.2014

Image 1: This image shows a titration example with short descriptions.

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order to determine an unknown concentration. Acid-Base titrations can be made up of both strong and weak acids or bases. However, in order to determine the unknown concentration of an acid or base, you must add the opposite so that neutralization can be reached. Therefore, an acid of unknown concentration will be titrated using a basic standard solution and a base of unknown concentration will be titrated using an acidic standard solution. Examples of acid-base titrations include include:

• Titration of a Strong Acid with a Strong Base• Titration of a Weak Acid with a Strong Base• Titration of a Weak Base with a Strong Acid• Titration of a Weak Polyprotic AcidAcid-Base titrations often require the use of some kind of indicator depending on the strength of acid or base that is being titrated. In some cases a weak base or weak acid is used or a ph meter which reads the pH of the solution being titrated. Once the pH of the titrated solution equals seven, either indicated by a change in color or on a pH meter one can determine that titrations is complete.

Titration of A Weak Acid With A Strong BaseIn this reaction a burette is used to administer one solution to another.

The solution administered from the burette is called the titrant. The solution that the titrant is added to is called the analyte. In a titration of a Weak Acid with a Strong Base the titrant is a strong base and the analyte is a weak acid.

Aspirin 3

Aspirin (BAN, USAN), also known as acetylsalicylic acid [ASA], is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. Aspirin also has an antiplatelet effect by inhibiting the production of thromboxane, which under normal circumstances binds platelet molecules together to create a patch over damaged walls of blood vessels. Because the platelet patch can become too large and also block blood flow, locally and downstream, aspirin is also used long-term, at low doses, to help prevent heart attacks, strokes, and blood clot formation in people at high risk of developing blood clots. It has also been established that low doses of aspirin may be given immediately after a heart attack to reduce the risk of another heart attack or of the death of cardiac tissue. Aspirin may be effective at preventing certain types of cancer, particularly colorectal cancer.Chemical properties

Aspirin decomposes rapidly in solutions of ammonium acetate or of the acetates, carbonates, citrates or hydroxides of the alkali metals. It is stable in dry air, but gradually hydrolyses in contact with moisture to acetic and salicylic acids. In solution with alkalis, the hydrolysis proceeds rapidly and the clear solutions formed may consist entirely of acetate and salicylate.

Aim3 http://en.wikipedia.org/wiki/Aspirin#Chemical_properties Retrieved Date : 01.05.2014

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The aim of this investigation is to determine the mass of acetyl

salicylic acid (C9H8O4) in a Coraspin, Aspirin and Baby Aspirin tablet. The method of strong base (NaOH) and weak acid (C9H8O4) titration will be used during the investigation with Phenolphthalein indicator that have appropriate pH change range (8.2 -10.0) for this experiment. Phenolphthalein indicator is colorless in acidic solutions and pink in basic solution so the change of color will be considered to determine equivalence point of this weak acid – strong base reaction. Then, by considering the information that the number of moles of acid and base are equal at equivalence point, the mass of acetyl salicylic acid (C9H8O4) can be calculated.

Variables

Dependent Volume of NaOH used to reach equivalence point during titration IndependentThe type of the tablet that consists acetyl salicylic acid (C9H8O4)

Controlled Variable

Molarity of NaOH, 0.1 moldm-3

Type of the indicator solution used in all trials, phenolphthalein Amount of phenolphthalein indicator used in all trials, 3 drops with

pipette

During the titration process, the aqueous solution of weak acids are used to prevent errors can be sourced by heterogeneous state of the reactant. To have a homogenous weak acid reactant used the titration, each tablet is dissolved in constant volume of ethyl alcohol and distilled water before titration, in this experiment. Ethyl alcohol is preferred for dissolving the tablets faster and more effective and water is used to prevent impurities. By this way, a homogenous aqueous ASA is used in weak acid and strong base titration

Volume of distilled water used in acetyl salicylic acid (C9H8O4) solution, 30.0 mL ± 0.1

Volume of ethyl alcohol used in acetyl salicylic acid (C9H8O4) solution, 20.0 mL ± 0.1

Room Temperature 21.0 ± 0.1°C. Temperature of (C9H8O4) Solution, 25.0 ± 0.1°C Temperature of NaoH Solution, 20.5 ± 0.1°C Room pressure, 1067.0 ± 0.2 hPa. Using the same equipments (the same graduated cylinder, erlenmeyer

flask, burette, thermometer etc.) in all trials so that the uncertainties are kept constant in all trials

Materials

Coraspin Tablet x3 Baby Aspirin Tablet x3

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Aspirin Tablet x3 0.1 M NaOH(aq)

Mortar & Pestle Goggles Burette (50.0 mL)• Stirring Rod• Phenolphthalein Indicator (27 drops)• Erlenmeyer Flask (x3)• Distilled Water, 270.0 mL ± 0.1 mL• Ethyl Alcohol, 180.0 mL ± 0.1 mL• Graduated Cylinder (50 mL)• Thermometer with a range of 0 ℃ to 100℃ (±0.1 ±℃ ) x3• Barometer• Ring Stand x1• Data Logger with pH probe • Weigh Scale

Safety Precautions

• Wear your goggles during the experiment to avoid any possible eye contact

• Chemical solutions can be irritant and corrosive depending on their concentrations so avoid skin and eye contact and handle with appropriate care

DisposalAll solutions in this experiment should be disposed in the proper

waste containers in the fume hood as provided by the instructor in the laboratory.

Procedure1. Wear your googles2. Measure the room temperature with thermometer and pressure with

barometer3. Find the mass of a Coraspin, Baby Aspirin and Aspirin tablet. Grind

each tablet into a fine powder by using a mortar and pestle.4. Place each powdered sample into different Erlenmeyer flask5. Start with the Erlenmeyer flask that contain the solution with a

Coraspin Tablet6. Add 10.0 ml portion of ethyl alcohol to the flask and stir to dissolve the

powdered tablet in the solution7. Measure the pH of water by Data logger with pH Probe to keep this

variable constant.8. Add 25.0 ml water to the flask and stir until the solution looks as a

homogenous solution9. Measure the temperature of the C9H8O4 (aq) with thermometer10. Put 3 drops of phenolphthalein indicator in your flask11. If there’s no 0.1 M NaOH solution in laboratory, take 10 ml 1M NaOH

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and add 100 mL distilled water and stir them in a beaker.12. Measure the temperature of the NaOH(aq)

13. The burette is filled with 0.1 M NaOH. Make sure there are no bubbles apparent in the burette. Record the initial volume of the burette.

14. Begin titrating, add NaOH in 1.0 ml increments. 15. Stir the flask during titration to understand if the color change is

temporarily or just for instant16. Close and open the stopcock of the burette until the C9H8O4 (aq) becomes

temporarily pink.17. Read the lowest point of NaOH(aq) stayed at the eye level on the burette

in order to measure the volume of NaOH(aq) needed to reach equivalence point (the point through the reaction where the number of moles of acid is equal to the number of moles of base)

18. Repeat steps 6 -17 for the remaining independent variables, Aspirin and Alka Seltzer tablets, make at least 3 trials for each different independent variable

19. Record your data on a table for each trials20. Pour the solutions in flask and burette into the waste container

Qualitative Data

• Each tablet grinded in mortar until they became powdered and emptied carefully into the Erlenmeyer flask after weighing by weighing scale to prevent any loss from the amount of a tablet.

Image 3: The color change of ASA solution after titration is shown in this image. As it seen through the images the color change from colorless to temporarily pink is observed during titration to determine the equivalence point of the reaction.

Image 2: The ASA solution at the beginning of titration.

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• Before titration, Acetyl Salicylic Acid (C9H8O4), phenolphthalein and NaOH solution were colorless.

• The color of solution which contains Ethyl Alcohol, water and acetyl Salicylic Acid didn’t change immediately when the indicator phenolphthalein is added.

• Acetyl Salicylic Acid (C9H8O4), phenolphthalein, water and NaOH solution were odorless but ethyl alcohol had a sharp odor that could be smelled from 1 m distance from the flask.

• When the burette opened and NaOH solution started to drop into the flask that contains Acetyl Salicylic Acid Solution and phenolphthalein, the color of solution started to turn into pink for short time periods and then it became colorless again.

• As the titration of NaOH continues, the color of pink of the solution in flask stayed for longer time periods.

Processed Data

1. Converting Volume Unit from mL to L 4

The unit of Molarity is mol L-1 or mol dm-3 , so we need to convert our raw data which is recorded as mL to L .1 L = 1 dm3

1 L = 1000 mL

To convert volume from mL to L

1 L 1000 mL ? n mL

For example,Trial 1 of Aspirin Titartion1 L 1000 mL? 6.5 mL

? = 0.0065 L

Volume of Volume of

4 http://en.wikipedia.org/wiki/LitreRetrieved Date : 01.05.2014

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Type Of Tablet

# Of Trials NaOH Used (L) ±0.0001

(C9H8O4) Solution

(L) ±0.0001

Aspirin1 0.0065 0.05002 0.0060 0.05003 0.0070 0.0500

Baby Aspirin

1 0.0010 0.05002 0.0015 0.05003 0.0024 0.0500

Coraspin1 0.0020 0.05002 0.0022 0.05003 0.0018 0.0500

Table 2: This table shows the converted Volumes of NaOH(aq) and (C9H8O4) in L with its constant uncertainty value according to the graduated cylinder used

during the experiment.

2. Finding The Molarity Of Acetyl Salicylic Acid (C9H8O4) Solution Used

Monoprotic acid is an acid that donates only one proton or hydrogen atom per molecule to an aqueous solution. Since Acetyl Salicylic Acid is a monoprotic acid, at the equivalence point, the number of moles of acid is equal to the number of moles of base. The equivalence point of Acetyl Salicylic Acid and NaOH reaction, can be determined during titration by using volume of base at the point the change of color started to stay longer. In this experiment the color change observed from colorless to pink by phenolphthalein indicator that added to the solution before the titration. To calculate the number of moles of acid and base at that point, the molarities should be multiplied by the volume of acid or base used. So the equation

5Mbase x Vbase = Macid x Vacid

where V is volume of solution in liters and M is molarity in mold dm-3

can be used to calculate the molarity of Acetyl Salicylic Acid (C9H8O4).

Example with the First Trial of Titration Of an Aspirin Tablet

Molarity of NaOH (aq) = 0.1 mold dm-3

Volume Of NaOH(aq) used = 6.5 mL = 0.0065 LVolume of C9H8O4 (aq) used = 50 mL = 0.05 L

Mbase x Vbase = Macid x Vacid

1. 0.1 x 0.0065 = ? x 0.05? = MAcid = 0.013 mol dm-3

Uncertainty Calculation

5 Mortimer, Fourth Edition, Chemistry a Conceptual Approach

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6Percentage Uncertainty =

The formula that used to calculate molarity of C9H8O4 (aq) is Percentage Uncertainty of Volume of C9H8O4 (aq)

Mbase x Vbase = Macid x Vacid

So to calculate the percentage uncertainty of the molarity of C9H8O4 (aq), thepercentage uncertainty of Mbase , Vbase , Vacid should be calculated and the sum of these three percentage uncertainty will give us the percentage uncertainty of Macid .

The Volume of ethyl alcohol and distilled water are controlled variables so their percentage uncertainty is constant for all trials.

Percentage Uncertainty of Volume of C9H8O4 (aq) = Percentage Uncertainty of Volume of Distilled Water + Percentage Uncertainty of Volume of Ethyl Alcohol

Percentage Uncertainty of Volume of Distilled Water= (1 x 10-4 / 30 x 10-3 ) = 0.3 %Percentage Uncertainty of Volume of Ethyl Alcohol = (1 x 10-4 / 20 x 10-3 )= 0.5 % Percentage Uncertainty of Volume of C9H8O4 (aq) = 0.3 % + 0.5 % = 0.8 %

To have 0.1 M NaOH, we take 10 mL ± 0.1 mL 1 M NaoH and make a solution with 100 mL ± 0.1 mL distilled water and stir them in a beaker. The uncertainty of 1 M NaOH cannot be calculated because it was prepared by laboratory technician but the percentage uncertainty of 0.1M NaOH can be calculated according to the uncertainty of volume of distilled water and 1 M NaOH. Themolarity of NaOH is another controlled variable so it will be constant for all trials.

Percentege Uncertainty of 0.1 M NaOH = Percentage uncertainty of V1 M NaOH + Percentage uncertainty of Vdistilled water = (1 x 10-4 / 10-2 ) x 100 + (1 x 10-4 / 10-1 ) = 1.1 %

For Example Trial 1 of AspirinPercentage Uncertainty of Volume of NaOH(aq) = (1 x 10-4 / 65 x 10-4 ) x

100 = 1.5 %

6 http://mauldinchemistry.com/PDF/uncertainty.pdfRetrieved Date : 01.05.2014

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Percentage Uncertainty of Molarity of C9H8O4 (aq) = % uncertainty of VNaOH + % Uncertainty Of V(ASA) + % uncertainty of MNaOH

= 1.5 % + 0.8 % + 1.1% = 3.4

Type Of Tablet # Of TrialsMolarity of C9H8O4 (aq)

(mol dm-3 )

Aspirin1 0.0130 ± 3.4%2 0.0120 ± 3.6%3 0.0130 ± 3.3%

Baby Aspirin1 0.0021 ± 11.9%2 0.0030 ± 8.6%3 0.0048 ± 6.0%

Coraspin1 0.0040 ± 6.9%2 0.0044 ± 6.4%3 0.0036 ± 7.4%

Table 3: In the table, the calculated Molarities of C9H8O4 (aq) for each trials are shown with their percentage uncertainties is shown.

3. Calculating Mole Of Acetyl Salicylic Acid

The formula of Molarity is 7 where M is molarity, V is volume of the solution in liter and n is mole , so to find the mole of known volume and molarity, the M and V should be multiplied.

For Instance, Trial 1 Of Aspirin Volume of C9H8O4 (aq) = 0.0500Molarity of C9H8O4 (aq) = 0.0130M x V = 0.0500 L x 0.0130 mol L-1 = 6.5 x 10-4 mole

Uncertainty of the mole of C 9H8O4 (aq)

The percentage uncertainty of mole is equals to the sum of the percentage uncertainty of MASA and Volume of C9H8O4 (aq) . The percentage uncertainties of both have already calculated at previous part of calculations.% Uncertainty of Volume of C9H8O4 (aq) = 0.8 %% Uncertainty of MASA → written on Table 3

For Example, Baby Aspirin Trial 1% Uncertainty of Mole = % uncertainty of Volume of C9H8O4 (aq) + %

uncertainty of MASA of Baby Aspirin in Trial 1

7 Mortimer, Fourth Edition, Chemistry a Conceptual Approach

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= 0.8 % + 11.9% = 12.7 %

Type Of Tablet # Of TrialsMole of C9H8O4

(aq)

(mol)

Aspirin1 6.5 x 10-4 ± 4.2%2 6.0 x 10-4 ± 4.4%

3 7.0 x 10-4 ± 4.1%

Baby Aspirin1 1.0 x 10-4 ± 12.7%2 1.5 x 10-4 ± 9.4%3 2.4 x 10-4 ± 6.8%

Coraspin1 2.0 x 10-4 ± 7.7%2 2.2 x 10-4 ± 7.2%3 1.8 x 10-4 ± 8.2%

Table 4: This table shows the Mole number of Mole of C9H8O4 (aq) for each trials with their percentage uncertainties.

4. Calculating the mass of Acetyl Salicylic Acid by The Mole of C9H8O4 (aq)

First of all, the mass of a mole C9H8O4 (aq) should be calculated to find the mass of ASA in tablets.8Molar mass of ,Carbon = 12.01 g/molHydrogen= 1.01 g/molOxygen = 16.0 g/mol

C9H8O4 (aq)

9 x 12.01 =108.09

1.01 x 8 = 8.08

Molar mass of C9H8O4 (aq) = 108.9 + 8.08 + 64.0 = 180.17 mol/g

To calculate the mass of n mole

1 Mole 180.17 g

n mole ? g

8 IB Chemistry Data Booklet page 3

16.0 g/mol x 4 =64 g

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For Example, Coraspin Trial 1Mole of ASA = 2.0 x 10-4

2.0 x 10-4 x 180.17 / 1 = 0.036 g

Uncertainty Of Mass of ASA in a Tablet

The Uncertainty of the molar mass of C9H8O4 (aq) cannot be calculated because the values of molar mass of atoms are taken from another source so the percentage uncertainty of mass is equal to the percentage uncertainty of mole of C9H8O4 (aq) (given on table 4).

Calculating Uncertainty value from the percentage Uncertainty100 nMass of C9H8O4 (aq) ? where n is the percentage value and ? is uncertainty value of mass.

For Instance, Baby Aspirin Trial 2% uncertainty of Mole = 9.4 %Mass of ASA in Trial 2 of Baby Aspirin = 0.027Uncertainty value of mass = ( 9.4 x 0.027) /100 = 0.0025 0.003≃

Type Of Tablet

# Of Trials

Mole of C9H8O4

(aq)

(mol)

Mass of C9H8O4(aq)

(g)

Aspirin1 6.5 x 10-4 ± 4.2% 0.117 ±0.0052 6.0 x 10-4 ± 4.4% 0.108 ±0.0053 7.0 x 10-4 ± 4.1% 0.126±0.005

Baby Aspirin

1 1.0 x 10-4 ± 12.7% 0.018 ±0.0032 1.5 x 10-4 ± 9.4% 0.027 ±0.0033 2.4 x 10-4 ± 6.8% 0.043 ±0.003

Coraspin1 2.0 x 10-4 ± 7.7% 0.036 ±0.0032 2.2 x 10-4 ± 7.2% 0.040 ±0.0033 1.8 x 10-4 ± 8.2% 0.032 ±0.003

Table 5: In the table the mole of ASA found in each tablet and the mass of ASA calculated by the mole is shown with uncertainty values of Mass and percentage

uncertainty value of mole of ASA.

5. Finding Average Mass of Acetyl Salicylic Acid (C9H8O4) in Each Type of Tablet

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9Average Mass in a Tablet =

For Example, Aspirin

= 0.117 g

Uncertainty of Average Mass

= where n is number of trials

For Example, Aspirin Max. Value of mass= 0.126 gMin. Value of mass = 0.108 g

Max. Value – Min. Value / = 0.2 → Uncertainty Of Average Mass of ASA found in Aspirin Tablet

Type Of Tablet Average Mass of ASA (C9H8O4 (aq)) (g)Aspirin 0.1170 ± 0.2000

Baby Aspirin 0.0296 ± 0.0500Coraspin 0.0360 ± 0.0600

Table 6 : In his table the average mass of ASA found in each type of tablet according to their 3 trials is shown with their uncertainties.

6. Percentage Difference

10 ⎜ Experimental Value –Literature Value ⎜ x 100Literature Value

For Instance, Baby Aspirin Literature Value of Mass of ASA in a Baby Aspirin Tablet = 0.1 gExperimental Value of Mass of ASA in a Baby Aspirin Tablet = 0.0294 g

⎜ 0.0294 -0.1 ⎜ x 100 = 70.6 %

Type Of Tablet Literature Value11 (g)

Experimental Value (g)

PercentageDifference (%)

Aspirin 0.5000 0.1170 ± 0.20 76.6

9 http://www.basic-mathematics.com/finding-the-average.htmlRetrieved Date : 01.05.201410 http://mauldinchemistry.com/PDF/uncertainty.pdfRetrieved Date : 01.05.201411 Prospectus of Coraspin, Aspirin & Baby Aspirin

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Baby Aspirin 0.1000 0.0296 ± 0.05 70.6Coraspin 0.1000 0.0360 ± 0.06 64.0

Table 7: This table shows the literature and experimental value of the mass of ASA found in a tablet in different type of tablets and the percentage difference between them.

CONCLUSION & EVALUATION Acetyl Salicylic Acid is an acid that often used in medicine and main ingredient of many painkillers. The aim of this investigation is to determine the mass of acetyl salicylic acid (C9H8O4 ) in a tablet of Coraspin, Baby Aspirin and Aspirin, that are easy to access and widely used . I chose ‘weak acid and strong base titration’ method to reach my aim. At first, the NaOH solution with 0.1 M is formed by mixing 10.0 mL ± 0.1 mL 1 M NaOH solution and 100.0 mL ± 0.1 mL distilled water. Then, this 0.1 M NaOH solution is filled in a clean burette. I measured the weight ach tablet of tablet of Aspirin, Baby Aspirin and Coraspin that used in trials with weighing scale. Also the pressure of the room and the temperature of the room, solutions are measured to keep them as controlled variables. Each tablet are powdered separately by using mortar pestle to make easy to dissolving of the tablet in 20.0 mL ±0.1 mL ethyl alcohol and 30.0 ± 0.1 mL distilled water solution. Distilled water is chosen to prevent any error that can source by minerals or chemicals that found in water we use in our daily lives. Ethyl alcohol is preferred to make the dissolving of the tablet in the solution easier and faster. Each powdered tablet transferred to a flask that consists mL distilled water solution from mortar pestle and stirred until the tablet dissolved completely. Then, 3 drops of phenolphthalein indicator dropped into the flask to obtain color change during titration and recognize the equivalence point. By opening and closing the stopcock of the burette, the equivalence point tried to be reached. When the color became temporarily pink, the stopcock is closed, and assumed that the reaction has reached the equivalence point. By using data gained by this experiment, the unknown molarity of C9H8O4 (aq), the mole and mass of ASA found in a tablet of Aspirin, Coraspin and Baby Aspirin are calculated and compared with the literature values that are taken from the prospectus of the tablets. Coraspin and Baby Aspirin had close mass values during experiment but they were not equal as their literature value shows. The experimental value of the mass of ASA in an Aspirin tablet is 0.117 g and the literature value is 0.500 g , the percent difference for Aspirin is 76.6%, for Coraspin the experimental value of the mass of ASA in a tablet is 0.029 g and the literature value is 0.100 g so the percent difference is 64.0% and for Baby aspirin the experimental value of the mass of ASA in a tablet is 0.036 g and the literature value is 0.100 g, the percent difference equals to 0.6%. High percent difference is calculated between experimental and literature values, so my experiment didn’t support the literature value of mass of ASA found in a tablet of each type of tablet. This high percent difference at each trail and in conclusion, small gaps between these percent differences shows us that there is a systematic error in the experiment that can be sourced by equipment, my method, my use of the method, or my knowledge. The accuracy of the results are low but they have high precision, that statement is also supports idea of any systematic error.

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The molarity of NaOH (0.1 M) was my controlled variable and to prevent any change during experiment, I prepared this solution in a 100 mL beaker and used it during the all experiment. Moreover, to keep uncertainties, sourced by equipment that used during experiment, constant; I used the same equipment (beaker, thermometer, e.g.) during the experiment. The whole experiment is done in the same laboratory to keep the physical conditions equal. The temperature and pressure of the room tried to keep constant by closing the doors and windows and measuring them before the trials but any other arrangement weren’t made like using water bath, but the method I used give efficient and satisfying results to these factors as controlled variables. Opening and closing the stopcock of the burette is arranged by me so errors may be occurred sourced by human reflexes and this may cause the deviations to determine the equivalence point. The time needed to reach the equivalence point or have color change, temporarily pink, was not measured during the experiment. Measuring the time needed to reach the equivalence point, the time intervals between the color change and duration of the color pink appearance would make data collection more accurate by assuming the duration of appearance of the color change to the pink as a controlled variable.

To prevent or decrease the errors in the experiment and have closer values to the literature values, a machine that stir the flask at same speed and with equal time intervals can be used during titration. By this way, the temporarily color change would be realized easily and accurately so the equivalence point would be determined more accurately. Waiting for longer time periods before each trial for better dissolving of tablet in the solution may decrease the errors. The experiment can be repeated with water bath to keep temperature as a more controlled variable and make the system more isolated. Some amount of the tablet can be lost during powdering and transferring it to the flask so grinding to powdering can be preferred to decrease the lost or powdering process can be occurred in a beaker with water and ethyl alcohol to prevent any loss of the amount of tablet, while powdering the tablets, the tablets will dissolve in water and ethyl alcohol solution by the same time but glass can break through the powdering process so high attention is needed for this method. Increasing the number of trials for each independent variable could help to decrease both systematic and random errors. By decreasing the volume of water and ethyl alcohol used to dissolve tablets, the molarity of ASA solution could be increased and may higher raw data are collected. A color receptor can be used to determine the color change faster and more accurate during titration can be used but these kind of equipment are hard to access especially for a high school laboratory. The values that are measured especially volume are small, using the equipment that has lower uncertainty values will also decrease the percentage uncertainty. Moreover, the burette can be cleaned with distilled water or NaOH for a few more times to decrease impurities in the burette.

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