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Equivalent Mass of an Acid

Name: Raphael Sevilla TA: Mayurbhai Patel

Partner: Christopher Rios-Ruiz Date Submitted: October 6, 2014

Objective: to standardize a solution of sodium hydroxide using hydrochloric acid and todetermine the equivalent mass of an unknown acid compound and to determine the percentage ofaspirin in a commercial aspirin tablet.

Procedure: 2 100 mL beakers, 2 25 mL burets, and 2 250 mL Erlenmeyer flasks were obtainedfrom the side bench. Lab groups were split as one person was to standardize the sodiumhydroxide solution and the other to perform a titration with an unknown acid. 75 mL of standardHCL solution were obtained and 125 mL of NaOH solution were obtained. One buret was filledwith the HCI solution and the other was filled with the NaOH solution. 15 mL of the HCL

solution were delivered into a 250 mL Erlenmeyer flask and 2 drops of phenolphthalein solutionwere added. The initial and final volume readings of the NaOH buret were recorded. Thetitration was carried out a second time and the initial and final volume readings were recorded. InPart 2, one sample of 200 mg of the unknown acid A was weighed on an analytical balance. Thesample was placed into a 250 mL Erlenmeyer flask. 12 mL of deionized water was added. Theflask was stirred with a glass rod to help the acid dissolve. Two drops of phenolphthalein wereadded. The solution was titrated with the standardized hydroxide solution. The volume of sodiumhydroxide solution was recorded to generate the light pink end point. In Part 3, an aspirin tabletwas obtained from the side bench and was weighed on an analytical balance. The tablet was

placed into a 250 mL flask filled with 100 mL of deionized water. The tablet with the 100 mL ofdeionized water was titrated until the color persisted.

Table:Part 1: Standardization of Sodium Hydroxide SolutionMolarity of HCL (aq) = .1M

ItemTrial1

Trial2

Initial Volume of HCL (aq) buret (mL) 25 mL25mL

Final Volume of HCL (aq) buret (mL) 11 mL13mL

Volume of HCL delivered (mL) 14 mL12mL

Initial Volume of NaOH buret (mL) 25 mL

25

mL

Final Volume of NaOh buret (mL) 10 mL10mL

Volume of NaOH delivered (mL) 15 mL15mL

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Part 2: Equivalent Mass of an Unknown Acid

Item Trial 1

Mass of unknown acid (g) .2 g

Initial volume of NaOH buret (mL) 26 mL

Final Volume of NaOH buret (mL) 44 mL

Volume of NaOH delivered (mL) 18 mL

Part 3: Mass of Acetylsalicylic Acid in Aspirin

Molar mass of acetylsalicylic acid: 180.15g

Item Trial 1

Mass of aspirin tablet (g) .3893 g

Initial volume of NaOH buret (mL) 0 mL

Final volume of NaOH buret (mL)19.5mL

Volume of NaOH delivered (mL)19.5mL

Part 1: Standardization of Sodium Hydroxide Solution

Item Trial 1 Trial 2

Concentration of HCL (aq) .1M .1M

Volume of HCL delivered (mL) 14 mL 12 mL

Moles of HCL used (mol) (1) .0014 mol.0012mol

Moles of NaOH used (mol) .0014 mol.0012mol

Volume of NaOH delivered (mL) 15 mL 15 mL

Concentration of NaOH (aq) (M) .093M .08 M

Average concentration of NaOH (aq) (2) .0865 M

Part 2: Equivalent Mass of an Unknown AcidItemConcentration of NaOH (aq) (M) (from part 1) .93 MMass of unknown acid (g) .2 gVolume of NaOH delivered (mL) 18 mLMoles of NaOH (mol) (3) .01674 MMoles of acid used (mol) .01674 MEquivalent mass of acid (g/equivalent) (4) 59.736 gAverage equivalent mass of acid: (5) 59.736 g

Part 3: Mass of Acetylsalicylic Acid in an AspirinTabletItemConcentration of NaOH (aq) (M) (from part 1) .093 MMass of aspirin tablet (g) .3893 gLabel claim mass of aspirin in tablet (g) 325 mgVolume of NaOH (aq) delivered (mL) 19.5 mLMoles of NaOH used (mol) (6) .0018135

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mol

Moles of aspirin used (mol).0018135mol

Mass of aspirin used (g) (7) .324 mgMass percent of aspirin in the tablet (%) (8) 99%

Percent label claim of aspirin in tablet (%)Calculation:Moles of HCL used (mol): (1) = (.1 M HCL)* ( .014 mL HCL) = .0014 mol , (.1 M HCL)*(.012 mL) = .0012 molAverage concentration of NaOH (aq) (2): (.093 M + .08M) / number of trials n =2 = .0865MMoles of NaOH (mol) (3): (.093M * .015 L) = .0014 mol, (.08 M * .015 mL) = .0012 molEquivalent mass of acid (g/equivalent) (4): .2 / .01674M = 11.9474313g * 5 = 59.7364. The molecular formula of this acid is C2H4O2 because the average equivalent mass is around60 grams, and if the ratio of C:H:O is 1:2:1 then multiply the total molar mass by 2 which is 60.Average equivalent mass of acid: (5): 11.9474313g

Moles of NaOH used (mol) (6): .093 * .0195 L = .0018135 molMass of aspirin used (g) (7): (.0018135 mol) (180 g) = .324 gMass percent of aspirin in the tablet (%) (8) .324 g / .325 g = 99%Pooled Data:Part 1: Concentration of the Standardized Sodium Hydroxide Solution(M)0.111M0.093 M0.108 M0.107 M0.109 M

0. 101 M0.0612 M

Average: .0986 MStandard deviation:.017M

Part 2: Equivalent Mass of an Unknown Acid0.001370.00151

0.00070.00192

0.0020.00224

0.00177

Average: .001644Standard deviation: .0005Average: .001644

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Discussion: In part 1, the concentration acquired of the standardized sodium hydroxide solutionwas .107 M. The average molarity is equal to .0986 M and it was within 1 standard deviation ofthe data. In part 2, the equivalent mass of an unknown acid was equal to .00192 g, it was within 1standard deviation of the average which means that it was precise towards the predicted result.

Observation: In part 1, a pink color was expected for the standardization of Sodium Hydroxideand Hydrochloric acid. For part 2, the unknown acid which was placed into the solution was notable to be fully dissolved, as a result, the pink state would disappear and continuously had to bestirred. The sample was not able to be fully dissolved, therefore, due to time constraints, part 2ended. In part 3, the tablet similarly was not able to be dissolved because the tablet would beineffective to the user if it dissolved that quickly and using the entire effect of aspirin.

Conclusion : The sodium hydroxide solution was standardized using the hydrochloric acid. Theequivalent mass was found through a titration however, the pink color was not able to subside,the percentage of aspirin in a commercial aspirin tablet was found to be 99%.