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Form 6 Chemistry Experiment NKMExperiment 13 p.1/3

Name : __________________________ ( ) Date : ____________ Mark : ______

Determination of the Equilibrium Constant for Esterification

Aim The purpose of this experiment is to determine the equilibrium constant of esterification between ethyl ethanaote and propan-1-ol.

IntroductionIn the presence of concentrated sulphuric(VI) acid, ethanoic acid reacts reversibly with

propan-1-ol when heated, forming propyl ethanoate and water.The reaction equation and the equilibrium expression will not be given as you will be

asked to write these for yourself in the questions.

RequirementsGlacial ethanoic acid

propan-1-ol0.50M NaOHanti-bumping granulesconcentrated sulphuric(VI) acid

phenolphthalein indicator

Quickfit set balancetitration apparatus1.0 cm 3 graduated pipettemeasuring cylinderice bath

Procedures[ H azard Warn ing : Glacial ethanoic acid and concentrated sulphuric(VI) acid are corrosive,

propan-1-ol is flammable, and 0.5M sodium hydroxide is irritant.] 1. Put 0.25 mole of glacial ethanoic acid (density = 1.05 g cm -3) and 0.25 mole of propan-1-ol

(density = 0.8 g cm-3

) into a clean, dry pear-shaped flask. Mix thoroughly.

2. Titration 1 : Transfer 1.0 cm 3 of the mixture by pipette to a 250 cm 3 conical flaskcontaining about 25 cm 3 deionized water and 2 drops of phenolphthalein indicator. Titrateto end point ( twice ) with 0.50M sodium hydroxide solution. Record the mean titre ( V 1 cm 3).

3. Titration 2 : Add 8 drops of concentrated sulpuric(VI) acid to the remainder of theacid-alcohol solution while continuously swirling the flask. Titrate ( twice ) another 1.0 cm 3 sample immediately. Record the mean titre ( V 2 cm 3). The difference between V 1 and V 2 represents the volume to be subtracted from subsequent titrations to correct for the amountof sulphuric(VI) acid present.

4. Titration 3 : Add a few anti-bumping granules to the flask, and attach it to a water-cooledreflux condenser. Reflux for 45 minutes. Cool the flask and its contents first underrunning tap water, then in an ice-bath. Remove 1.0 cm 3 sample from the flask for titrationwith the 0.50M sodium hydroxide as before. Record the titre needed and correct it for thesulphuric(VI) acid.

5. Titration 4 : Continue refluxing for an additional half hour, cool, and titrate another 1.0 cm 3 sample. The two titres should agree to within 0.2 cm 3. Otherwise, repeat this step.

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Form 6 Chemistry Experiment NKMExperiment 13 p.2/3

Results Tables :

Ti t r a t ion 1 Ti t r a t ion 2

1 2 1 2

Final burette reading / cm 3

Initial burette reading / cm 3

Volume delivered / cm 3

Mean titre / cm 3 V 1 = V 2 =

Ti t r a t ion 3 Ti t r a t ion 4*

1 2 1 2Final burette reading / cm 3

Initial burette reading / cm 3

Volume delivered / cm3

Mean titre / cm 3

* If the mean titre in titrations 3 and 4 do not agree, reflux for another half hour and carryout titration 5.

Questions

1. What is the purpose of adding a small amount of concentrated sulphuric(VI) acid to thereaction mixture at the beginning of the experiment ?

2. Why should anti-bumping granules be added to the reaction mixture before refluxing ?

3. Why should the refluxing be continued in step (5) until the titre of sodium hydroxide usedapproaches constant ?

4. Write the equation for the esterification reaction between ethanoic acid and propan-1-ol.

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Form 6 Chemistry Experiment NKMExperiment 13 p.3/3

5. Calculate the concentration of ethanoic acid remaining at the end of the reflux.

6. Calculate the concentrations of the other species present at equilibrium.

7. Write an equilibrium expression for the esterification reaction.

8. Calculate the equilibrium constant for the esterification.