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acid base 2014

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https://docs.google.com/document/d/1yGpLZMNsR2PAW4axy1!Z #M$%&'g(Z&Z)cn'(*WLA/expo+t, o+mat-docxd-1yGpLZMNsR2PAW4axy1!Z #M$%&'g(Z&Z)cn'(*WLA
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Marisol Morales per. 14/1/13Determination of the Ka of Acetic AcidIntroThe purpose of this experiment was to determine the Ka of a weak acid and to determinethe endpoint of a titration from the titration cure. The Ka is the acid dissociation constant for weak acids and the endpoint of a titration is the point in a titration where no more titrant is to !eadded which is shown ! the color chan#e of the indicator. In this experiment$ we used sodiumh droxide to titrate acetic acid$ ! addin# it in ! %.&$ 1$ or ' m( at a time dependin# at which p) it was at and recorded the p) after each m( was added. *e added titrant to the solution untilit reached p) 1'. +sin# the information we collected$ we were a!le to #raph the titration cure,p) s. total olume of titrant added-. *e then used the titration cure to determine the Ka. *e needed to know halfeuialence point for this la! to determine the Ka of acetic acid.The euialence point is reached when the moles of the acid and the moles of the titrant !aseadded are eual and the halfeuialence point is when the moles of the acid and the moles of thecon0u#ate !ase are eual. o the p) is eual to the pKa. The )enderson)assel!ach euation$ p)2 pKa lo# A5 / )A5$ can !e used to sole for the p) of the solution. After the p) is found$we can determine the Ka ! usin# the euation 1%6pKa. 7efore !e#innin# the la!$ weh pothesi8ed that the pKa of acetic acid would !e 9.Materials:rlenme er ;lask sodium h droxide solution
funnel!uretstock acetic acidp) paper <rocedure1.<lace a!out &% m( of sodium h droxide solution in a 1'& m( :rlenme er flask. <our a!out 4& m( of this solution throu#h a funnel into a !uret. =emoe the funnel and drainseeral milliliters of titrant if necessar to remoe an air !u!!les from the !uret tip.'.*ait 3% seconds after fillin# the !uret to record the olume in order to allow all the addedtitrant to cascade down the !uret. =ecord the initial olume of the titrant exactl ,/ %.%1m(-. If desired$ place a card with a !lack !and drawn on it !ehind the !uret to aid iniewin# the meniscus.3.>onstruct a ta!le for our data that contains three columns? !uret olume$ p) of thesolution$ and the total olume of titrant added at each p) alue.4.To a 1'& m( :rlenme er flask$ add '& m( of the stock acetic acid solution usin# a '&m(olumetric !uret. Measure the p) of the acid stock solution in the :rlenme er flask andrecord. Make sure the readin# had sta!ili8ed !efore recordin# the p).&.Add titrant to the acid in ' m( portions$ measurin# the p) and !uret olume after eachaddition. *hen the p) of the solution is #reater than or eual to &.%$ add titrant in 1 m(increments. =emem!er to record the p) and !uret olume after each addition. *hen the p) is #reater than or eual to &.&$ add titrant in %.& m( increments. >ontinue %.& m(additions until p) of the solution reaches 11.% units. Increase the titrant addition olumeto 1 m(. *hen the p) is #reater than or eual to 11.&$ add titrant in ' m( proportions.top addin# titrant when the p) reaches 1' or the titrant is exhausted$ whicheer occursfirst.@.raph the p) of the acid sample a#ainst the total olume of titrant added and determinethe Ka of acetic acid from the titration cure.B.Determine the endpoint of the titration.Data7uret olume,m(- p) of thesolutiontotal olumeof titrant7uret olume,m(- p) of thesolutiontotal olumeof titrant
added at each p) alueadded at each p) alue43.34%''.&@'141.44'''@'1.&3C.&44'1.&@''3B.&4@'1@.&''.&3&.&49'%.&@.&'333.&4.&1%'%B'3.&31.&4.&1'1C.&9'4'C.&&141CC'4.&'9.&&1&19.&C.&'&'B.&&.&1@191%'&.&'B&.&1@.&1B.&1%.&'@'@.&&.&1B1B11'@.&'@&.&1B.&1@11'B.&'&.&@191&11.&'9.&'&@19.&1311.&3%.&'4.&@1C1111.&3'.&'4@1C.&C11.&34.&'3.&@'%B11.&3@.&'3@'%.&&11.&39.&311.&4%.&11'4'.&
:ndpoint? 9 p)Anal sis 1.The acid and the con0u#ate !ase hae the same olume at @ p) and this is the halfeuialence point. p)2pKa at the half euialence point so pKa2@. 7 doin# pKa2lo#,Ka-$ we find that Ka is 1.% x 1%6@. The actual alue of acetic acids pKa is 4.B4while the actual alue of the Ka is 1.9' x 1%6&. To calculate the percent error we use theeuation ,actual/theoretical-and the multipl it ! 1%% to #et the percent error. ,4.B4/@-2%.BC$ and then 1%.BC2 %.'1 x 1%% 2 '1E error. This is a hu#e percent error so our aluesare er different from the true alues. '.4'.& m( of %.1 M FaG) was added to '& m( of %.1 M >')4G',%.1 mol FaG)/ 1(- x ,%.%4'& (- 2 %.%%4'& mol FaG) ,%.1 mol >')4G'/ 1(- x ,%.%'&% (- 2 %.%%'& mol >')4G' %.%4'& ( %.%'&% 2 %.%@B& (G)5 2 ,.%%1B& mol/ %.%@B& (- 2 %.%'&C M3.Ka 2 )5A5/)A5lo#Ka 2 lo# )5A5/)A5lo#Ka 2 lo#)5 x A5/)A5lo#Ka 2 lo#)5 lo# A5/)A5 pKa2 p) lo#A5/)A5 p) 2 pKa lo#A5/)A5 >onclusion ;or this la! we titrated acetic acid with sodium h droxide ! releasin# %.&$ 1.%$ or '.% m( of

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