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AceticAcidlab (1)

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acid base 2014
Transcript1!Z #M$%&'g(Z&Z)cn'(*WLA/expo+t, o+mat-docxd-1yGpLZMNsR2PAW4axy1!Z #M$%&'g(Z&Z)cn'(*WLA ᄃ 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 cure. 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 cure,p) s. total olume of titrant added-. *e then used the titration cure to determine the Ka. *e needed to know halfeuialence point for this la! to determine the Ka of acetic acid.The euialence point is reached when the moles of the acid and the moles of the titrant !aseadded are eual and the halfeuialence point is when the moles of the acid and the moles of thecon0u#ate !ase are eual. o the p) is eual to the pKa. The )enderson)assel!ach euation$ p)2 pKa  lo# A5 / )A5$ can !e used to sole for the p) of the solution. After the p) is found$we can determine the Ka ! usin# the euation 1%6pKa. 7efore !e#innin# the la!$ weh pothesi8ed that the pKa of acetic acid would !e 9.Materials:rlenme er ;lask sodium h droxide solution  funnel!uretstock acetic acidp) 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. =emoe the funnel and drainseeral milliliters of titrant if necessar to remoe 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 iniewin# 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 eual 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 eual 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 eual to 11.&$ add titrant in ' m( proportions.top addin# titrant when the p) reaches 1' or the titrant is exhausted$ whicheer 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 cure.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 hae the same olume at @ p) and this is the halfeuialence point. p)2pKa at the half euialence point so pKa2@. 7 doin# pKa2lo#,Ka-$ we find that Ka is 1.% x 1%6@. The actual alue of acetic acids pKa is 4.B4while the actual alue of the Ka is 1.9' x 1%6&. To calculate the percent error we use theeuation ,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 )5A5/)A5lo#Ka 2 lo# )5A5/)A5lo#Ka 2 lo#)5 x A5/)A5lo#Ka 2 lo#)5  lo# A5/)A5 pKa2 p)  lo#A5/)A5 p) 2 pKa  lo#A5/)A5 >onclusion ;or this la! we titrated acetic acid with sodium h droxide ! releasin# %.&$ 1.%$ or '.% m( of 
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