Spectrophotometric Determination of the Acid Dissociation Constant of Methyl Red J.P. J.P. Loja Institute of Chemistry, University of the Philippines, Diliman, Quezon City September 3, 2013 September 11, 2013 I. XIII. S XI. olume II. Methodology a !.!"! III. m M #Cl IV. The ma materials used in in th the p $m%& exper experime iment nt ere ere !olume !olumetri tri" " #as$s, #as$s, l bea$ers, p% meter and &V'Vis e Spe"trophotometer. V. The (rst part o) the experiment as the preparation o) solutions. In S a *0 mL !olume !olumetri tri" " #as$, #as$, meth+l meth+l o red sto"$ solution as prepared b+ l dissol!in 0.0* meth+l red in 3* ’ mL -* ethanol and as diluted to n mar$. VI. /eth+l red standard solution N as made in a *0 mL !olumetri" #as$ usin 2.*0 mL o) sto"$ mixed u ith 2* mL -* ethanol. m VII. orrespondin masses ere b ei eihe hed d to ma$ ma$e the the reae eaent nts s e name namel+ l+ 10 100 0 mL 0.0 0.00 0 / a45 a45" " r throuh a45"63% a45"63% 24 "r+sta "r+stals, ls, *0 :VI. 1 :VII. *.0 mL mL 0.010 / a45" )rom 0.00 / a45" solution, solution, *0 mL 1.0 / %45", *0 mL 0.020 / %45" )rom 1.0 / %45" , *0 mL 0.10 / %l, and *0 :I:. 2 ::. 10.0 mL mL 0.010 / %l )rom 0.10 / %l. These ere dissol!ed in a !olu !olume metr tri" i" #as$ #as$ and and dilu dilute ted d to ::II. 3 ::III. 1*.0 mL mar$. VIII. The a"idi" meth+l red 7%/89 as prepared in a *0 mL ::V. ::VI. olume !olumetri" #as$ b+ addin *.00 mL !.!"! meth meth+l +l red stan standa dard rd solu soluti tion on in *.00 mL 0.100 / %l solution. The M Na'c solution as dissol!ed to mar$ and $m%& the p% measured i) it as 2. I:. The al a l$aline me m eth+l re red 7/ 7 /8 '9 as made in a *0 mL !olumetri" ::VIII. ::I:. *.0 mL #as$ b+ addin *.00 mL meth+l red stand tanda ard soluti lutio on in 12. 2.0 mL 0.00 / a45" solution. This as :::I. * :::II. 10.0 mL then then dilu dilute ted d to mar$ mar$ and and the the p% measured should be ;. :. The so solutions ere pr prepared as indi"ated in Table I. :::IV. < :::V. 1*.0 mL :I. :II. Table I. Sample Solution :::VII. Preparation :::VIII.
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1'< and 100 mL or 1*0 mL !olumetri" #as$ )or 1'=. The sample ere prepared but as not diluted to mar$. L:I. The spe"tra o) %/8 and ' /8 solution as obtain beteen 3*0 and <00 nm usin distilled ater )or a re)eren"e "ell. 5 mat"hed "ell as used )or all the absorban"e measurement. L:II. /aximum absorption 7>max9 o) a!elenths as determined )rom the obtained spe"tra o) a"idi", >%/8, and basi", > /8', )orms o) meth+l red. %XIII. The absorban"e o) sample 1'< both a"idi", > %/8, and basi", > /8', usin distilled ater as re)eren"e "ell as determined. %XI. %X. Results and Discussion %XI. L:VII. 4ne o) the methods $non to determine the absorption o) liht as spe"trophotometr+. L:VIII. 5 "omplimentar+ "olor o) the solution as "ommonl+ used sin"e di?erent "ompounds absorb di?erent amount o) liht. L:I:. Spe"trophotometer is a ma"hine that "an determine the absorban"e o) a solution. It ould pass a series o) mono"hromati" liht on the substan"e and a part o) it ould be absorbed and the rest transmitted. L::. The amount o) liht absorbed b+ a solution "an be used to "ompute an un$non "on"entration o) an anal+te b+ ettin the absorban"e throuh @eer'LambertAs La. L::I. The @eer'LambertAs la shos the linear relationship o) absorban"e and "on"entration as shon in BCuation. 1. D2E L::II. A - $b" L::III. /uation ". @eer'LambertAs La L::IV. L::V. A - absorban"e L::VI.0 - proportionalit+ "onstant L::VII. b - path lenth L::VIII. c - "on"entration o) absorbin spe"ies %XXIX. L:::. In the experiment, the un$non "on"entration o) a solution as determined b+ ta$in readins on
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ea"h ti"e in di?erent a!elenths as shon in Table II. L:::I. L:::II. Table II. /easured p% and 5bsorban"e )or %/8 and /8 ' L:::III. L:::IV. These a!elenths ere made to "alibration "ur!es here the absorban"e as raphed aainst "on"entration to ta$e the linear reression. L:::V. In the mixture o) ' %/8 and /8 , the absorban"e at a parti"ular %XXXI. %XXXII. %XXXIII. Conclusion %XXXIX. References Appendices :.