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University of Pittsburgh at Bradford Science In Motion Chemistry Lab019

SPECTROPHOTOMETRIC A NALYSIS OF A SPIRIN

Introduction:

A co ored com! e" is formed bet#een as!irin and the iron $III% ion& 'he intensity of the co or isdirect y re ated to the concentration of as!irin !resent( therefore) s!ectro!hotometric ana ysis can be used&A series of so utions #ith different as!irin concentrations #i be !re!ared and com! e"ed& 'he absorbanceof each so ution #i be measured and a ca ibration curve #i be constructed& Using the standard curve)the amount of as!irin in a commercia as!irin !roduct can be determined&

'he com! e" is formed by reacting the as!irin #ith sodium hydro"ide to form the sa icy ate dianion&

* C C+

*

C

*

*+

,

$a-% . C+ C * $a-% . /+ *$ %

*

C

*

*

0

0$s% . ,*+ $a-%0

*

0, /

'he addition of acidified iron $III% ion !roduces the vio et tetraa-uosa icy atroiron $III% com! e"&

*

C

*

*

0

0. 12e$+ *% 3/ 4.,

*

C

*

*

.

/ 52e$+ *%

/ ,.

. + * . + *

Purpose:

'he !ur!ose of this ab is to determine the amount of as!irin in a commercia as!irin !roduct& 'his abmay a so be used to determine the !urity of the as!irin !roduced in the Microsca e Synthesis ofAcety sa icy ic Acid ab&

Equipment / M teri !s:

1/6 mL er enmeyer f as7s / cuvettes10 mL graduated cy inder 6 mL !i!et/60 mL vo umetric f as7 acety sa icy ic acid60 mL vo umetric f as7 1 M 8a*+ana ytica ba ance $o!t&% 0&0/ M iron $III% buffer s!ectro!hotometer disti ed #ater commercia as!irin !roduct or as!irin the student has made

S "et#:

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A #ays #ear gogg es and an a!ron in the ab& Be carefu #hi e boi ing the sodium hydro"ide so ution& 8a*+ so utions are dangerous)

es!ecia y #hen hot&

Procedure:

P rt I: M $in% St nd rds&

1& Mass 500 mg of acety sa icy ic acid in a 1/6 mL r enmeyer f as7& Add 10 mL of a 1 M 8a*+so ution to the f as7) and heat unti the contents begin to boi &

/& :uantitative y transfer the so ution to a /60 mL vo umetric f as7) and di ute #ith disti!!ed ' ter to themar7&

,& Pi!et a /&6 mL sam! e of this as!irin standard so ution to a 60 mL vo umetric f as7& ;i ute to the mar7#ith a (&() M iron *III+ so!ution & Labe this so ution

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4& *btain absorbance readings for each of the other standard so utions& ecord the resu ts on

the data sheet&

& *btain an absorbance reading for the un7no#n sam! e$s%&

D& Ma7e a gra!h of concentration $" a"is% vs& absorbance $y a"is%&

9& 2rom the standard curve) determine the concentration of as!irin in the un7no#n

Sam! e$s%&

8ameEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE

;ateEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE

Spectrop-otometric An !#sis o" AspirinStudent E5 !u tion

,

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Spectrophotometric Analysis of Aspirin Standards Data6 t :

So!ution Concentr tion *m%/L+ A,sor, nce

A

B

C

;

2

Spectrophotometric Analysis of Unknown Aspirin6 t :

So!ution Concentr tion *m%/L+ A,sor, nce

A

B

C

;

unknown

For commerci ! Product:

amount of as!irin in un7no#n mg

acce!ted va ue mg

!ercent error EEEEEEEEEEEEEEEEEEEF

For microsc !e ! , product:

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mass of im!ure !roduct EEEEEEEEEEEEEEEEEEE mg

mass of as!irin in !roduct EEEEEEEEEEEEEEEEEEE mg

F !urity of !roduct EEEEEEEEEEEEEEEEEEEF

7uestions:

1& "! ain #hy the #ave ength of 6,0 nm #as used&

/& +o# did the concentration of your as!irin so ution com!are to the acce!ted va ueG

,& Is it better to buy generic or brand name as!irinG Su!!ort your conc usion&

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