A solution containing 50 mL of 2 x 10 -3 M of an indicator H...

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Chemistry

A solution containing 50 mL of 2 x 10 -3 M of an indicator H 2In is measured to have an absorbance of 0.240 at 540 nm with a 1 cmthick cuvette. After 50 mL of 2.8 x 10 -3 M NaOH was added to thesolution, the absorbance became 0.048. A second solution containing50 mL of 2 x 10 -3 M of the same indicator in its basic form, In =, is measured to have an absorbance of 0.060 at 540 nm. After 50 mLof 6 x 10 -4 M HC1 was added, the absorbance became 0.039. Theindicator is known to have dissociation constants of K 1 = 4.0 x 10-7 , K 2 = 6.67 x 10 -8 .
a) What is the pH of the original solution of H 2 In?
b) What is the pH after the NaOH was added to it?
c) If I mix the first and second solutions together (i.e. the H2 In solution with the NaOH added plus the In = solution with theHC1 added), what pH will I get?
d) What are the molar absorptivities of H 2 In, HIn - , and In =?
e) What is the absorbance of the mixed solution in part c)?

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4.5 Ratings (930 Votes)

a the dissociation equation will be H2In H HIn Initial conc 0002 0 0 change x x x equilibrium 0002x x x Ka 40 x 10 7 x2 0002x we may ignore x in denominator 40 x 10 7 x2 0002 x 282 X 105 H pH logH 455 b Moles of indicator present Molarity X See Answer

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