An unknown sample of Cu2+ gave an absorbance of 0.257 in an atomidc absorption a

Question

An unknown sample of Cu2+ gave an absorbance of 0.257 in an atomidc absorption analysis. Then 1.30 mL of solution containing 100.0 ppm (= g/mL) Cu2+ was mixed with 91.0 mL of unknown, and the mixture was diluted to 100.0 mL in a volumetric flask. The absorbance of the new solution was 0.501 (a) Denoting the initial, unknown concentration as [Cu2+, write an expression for the final concentration, [Cu2+]f, after dilution. Units of concentration are ppm. (Use the following as necessary: Vo, Vs, and V.) (b) In a similar manner, write the final concentration of added standard Cu2+, designated as [Slf. (Use the following as necessary: Vo, Vs, and [S]f= [S], x

Explanation / Answer

[Cu^2+]i = 100ppm [Cu^2+]final = ? , V = 100mL

Vo = 1.3 mL

[Cu^2+]i * 1.3 mL = [Cu^2+]final * 100mL

or,  [Cu^2+]final = [Cu^2+]i * 1.3/100 = [Cu^2+]i * Vo/V

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91 mL * [S] i = 100mL * [S]f

or, [S]f = [S]i * Vs/V

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