Question

A 5.00-mL aliquot of a solution that contains 3.57 ppm Ni2+ is treated with an appropriate excess of 2,3-quinoxalinedithiol and diluted to 50.0 mL. The molar absorptivity of a Ni2+- 2,3-quinoxalinedithiol solution at 510 nm is 5520 L mol-1 cm-1. What is the absorbance of the above diluted Ni2+- 2,3-quinoxalinedithiol solution at 510 nm in a 2.00-cm cell?

Answer 1

As per the given information in the problem

Amount of Ni+2 = 3.57 ppm

The solution is diluted to 50.0 mL

Path length is b = 2.00 cm

molar absorptivity is = 5520 L mol^-1 cm^-1 at 510 nm

Absorbance is A₅₁₀ = ?

First we have to calculate concentration of Ni+2

Atomic mass of Ni is 58.69 g/mol

Hence molarity is-

molarity = (3.57 mg / L ) / (58.69 g /mol)

= 0.061 M

therefore concentration is 0.061 M

Final concentration after dilution can be calculated as

M_i V_i = M_f V_f

0.061 X 5.00 = M_f X 50

M_f = 0.0061

Absorbance at 510nm can be calculated

A = molar absorptivity X path length X concentration

A₅₁₀ = 5520 L mol^-1 cm^-1 X 2.00 cm X 0.0061

A₅₁₀  = 67.34

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