At 580 nm, the wavelength of its maximum absorption, the complex Fe(SCN)^2+ has

Question

At 580 nm, the wavelength of its maximum absorption, the complex Fe(SCN)^2+ has a molar absorptivity of 7.00 Times 10^33 L cm^-1 mol^-1. Calculate the absorbance of a 6.34 Times 10^-5 M solution of the complex at 580 nm in a 1.00-cm cell. the absorbance of a solution in which the concentration of the complex is twice that in (a). the transmittance of the solutions described in (a) and (b). Transmittance of the solution described in (a) = Transmittance of the solution described in (b) = the absorbance of a solution that has half the transmittance of that described in (a).

Explanation / Answer

Absorbance = molar absorptivity x concentration x path length

a. Absorbance = 7 x 10^3 M-1.cm-1 x 6.34 x 10^-5 M x 1 cm = 0.4438

b. When concentration is doubled

absorbance = 7 x 10^3 M-1.cm-1 x 2 x 6.34 x 10^-5 M x 1 cm = 0.8876

c. Transmittance for,

Solution (a)

log%T = 2 - absorbance = 2 - 0.4438

%T = 36%

T = 0.360

Solution (b)

%T = inv.log(2 - 0.8876) = 12.954%

T = 0.1295

d. When transmittance is 1/2 of (a)

T = 0.360/2 = 0.180

Absorbance = 2 - log(18) = 0.745

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