A mixture of ni2+ and co2+ is analyzed by forming the salicyaldoxime complexes in chloroform solvent. the molar absorptivities for Ni and Co ions at 500 nm are 10 and 1000 respectively.However, at 400 nm both molar absorptivities are 5.0 * 10^3 cm1mol1dm3.the absorbances were recorded using 1 cm cuvette and were found to be 0.091 at 500 nm and 0.615 at 400 nm.calculate the concentration of ni2+ and co2+ in the given mixture.

Concentration of Ni²⁺ = ?3.2×10−5mol.dm−3?

Concentration of Co²⁺ = ?9.1×10−5mol.dm−3?

Absorbance (A) at a particular wavelength for a binary mixture: A = ??1?.C1?.l+?2?.C2?.l?

Here, absorbance at a particular wavelength for the mixture of Ni²⁺ and Co²⁺, ?A=?Ni2+?.CNi2+?.l+?Co2+?.CCo2+?.l?

where, ??? , C and l represent molar absorptivity at the wavelength, molarity and path length of cell respectively.

At 500 nm: A = 0.091, ??Ni2+?? = 10 cm^-1.mol^-1.dm³, ??Co2+?? = 1000 cm^-1.mol^-1.dm³ and l = 1 cm

0.091 = ?(10cm−1.mol−1.dm3×CNi2+?×1cm)+(1000cm−1.mol−1.dm3×CCo2+?×1cm)?

?⇒(10CNi2+?mol−1.dm3+1000CCo2+?mol−1.dm3)=0.091? ..................... (1)

At 400 nm: A = 0.615, ??Ni2+?? = 5000 cm^-1.mol^-1.dm³, ??Co2+?? = 5000 cm^-1.mol^-1.dm³ and l = 1 cm

0.615 = ?(5000cm−1.mol−1.dm3×CNi2+?×1cm)+(5000cm−1.mol−1.dm3×CCo2+?×1cm)?

?⇒(5000CNi2+?mol−1.dm3+5000CCo2+?mol−1.dm3)=0.615? ..................... (2)

[5?×? Equation(1)] - [Equation(2)]:

?−4950CNi2+?mol−1.dm3=−0.160?

?⇒CNi2+?=−4950−0.160?mol.dm−3=3.2×10−5mol.dm−3? (rounded off to two significant figures)

Plug-in the value of ?CNi2+?? in the equation (1):

?(10×3.2×10−5)+(1000CCo2+?mol−1.dm3)=0.091?

?⇒CCo2+?=9.1×10−5mol.dm−3? (rounded off to two significant figures)