Answer to Question #225997 in Chemistry for Abdul

Question

 Aniline, C6H5NH2, when reacted with picric acid gives a derivative with an absorptivity of 

 134 cm−1

g

−1 L at 359 nm. What would be the absorbance of a 1.00 × 10−4 M solution of 

 reacted aniline in a 1.00-cm cell

Answer 1

Solution:

The molar mass of aniline is 93.13 g mol⁻¹.

Therefore,

(134 cm⁻¹ g⁻¹ L) × (93.13 g mol⁻¹) = 12479.42 cm⁻¹ L mol⁻¹ = 12479.42 cm⁻¹ M^-1

ε = 12479.42 cm⁻¹ M^-1

The Beer–Lambert law can be used.

A = ε × l × C

where:

A = absorbance (no units)

ε = molar absorptivity (cm⁻¹ M^-1)

l = the pathlength (cm)

C = concentration

Therefore,

A = (12479.42 cm⁻¹ M^-1) × (1.00 cm) × (1.00 × 10⁻⁴ M) = 1.2479 = 1.25

A = 1.25

Answer: The absorbance (A) of a solution is 1.25