Answer to Question #225970 in Chemistry for Mohammad Fawad

Question

7. 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 Beer–Lambert law can be used.

The Beer–Lambert law can be expressed as:

A = ε × l × C

where:

A is absorbance (no units)

ε is molar absorptivity (cm⁻¹ M^-1)

l is the optical path length (cm)

C is the concentration

Convert [cm⁻¹ g⁻¹ L] to [cm⁻¹ M^-1]:

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

Thus,

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