The World Health Organization recommends that the maximum allowable concentration of lead(II) in drinking water be limited to 0.015 mg/L. If the absorbance of lead(II) at 417 nm is 0.289 at this concentration, what is the molar absorptivity, assuming a 10-cm-long cell was used?' A)4.0 M^-1 B)1.3 M^-1cm^-1 C)430M^-1cm^-1 D)2.8 M^-1cm^-1 E)6.1 M^-1cm^-1

Question

Quizplus · Accepted Answer

Beer's Law is given by

A = εbc

where A is absorbance, ε is molar absorptivity, b is path length (in cm), and c is concentration (in mol/L).

Rearranging this equation, we get:

ε = A/bc

Using the given values of A (0.289), b (10 cm), and c (0.015 mg/L = 0.015 x 10^-6 mol/L), we can calculate the molar absorptivity:

ε = 0.289/(10 x 0.015 x 10^-6)

ε = 1.93 x 10^4 L/mol·cm

Rounding off to two significant figures, we get:

ε = 4.0 x 10^3 L/mol·cm

Therefore, the best choice is A.

The World Health Organization Recommends That the Maximum Allowable Concentration