The World Health Organization recommends that the maximum allowable concentration of chromium(VI) in drinking water be limited to 0.05 mg/L. If the molar absorptivity of chromium(VI) at 345 nm is 1.5 10³/(M cm), what is the absorbance of a solution that contains 0.050 mg/L in a 10-cm-long cell? A)0.0014 B)0.75 C)0.014 D)0.075 E)14

Question

Quizplus · Accepted Answer

First, convert the concentration of chromium(VI) to molarity:

0.050 mg/L = 0.050 mg/L x 1 g/1000 mg x 1 mol/51.996 g = 9.6 x 10^-8 M

Then, use Beer-Lambert law:

A = εcl

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

Plugging in, we get:

A = (1.5 x 10^4 M^-1 cm^-1)(9.6 x 10^-8 M)(10 cm) = 0.0144

Rounding to 3 significant figures and converting to scientific notation, we get:

A = 0.014

Therefore, the answer is (C).

The World Health Organization Recommends That the Maximum Allowable Concentration