Assume the molar absorptivity (ε) for CoCl42 - at 700 nm is 409.7 M-1 cm-1. If d, the cell path length, is equal to 1.48 cm for the cuvettes being used, and if the measured absorbance (A) at 700 nm is 1.147, what is [CoCl42-]?

1.89 * 10⁻³ M

Explanation:

In a UV Visible Spectrometer, we can determine the concentration of a species using Beer-Lambert law.

A = ε * l * c

where,

A: absorbance ε: molar absorptivity l: the cell path length c: concentration of the species

We can find [CoCl₄²⁻] from this expression.

A = ε * l * c

c = A / ε * l

c = 1.147 / 409.7 M⁻¹ cm⁻¹ * 1.48 cm

c = 1.89 * 10⁻³ M