Question

Suppose a solution of Co(NO3)2 has an extinction coefficient of 5.1 L/mol-cm at 505nm, show that a 0.0300M Co(NO3)2 solution will give an absorbance of 0.15.

Answer 1

Task:

Suppose a solution of $\mathrm{Co(NO3)2}$ has an extinction coefficient of 5.1 L/mol-cm at 505nm, show that a 0.0300M Co(NO3)2 solution will give an absorbance of 0.15.

Solution:

The Beer-Lambert law (or Beer's law) is the linear relationship between absorbance and concentration of an absorbing species.

According to the Buger - Beer-Lambert law

$$A = \varepsilon \cdot I \cdot c$$

A – absorbance

$\varepsilon$ – extinction coefficient L·mol⁻¹·cm⁻¹

I – length of the cuvette, cm (usually it’s 1 cm)

The absorbance of 0.0300M Co(NO₃)₂ solution is

$$A = 5.1 \cdot 1 \cdot 0.0300 = 0.15$$

Answer: $A = 0.15$