Question

Assume the molar absorptivity (ε) for CoCl42- at 700 nm is 446.9 M-1 cm-1. If d, the cell path length, is equal to 0.71 cm for the cuvettes being used, and if the measured absorbance (A) at 700 nm is 0.935, what is [CoCl42-]?

Answer 1

Answer : The concentration of [CoCl₄]²⁻ is, $2.95\times 10^{-3}M$

Explanation :

Using Beer-Lambert's law :

$A=\epsilon \times C\times l$

where,

A = absorbance of solution  = 0.935

C = concentration of solution = ?

l = path length = 0.71 cm

$\epsilon$ = molar absorptivity coefficient = $446.9M^{-1}cm^{-1}$

Now put all the given values in the above formula, we get:

$0.935=(446.9)\times C\times (0.71)$

$C=2.95\times 10^{-3}M$

Therefore, the concentration of [CoCl₄]²⁻ is, $2.95\times 10^{-3}M$