Question

Will Beer's law apply if in lab we choose to use concentrations in g/L, instead of moles? Explain

Answer 1

According to Beer's law,

A = ecl

where,

e = molar absorptivity with a unit of L.mol-1.cm-1

c = concentration in mol/L

l = parth length in cm

So, as we can see the molar absorptivity of the compound relates to the concentration of the solution taken for the absorption studies. It compensates any changes in the concentration and container size in the absorption studies and allows for easy comparison of samples with each other. Always rememeber absorption of a substance changes with the concentration and size. Molar absorptivity is a standard absorption value for a particular substance. We know moles of every substance has 6.022 x 10^23 molecules in it, so it is a comparible value for different substances, that is a standard value term. Now If we to have concentration in g/L, the value cannot be matched with the molar absorptiivity of the substance. the value of absortion would thus be widely varied and comparison of samples is not possible. This would thus not follow the Beer's law as required. So, it is necessary to have concentration in moles/L and not g/L to avoid errors and to follow Beer's law.