Question

Is there a mathematical relationship between absorbance and concentration of the solution? If so, indicate the relationship.

Answer 1

Many compounds absorb ultraviolet (UV) or visible (Vis.) light. The diagram below shows a beam of monochromatic radiation of radiant power P₀, directed at a sample solution. Absorption takes place and the beam of radiation leaving the sample has radiant power P.

The amount of radiation absorbed may be measured in a number of ways: Transmittance, T = P / P0 % Transmittance, %T = 100 T Absorbance,

A = log10 P0 / P A = log10 1 / T A = log10 100 / %T A = 2 - log10 %T The last equation, A = 2 - log10 %T , is worth remembering because it allows you to easily calculate absorbance from percentage transmittance data. The relationship between absorbance and transmittance is illustrated in the following diagram: So, if all the light passes through a solution without any absorption, then absorbance is zero, and percent transmittance is 100%. If all the light is absorbed, then percent transmittance is zero, and absorption is infinite.