Question

Erioglucine is a blue­colored dye that absorbs its complementary color, red, in aqueous solution around 645 nm. Unfortunately, the local distilled water supply is consistently contaminated with a trace amount of a metal cation that also absorbs 645 nm light. Suppose then, a control sample of 0.0552 M erioglucine (aq; same water supply) has an absorbance of 0.331 and that a distilled water sample in a similar cuvette has an absorbance of 0.019. Determine the concentration of an erioglucine (aq) sample (same water supply) that has an absorbance of 0.237. Concentration: _____ M

Answer 1

According to Beer's law, absorbance (A) is as calculated as follow

A = c l

= molar absorptivity, c = concentration and l = length of sample tube

For a substance at two different concentration will remain same and l will be remain same.

Therefore we can write as A₁/A₂ = c₁ /c₂

A₁ = 0.331 , c₁ = 0.0552 and A₂ = 0.237

From this equation unknown concentration can be calculated.

c₂= c₁ x A₂ /A₁ = 0.0552 x 0.237 / 0.331 = 0.0395 M