An acidic solution of methyl red has an absorbance of0.451 at 530 nm in a 5.00 mm cell. Calculate the molarity of methyl red in this solution.

[Molar absorptivity$=1.06\times {10}^5\mathrm{L}{\mathrm{mol}}^{-1}{\mathrm{cm}}^{-1}$ at 530nm]

According to Beer Lambert Law

$\mathrm{A}=\mathrm{ebc}$

Where A is absorbance (no units), since

$A={\log }_{10}\left(P^0/P\right)$

e is the molar absorptivity with units of ${\mathrm{L} \mathrm{mol}}^{-1}{\mathrm{cm}}^{-1}$

b is the path length (in cm) of the sample-- that is, the path length of the cuvette in which the sample is contained. We will express this measurement in centimeters.

c is the concentration of the compound in solution expressed in  $\text{ mol }{\mathrm{L}}^{-1}$

$\begin{array}{r}0.451=1.06\times {10}^5\times 5\times {10}^{-1}c\\ c=8.51\times {10}^{-6}\mathrm{M}\end{array}$