91Ó°ÊÓ

Molar absorptivity is a property of a substance which determines the fraction of light absorbed by it at a particular wavelength. Absorbance is the fraction of light absorbed.

$\mathrm{A}=\mathrm{Î\mu ³¦²ú}$

Where,

$$\begin{gathered} \mathrm{Î\mu }=molarabsorptivitycoefficient \\ b=lengthofcuvet \\ c=concentrationofsolution \\ A=absorbance \end{gathered}$$

TheSample of 2.025mL semi-xylenol orange at pH 5.9 was titrated with$7.515×{10}^{-4}\mathrm{MPb}({\mathrm{NO}}_3{)}_2.$. The reaction of semi-xylenol orange with${\mathrm{Pb}}^{2+}$has a 1 : 1 stoichiometry.

The absorbance correction is done by multiplying observed absorbance by (total volume / initial volume).

For example, at$36.0\mathrm{μ}L$

Absorbance $$\begin{gathered} =(0.399)×\left[\right(2.025+36)/2.025] \\ =0.406 \end{gathered}$$

$\mathrm{A}\mathrm{graph}\mathrm{for}\mathrm{the}\mathrm{corrected}\mathrm{absorbance}\mathrm{versus}\mathrm{volume}\mathrm{of}{\mathrm{Pb}}^{2+}$

A graph for the corrected absorbance versus volume of${\mathrm{Pb}}^{2+}$has two linear regions intersecting at$46.7\mathrm{μ³¢}$. The moles of ${\mathrm{Pb}}^{2+}$at$46.7\mathrm{μ³¢}$volume is given by

$(46.7×{10}^{-6}\mathrm{L})(7.515×{10}^{-4}\mathrm{M})=3.510×{10}^{-8}\mathrm{mol}$

Calculate the concentration of semi-xylenol

$$\begin{gathered} \mathrm{Molarity}=\frac{\mathrm{molesofsolute}}{\mathrm{Volumeofsolvent}} \\ [\mathrm{Semi}-\mathrm{xylenol}]=\frac{3.510×{10}^{-8}\mathrm{mol}}{2.025×0^{-3}\mathrm{L}}=1.73×{10}^{-5}\mathrm{M} \end{gathered}$$