Question

The molar absorptivity for aqueous solutions of phenol at 211 nm is 6.17x103L/mol/cm. Calculate the linear range of phenol concentrations if the transmittance is to be less than 85% and greater than 7% when the measurements are made in 1cm cell.

Answer 1

Step-by-step explanation:

The given data is as follows.

`\lambda` = 211 nm,
`\sum = 6.17 * 10^(3) mol/L/cm`

l = 1 cm, 7% < Transmittance < 85%

Suppose the aqueous solution follows Lambert-Beer's law. Therefore,

Absorbance =
`-log \frac{\text{Percentage transmittance}}{100}`

Hence, for 7% transmittance the value of absorbance will be as follows.

Absorbance =
`-log (7)/(100)`

`A_(1)` = 1.155

For 85% transmittance the value of absorbance will be as follows.

Absorbance =
`-log (85)/(100)`

`A_(2)` = 0.07058

According to Lambert-Beer's law.

A =
`\sum * l * C`

where, A = absorbance

`\sum` = molar extinction coefficient

C = concentration

Therefore, concentration for 7% absorbance is as follows.

`A_(1) = \sum * l * C_(1)`

`C_(1)` =
`(1.155)/(6.17 * 10^(3) * 1)`

=
`0.187 * 10^(-3) mol/L`

= 0.187 mmol/L

Concentration for 85% absorbance is as follows.

`A_(2) = \sum * l * C_(2)`

`C_(2)` =
`(0.07058)/(6.17 * 10^(3) * 1)`

=
`0.01144 * 10^(-3) mol/L`

= 0.01144 mmol/L

Thus, we can conclude that linear range of phenol concentration is 0.01144 mmol/L to 0.187 mmol/L.