Question

gesi - Show ALL work 311 NAME "1. The following data were obtained for KMnO, at 540 nm with a 1 cm cell: KMnO4 Molarity Absorbance .101 0.000005 0.000010 0.000020 0.000030 0.000040 0.1010 0.202 0.405 0.606 0.809 (a) Prepare a caliberation plot (use graph paper). (b) Calculate the molar absorptivity at this wavelength (C) using the plot, find the concentration of an unknown that has absorbance of 0.300

Answer 1

a)

Scale -ons 2 cm = 1X1on Yasament 0.8 A Slope 06 09.3-0. Slopet (1.5x135L 1.0x105) 0-4 = 20,000 M olt c& B Unknown conc. 1:5X10 (0,0) 37165 sxiot Kno

b)

We have relation, Absorbance = $\epsilon$ b c

Where, $\epsilon$ is molar absorptivity , b is path length and c is concentration of substance.

If we plot Absorbance against concentration, we get a straight line passing through origin.

The slope of this line =  $\epsilon$ b

From graph , Slope of line = 20,000 M ^-1

$\therefore$ 20,000 M ^-1 =   $\epsilon$ b

$\therefore$$\epsilon$ = 20,000 M ^-1 / b

We have, path length b = 1 cm

$\therefore$$\epsilon$ = 20,000 M ^-1 / 1 cm

$\epsilon$ = 20,000 M ^-1 cm ^-1

ANSWER : molar absorptivity of KMnO₄ = 20,000 M ^-1 cm ^-1

C) Concentration of unknown = 1.5 $\times$ 10 ^-05 M