Question

Calculate the %T of a solution that is measured in a 4.00cm cell and has a molar absorptivity of 431 M-1cm-1 , given that the solution is 0.02%w/v. The compound has a formula weight of 650.86 g/mol.

Answer 1

consider 100 ml of soution

then

% w/v = mass of compound x 100 / volume of solution

so

0.02 = mass of compound x 100 / 100

mass of compound = 0.02 g

now

moles = mass / formula mass

so

moles of compound = 0.02 / 650.86

moles of compound = 3.073 x 10-5

now

concentration = moles x 1000 / volume (ml)

so

concentration (C) = 3.073 x 10-5 x 1000 / 100

conc (C) = 3.073 x 10-4

now

according to Beers law

A = e x l x c

so

A = 431 x 4 x 3.073 x 10-4

A = 0.53

now

we know that

A = 2 - log %T

so

0.53 = 2 - log %T

%T = 29.53

so

%T of the solution is 29.53