pH= 8 Absorbance = 0.997 Concentration mol/l = 6.01E-05

In this experiment I used Beer's law to convert absorbance to concentration with a known extinction coefficient (16.6*10^3) - so 0.997/16600 = concentration.

Next I want to find the amount of solute in the solution, which is that triangle formula, Amount in moles (mol) = concentration (mol/l) / volume (l), with a given volume of 8ml.

There are two stipulations: the given volume was 8ml not 8L, and I should be presenting the 'amount in moles' as micromoles. So 6.01E-05 moles is equal to 60.06 µmol, but it is still in µmol/L, whereas I want it µmol/ml. Therefore I multiply by 1000 again, giving 60060 µmol/ml.

Then to find Amount in moles using that triangle thing, I would multiply 60060 by 0.008 - right? This gives 480.48 moles, however I need µmol, so it's 480481 µmol?

This really seems wrong and I would appreciate some help!


1 Answer 1


Firstly,$ concentration (mol/L.)* Volume (L) = moles.$, is the correct statement.You have written that wrong.
Secondly, you have 60.06 $\mu$mol/L. For,converting that to $\mu$mol/mL. you should DIVIDE by 1000, because 60.06 $\mu$mol/L means in 1L i.e. in 1000 mL. 60.06 $\mu$moles are present.So, in 1 ml, $60.06/1000$ $\mu$moles are present.So, the concentration is now $0.06006 $ $\mu$mol/mL. Finally multiply by 8 to get $0.4808$ $\mu$moles are present in the solution.


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