Question

Calculate the molar concentration of a solution that has a
measured absorbance of 0.635 using a 1-cm pathlength cuvette and an
extinction coefficient of 46,000.0
M^{-1}cm^{-1}.

Answer #1

Molar concentration from absorbance

To solve this problem, we use Beer's Law:

**A= lc**

where

A= the absorbance

ε= the molar absorptivity constant

l= the path length

c= the molar concentration of the solution.

We can rearrange this equation to get

**c=A/εl**

A=absorbance = 0.635

l= the path length = 1 cm

= extinction
coefficient = 46,000.0 M^{-1} cm^{-1} = 46,000.0 L
mol ^{-1} cm^{-1}

c= 0.635/ 46000 1 =
1.3810^{-5}
mol L^{-1} = 1.3810^{-5}
M

1.3810^{-5}
mol L^{-1} = 1.3810^{-5}
M |

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