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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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micro123 micro123
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11 years ago
A molecule has an extinction coefficient ? of 1.80 for a 1% solution, and has a molecular weight of 222 g/mol.

The absorbance is 0.40. What is the molarity of this solution (expressed in mM)?

(The answer is 10 mM, but I?m not sure how to get there. I calculated the concentration to be 0.22.)

Can anyone help me figure this out?
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rjavier1rjavier1
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11 years ago
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11 years ago
use Beer-Lambert Law

A = E b c

where E is the wavelength-dependent molar absorptivity coefficient with units of M-1 cm-1.
A = is absorbance

b is the path length which = 1cm, and c is the analyte concentration

0.4 = 1.8 * 1 * C
C =0.222 M =222 mmole/litre
you have 1% sol
supose it 1gm in 100of sol  so in 1000 = 0.1

moles of solute = 0.1/222=0.00045mol =0.45 mmol
0.45 mmol* 22.2 mM = 9.99mM
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