# How to get new concentration from percent transmittance?

##### 1 Answer

Transmittance and absorbance are related as follows.

#A = -log(T)#

Evidently, percent transmittance is simply some fraction of

#A = epsilonbc# where

#epsilon# is the molar absorptivity,#b# is the path length, and#c# is the concentration in#"M"# .#epsilon# and#b# are CONSTANTS for the same substance.

Therefore:

#-log(T_1) = epsilonbc_1#

#-log(T_2) = epsilonbc_2#

And we have:

#c_2/c_1 = log(T_2)/(log(T_1)#

Thus, the new concentration is:

#color(blue)(c_2) = c_1log(T_2)/log(T_1)#

#= ("26 mg/L")log(0.617)/log(0.528)#

#=# #color(blue)("19.66 mg/L")#

This should make sense... if it transmits more, it absorbs less. It absorbs less if less particles are in solution that block the path of the incoming light.