Question

Which of the following would transmit the least amount of 625 nm light?

                    

		a 0.50 molar solution of Cu(NO3)2
		a 0.040 molar solution of Cu(NO3)2
		a 0.100 molar solution of Cu(NH3)4+2
		a 0.050 molar solution of Cu(NH3)4+2
		a blank of pure water

Answer 1

The relation between absorbance and transmittance is that -

absorbance, A = log ( 1/T) where T is transmittance.

Thus, least transmittance would mean maximum absorbance. Beer-Lambert's law gives the relationship between the absorbance and concentration. A = ecl [ e = epsilon, I have used the alphabet 'e' due to unavailability of greek letter epsilon]

Since Cu2+ salts are given in question, the absorbance or transmittance would depend solely on the concentration of the salt.

0.50 molar solution of Cu(NO3)2 will exhibit maximum absorbance and therefore, least transmittance as absorbance is directly proportional to concentration.