Question

A 2.00 x10-3 M solution of a compound absorbs 50% of the light of a certain wavelength passing through 1.00 cm of a sample. Calculate the molar absorption coefficient(E) at this wavelength.

A. 0.301.
B 0.602.
C. 0.500.
D. 0.788.
E. 1.00

Answer 1

Answer : The molar absorptivity coefficient is,
`1.505* 10^(2)M^(-1)cm^(-1)`

Explanation :

Using Beer-Lambert's law :

Formula used :

`A=\epsilon * C* l`

`A=\log (I_o)/(I)`

`\log (I_o)/(I)=\epsilon * C* l`

where,

A = absorbance of solution

C = concentration of solution =
`2.00* 10^(-3)M`

l = path length = 1.00 cm

`I_o` = incident light

`I` = transmitted light

`\epsilon` = molar absorptivity coefficient = ?

A compound absorb 50 % of the light that means,

Incident light =
`I_o`

Transmitted light =
`0.5* I_o`

Now put all the given values in the above formula, we get the molar absorptivity coefficient.

`(I_o)/(0.5* I_o)=\epsilon * (2.00* 10^(-3)M)* (1.00cm)`

`\epsilon=1.505* 10^(2)M^(-1)cm^(-1)`

Therefore, the molar absorptivity coefficient is,
`1.505* 10^(2)M^(-1)cm^(-1)`