Question

A photometer with a linear response to radiation gave a reading of 690 mV with a blank in the light path and 101 mV when the blank was replaced by an absorbing solution. Calculate

the transmittance and absorbance of the absorbing solution.

Transmittance =

Absorbance =

the expected transmittance if the concentration of absorber is one half that of the original solution.

Transmittance =

the transmittance to be expected if the light path through the original solution is doubled.

Transmittance =

Answer 1

Explanation:

When light moves through a transparent (or semi-transparent) material, it can be transmitted, absorbed, or reflected. The transmittance of a material is the proportion of the incident light that moves all the way through to the other side.

For example:

let's say shining a flashlight on a semi-transparent glass block. You start off with 100% of your incident light. The first thing that happens is that 30% of that light is reflected off the outer surface of the glass. This leaves you with 70% to continue through the glass block. Another 50% of the light is absorbed by the molecules inside the glass block itself. That leaves you with 20% that emerges from the opposite side. So you could say that the glass block has a transmittance of 20%.

According to the question:

With blank reading = 690 mV

Reading with the sample = 101 mV

So the transmittance is 101 mV.

The Absorbance = 690-101

= 589 mV.

If the concentration of absorber is one half that of the original solution:

According to the Lambert-Beers law: A = ¹Cx,   ¹ = molar extinxction Coefficient.

C = concentration, x = path length (light travel distance)

A = Absorbance

A C, (Absorbance directly prapotional to concentration according to the formula)

According to the question concentration becomes half, Then the absorbance also becomes half as a result of this the Transmittance becomes double.

If the light path through the original solution is doubled:

   A = ¹Cx

A x, (Absorbance directly prapotional path of the light)

According to the question light path is doubled, Then the absorbance also becomes double as a result of this the Transmittance becomes half.