A 0.1% (w/v) solution of a protein absorbs 20% of the incident light. ...
Given information:
- Concentration of protein solution: 0.1% (w/v)
- Absorbance of the solution at this concentration: 20%
To find:
- Fraction of light transmitted when the concentration is increased to 0.4%
Solution:
Step 1: Understanding Absorbance
Absorbance is a measure of how much light is absorbed by a solution. It is calculated using the equation: A = log(Io/I), where A is the absorbance, Io is the intensity of the incident light, and I is the intensity of the transmitted light.
The absorbance can be converted to a percentage by multiplying it by 100.
Step 2: Relationship between Concentration and Absorbance
The absorbance of a solution is directly proportional to the concentration of the solute. This relationship is described by the Beer-Lambert Law, which states that the absorbance is equal to the product of the molar absorptivity (ε), the path length (l), and the concentration of the solute (c): A = εcl.
In this case, the concentration of the protein solution is given as 0.1% (w/v) and the absorbance is given as 20%. We can use these values to determine the molar absorptivity.
Step 3: Calculating Molar Absorptivity
Using the equation A = εcl, we can rearrange it to solve for ε: ε = A/(cl).
Given:
- Concentration (c) = 0.1% (w/v) = 0.1 g/100 mL = 0.001 g/mL
- Absorbance (A) = 20%
- Path length (l) = 1 cm (assuming standard cuvette)
Substituting these values into the equation, ε = (0.2)/(0.001 * 1) = 200 mL/g/cm.
Step 4: Calculating Fraction of Light Transmitted
Now that we have determined the molar absorptivity, we can calculate the fraction of light transmitted at a new concentration of 0.4%.
Given:
- Concentration (c) = 0.4% (w/v) = 0.4 g/100 mL = 0.004 g/mL
- Path length (l) = 1 cm (assuming standard cuvette)
Using the Beer-Lambert Law (A = εcl), we can rearrange it to solve for the absorbance (A): A = εcl.
Substituting the values into the equation, A = (200 mL/g/cm) * (0.004 g/mL) * (1 cm) = 0.8.
The absorbance at the new concentration is 0.8. Since absorbance is directly proportional to the fraction of light absorbed, the fraction of light transmitted is 1 - absorbance = 1 - 0.8 = 0.2.
Final Answer:
The fraction of light transmitted when the concentration is increased to 0.4% is approximately 0.20, or 20%.