In this Case assignment, you will determine the spectroscopy of unknowns at:

http://amrita.vlab.co.in/index.php?sub=2&brch=190&sim=338&cnt=1

Part 1:

Procedure:

Determination of Molar Absorption Coefficient:

1. Select a blank cuvette and place it in the spectrophotometer. Close the lid.

2. Click on 0 ABS 100%T button, the instrument now reads 0.00000 A.

3. Choose a solution with known concentration and measure the absorbance between the wavelengths 350 nm to 700 nm.

4. Record the wavelength at the maximum absorbance value.

5. Calculate the value of molar absorption coefficient, using the equation.

∈ = A/cl

Determination of Unknown Concentration:

1. Set the wavelength to the value corresponding to maximum absorbance (recorded above).

2. Place the cuvette with same solution but at an unknown concentration.

3. Read the absorbance for this wavelength.

4. Calculate the concentration with the help of the equation, molarity

= A/∈l

5. Enter the calculated concentration value in the given box. (Note : Should enter the value correct to four decimal places)

6. Repeat the same procedure for a second solution.Procedure:

Determination of Molar Absorption Coefficient:

1. Select a blank cuvette and place it in the spectrophotometer. Close the lid.
2. Click on 0 ABS 100%T button, the instrument now reads 0.00000 A.
3. Choose a solution with known concentration and measure the absorbance between the wavelengths 350 nm to 700 nm.
4. Record the wavelength at the maximum absorbance value.
5. Calculate the value of molar absorption coefficient, using the equation.

Determination of Unknown Concentration:

1. Set the wavelength to the value corresponding to maximum absorbance (recorded above).
2. Place the cuvette with same solution but at an unknown concentration.
3. Read the absorbance for this wavelength.
4. Calculate the concentration with the help of the equation, molarity
5. Enter the calculated concentration value in the given box. (Note : Should enter the value correct to four decimal places)
6. Repeat the same procedure for a second solution.

Observations and Calculations:

Concentration (c) of Solution =.............................M
Absorbance (A) of known conc. solution =...............................A
Cuvette length (l) =.............................cm
Wavelength(λ) at maximum absorbance value =..............................nm
Molar Absorption Coefficient, (∈) =............................. M-1 cm-1
Absorbance (A) of given solution =..............................A
Therefore, concentration (c) =.............................M

Result:

Concentration of the given solution =...............................M

Part II

1. The molar extinction coefficient of a solution of concentration 0.04 M and thickness 10.5 cm is 80.08 L mol-1 m-1. Find the value of optical density.

2. Absorbance of a solution is found to be 0.83 .Calculate % Transmittance.

3. When a wavelength of 250 nm is passed through a solution, the light intensity is reduced to 20% of its initial value. Then absorbance is given by _____

4. The absorbance of 1 mm of a sample solution whose concentration is 0.03 M is _____. (Given that the molar absorption coefficient is 10 L mol-1 m-1)

5. An unknown solution showed absorbance 5.000 and molar absorption coefficient, ε= 160 L mol-1 m-1, (Thickness, l=2 cm). Calculate the concentration of the solution.