Discuss the Important applications of U.V. AND Visible Spectroscopy.

1. Quantitative Analysis: The metal salt solutions which are coloured for e.g. Cu (II), Fe (III), Ni (II) etc and some organic coloured compounds can be easily analyzed quantitatively by using Beer Lambert’s Law. Thus, from OD we can calculate the concentration of the solution.

2. Identification of functional group (Qualitative analysis): The spectrophotometers are the instruments working on the principle of ${\lambda }_{max}$. This ${\lambda }_{max}$ is constant for each functional group. If we know λmax for the particular sample, we can decide the type of functional group present in it, as ${\lambda }_{max}$ is characteristic property.

3. Distinguish between geometrical isomer: Each geometrical isomer have its own characteristic ${\lambda }_{max}$, therefore from ${\lambda }_{max}$ we identify geometrical isomers. E.g. Cinnamic acid exists in Cis and Trans form.

4. Chemical Analysis: With the help of spectrophotometer we can find out the rate constant (K) of any chemical reaction. As we know the first order reaction. $$K=\frac{2.303}{t}\log \left(\frac{a}{a-x}\right)$$ Where a is initial concentration and (a - x) is final concentration.

We will take some ester and keep in the instrument and find out the absorbance then with the help of Beer-Lamberts Law we can find out the concentration.

Now add some reagent the reaction will take place at the time t. Now we will find out the O.D. of the solution in the cuvette which is (a-x) then by using the above eqn. for first order we can find out the K (rate constant).

Similarly we can find out the K for zero order, second order and so on by using its expression.

5. Determination and estimation of tautomers: Keto and Enol form are present in equilibrium which can be determined by spectrophotometer. E.g. Acetoacetic ester exists in two tautomeric forms which show different ${\lambda }_{max}$ values.