Question

How could spectrophotometry be used to determine an unknown salt?

Answer 1

Hint: Spectrophotometry depends on the concentration of the solute which is present in an unknown solution. Spectrophotometry is going to work on the principle of Beer-Lambert law.
\[A=\varepsilon \times b\times c\]
Here A = absorbance
$\varepsilon $ = extinction coefficient
b = path length
c = concentration of the solution in the cuvette

Complete answer:
- In the question it is asked how spectrophotometry is used to determine the presence of an unknown salt.
- For example if we are supposed to find the concentration of a salt in the solution, we have to prepare a standard solution of the same salt in different concentrations.
- Prepare 1 M , 2M, 3M, and 4M solutions of the unknown salt.
- In the next step take the absorbance of the unknown salts by using the spectrophotometer.
- Now take the absorbance of the unknown salt.
- Tabulate all the readings and draw a graph by taking the centration of the unknown salts on x- axis and absorbance on y-axis.
- Now draw a graph by basing on the readings from the tabular form.
- Maybe the graph will look like the below image.

- Now we have to interpret the unknown salt concentration in the above graph and intersect the line from unknown salt concentration to x-axis to get the concentration of the unknown salt.

Note:
Without knowing the absorbance of the unknown salt it is not possible to get the concentration of the unknown salt by using spectrophotometry. Spectrophotometry works on the principle of the absorbance of the chemical.