Question

How can a spetrophemeter be used to determine the concentration of unknown red food coloring solution?

Answer 1

Answer – Spectrophotometry is the good technique for determine of the concentration of unknown compounds. This technique is mainly based on the interaction of matter with electromagnetic radiation. Spectrophotometer used the electromagnetic radiation range between 400 to 800 nm which is for visible portion of the electromagnetic spectrum. There are used different concentration of the red food coloring solution and there are measure the absorption in the spectrophotometer. The substance absorbed a particular light and due to that we will see the specific color for each substance.

We know Beer's Law which explain the relationship between concentration and absorption at specific wavelength. From this law we know concentration is directly proportional to absorption. So the formula for this law is as follow-

A = εbc

Where, A = measured absorbance, ε = absorptivity constant. b = length of cell and C = concentration

In the spectrophotometer there are measured the absorbance of different known concentration diluted solution with unknown one and then plot the graph absorbance verses concentration of dilute solution. This graph is liner line, since concentration is directly proportional to absorption and using this graph we can determine the concentration of unknown solution. We measured the absorbance in the spectrometer for unknown solution, so from the axis of absorbance we need to draw the line up to the liner line of graph and from than make the tangent to the concentration axis and that will show the concentration of unknown solution.