Question

post-lab questions

oncentration of swimming pool / hot tub sample POST-LAB QUESTIONS 1) What happens in the Spectrophotometer when a light beam is passed through a solution that has a certain color or color mixtures? 2) Define Beer's Law? (First write the formula, and then explain...) BeeにレauDenis-Absorber) ce- L c e the photos in color above have two samples of the same solution. They have the same color intensity Here we icture where you look from one side. In the second picture with the che firautions the one on the right has more color intensity if you look from the top. sste snhe reason of seeing different color intensity for the same sample solution in this picture. Hint -Remember Beer's Law) 4) The absorptivity of a particular made from this chemical if a 1.5 cm sample has an absorbance of 1.80? Chemical is 1.2/M.cm. What is the concentration of a solution 5) A solution with a concentration of 0.14M is measured to have an absorbance of 0.38. Another solution of the same chemical is measured under the same conditions and has an absorbance of 0.26. What is its concentration?

Answer 1

3)

In the first picture, the path length that light travels is same for solutions in both test tubes. In the second picture, the path length that light travels is different, the test tube with less amount of solution has lower path length length and the test tube with more amount of solution has more path length. Because of the difference in path lengths the color intensity observed is different because the absorbance is different.

4)

The mathematical statement for Beer's Law is as follows:

$A=\epsilon Cl$

Here, A is the absorbance, C is the concentration of the solution, l is the path length of the solution, and $\epsilon$ is the molar absorptivity.

Given, A=1.80, l=1.5 cm, $\epsilon$=1.2/M.cm

calculate the concentration as follows:

C=A/$\epsilon$l

=1.80 /(1.2/M.cm x 1.5 cm)

C = 1 M

5)

Use the Beer's law given in question 4 as follows:

$A_1=\epsilon C_1l$$A_2=\epsilon C_2l$

Divide these equations as shown below:

$\frac{A_1}{A_2}=\frac{\epsilon C_1l}{\epsilon C_2l}$

A1 C1 АзСъ

Ai 0.38. C1-0.14M. A2-0.26

0.38 0.14M 0.26 0.14M × 0.26 C2 = 0.38 C2 0.096M