Concentration as discussed before follows the logic of absorbance and quantity

# Concentration as discussed before follows the logic

• 6

This preview shows page 2 - 4 out of 6 pages.

Concentration, as discussed before, follows the logic of absorbance and quantity: the more ions, the absorption would take place. Lastly is the path of length, it would be explained by

Subscribe to view the full document.

probabilities, as light passes through a longer path on the solution, the probability of interacting with the molecules and its absorption would be higher (Skoog, 718-720). Assimilating all these relationships and proportionality, we would now derive the Beer-Lambert-Bouguer Law or simply Beer’s Law: A = abc ( 5 ) A = εbc ( 6 ) Named after scientists August Beer, Johann Heinrich Lambert and Pierre Bouguer, the Beer’s Law (5) relates absorbance of the solution directly to the three factors mentioned before, the absorptivity which is denoted as a or the greek letter ε when the concentration is in molar units, the path length which is b, concentration which is represented by c. This expression and the concepts discussed before would be utilized by the Uv-vis spectrophotometer, a singe beam of light would pass through cells with different known concentrations of Cu 2+ to determine each solution’s absorbance, the data would then be regressed linearly to determine a working equation. To further understand the mechanics of the instrument, take a close look at Figure 2. Figure 2 . Spectrophometer Mechanics The main objective of this experiment is to find the concentration of a Cu 2+ solution and then find the volume of the initial analyte, to determine this; the determined working equation and the absorbance of the copper solution with unknown molarity was used. The same cell was used to keep the path length constant and since the sample is at the same composition and working conditions, its absorptivity barely changed. Knowing these facts, the absorbance determined by the spectrophometer was injected to the working equation between the relationship of the absorbance and concentration, multiplying it with the dilution factor would then give us the sought after molarity of the sample analyte. METHODOLOGY The concentration of unknown sample was analyzed through the determination of the relationship of absorbance and concentration. Seven 50 mL solutions are prepared from a 250mL 2500ppm Cu 2+ and concentrated NH 3 solutions. Table 1 shows the composition of each working solution. Table 1. Absorbing Analytes Solution Added 2500 ppm Cu 2+ solution (mL) Added concentrated NH 3 (mL) Solution 1 0.00 10.00 Solution 2 2.00 10.00 Solution 3 4.00 10.00 Solution 4 6.00 10.00 Solution 5 8.00 10.00 Solution 6 10.00 10.00 Sample 7.4 10.00 The said components are added to a 50 mL volumetric flask. Copper (II) is the absorbing particle and NH 3 is the color-intensifying particle. The reason for the addition of ammonia is to intensify the color of the solution; this will amplify the absorbance of the solution and will yield to better results.

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask 0 bonus questions You can ask 0 questions (0 expire soon) You can ask 0 questions (will expire )
Answers in as fast as 15 minutes