Relationship between Solution Concentration and Transmitted Light Informal Lab Report PDF

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Relationship between Solution Concentration and KCLO3 Molecules, an experiment on Molarity and Concentrations, Dilutions, and Saturation...

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Relationship between Solution Concentration and Transmitted Light Paul Jang and Maya Lewis Purpose The purpose of this lab is to use spectroscopy and graphical analysis to determine the concentration of a colored beverage and hence solve a crime. Materials: ● Five test tubes ● Test tube rack ● Colorimeter ● 5 cuvettes ● One 10 mL serological buret ● One pipette hand pump ● One 200 ml beaker ● Grape soda ● Mystery solution ● Lab safety materials ● Kimwipes Procedure: 1) Put five test tubes on the test tube rack. Label them with colored tape. 2) Pour grape soda into the 50 ml beaker. 3) Using the burette and pipette hand pump, measure out varying measurements of grape soda and put them into the test tubes. 4) Then, using the burette and pipette hand pump, make 10 mL dilutions by adding water to the test tubes until the volume measures 10 mL. 5) Label five cuvettes with colored tape. Use the same colors that were used for the test tubes. 6) Pour the contents of each test tube into its corresponding cuvettes. Fill it up to the fill line. 7) Put each cuvette into the spectrophotometer. Record the transmittance percentage, transmittance, and absorbance.

Data Concentration (%)

%T

Transmittance

Absorbance

25%

52.6 %

0.526 T

0.247

35%

46.7 %

0.467 T

0.321

50%

35.0 %

0.350 T

0.489

75%

17.1 %

0.171 T

0.658

95%

9.1 %

0.091 T

0.862

Mystery (65)

26.1 %

.261 T

.573

Calculation: Beer-Lambert Law: A = abc Using best fit line: y = mx + b → A = m(concentration) + 0 0.573 = 0.867 (concentration) + 0 → (concentration) = 0.573/0.867 Concentration in the Mystery Solution = 66.1% 100 - 66.1 = 33.9 mL 33.9 x 6 = 203.4 minutes → 203.4 minutes / 60 = 3.39 hours Percent Error: |(Experimental Value) - (Accepted Value) / (Accepted Value)| x 100% [|66.1 - 65| / (65)] → 0.01692308 x 100% → 1.69% error

Analysis/Post-Questions 1. Who killed Toby Flenderson? Explain your conclusion. Dwight Schrute killed Toby Flenderson. Our calculations show that it took 3.39 hours for the grape soda that Toby Flenderson was drinking to be diluted to 66.1% concentration. In these 3.39 hours, the grape soda that Toby Flenderson had been drinking before he was murdered had diluted due to condensation from an overhead air conditioning duct dripping into his glass of grape soda at a rate of 1.0 mL every 6 minutes. The grape soda was found at 3:00 pm, and 3.39 hours from that time is 11:37 am. Dwight Schrute had no alibi from 11:00 am - 12:00 pm, therefore making him the killer. 2. Calculate the value of % T for an absorbance value A = 0.80. Using our graph of Concentration v. Absorbance, we estimated that %T ≈ 87% 3. The student handles the cuvette and leaves fingerprints in the path of the light beam. How will this affect the calculated concentration of the unknown? Explain your answer. Fingerprints in the path of the light beam would affect the calculated concentration of the unknown because it would affect the light transmittance (T) of the spectrophotometer and in turn would affect the calculated concentration of the unknown using Beer’s Law. 4. Transition metals from a wide selection of colored compounds. The complex ion tetraamminecopper (II) contains four ammonia molecules covalently bonded to a copper (II) ion. In aqueous solutions, Cu2+ ions will bond to four water molecules. The solution is light blue in color. The water molecules can be displaced by ammonia molecules, which

form more stable complex bases than water. The appearance of the intense dark blue-violet color of the [Cu(NH3)4]2+ ion is often used as a positive test to verify the presence of Cu2+ ions. a. Write a balanced chemical equation for the reaction of copper (II) sulfate and concentrated ammonia to produce a tetraamminecopper (II) sulfate. CuSO4 + 4NH3

→ [Cu(NH3)4]SO4

b. [Cu(NH3)4]2+ solutions exhibit a deep blue-violet color. How can you use spectrophotometry to confirm that this reaction has occurred and that the product formed is tetraamminecopper (II) sulfate? You can use spectrophotometry or a spectrophotometer to confirm that the product formed is tetraamminecopper (II) sulfate by comparing the absorbance and transmittance of the [Cu(NH3)4]2+ solution with that of tetraamminecopper (II) sulfate. c. Would you expect the wavelength of maximum absorbance for [Cu(NH3)4]2+ to be greater than or less than the wavelength of maximum absorbance for Cu(H2O6)2+? Explain. We would expect the wavelength of maximum absorbance for [Cu(NH3)4]2+ to be less than the wavelength of maximum absorbance for Cu(H2O6)2+. Cu(H2O6)2+, or hexaaquacopper, is pale blue in color, whereas tetraamminecopper is blue-violet in color. According to the visible light spectrum, the wavelength of pale blue would be around 525 nm and the wavelength of blue-violet would be around 400 nm....