S W I S S G E R M A N U N I V E R S I T Y

INORGANIC & ORGANIC CHEMISTRY LABORATORY REPORT |

Subject | : Inorganic & Organic Chemistry Laboratory | Lecturer | : Hery Sutanto S.Si | Instructor | : Tabligh Permana S.Si., Dian Sukmayanda S.Si | Faculty/Class | : Life Science/LS 2 A | Date of Experiment | : 11 April 2012 | Date of Lab. Report | : 18 April 2012 | Semester | : 2 | Time of Experiment | : 14.00-17.00 | | | | | | | | | | | | | | | | Experiment: | Principle of Spectroscopy |

NAME : Melisa Grace (14211043) Nur Ratih K. (14111005)

Group : G

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EXPERIMENT 5: Extraction of Caffeine From Tea Leaves

1. Objective:

To demonstrate the extraction of Caffeine as natural substance by using organic solvent and distillation technique.

2. The Materials, Equipments and Procedures:

A) Materials

* K2CrO4(Potassium Chromate) * H2SO4 (Sulphuric Acid) * Aquades

B) Equipments

* Beaker * Volumetric flask (50 ml and 25 ml) * Glass rod * Spatula * Watch glass * Graduated pipette * Pipette * Scale * UV-Vis spectrophotometer * Cuvette

C) Methods

1. Equipment and materials necessary for the experiment were prepared on the working table. 2. Calculation were made to make the parent solution (50 ml 0.1 M K2CrO4 needed to be made. a. TOLONG MASUKIN CALCULATION YG HASILNYA BRP GRAM YG MESTI DIAMBIL BUAT BIKIN 0.01 LARUTAN 3. 0.1 M of K2CrO4 was added with 2 ml of H2SO4. Then it was diluted to 0.01 M K2CrO4 based on this calculation:
M1 x V1 = M2 X V2
0.1 x GUE GA TAU CALCULATION YG KMRN GMN

4. 0.01 M K2CrO4 was diluted to four different solutions from the higher concentration until the lower one: M1 | x | V1 (ml) | = | M2 | x | V2 (ml) | 0.01 | x | 5 | = | 0.002 | x | 25 | 0.002 | x | 12.5 | = | 0.001 | x | 25 | 0.001 | x | 12.5 | = | 0.0005 | x | 25 | 0.0005 | x | 10 | = | 0.0002 | x | 25 | 5. All this solution were moved into different cuvette. 6. The unknown sample was compared with the 4 solutions that already been made. Then, the concentration of the sample was found out by seeing the colour different for qualitative analysis. 7. The spectrophotometer (UV-Vis) was used and the absorbance of the light was observed for each solution as quantitative analysis. Then, the graph was gotten 8. The unknown sample’s concentration was found by the graph

3. Introduction and Background

The Light of Knowledge is an often used phrase, but it is particularly appropriate in reference to spectroscopy. In Spectrophotometry, a spectrophotometer is used. Basically, this is a device that measures the amount of light that a certain sample absorbs. It operates by passing a beam of light that consists of photons through the sample and measuring the intensity of light reaching a detector.
• Ultraviolet-Visible Spectroscopy: Absorption of this relatively high-energy light causes electronic excitation. The easily accessible part of this region (wavelengths of 200 to 800 nm) shows absorption only if conjugated pi-electron systems are present.

A useful analytical tool for determining the concentration of colored material in solution is ultraviolet visible spectrophotometry. Colored substances absorb light in the visible spectrum and the amount of light absorbed is proportional to the concentration of the substance in solution.
,
where A is the measured absorbance, is the intensity of the incident light at a given wavelength, is the transmitted intensity, L the pathlength through the sample, and c the concentration of the absorbing species. For each species and wavelength, ε is a constant known as the molar absorptivity or extinction coefficient. This constant is a fundamental molecular property in a given solvent, at a particular temperature and pressure, and has units of or often .

The absorbance of a solution depends on the quantity of light absorbed by the species in the solution, the wavelength of the light entering the solution, the length of the solution the light has to pass through, and the concentration of the solution.

4. Data and Observation

* The peak wavelength: 340 nm * Qualitative analysis of the unknown sample: between 0.002 and 0.001 * Quantitative analysis of the unknown sample: 0.0016 * The absorbance of the unknown sample: ADA DI GRAPH * GRAPH ATO FOTO PERLU DIMASUKIN GA?

5. Discussion

The reaction of Pottasium Chromate with Sulfuric Acid In this experiment, two ml of concentrated Sulfuric Acid was added to the Potasium chromate in order to make the colour of the solution more significant. The colour of K2CrO4 was yellow, which is harder to be identified in small concentration. The addition of sulfuric acid made the solution can maintain its colour better in a very small concentration.
The reaction is : K2CrO4(s) + H2O(l) → K2CrO4(aq) 2 K2CrO4(aq) + H2SO4(aq) ↔ K2Cr2O7(aq) + H2O(l) + K2SO4(aq)

6. Conclusion * When the colour of a solution is more visible, the higher the concentration is. The relationship between these two factor is proportional for each other. * From our experiment, the quantitative concentration of the unknown sample was 0.0016 M

7. Reference http://faculty.ccri.edu/aahughes/GenChemII/Lab%20Experiments/Spectroscopy_Beer's_Law.pdf 8. MSDS