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Identification of Unknown Organic Compound by Melting Point Essay

The main objective of this lab is to identify the given unknown organic compounds with various methods. Identification of an unknown compound is important to perform through the process of melting point (M.P), boiling point (B.P) and Infrared spectroscopy (I.R). Index of Hydrogen deficiency (IHD) and elemental analysis makes an experiment more efficient in determination of unknown compound. The color, odor, melting point and boiling point determines the physical state and properties of a compound. It also determines its volatility in respect to temperature.

The functional group of a compound can be determined on a basis of a spectra formed by a NICOLET iS5 FT infrared spectrometer. The IR sample of a liquid is obtained on a pure liquid called a neat sample whereas solid sample was obtained with the help of an Attenuated total reflectance IR spectra. The index of hydrogen deficiency determines the saturation of a compound (double bonds, triple bonds or rings).

Elemental analysis helps in determining the molecular formula of a compound. The boiling point of an unknown liquid sample was determined with a mini scale technique. It consists of a heating mantle, a long narrow Pyrex text tube and heating stone. The thermometer is placed 2 cm above the level of liquid to get an accurate readings. Melting point of a sample was determined by electric melting point apparatus.

The melting point of the crystalline solid is determined by heating the packed capillary tube until the solid melts. The accurate measure of melting point is obtained by heating at the rate of 1-2oC/min to ensure the heat is transferred to the sample rate as the temperature increases and the mercury in the thermometer and the sample in capillary tube are in thermal equilibrium. The boiling point and melting point of unknown compounds helps to confirm the hypothetical structure from unknown to known compound.

Experimental Procedure
Two unknown organic compound was given one solid and other liquid. A melting point of a solid was determined with the help of an electric melting
apparatus. A sample of crystal solid was taken in a bulb of capillary and inserted inside the melting apparatus. The temperature difference of 1-20C/min was maintained. Two trails of initial and final temperature were taken. The initial temperature was noted when the first tiny drop of liquid appears and final temperature was noted when all crystal was completely melted.

Boiling point was performed with the help of mini scale technique. 0.5-1.0 ml of liquid was taken in a clean test tube, clamped and held on top of a heating mantle. A thermometer was placed just 2 cm above the liquid with another clamp. Two trails of reading were noted. Initial temperature was taken when the first bubble came out whereas final temperature was taken when there was a vigorous movement.

Both samples of solid and liquid were then scanned to a NICOLET iS5 FTIR operating spectrometer. The surface was carefully cleaned with the drops of acetone to a Q-tip and gently wiped the ATR crystal and pressure tip to clean. The spectrum of background was collected first to ensure the machine was working fine and then the sample spectra was collected and printed. Data Acquisition

The unknown solid compound obtained from the elemental analysis and composition was C7H6O2. According to the calculation of IHD of 5 (i.e. 4 double bonds and 1 ring) and the functional groups obtained from the spectra was similar to the hypothesis structure, benzoic acid. The experimental value of melting point of benzoic acid was 116.7 and was almost close to the value found from reference book which was 122.41. The error might be the impurities from container.

The liquid compound obtained from similar processes had an empirical value C5H10O. The IHD for the compound came 1 which might be 1ring or double bond. Since, the sample had a strong smell, and the spectrum was similar to the hypothesis structure, 2- Pentanone. Experimentally, the boiling point of Pentanone or acetone was 950C. But from
reference it was 1010C. The error in boiling point of experiment might be due to the impurities found in test tube.

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