Please provide very short explinations for the concepts. Melting point analysis:
ID: 1060538 • Letter: P
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Please provide very short explinations for the concepts. Melting point analysis: Describe the effect of impurity on the melting points of compounds. Recrystallization: Explain why is the solubility of a compound important in the recrystallization process. Extraction: Be able to calculate partition coefficient and the amount of sample extracted into an organic layer using partition coefficient. Polarimetry: Be able to calculate specific rotation. Distillation: Be able to describe and explain boiling point composition curve and the formation of an azeotrope. Synthesis: Be able to calculate % yield. Synthesis: Describe the use of reflux in organic synthesis. Be able to describe what it is and why we use it. Thin layer chromatography Be able to explain how it can be used to identify the presence of a desired product. Column Chromatography: Be able to explain the effect of solubility in separation of mixtures.Explanation / Answer
Meiting point analysis: Melting point is an important physical property of a solid compound which gives the temperature at which a soild becoms a liquid. Every pure soild compound has a characteristic melting point. A pure crystalline usually have a sharp meliting point. If soluble impurity is present in a compound, it will result in depression of meliting point and in that case it can melt over a wide range of temperature. Organic compounds have relatively lower melting point (usually < 200oC) than inorganic compounds (usually >200oC).
Recrystallization: Recrystallization is process of purification of compounds where impure compounds can be dissolved in minimum amount of apporiate solvent (or mixture of solvents) by heating and then cooling the saturated solution so that pure crystals of the desired compound come out of the solution leaving the impurities in the solvent. Before recystallization, the solubilty of the pure compound has to be throughly studied (usually by solubilty test for unknown compounds and from the structural features of known compound) so that one can separate slouble or inslouble impurities from a compound b choosing appropirate solvent (or combination of solvents).
Extraction: Extraction is a separation technique which is used to isolate one or more components from a mixture which is based on the fact that if a substance is insoluble to some extent in two immiscible liquids, it can be transferred from one liquid to the other by shaking it together with the two liquids. When two immiscible solvents are shaken together, the solute distributes itself between them in a ratio roughly proportional to its solubility in each. The ratio of the concentration of the solute in each solvent at equilibrium is a constant called the distribution ratio(d) or partition coefficient (Kd).
Polarimetry: It is a technique for measuring the optical activity exhibited by inorganic and organic compounds by using an instrument called polarimeter. A compound is considered to be optically active if it can rotate plane polarized when passing through it. The amount of optical rotation depends on the molecular structure and concentration of chiral molecules in the substance. Each optically active substance has its own specific rotation Specific rotation, [], is a fundamental property of chiral substances that is expressed as the angle to which the material causes polarized light to rotate at a particular temperature, wavelength, and concentration which is given by the following relation
[]T= T/c.l
where, [] = specific rotation, T = temperature,
= wavelength, = optical rotation,
c = concentration in g/100ml, l = optical path length in dm.
Optical rotation () can be detected by polarimeter.
Distillation: An azeotrope is a constant boiling mixture of two or more liquids whose proportions cannot be altered by simple distillation. For example, an ethanol-water mixture yields an azeotropic solution containing approximately 95% by volume of ethanol. Azeotropic distillation is a technique that is used to break an azeotrope in distillation by adding another component such as addition of benzene to water and ethanol.
Synthesis: A synthesis is a chemical reaction in which two or more simple substances combine to form a more complex product. The reactants may be elements or compounds. The product is always a compound. The yield of a reaction, is the amount of product obtained in a reaction.T
% yield= (Actual yield/theoretical yield) x 100
Reflux in organic synthesis: Reflux involves heating of a reaction mixture for a specific amount of time, while continually cooling the vapour produced back into liquid form, using a condenser. The vapours produced above the reaction continually undergo condensation, returning to the flask as a condensate. Reflux allows heating for a long without losing the volatile reactants and products. It helps speed up chemical reactions without having it evaporate or explode. By cooling the vapors before it escape the system, the apparatus is able to not only maintain a constant volume of solution but also induce reactions.
Thin layer chromatography(or TLC): In TLC, a solid phase, the adsorbent, is coated onto a solid support (thin sheet of glass, plastic, and aluminum ) as a thin layer (about 0.25 mm thick). In many cases, a small amount of a binder such as plaster of Paris is mixed with the absorbent to facilitate the coating.
It is used for separation of all classes of natural products and is established as an analytical tool in modern pharmacopoeias.E.g. Acids, alcohols, glycols, alkaloids, amines, macromolecules like amino acids, proteins and peptides, and antibiotics
It is used - for checking the purity of samples
- as a purification process
- examination of reaction
- for identifying organic compounds
TLC is extensively used for in-process checking of a progress of reaction, checking of distillation fractions.
Column chromatography: The principle of column chromatography is that organic compounds can separated due to differences in their partitioning behavior between the mobile liquid phase and the solid stationary phase in the column. Column chromatography involves use of a glass or plastic column that is filled with the solid stationary phase (such as silica or alumina). The sample to be purified by column chromatograpghy, is dissolved in minimum amount of solvent and loaded on the column. The separation is carried out by passing solvent through the column at atmospheric pressure. The solvents elutes different components present in the sample based on adsorption or partition. The polarity of the eluant is increased stepwise and it is collected as small fractions. Each small fractions are concentrated and checked by TLC for purity. The apparatus used is simple but the technique involves use of large amount of solvent.
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