Extraction in chemistry is a separation process consisting in the separation of a substance from a matrix. Liquid-liquid extraction Liquid–liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent. It is an extraction of a substance from one liquid phase into another liquid phase. Liquid– liquid extraction is a basic technique in chemical laboratories, where it is performed using a separatory funnel. This type of process is commonly performed after a chemical reaction as part of the work-up. The term partitioning is commonly used to refer to the underlying chemical and physical processes involved in liquid–liquid extraction but may be fully synonymous. The term solvent extraction can also refer to the separation of a substance from a mixture by preferentially dissolving that substance in a suitable solvent. In that case, a soluble compound is separated from an insoluble compound or a complex matrix. Solvent extraction is used in nuclear reprocessing, ore processing, the production of fine organic compounds, the processing of perfumes, the production of vegetable oils and biodiesel, and other industries. Liquid–liquid extraction is possible in non-aqueous systems: In a system consisting of a molten metal in contact with molten salts, metals can be extracted from one phase to the other. This is related to a mercury electrode where a metal can be reduced, the metal will often then dissolve in the mercury to form an amalgam that modifies its electrochemistry greatly. For example, it is possible for sodium cations to be reduced at a mercury cathode to form sodium amalgam, while at an inert electrode (such as platinum) the sodium cations are not reduced. Instead, water is reduced to hydrogen. A detergent or fine solid can be used to stabilize an emulsion, or third phase. Chemical Extraction Chemical extraction is a process that separates contaminants from soils and thereby reduces the volume of the hazardous waste that must be treated. The process differs from soil washing, which generally uses water, and varies with contaminant and soil type. Often, physical separation is used before chemical extraction on the assumption that smaller particles contain most of the contamination. The two major chemical extraction processes are described below Acid Extraction Acid extraction uses hydrochloric acid to extract heavy metal contaminants from soils. In this process, hydrochloric acid is mixed with soil in a closed extraction unit. The residence time in the extraction unit generally ranges between 10 and 40 minutes. When extraction is complete, the soils are rinsed with water to remove entrained acid and metals. The extraction solution and rinse waters are regenerated using precipitation. The heavy metals are potentially suitable for recovery. The clean soils are dewatered and mixed with lime and fertilizer to neutralize any residual acid. Solid-liquid extraction allows soluble components to be removed from solids using a solvent. Applications of this unit operation include obtaining oil from oil seeds or leaching of metal salts from ores. An everyday example is the preparation of coffee. Here, water (solvent) is used to remove the coffee flavours (transition component) from the coffee powder (extraction material, consisting of solid carrier phase and transition component). Ideally, this results in drinkable coffee (solvent with dissolved flavours), with the completely depleted coffee grounds (solid carrier phase) remaining in the coffee filter. In reality, the solid carrier phase will still contain some transition component after completion of the extraction. In addition, some of the solvent will still be adsorptively bonded to the solid carrier phase. To achieve the fastest and most complete solid extraction possible, the solvent must be provided with large exchange surfaces and short diffusion paths. This can be done by pulverising the solid to be extracted. However, an excessively small grain size can cause agglutination and make it more difficult for the solvent to permeate. In the simplest form of this unit operation, the extraction material and the solvent are mixed well. The solvent and the dissolved transition component are then removed and regenerated. The extraction material can also take the form of a fixed bed with the solvent flowing through it. In a further form of the application, the extraction material is led through the solvent. The solvent is normally regenerated using evaporation / distillation. The solvent is evaporated and a concentrated extract solution is left behind as the product. The solvent is condensed and can then be reused. LIQUID-LIQUID EXTRACTION Liquid-liquid extraction involves using a liquid solvent to remove a liquid component from a liquid mixture. The component dissolves preferably in the solvent. Applications of this process include removal of vitamins from aqueous solutions and aromatic compounds from crude oil fractions. In the simplest case, three components are involved: Transition component A Solvent B Carrier liquid C The transition component A is combined with the carrier liquid C as the initial mixture (feed). If the initial mixture and the solvent B are mixed together, the transition component A is transferred into the solvent B. The requirement for this is that the solubility of the transition component A in the solvent B is higher than in the carrier liquid C. In turn, the carrier liquid C should be almost insoluble in the solvent B. The example illustration assumes an ideal situation in which the transition component A is completely taken up by the solvent. In reality, residual transition component always remains in the carrier liquid. In addition, complete insolubility of the carrier liquid in the solvent is assumed. In practice, parts of one substance will always be found in the other. This means that the actual separation process results in two phases after settling: Extract phase (mainly A and B, with residue of C) Raffinate phase (mainly C, with residue of A and B) To obtain the purest possible transition component, the extraction is normally followed by a separating stage that takes the form of rectification, in which the solvent is separated from the transition component. The solvent can be recirculated and is then available for the extraction again. Extractions of certain solids can be performed by utilizing the different chemical properties of various solvents. The initial solvent used in the extraction of caffeine is water. Caffeine is sparingly soluble in water at ambient temperatures but highly soluble in water at 100oC. The boiling of coffee beans and tea leaves dissolves caffeine and other materials to produce coffee and tea beverages. We will take advantage of the solubility properties of caffeine in water to create an aqueous solution of caffeine at room temperature. First, the caffeine will be dissolved from tea leaves by boiling them in water. The solution will be allowed to cool to room temperature. Although the solubility of caffeine is low at room temperature; the caffeine will remain in solution and must be extracted with another solvent. The solubility of caffeine in chloroform is quite high at room temperature. Therefore, when chloroform is added to the aqueous caffeine solution, the caffeine is transferred to the chloroform. The chloroform- caffeine mixture can then be separated by utilizing the different densities of chloroform and water. Because chloroform is much denser than water and insoluble in it, the chloroform will form a layer under the water and can be separated from it. Residual water is removed by filtering the chloroform through reverse-phase filter paper, which allows nonpolar solvents such as chloroform to filter through the paper while polar solvents such as water are retained. The caffeine is then crystallized on a watch glass.
Chloroform is aprotic, not very polar solvent. - so it wouldn't dissolve the water soluble junk in the coffee, but only the alkaloids. It has low boiling point, making it easy to remove from the extract. And it's not flammable, making the extraction safe (instead of hexane, or ether :) Sodium sulfate serves as a drying agent in most reactions to absorb all excess water from the sultion. What is the role of sodium carbonate in the isolation of caffeine? to prevent the tannins from joining the caffeine during extraction. this saves time in the isolation of caffeine Discuss briefly the role of the ff. in the isolation of caffeine. a. sodium carbonate. b. sodium sulfate.? I am not sure of your question but a way that is done typically is to steep the tea in water, take the water and add the sodium carbonate (deprotanates the caffeine so the caffeine will transfer to an organic layer in extraction, the protonated form is water soluble). The organic layer (typically CH2Cl2) is then dried with Sodium sulfate. The sodium sulfate serves to dry any remaining water that may accidently be in the organic layer. Sodium sulfate, magnesium sulfate these are called drying agents. Not sure if this is what you want but hope it helps. What is the role of sodium carbonate in the extraction of caffeine in tea leaves? The sodium carbonate acts as a base - you could use sodium hydroxide instead. When you boil tea leaves tannins dissolve in the water as well as the caffeine. If you do not use a base the tannins will also be extracted into the solvent (i.e. methylene chloride) used in the subsequent extraction . The base converts the tannins into their sodium salts - being ionic these salts are not soluble in solvents like methylene chloride so remain in the aqueous layer during extraction. This allows purer caffeine to be extracted. Extraction: Isolation of Caffeine from Tea 1. Solvents for extraction experiments should have desirable properties. Here is a list. For both liquid-liquid and liquid-solid extractions, the solvent should have a relatively low boiling point for easy removal by evaporation; and it should not react with any of the substances present (unless you are performing an acid-base extraction). In liquid-liquid extraction, the compound being extracted should have a favorable distribution coefficient in the extracting solvent; in liquid-solid extraction, the solvent must dissolve the compound being extracted. 2. The caffeine extraction procedure has several features that may seem pointless at first. Here are some explanations. Caffeine is an alkaloid, an organic base. Sodium carbonate also a base, and it is added in the first extraction to make sure that the caffeine remains in the free base form (that is, to prevent it from reacting with any acids that may be present). An emulsion is a suspension of one liquid as droplets in another (the two liquids must be insoluble in one another). Emulsions are almost always undesirable. To avoid them, you can shake mixtures of insoluble liquids gently and add salt to aqueous layers. You will use a centrifuge in this experiment break up emulsions once they form. The visualization technique used in the TLC portion of this experiment involves the use of ultraviolet (UV) light. The caffeine absorbs the UV light and gives off visible light. This phenomenon is called fluorescence. 3. The equation for calculating the percentage of caffeine in tea is as follows: amount of caffeine recovered percentage of caffeine = -------- x 100% weight of tea There are some systematic errors in this experiment as we perform it. For example, you do not weigh the tea, you weigh the tea bag, which has not only tea but also string and paper in its weight. When you squeeze the tea (liquid) out of the tea bag, some of the liquid (containing caffeine) remains behind in the wet bag. The distribution coefficient of caffeine between water and dichloromethane is not perfect; some caffeine will remain behind in the water. Dichloromethane evaporates rapidly, cooling the watch glass as it does; water can condense on the cool watch glass, influencing the weight of your final product. http://www.xula.edu/chemistry/organic/No… Caffeine can be extracted easily from tea bags. The procedure one would use to make a cup of tea, simply "steeping" the tea with very hot water for about 7 min, extracts most of the caffeine. There is no advantage to boiling the tea leaves with water for 20 min. Since caffeine is a white, slightly bitter, odorless, crystalline solid, it is obvious that water extracts more than just caffeine. When the brown aqueous solution is subsequently extracted with dichloromethane, primarily caffeine dissolves in the organic solvent, leaving the other substrates in the aqueous layer. Evaporation of the solvent leaves crude caffeine, which on sublimation yields a relatively pure product. When the concentrated tea solution is extracted with dichloromethane, emulsions can form very easily. There are substances in tea that cause small droplets of the organic layer to remain suspended in the aqueous layer. This emulsion formation results from vigorous shaking. To avoid this problem, it might seem that one could boil the tea leaves with dichloromethane first and then extract the caffeine from the dichloromethane solution with water. In fact, this does not work. Boiling 25 g of tea leaves with 50 mL of dichloromethane gives only 0.05 g of residue after evaporation of the solvent. Subsequent extractions give less material. Hot water causes thetea leaves to swell and is obviously a much more efficient extraction solvent. An attempt to sublime caffeine directly from tea leaves also was unsuccessful. emulsion, in physical chemistry, mixture of two or more liquids in which one is present as droplets, of microscopic or ultramicroscopic size, distributed throughout the other. Emulsions are formed from the component liquids either spontaneously or, more often, by mechanical means, such as agitation, provided that the liquids that are mixed have no (or a very limited) mutual solubility. Emulsions are stabilized by agents that form films at the surface of the droplets (e.g., soap molecules) or that impart to them a mechanical stability (e.g., colloidal carbon or bentonite). Unstable emulsions eventually separate into two liquid layers. Stable emulsions can be destroyed by inactivating or destroying the emulsifying agent—e.g., by adding appropriate third substances or also by freezing or heating. Some familiar emulsions are milk (a dispersion of fat droplets in an aqueous solution) and butter (a dispersion of droplets of an aqueous solution in fat). Emulsions are important in many fields—e.g., in the dyeing and tanning industries, in the manufacture of synthetic rubber and plastics, in the preparation of cosmetics such as shampoos, and of salves and therapeutic products. The term emulsion is often applied to mixed systems that should better be characterized as solutions, suspensions, or gels. For example, the so-called photographic emulsion is actually a gelatin gel in which tiny crystals (e.g., of silver bromide) are dispersed. Why does emulsion form during extractions? How is the formation of an emulsion is minimized?? If you preform an organic extraction from a solution and the alkali goo is final product, you may convert it into a salt by adding an acid into the solution before you evaporate the solvent. It's the simple acid-alkali reaction. Remember to balance the proportions and to check the pH of the solution before evaporation.