Chapter 15: Basic Separation Techniques

Usually during a chemical reaction ee. when products are obtained they are mixed is some amount of reactant and side products, such a product is called crude product. As the crude product is impure therefore crystallization must be carried out to purify it.

Filter paper is folded in accordion shape to get the fluted filter paper which has alternative elevations and depressions. Rate iS of filtration through conical funnel considerably increased using fluted filter paper.

Gooch crucible Sintered glass crucible It is made of It is made up of glass with porcelain with a porous glass disc sealed into the perforated bottom. bottom. Pores in bottom are No such preparation is needed. covered with paper pulp, filter paper Cu2+ to its size or asbestos mat. Convenient to use as for Useful no preparation precipitate need to needed. be ignited at high temperature.

See Q4. from theory

(i) Gooch crucible is useful in separating mixtures need to be ignited at high temperature. (ii) If its perforations are covered with asbestos mat, it may be used to filter solutions that react with paper e.g. concentrated Hcl and KMnO4 solutions.

See Q3. from theory. Purity of product

petroleum, a fractionating tower is used. Different fractions are obtained at different sites along the column depending on their boiling points. The fraction with lowest boiling point is collected at the top of tower.

The stationary phase may be a solid or a liquid supported as a thin film on the surface of an inert solid. Water entrapped in cellulose fibers act as stationary phase

If the components of mixtures have a comparable attraction for stationary phase the will travels equal distances along the chromatographic paper and appear as a single dot and will not be separated. 1S

Developing means immersing the paper in mobile phase. Moving the mobile phase over the stationary phase due to capillary action, drying the paper and identifying the compounds.

Chromatography is based on the principle that distance travelled by components of mixture depends on the distribution between stationary and mobile phase.

(i) Water has high polarity comparable to that of cellulose fibers. (i) Usually the focus of chromatography is organic compounds which are usually insoluble in water.

were Methods of analysis

Paper convenient way of checking if a substance formed in a chemical reaction is pure or impure using a suitable solvent in which the substance dissolves. A pure substance produces one spot on the chromatogram while an impure substance produces more than one spot.

Glucosazone is a yellow colored crystal its purity can be checked by (i) Chromatography: Only one spot will be produced by pure glucosazone (ii) Melting point: If sample has a sharp and fixed melting point of 204°C than it pure. if it gives any other temperatures or range of temperatures it is an impure sample

A complete quantitative determination generally consists of four major steps. • Obtaining a sample for analysis • Separation of the desired constitüent • Measurement, and calculation of results • Drawing conclusion from the analysis.

The components of a mixture can. be separated by any of the following physical methods. • Filtration • Crystallization • Simple distillation • Fractional distillation • Paper

Solute: The substance that is present in lesser amount in a solution is called solute. Example: Salt in solution is solute. Solvent: The substance that is present in a larger amount in a solution is called solvent. Example: In salt solution, water is called solvent. filtrate and

Separation techniques are methods used to separate different components of a mixture. They work on differences in physical properties such as boiling point, density, or solubility These techniques help in obtaining pure substances. Examples: Filtration, distillation, and chromatography etc Filtration filtration to

The process that is used to separate one of the components of a two-component heterogeneous mixture from a solution is called filtration. Following are the methods to increase rate of filtration. • Using fluted filter paper • Using suction filtration

Add water to dissolve the salt. remove the sand. Filter Evaporate the water from the salt solution. Pure salt crystals are obtained.

If the perforations of gooch crucible are covered with asbestos mat, it may be used to filter solutions that react with paper e.g. concentrated HCl and KMnO4 solutions.

Quick filtration can be done by placing such crucible in a suction filtering apparatus. It is useful for the filtration of precipitates, which need to be ignited at high temperature. If its perforations are covered with asbestos mat, it may be used to filter solutions that react with paper e.g. concentrated HCl and KMn04 solutions.

Filter papers are available in a variety of porosites (pore sizes). Which pore size is to be used, depends upon the size of particles in the precipitate.

Whatmann's filter paper which are used in paper chromatography are made cotton cellulose. from specially selected Whatmann's filter paper No. 1 is used for and it has medium routine applications retention and medium flow rate. Its pore size is 11 um

Sometimes during the preparation of a crude substance, the coloring matter or resinous products affect the appearance of product. Such impurities are conveniently removed by boiling the substance in the solvent with the sufficient quantity of finely powdered animal charcoal and then filtering the hot solution. The colored impurities are adsorbed by animal charcoal and the pure decolorized substance crystallizes out from the filtrate on cooling

Crystallization is the process forming pure solid crystals from a solution. A hot saturated solution is cooled to allow crystals to form. It gives more pure solids than evaporation. It is used to purify sugar, salt, and copper sulfate.

If the solvent is inflammable, then precaution should be taken while heating the solution so that it does not catch fire. In such cases, water bath is used for heating purpose.

Vacuum desiccator is temperatures sensitive crystals. In this process the crystals are spread over a watch glass and kept in a vacuum desiccator for several hours. The drying agents used in a desiccator are CaCl2, Silica gel Phosphorus pentoxide

During crystallization, sometimes the crystals start to appear during the process of filtration. This result in choking the filter paper or the runnel. To avoid this a hot water funnel may be used. Distillation process.

Petroleum in natural form is a mixture of many compounds which are commonly used as fuels. Examples of such fuels are petrol, diesel, kerosene oil and furnace oil. These components have boiling points not very different from one another These components are separated as fractions a by fractional distillation using fractionating or distillation column.

It produces pure nitrogen, oxygen, and argon. Liquid air is fractionally distilled at low temperature. Nitrogen boils off first due to lower boiling point. Oxygen and argon are collected afterwards.

It has a fractionating column with condensation. surfaces repeated This allows better separation of liquids with close boiling points. It fractions. produces purer It is used in petroleum and air separation.

Evaporation removes solvent and leaves behind solute. Distillation recovers both solvent and solute. • is simpler but less pure. Evaporation Distillation is more precise and controlled.

Thermometer reading 100°C Water distils 78°C Ethanol distils time When a mixture of ethyl alcohol and water is heated first ethyl alcohol will be distilled over because its boiling point is 78°C less than that of water whose boiling point is 100°C. As long as the alcohol is being the temperature of the distilled over, thermometer will remain at 78°C.

Distillation separates liquids based on differences in boiling points. The mixture is heated until one component boils and vaporizes. The vapor is then condensed back into liquid form. It is used to get pure water from seawater.

Petroleum is separated by fractional In distillation towers. large It is heated and vapors rise through the column. Fractions condense at different heights based on boiling point. Products include petrol, diesel, kerosene, and bitumen

visualizing the colorless chromatogram is to see it under the light of a UV. lamp. The spots look colored under UV light. Alternatively, a locating agent like ninhydrin can be used to locale the spots. A locating agent is generally a chemical that reacts with the colorless substances like amino acids to are visible for give colored products that inspection. use the

It identifies substances in crime evidence. Ink from documents can be analysed. Blood and drug samples can be tested. It helps in criminal investigations.

It is the solvent that moves up the paper. it It carries the mixture along with Components travel at different rates. This causes separation of the mixture.

It is the paper on which the mixture is placed It holds substances based on adsorption. Different substances stick differently to the paper. This helps in their separation.

The stationary phase is the filter paper. The mobile phase is the solvent used. Substances travel at different speeds based on solubility. This results in separation of components. value in is Rr

Rf is the ratio of distance moved by the substance to distance moved by the solvent front. It is always less than 1. It helps identify unknown substances. Different compounds have different Rf values. of

Chromatography separates substances based on solubility and adsorption. Paper chromatography uses paper as the stationary phase. The solvent carries different substances at different rates. It is used to separate pigments in ink.

It is the ratio of distance travelled by a component from the original to distance travelled by solvent from the original spot. R,.= Distance travelled by a component from theoriginal spot Distance travelled by solvent from the originalspot R, (A) = R, (B) = Z Z Z B mixture A Chromatogram DESCRIPTIVE QUESTIONS (EXERCISE)

Separation is needed to remove unwanted materials from useful substances. It helps in purifying chemicals for industrial and laboratory use. It is important for safety, health, and quality control.

Air is cooled until it liquefies. Fractional distillation is used at very low temperatures. Nitrogen boils off first, followed by oxygen and argon. It is used for industrial gases supply. paper chromatography? Give its three practical life applications. Ans. See Q5. from theory.