Experimental techniques in chemistry

Analytical chemistry:

The branch of chemistry which gives a complete characterization of substance that is the qualitative and quantitative analysis of a substance

Qualitative analysis:

The type of analysis in which identification of elements in a compound is carried out for example detection of elements by the sodium fusion test and salt analysis and mixture analysis

 Quantitative analysis:

The type of analysis in which relative amounts of different elements are carried out for example volumetric analysis (titration)

The main steps in the quantitative analysis are involved

·        Obtaining a sample for analysis

·        Separation of the desired component

·        Measurement and calculation of the result

·        Drawing conclusion from the analysis

Filtration:

The separation of insoluble particles precipitate from the liquid by passing the mixture through a the filter medium is called filtration

Filter medium:

The porous medium which is used to separate insoluble solid particles from a solution or a mixture is called filter medium

Filtrate:

The liquid part of a solution that passed through the filter medium is called filtrate

Residue:

The insoluble particles which cannot pass through the filter medium is called Residue

Selection of a filter medium 

·        Nature of precipitate

·        Size of precipitate

                    Why fluted filter paper is used instead of normal filter paper

Fluted filter paper increase the rate of filtration because alternate elevations and depressions on a filter paper provides an increased area for filtration Hans it increases the rate of filtration

                  Differentiate between gooch crucible and sintered glass crucible

Gooch crucible:

Composition: it is made of porcelain having a perforated bottom which is covered with the paper pulp are filter paper are asbestos mat cut to its size. Filtration is useful for the filtration of the precipitate which needs to be ignited at heart temperature. If its perforation is covered with asbestos mad then it may be used to filter solution that reacts with paper

For example: concentrated hydrochloric acid and potassium permanganate solution

Sintered glass crucible: is made up of Glass having a porous glass disc sealed into bottom

Advantages:

It is convenient to use because no preposition is needed as with the crucible moreover the process is very e smooth

Crystallization:

Crystallization is the removal of solid from a solution by increasing its concentration above the saturated point in such a manner that the excess solid separate out in the form of crystals

                        Why there is a need to crystallize the crude product

 There is a need to crystallize the crude product for the purification

  Steps of crystallization

•           Choice of solvent

•           Preparation of saturated solution

•           Filtration

•           Cooling

•           Collecting of crystals

•           Drawing to the crystalline substance

•           Decolorizing of undesired colors

 

Write the steps for the choice of solvent in crystallization

 •           It should dissolve a large amount of a substance at its boiling point and only a small amount at                the room temperature

•           It should not react chemically with the solute

•           It should either not dissolve the imperative are the impurities should not crystallize from it along with the solute

•           On cooling it should deposit well-formed crystals of the pure compound

•           It should be inexpensive

•           It should be safe to use

•           It should be easily removable

Note: If none of the solvents is found suitable for crystallization a combination of two or more miscible solvents may be employed

           Give the name of drying agents used in the drying of crystallized substance

Drying agents:

•           Calcium chloride

•           Phosphorus pentoxide

•           Silica Gel

Decolorizing of undesirable color:

Sometimes during the preparation of crude substance that coloring matter are resonance product affect the appearance of the product and it may appear color Such color 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 impurities are absorbed by the animal charcoal and the pure decolorize substance crystallizes out from the filter on the cooling

             How color impurities are removed from crystallized substances

 Animal Charcoal is used to decolorize the undesirable color from crystallizing substances

 Sublimation:

A process in which a solid when heated vaporized directly without passing through the liquid phase and these vapors can be condensed from the solid again

For example Iodine, ammonium chloride, naphthalene, benzoic acid, and dry ice

                       Differentiate between sublimand and sublimate

Sublimand:

The substance whose sublimation is required or impure substance for sublimation is called sublimand

Sublimate:

The pure substance after sublimation is called sublimate

                              Define solvent extraction

Solvent extraction:

The technique in which a solute is separated from a solution by shaking it with an immiscible solvent in which the solute is more soluble is called solvent extraction

                               Define distribution law

Distribution law:

Solvent extraction is an equilibrium process and it is controlled by distribution law or partition La which is defined as

“A solute distributes itself between two immiscible liquids in a constant ratio of concentration irrespective of the amount of solute added”

                                     Define distribution coefficient K

 Distribution Coefficient k:

 The ratio of the concentration of solute in an organic solvent to the concentration of solute in an aqueous solution is called distribution Coefficient and it is represented by k

 Chromatography: 

A process that is used to separate the components of a mixture on the basis of their difference in a relative affinity with two faces that is stationary and the mobile phase is called chromatography

The word chromatography original from the Greek words Chroma toes which means color and graphene which means writing so chromatography means color writing

                                     Differentiate between the stationary phase and mobile phase

Stationary phase:

The stationary phase is a solid or liquid spotted as a thin film on the surface of an inert solid. This phase is in rest and the mobile phase flows over it. Component of a mixture with a small value of k mostly remains in this phase

 Example: Glass Silica or Alumina

 Mobile phase: 

The mobile phase may be liquid or a gas. It flows over the surface of a stationary phase. Component of a mixture with a great value of k mostly remains in this phase

Example: helium argon nitrogen and organic solvents

 

Distribution coefficient:

The distribution of components of a mixture between the two phases are governed by the distribution  coefficient is the ratio of the component in a mobile phase and a concentration of that component in a stationary phase

 A smaller value of k:

 The component of a mixture with a small value of k mostly remains in the stationary phase and the mobile phase flows over it

 The greater value of k:

The component with a the greater value of k largely remains dissolved in the mobile phase and pass over the stationary phase quickly

 Types of chromatography

•           Adsorption chromatography

•           Paper chromatography

Differentiate between adsorption chromatography and partition chromatography

Adsorption chromatography:

A type of chromatography in which the stationary phase is solid. In this type, a substance leaves the mobile Phase to become absorbed on the surface of the solid phase

For example a thin layer chromatography and column chromatography

Partition chromatography:

It is a type of chromatography in which the stationary phase is liquid in this type the a substance being separated are distributed throughout both the stationary and mobile phase

For example paper chromatography

Chromatogram: once the paper is dried the pattern on the paper is called a chromatogram

Retardation factor:

Each component has a specific retardation factor called Rf value this value is related to its distribution Coefficient and is given by

 “The ratio between the distance traveled by the component from the originals part and the distance traveled by the solvent from the original spot”

                         Write important uses of chromatography

 Uses of chromatography

 It is used for separation and purification

 It is used for checking the purity of components

 It is used in the qualitative and quantitative analysis

 It is used for the separation and identification of colored pigments

 It is used for the identification of amino acids

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