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Class 11-- chemistry Chapter 2: EXPERIMENTAL TECHNIQUES IN CHEMISTRY

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    Class 11-- chemistry Chapter 2: EXPERIMENTAL TECHNIQUES IN CHEMISTRY

    Class 11-- chemistry
    Chapter 2: EXPERIMENTAL TECHNIQUES IN CHEMISTRY

    Q1 Give short answers


    A. what is Gooch crucible?

    Ans. Gooch Crucible is a simple crucible with small pores at the bottom. It is used as a support for asbestos or plastic or Paris. Slurry is produced by mixing asbestos with concentrated HCl or by mixing plaster of Paris with water. The slurry is poured into the crucible. As a result wet bedding is produced on the porous bottom of the crucible. The crucible is dried in an oven. For quick and effective filtration the flask is connected with a vacuum pump and the crucible is fixed in a rubber holder. The rubber holder is called Gooch funnel.

    B. list the purification methods used for purification of organnic substances.

    Ans. different purification methods used for the purification of organic compounds are recrystallization, sublimation, chromatographic techniques, etc.

    C. how you will define a crystal??

    Ans. crystal is a piece of pure substance which has definite natural geometrical shape. Particles like atoms, ions or molecules are arranged in a regular pattern. The same pattern is repeated throughout. Unit cell is the smallest repeating unit of a crystal which represents all properties of a crystal. A unit cell upon repetition in three dimension produces the crystalline lattice or crystal.

    D. what is partition chromatography?

    Ans. the type of chromatography in which separation is based mainly on differences between the solubility of the sample components in the stationary phase, or on differences between the solubility’s of the components in the mobile and stationary phases.

    E
    . what do you mean by Rf?
    Ans. retention factor or ratio of fronts (Rf value) each component is calculated by the following formula:
    Rf = distance covered by solute (cm) / distance covered by the solvent (cm)
    Retention factor is the ratio of distance traveled by a component to the distance traveled by solvent front. Retention factor also called ratio of fronts is a quantitative indication of how far a particular compound travels in a particular solvent. the Rf value is a good indicator of whether an unknown compound is close or same as Rf value of a known compound then the two compounds are most likely similar or identical. Rf values often depends on the temperature, solvent and type of paper used in the experiment.

    Question 6: how do you purify a solid organic compounds?

    Ans. solid organic compounds can be purified by re-crystallization technique. Impure organic compound is dissolved in a suitable solvent. Maximum quantity of the organic compound can be dissolved at higher temperatures. The hot solution is filtered for the removal of impurities. The filtrate is cooled to crystallize out the excess organic compound. Crystals of the organic compound are then separated from the mother liquor by filtration.

    Question 7: how do you purify a liquid organic compound?

    Ans. a liquid organic compound can be purified by distillation. "Distillation is a process in which two or more miscible liquids are separated due to the difference in their boiling points".
    The mixture having dissolved impurities is heated and the vapors formed are condensed in a condenser. The condensate is relatively pure as compared with the mixture. Organic liquid can be purified further by re-distillation, fractional distillation or systematic fractionation. Application of the distillation techniques depend on the difference of the volatilities in the dissolved substances.


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