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What is empirical formula? Grade XII | Chemistry

1. What is empirical formula?

Ans: The empirical formula of a compound is the simplest formula, which indicates the relative number of atoms of each type of element present in a molecule of that compound or a substance. It indicates the whole number ratio of different kinds of atoms in the molecule, which can be obtained from the percentage composition of the given compound.

e.g. empirical formula of benzene (C6H6) is CH. Empirical formula of KCLO3. Empirical formula of Hydrogen Peroxide (H2O2) is HO.

2. What is metamerism?

Ans: Metamerism is a type of structural isomerism, which is due to the unequal distribution of C atoms on either side of the same functional group. The compound, which exhibits such pehnomena, is known as metamers. Therefore metamers have same molecular formula but they differ in-alkyl groups.

e.g. HC3-CH2-O-CH2-CH3→CH3-O-CH2-CH2-CH3

(ethoxy ethane)                       (methoxy Propane)

3. Explain any four methods for preventing rusting of iron.

Ans: The four methods for the prevention of rusting of iron can be explained as follows:

(a) Protective Coating: Iron can be prevented from rusting by coating the surface of iron with any one of the following coatings.

(i) by coating the iron surface with non-coroding metals like Ni, Cr, Zn etc.

(ii) by coating with oil, grease, paints, varnishes, enamels etc. on the metal surface,

(iii) by the deposition of a thin layer of oxide film or metallic film over the surface of iron eg. Fe3 O4 etc.

(b) Cathodic Protection: In this process, iron is connected with more electropositive metals like Mg, Zn, Al etc. During this process, iron becomes Cathode while more electropositive metals become anode and an electrochemical cell is established. The electropositive metals undergo Corrosion in preference to iron. Thus, iron is prevented from rusting. This process is known as Cathode Protection .

(c) Application of antirust solution (Corrosion inhibitor): In this process, iron is treated with antirust solution like Potassium chromate, conc. nitric acid, phosphoric acid which prevents the iron from corrosion.

(d) By galvanising iron: When iron is coated with a thin film of Zinc, it is prevented from corrosion. This provess is know as galvanisation.

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