NCERT Chemistry Textbook Solutions for Class XII

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Chapter 1 The Solid State
Question 1.1 Define the term 'amorphous'. Give a few examples of amorphous solids. Answer Amorphous solids are the solids whose constituent particles are of irregular shapes and have short range order. These solids are isotropic in nature and melt over a range of temperature. Therefore, amorphous solids are sometimes called pseudo solids or super cooled liquids. They do not have definite heat of fusion. When cut with a sharp-edged tool, they cut into two pieces with irregular surfaces. Examples of amorphous solids include glass, rubber, and plastic.
Question 1.2 What makes a glass different from a solid such as quartz Under what conditions could quartz be converted into glass Answer The arrangement of the constituent particles makes glass different from quartz. In glass, the constituent particles have short range order, but in quartz, the constituent particles have both long range and short range orders. Quartz can be converted into glass by heating and then cooling it rapidly.
Question 1.3 Classify each of the following solids as ionic, metallic, molecular, network covalent or amorphous. i Tetra phosphorus decoxide P4O10 vii Graphite ii Ammonium phosphate NH4 3PO4 viii Brass iii SiC ix Rb iv I2 x LiBr v P4 xi Si Answer Ionic ii Ammonium phosphate NH4 3PO4, x LiBr Metallic viii Brass, ix Rb Molecular i Tetra phosphorus decoxide P4O10 , iv I2, v P4. Covalent network iii SiC, vii Graphite, xi Si Page 1 of 34
Amorphous vi Plastic
Question 1.4 i What is meant by the term 'coordination number' ii What is the coordination number of atoms a in a cubic close-packed structure b in a body-centred cubic structure Answer i The number of nearest neighbours of any constituent particle present in the crystal lattice is called its coordination number. ii The coordination number of atoms a in a cubic close-packed structure is 12, and b in a body-centred cubic structure is 8