NCERT Solutions for Class 12 Science Chemistry Chapter 1 – The Solid State
Explore comprehensive NCERT solutions for Class 12 Science Chemistry Chapter 1 – The Solid State, complete with clear step-by-step explanations. Widely favored among Chemistry students in Class 12 Science, these solutions for The Solid State serve as valuable resources for efficiently completing homework assignments and preparing for exams. Free access to all questions and answers from Chapter 1 of the NCERT Book for Class 12 Science Chemistry is provided here, ensuring a convenient and effective study experience. Page No 4: Question 1.1: Why are solids rigid? ANSWER: The intermolecular forces of attraction that are present in solids are very strong. The constituent particles of solids cannot move from their positions i.e., they have fixed positions. However, they can oscillate about their mean positions. This is the reason solids are rigid. Page No 4: Question 1.2: Why do solids have a definite volume? ANSWER: The intermolecular forces of attraction that are present in solids are very strong. The constituent particles of solids have fixed positions i.e., they are rigid. Hence, solids have a definite volume. Page No 4: Question 1.3: Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid, teflon, potassium nitrate, cellophane, polyvinyl chloride, fibre glass, copper. ANSWER: Amorphous solids Polyurethane, teflon, cellophane, polyvinyl chloride, fibre glass Crystalline solids Naphthalene, benzoic acid, potassium nitrate, copper Page No 4: Question 1.4: Why is glass considered a super cooled liquid? ANSWER: Similar to liquids, glass has a tendency to flow, though very slowly. Therefore, glass is considered as a super cooled liquid. This is the reason that glass windows and doors are slightly thicker at the bottom than at the top. Page No 4: Question 1.5: Refractive index of a solid is observed to have the same value along all directions. Comment on the nature of this solid. Would it show cleavage property? ANSWER: An isotropic solid has the same value of physical properties when measured along different directions. Therefore, the given solid, having the same value of refractive index along all directions, is isotropic in nature. Hence, the solid is an amorphous solid. When an amorphous solid is cut with a sharp edged tool, it cuts into two pieces with irregular surfaces. Page No 6: Question 1.6: Classify the following solids in different categories based on the nature of intermolecular forces operating in them: Potassium sulphate, tin, benzene, urea, ammonia, water, zinc sulphide, graphite, rubidium, argon, silicon carbide. ANSWER: Potassium sulphate → Ionic solid Tin → Metallic solid Benzene → Molecular (non-polar) solid Urea → Polar molecular solid Ammonia → Polar molecular solid Water → Hydrogen bonded molecular solid Zinc sulphide → Ionic solid Graphite → Covalent or network solid Rubidium → Metallic solid Argon → Non-polar molecular solid Silicon carbide → Covalent or network solid Page No 6: Question 1.7: Solid A is a very hard electrical insulator in solid as well as in molten state and melts at extremely high temperature. What type of solid is it? ANSWER: The given properties are the properties of a covalent or network solid. Therefore, the given solid is a covalent or network solid. Examples of such solids include diamond (C) and quartz (SiO2). Page No 6: Question 1.8: Ionic solids conduct electricity in molten state but not in solid state. Explain. ANSWER: In ionic compounds, electricity is conducted by ions. In solid state, ions are held together by strong electrostatic forces and are not free to move about within the solid. Hence, ionic solids do not conduct electricity in solid state. However, in molten state or in solution form, the ions are free to move and can conduct electricity. Page No 6: Question 1.9: What type of solids are electrical conductors, malleable and ductile? ANSWER: Metallic solids are electrical conductors, malleable, and ductile. Page No 12: Question 1.10: Give the significance of a ‘lattice point’. ANSWER: The significance of a lattice point is that each lattice point represents one constituent particle of a solid which may be an atom, a molecule (group of atom), or an ion. Page No 12: Question 1.11: Name the parameters that characterize a unit cell. ANSWER: The six parameters that characterise a unit cell are as follows. (i) Its dimensions along the three edges, a, b, and c These edges may or may not be equal. (ii) Angles between the edges These are the angle ∝ (between edges b and c), β (between edges a and c), and γ (between edges a and b). Page No 12: Question 1.12: Distinguish between (i)Hexagonal and monoclinic unit cells (ii) Face-centred and end-centred unit cells. ANSWER: (i) Hexagonal unit cell For a hexagonal unit cell, Monoclinic unit cell For a monoclinic cell, (ii) Face-centred unit cell In a face-centred unit cell, the constituent particles are present at the corners and one at the centre of each face. End-centred unit cell An end-centred unit cell contains particles at the corners and one at the centre of any two opposite faces. Page No 12: Question 1.13: Explain how much portion of an atom located at (i) corner and (ii) body-centre of a cubic unit cell is part of its neighbouring unit cell. ANSWER: (i)An atom located at the corner of a cubic unit cell is shared by eight adjacent unit cells. Therefore, portion of the atom is shared by one unit cell. (ii)An atom located at the body centre of a cubic unit cell is not shared by its neighbouring unit cell. Therefore, the atom belongs only to the unit cell in which it is present i.e., its contribution to the unit cell is 1. Page No 21: Question 1.14: What is the two dimensional coordination number of a molecule in square close packed layer? ANSWER: In square close-packed layer, a molecule is in contact with four of its neighbours. Therefore, the two-dimensional coordination number of a molecule in square close-packed layer is 4. Page No 21: Question 1.15: A compound forms hexagonal close-packed structure. What is the total number of voids in 0.5 mol of it? How many of these are tetrahedral voids? ANSWER: Number of close-packed particles = 0.5 × 6.022 × 1023 = 3.011 × 1023 Therefore, number of octahedral voids = 3.011 × 1023 And, number of tetrahedral voids = 2 × 3.011 × 1023 = 6.022 ×1023 Therefore, total number of voids = 3.011 × 1023 + 6.022 × 1023 = 9.033 × 1023 Page No 22: Question 1.16: A compound is formed by two elements M and N. The element N forms ccp and atoms of M occupy 1/3rd of tetrahedral voids. What is the …
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