Chapter 1 The Solid State Solutions
Question - 1 : - Ionic solids, which have anionic vacancies dueto metal excess defect, develop colour. Explain with the help of a suitableexample.
Answer - 1 : -
The colour develops because of the presenceof electrons in the anionic sites. These electrons absorb energy from thevisible part of radiation and get excited.
For example, when crystals of NaCl are heated inan atmosphere of sodium vapours, the sodium atoms get deposited on the surfaceof the crystal and the chloride ions from the crystal diffuse to the surface toform NaCl with the deposited Na atoms. During this process, the Na atoms on thesurface lose electrons to form Na+ ions and the releasedelectrons diffuse into the crystal to occupy the vacant anionic sites. Theseelectrons get excited by absorbing energy from the visible light and impartyellow colour to the crystals.
Question - 2 : - Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid, Teflon, potassium nitrate, cellophane, polyvinyl chloride, fibreglass, copper
Answer - 2 : - Crystalline solids: Benzoic acid, potassium nitrate, copper Amorphous solids: Polyurethane, Teflon, cellophane, polyvinyl chloride, fibreglass
Question - 3 : - Why are solids rigid?
Answer - 3 : - The constituent particles in solids have fixed positions and can oscillate about their mean positions. Hence, they are rigid.
Question - 4 : - Why do solids have definite volume.?
Answer - 4 : - Solids keep their volume because of rigidity in their structure. The interparticle forces are very strong. Moreover, the interparticle spaces are very few and small as well. As a result, their volumes cannot change by applying pressure.
Question - 5 : - Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid, Teflon, potassium nitrate, cellophane, polyvinyl chloride, fibreglass, copper
Answer - 5 : - Crystalline solids: Benzoic acid, potassium nitrate, copper Amorphous solids: Polyurethane, Teflon, cellophane, polyvinyl chloride, fibreglass
Question - 6 : - Why is glass considered a super cooled liquid?
Answer - 6 : -
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.
Question - 7 : - 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 - 7 : -
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.
Question - 8 : - Classify the following solids in different categories based on the nature of intermolecular forces operating in them:
Answer - 8 : -
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
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 - 9 : -
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).
Question - 10 : - Ionic solids conduct electricity in molten state but not in solid state. Explain.
Answer - 10 : -
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.