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Question
Which of the following features are not shown by quartz glass?
(i) This is a crystalline solid.
(ii) Refractive index is same in all the directions.
(iii) This has definite heat of fusion.
(iv) This is also called super cooled liquid.
Solution
(i) This is a crystalline solid.
(iii) This has definite heat of fusion.
Explanation:
Quartz glass is an amorphous solid so it has not definite heat of fusion. This is due to short range order of molecule while quartz glass is also known as super cooled liquid and isotropic in nature.
| Crystalline Silica (Quartz) | Amorphous Silica (Glass) | |
| 1. | Crystalline in nature. Also called quartz. |
Light white powder. |
| 2. | All four corners of \[\ce{SiO^{4-}4}\], tetrahedron are shared by others to give a network solid. |
The \[\ce{SiO^{4-}4}\], tetrahedron are randomly joined giving rise to polymeric chains, sheets or three - dimensional units |
| 3. | High and sharp melting point (1710°C) |
Does not have sharp melting point. On heating softens gradually to liquid. |
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