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The Solid State

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Chemistry I

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Class 10 Class 12
Silver crystallises in an fcc lattice. The edge length of its unit cell is 4.077 x 10–8 cm and its density is 10.5 g cm-3. Calculate on this basis the atomic mass of silver. (N= 6.02 x 1023 mol–1).

We have,
Edge of length of cell a = 4.07x10–8cm
Density p = 10.5 g /cm3
Number of atoms in unit cell of fcc lattice = 4
Avogadro number NA = 6.022x1023

By using formula,

Density space equals straight p space equals fraction numerator ZM over denominator straight a cubed straight N subscript straight A end fraction
straight M space equals space fraction numerator Pa cubed straight N subscript straight A over denominator straight Z end fraction

Putting space the space value space in space the space above space equation space we space get comma

fraction numerator 10.5 space straight x left parenthesis 4.07 right parenthesis cubed space straight x 6.022 space space straight x 10 to the power of 23 over denominator 4 end fraction
solving space the space equation space we space get comma

straight M equals space 107.09 straight g space Mol to the power of negative 1 end exponent


Why are solids rigid?

Solids are rigid because the internuclear distance between the  molecules of a solid are very less and closely packed and their positions are fixed due to the strong forces of attraction between them.

Why do solids have a definite volume?

A solid have a definite volume because the inter molecular distance  between its molecules are fixed.

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 clevage property?

Refractive index of a solid which have the same value along all directions are isotropic in nature. It would not show cleavage property.

Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid, teflon, potassium nitrate, cellophane, polyvinyl chloride, fibre glass, copper.

Amorphous solids: Polyurethane, teflon, cellophane, polyvinyal chloride, fibre glass.
Crystalline solids: naphthlene, benzoic acid, potassium nitrate, copper.

Why is glass considred a super-cooled liquid?

Glass is amorphous solids and  have a tendency to flow, though very slowly. Therefore, these are called pseudo solids or super cooled liquids .