1.

Ice crystallizes in hexagonal lattice. At the low temperature at which structure was determined, the lattice contents were were `a=4.53Å` and `c=7.41Å`. `c=741Å`. Calcuate the no. of `H_(2)O` molecules present in a unit cell. `(` Density of ice `=9.22g//cm)`

Answer» Correct Answer - 4
Volume of unit cell,
`V=`Area of base `xx` Height
`=2xx(sqrt(3))/(4)a^(2)xxc`
`=(sqrt(3))/(2)xx(4.53xx10^(-8))xx7.41xx10^(-8)` ltbr. `=13.17xx10^(-23)cm^(3)`
`:. ` Mass of unit cell `=Vxxrho=13.17xx10^(-23)xx0.92`
`=1.21xx10^(-22)g`
Let there are `n` effective water molecules in the given unit cell. Then `n` times the mass of each water molecule would be the mass of unit cell.
`:. 1.21xx10^(-22)=nxx(8)/(6.023xx10^(23))`
`:. n=4`


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