Calculate the value of Avogadro's number from the following data:
Density of `NaCl = 2.165 g cm^(-3)`
Distance between `Na^(o+)` and `Cl^(Θ)` in `NaCl = 281` pm

Explanation

A unit cell of NaCl contains 4 NaCl units, therefore , Z = 4
M = 23 + 35.5 = 58.5 g ` "mol"^(-1)` , p = 2.165 g` cm^(-3)`
As distance between ` Na^(+) and Cl= 281` pm ` therefore ` Edge of the unit cell ` = 2 xx 281 = 562 ` pm
( Edge is the distance from ` Na^(+) "to" Na^(+) " ion or " Cl^(-) "to" Cl^(-)` .see Fig .1.33 g , page 1/26)
substituting these values in the expression , ` p = ( Z xx M)/ (a^(3) xx N_(0)) `
`2.165 "gcm" ^(-3) = ( 4 xx 58.5"g mol"-1)/( 562 xx 10^(-10) "cm") ^(3) xx N_(0) or N_(0) = 6.09 xx 10^(23) mol ^(-1)`