Question

Number of unit cells in 0.97g of zns (sphalerite) is
A. 0.25NA
B. 0.025NA
C. 2.5*10^-3 NA
D. 2.5*10^-4 NA

Answer 1

We have to find the number of unit cells in 0.97 g of ZnS (sphalerite).

solution : molecular weight of ZnS = 97 g/mol ( approximately)

given weight of ZnS = 0.97 g

so no of moles of ZnS = given weight/molecular weight

= 0.97/97

= 0.01

now no of molecules in 0.01 moles of ZnS = 0.01 × Avogadro's number

= 0.01 NA

as structure of ZnS is face centered cubic lattice.

so, number of molecules per unit cell is 4

now number of unit cell in 0.01 NA molecules = 0.01 NA/4

= 0.25 × 10¯² NA

= 2.5 × 10¯³ NA

Therefore the number of unit cells in 0.97 g of ZnS is 2.5 × 10¯³ NA