Question

One crystalline form of silica (SiO2) has a cubic unit cell, and from X-ray diffraction data it is known that the cell edge length is 0.700 nm. If the measured density is 2.32 g/cm3, how many (a) Si4 and (b) O2- ions are there per unit cell

Answer 1

Answer:

There are 8Si atoms and 16 O atoms per unit cell

Explanation:

From the question we are told that:

Edge length $l=0.700nm=>0.7*10^9nm$

Density $\rho=2.32g/cm^3$

Generally the equation for Volume is mathematically given by

$V=l^3$

$V=(0.7*10^9)m^3$

$V=3,43*10^-{22}cm$

Where

Molar mass of  (SiO2) for one formula unit

$M=28+32$

$M=60g/mol$

Therefore

Density of Si per unit length is

$\rho_{si}=\frac{9.96*10^{23}}{3.43*10^22}$

$\rho=0.29$

Molar mass of  (SiO2) for one formula unit

$M=28+32$

$M=60g/mol$

Therefore

There are 8Si atoms and 16 O atoms per unit cell