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

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

Explanation:

From the question we are told that:

Edge length

Density

Generally the equation for Volume is mathematically given by

Where

Molar mass of  (SiO2) for one formula unit

Therefore

Density of Si per unit length is

Molar mass of  (SiO2) for one formula unit

Therefore

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

every chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed. therefore, there must be the same number of atoms of each element on each side of a chemical equation.