Question

How many unit cells are present in a cube-shaped ideal crystal of NaCI of mass 1.00 g? [Atomic masses : Na = 23, Cl = 35.5)

Options

• 5.14 × 10²¹ unit cells

• 1.28 × 10²¹ unit cells

• 1.71 × 10²¹ unit cells

• 2.57 × 10²¹ unit cells

Answer 1

2.57 × 10²¹ unit cells

Explanation:

Since in NaCl type of structure 4 formula units for a cell.

No. of unit cell s present in a cubic crystal

`= "Mass of all unit cells"/"Mass of one unit cell"`

`= ("d" xx "a"^3)/("M"//"N"_"A" xx "Z")`

`= ("m" xx "N"_"A")/("M" xx "Z")`

∴ units cells = `(1.0 xx 6.02 xx 10^23)/(58.5 xx 4)`

= 2.57 × 10²¹ unit cells