Question

6. How many unit cells are present in a cube
shaped ideal crystal of NaCl of mass 1.00 g?
(a) 2.57 x 1021
(b) 5.14x 1021
(c) 1.28 x 1021
(d) 1.71 x 1021
​

Answer 1

Answer:

Molar mass of NaCl=58.5

1g of NaCl contains =

58.5

1

moles of NaCl

1g of NaCl contains

58.5

1

×6.022×10

23

molecule of NaCl in cube-shaped ideal crystal of NaCl (Rock salt type)

4 molecule of NaCl are present as Cl

−

present occupy the FCC lattice=4 ions of Ce

−

Na

+

occupy the octanedral site =4 ions of Na

+

1 unit cell contain 4 molecules of NaCl

1 molecule contain

4

1

unit cell

58.5

1

×6.022×10

23

molecule contains=

58.5

1

×

4

6.022×10

23

unit cell

Thus

1g of NaCl contain=2.57×10

21

unit cell.