Question

The mass of one unit cell of NaCl is​

Answer 1

Answer:

One unit cell of NaCl contains 4 NaCl units (ie) has mass

Number of unit cell present in a cube shaped crystal of NaCl of mass 1 g = m×Na(M×Z)

Hence Z = 4

Molecular Weight of NaCl (M) = 58.5

m = 1.00 g

Na=6.023×1023

Hence substitute the value in the above equation We get

No. of unit cell in 1g =1×6.02×10234×58.5

⇒2.57×1021

Answer 2

Answer:

The number of NaCl units present in a unit cell of NaCl is 4

Explanation:

Hint: In order to solve this problem, we must firstly understand the type of unit cell present in the structure of NaCl. Then we can calculate the total number of atoms present in this unit cell and by relation, correspond the value of the total number of atoms to NaCl.

• NaCl is an ionic crystalline compound. While formation of the crystal structure of sodium chloride, it crystallizes into a packing structure known as face – centred cubic.
• This packing structure forms a single unit in the multi – molecule lattice structure of sodium chloride. In this type of unit – cell, i.e. face centred cubic, the following characteristics are observed:

• In face centred cubic structure, there are atoms on all the vertices of the cube
• Atoms are also present on all the sides of the cube
• The vertices have 18 th of an atom on every vertex due to geometric constraints
• Similarly, all faces have only 12  of an atom on every face due to geometric constraints
• From this, we can infer that there are 8 portions of the 18 th of an atom on the 8 vertices of the cube, while all the 6 sides of the cube have ½ atoms each. Hence the total number of atoms present in the face centred cubic structure can be calculated to be:

• Total number of atoms = 18 (8 vertices) + 12
• (6 faces) = 1 + 3 = 4 atoms
• Hence, there are 4 atoms present in each unit cell of a face centred cubic structure.
• Hence, the number of NaCl units present in a unit cell of NaCl is 4