Question

13) if a metal crystallises in fcc lattice then number of unit cells present in 13g of metals is(Atomic mass of metal = 65u)

a) 3*10^23
b)6*10^21
c) 3*10^20
d)3*10 ^22

Answer 1

Answer:

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Answer 2

Answer:

The number of unit cells in $13g$ of metals measured is $3 \times 10^{22}$.

Therefore, option d) $3 \times 10^{22}$ is correct.

Explanation:

Given,

The mass of metal = $13g$

The molar mass of metal = $65u$ = $65g/mol$

The number of unit cells in $13g$ of metals =?

Firstly, we have to calculate the total number of atoms in $13g$ of metal.

For this,

• The number of moles = $\frac{Given mass}{Molar mass}$ = $\frac{13}{65}$ = $0.2 mol$

As we know,

• $1 mole$ = $6.022\times 10^{23}$ atoms
• $0.2 moles$ = $0.2 \times 6.022\times 10^{23}$ atoms = $1.2\times 10^{23}$ atoms

In fcc,

• 1 unit cell = $4 atoms$
• 1 atom = $\frac{1}{4}$ unit cells

Therefore,

• $1.2\times 10^{23}$ atoms = $\frac{1.2\times 10^{23}}{4}$ unit cells = $3 \times 10^{22}$ unit cells.

Hence, the number of unit cells = $3 \times 10^{22}$ unit cells.