Question

The number of atoms present in 120 amu of Ca are

Answer 1

We have to find the number of atoms present in 120 amu of Ca.

We know that number of moles = number of atoms/Avogadro number = given mass/Molar mass

i.e., Number of moles = N₀ / Nₐ = W/M

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We know that 1 amu = 1.66056 x 10^-24 g

So, 120 amu of Ca = 120 x 1.66056 x 10^-24 g

Nₐ = 6.022 x 10²³

Also, the molar mass of calcium = 40

Now, N₀ / 6.022 x 10²³ = 120 x 1.66056 x 10^-24 / 40

N₀ / 6.022 x 10²³ = 3 x 1.66056 x 10^-24

N₀ = 3 x 1.66056 x 10^-24 x 6.022 x 10²³

= 3 x 9.999 x 10^-1

= 3 x 9.999/10

= 3 x 0.999

= 3 x 1

= 3

Therefore, the required number of atoms is 3.