Question

12. Suppose that there were two isotopes of Sodium. 28% of the naturally occurring sodium atoms
had a mass of 22, and 72% atoms had a mass of 23. Find the average atomic weight of sodium​

Answer 1

Answer:

Answer = 632.56

Explanation:

If there are a hundred atoms, then 28% of them (28) would be of atomic mass, 22, ad 72% of them (72) would have an atomic mass of 23.

Of 100 Na atoms, 28 of atomic mass 22 would then have a total atomic mass = 22 28

Of 100 Na atoms, 72 of atomic mass 23 would then have a total atomic mass = 23 × 72

$A_{r} of Pb = \frac{22* 28+23*72 }{100} = \frac{616+1656}{100} = 632.56$

Answer 2

The average atomic weight of sodium atom is 22.72 amu.

Suppose that there were two isotopes of sodium. 28% of the naturally occurring sodium atoms had a mass of 22, and 72% atoms had a mass of 23.

We have to the average atomic weight of sodium.

The average atomic weight of sodium is given by,

$=\frac{x_1\times M_1+x_2\times M_2}{100}$

Where,

• M₁ is atomic weight of first isotope of sodium atom.
• x₁ is the percentage occurrence of 1st sodium isotope.  
• M₂ is the atomic weight of 2nd isotope of sodium atom.
• x₂ is the percentage occurrence of 2nd sodium isotope.

Given,

M₁ = 22, x₁ = 28% , x₂ = 72% and M₂ = 23

∴ average atomic weight of sodium atom =

$=\frac{28\times22+72\times23}{100}\\\\=\frac{616+1656}{100}\\\\=22.72$

Therefore the average atomic weight of sodium atom is 22.72 amu.

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