Question

What is the mass in grams of 9.76 x 10 12 atoms of naturally occurring sodium?

Answer 1

The number of moles in a substance indicates the amount of the substance that contains the same number of particles as 12 g of the Carbon-12 isotope [or equivalent to 6.02 × 10²³] (which is used as a standard in the world of moles).

Now,

          if     6.02 × 10²³ atoms are found in 1 mole ofsodium
   then let  9.76 × 10¹² atoms are found in     x

⇒     x  =    (9.76 × 10¹² )  ÷  (6.02 × 10²³)

            =  1.619 × 10⁻¹¹ mol


Now, mass = moles × molar mass

∴ mass of Na = 1.619 × 10⁻¹¹ mol ×  23 g/mol
                      = 3.72 × 10⁻¹⁰ g