Calculate the mass of 1.23×1024 helium atoms. express your answer in grams of helium.

The  mass   of 1.23  x10^24  helium atoms  is   8.16  grams

Calculation

Step 1  :  calculate the number of moles of He  using Avogadro's  constant

that  is   according to Avogadro's law  1 mole =    6.02 x10^23 atoms

                                                                  ? moles=  1.23  x10 ^24  atoms

 by cross multiplication

= (1.23 x 10^ 24 atoms  x 1  moles) / 6.02 x10^23  atoms =2.04  moles

Step 2 : calculate  mass

 mass  =moles x molar mass of He

from periodic table  the molar mass of He  is 4.0  g/mol

moles= 2.04  moles  x 4.0 g/mol  = 8.16  grams

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