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