Question

calculate the no of moles for the following

(a) 52g of He {finding moles from mass}

{b}12.046 x 10²³ no of atoms [finding mole from the no of particles]

Answer 1

The molar mass of helium is 4 g. Thus the mass of one mole of helium atoms (6.023 X 10²³ atoms of helium) is 4g. Hence

4 g of helium atoms = 1 mole of helium atoms

1g of helium atoms = (1/4) moles of helium atoms

52g of helium atoms = (1 X 52)/4 moles of helium atoms

= 13 moles of helium atoms.

6.023 X 10²³ atoms of helium = 1 mole of helium atoms

1 atom of helium = 1 / (6.023 X 10²³) mole of helium atoms

So 12.046 X 10²³ atoms of helium = (12.046 X 10²³) / (6.023 X 10²³) mole of helium atoms

= 2 moles of helium atoms.