Question

From 2mg of calcium 1.2 × 10¹⁹ atoms are removed. The number of Gram atoms of calcium left is?

Answer 1

Mol at first:
= m/Ar
= 2/40
= 0.05 milimoles

-) Number of atoms at first:
= n x L
= 0.05 x 10^-3 x 6.02 x 10^23
= 3.01 x 10^19

-) Number of atoms after it was removed:
= (3.01 - 1.2) x 10^19
= 1.81 x 10^19 atoms

-) Mol after it was removed:
= (1.81 x 10^19)/(6.02 x 10^23)
= 3 x 10^-5 moles

-) No. of gram atoms:
= n x Ar
= 3 x 10^-5 x 40
= 120 x 10^-5 grams
= 1.2 miligrams