Question

What mass of F2 would have the same number of diatomic molecules as there are hydrogen atoms in 20 grams of ammonia(NH3)?

Answer 1

Molecular mass of Ammonia (NH₃ ) = (14 x 1) + (1 x 3) = 17 g mol^-1

17 g of Ammonia contains 3 g of hydrogen

1 g of Ammonia contains 3 / 17 g of hydrogen

20 g of Ammonia contains (3 / 17) x 20 = 3.5294 g of hydrogen

Atomic mass of hydrogen = 1 amu

No. of atoms in 1 g of hydrogen = 6.022 x 10²³

No. of atoms in 3.5294  g of hydrogen = 3.5294 x 6.022 x 10²³

No. of hydrogen atoms in 20 g of ammonia    =  3.5294 x 6.022 x 10²³

Atomic mass of fluorine = 19

Molecular mass of fluorine = 19 x 2 = 38 g mol^-1

38 g of fluorine contains   6.022 x 10²³ diatomic molecules of fluorine

Mass of fluorine which would contain 3.5294 X 6.022 x 10²³ diatomic molecules of fluorine = 3.5294 x 38 = 134.1172 g

Mass of F₂ which would have same number of diatomic molecules as there are hydrogen atoms in 20 grams of ammonia =   134.1172 g