630 g of 5% nitric acid reacts with barium. Find the volume of evolved gas and the number of salt atoms.

Ba + 2HNO3 = Ba (NO3) 2 + H2

Mass HNO3 = (630g * 5%) / 100 = 31.5g

M (HNO3) = 14 + 1 + 16 * 3 = 63 g / mol

Moles HNO3 = 31.5 g / 63 g / mol = 0.5 mol

HNO3 refers to the amount of H2 as 2/1, i.e. nitric acid will react twice as much as hydrogen is formed.

mol H2 = 0.5 mol / 2 = 0.25 mol

V = 22.4 (gas constant) * 0.25 mol = 5.6 L

mol H2 = Ba (NO3) 2 = 0.25 mol

N = 6 * 1023 (Avogadro) * 0.25 mol = 1.5 * 10 ^ 23molecules

There are 9 atoms in a molecule

N = 1.5 * 10 ^ 23 * 9 = 13.5 * 10 ^ 23 atoms.