What is the mass of a sample of NH3 containing 7.20 * 1024 molecules of NH3? 161 grams 187 grams 203 grams 214 grams

203 grams

Explanation:

It is known that 1.0 mole of a compound contains Avogadro's number of molecules (6.022 x 10²³).

Using cross multiplication:

1.0 mol contains → 6.022 x 10²³ molecules.

? mol contains → 7.2 x 10²⁴ molecules.

∴ The no. of moles of (6.3 x 10²⁴ molecules) of NH₃ = (1.0 mol) (7.2 x 10²⁴ molecules) / (6.022 x 10²³ molecules) = 11.96 mol.

∴ The no. of grams of NH₃ present = no. of moles x molar mass = (11.96 mol) (17.0 g/mol) = 203.3 g ≅ 203.0 g.