Chemical composition

Question

Determine the number of miles of molecules (or formula units) in each sample.

a) 27.6 g sodium chloride

b) 30.8 g nitrogen monoxide

c) 3.95 kg carbon dioxide

Answer 1

There are Avogadro's number of molecules or formula units in a mole.

a) 27.6 g NaCl. Since NaCl is an ionic compound, we'll be looking for formula units. The molar mass of NaCl is 58.44 g/mole. Thus, 27.6 g x 1 mol/58.44 g x 6.01x10²³ formula units/mol = 2.84x10²³ formula units NaCl

b) 30.8 g NO. Since nitrogen monoxide is a covalent compound, we'll be looking for molecules. The molar mass of NO is 30.01 g/mol. Thus, 30.8 g x 1 mol/30.01 g x 6.02x10²³ molecules/mol = 6.18x10²³ molecules

c) 3.95 kg CO₂. Since carbon dioxide is covalent, we'll be looking for molecules. The molar mass of CO₂ is 44 g/mol. Thus, 3.95 kg x 1000 g/kg x 1 mol/44 g x 6.02x10²³ molecules/mol = 5.40x10²⁵ molecules of CO₂