Problem solving strategy:

Hydrogen and ice both are molecular substances. Determine their molar masses. Use the molar mass of each to convert masses in grams to moles.

(a) Molar mass of H₂ = 1.008 x 2 = 2.016 g

1 mole of H₂ = 2.016 g

$\therefore$ 2.016g of H₂ = 1 mole of H₂

1 g of H₂ = $\frac{1}{2.016}$ moles of H₂

5 g of H₂ = $\frac{1}{2.016} \times 5$ moles of H₂

= 2.48 moles of H₂

(b) 1 mole of ice (H₂O) = (2 x 1.008) + 16 = 2.016 +16 = 18.016 g

1 mole H₂O = 18.016 g

$\therefore$ 18.016g of H₂O = 1 mole

1 g of H₂O = $\frac{1}{18.016}$ moles

100 g of H₂O = $\frac{1}{18.016} \times 100$ moles

= 5.55 moles of H₂O