Gay Lussac's Law — Avogadro's Law — Mole Concept — Question 18

Gram molecular mass of C₂H₆ = (2 x 12) + (6 x 1)
= 24 + 6
= 30 g

1 mole of C₂H₆ weighs 30 g

∴ 2.5 moles weighs = $\dfrac{ 30}{1} \times 2.5 = 75 \text{ g}$

Hence, weight of 2.5 moles of ethane [C₂H₆] is 75 g.