If you needed to generate 66mL of H2 gas at STP, how many grams of Na would be required?

Question

Given: 2 Na+ 2 H₂O —> 2 NaOH + H₂

Answer 1

2 Na⁺ + 2H₂O ==> 2NaOH + H₂ ... balanced equation

Since it is at STP, we know that 1 mole of gas (ideal) = 22.4 liters. So, find out how many moles of H₂ gas is represented by 66 ml, then convert that to moles of Na, and finally to grams of Na.

moles of H₂ gas:

66 ml H₂ x 1 L/1000 ml x 1 mol/22.4 L = 0.002946 moles H₂

moles Na to generate 0.002946 moles H₂:

0.002946 moles H₂ x 2 moles Na⁺ / mole H₂ = 0.005893 moles Na+

mass of Na⁺ needed:

0.005893 moles Na⁺ x 22.99 g/mole = 0.135 g = 0.14 g Na⁺ (to 2 significant figures)