Chemistry Gas Law

Question

How much Na is needed to react with H2O to

liberate 579 mL H2 gas at STP?

Answer 1

The starting point here is to get the balanced chemical reaction between Na and H2O:

2Na + 2H₂O → 2NaOH + H₂ 

What that means is that 2 moles of Na is needed to produce 1 mole of H2

The next step then is to convert the 579 mL H2 gas into moles by taking

0.579 L x 1 mole / 22.4 L = 0.0258 mole H2

That means that you’re getting (0.0258 mole H2 x 2 moles Na / 1 mole H2) = 0.0516 mole Na as a part of this reaction.

I hope that helps! :)