Having some trouble with this ideal gas problem

Really struggling with what is probably an easy question - please help! It's a problem from the Crash Course Chemistry youtube series. (9.06 mins at this link: https://www.youtube.com/watch?v=8SRAkXMu3d0)

We've worked out that the Hindenburg is carrying 9.00x10^6 moles of Hydrogen. The question is: "How much extra could the Hindenburg carry because it was using hydrogen instead of helium?"

We then work out that 9 moles of hydrogen is about 1.8x10^4kg, and that 9 moles of helium is about 3.6x10^4kg. The presenter then concludes that with hydrogen instead of helium, the Hindenburg carried 18 metric tons more - but surely the figures show that actually hydrogen is 18 metric tons *less* than helium at the same number of moles? I don't understand how these figures show that the Hindenburg was carrying 18 metric tons more because it had hydrogen instead of helium?

Help please!

Reply 1

Cowy97

because for the same weight (3.6x10^4kg) you get 18 moles of hydrogen but 9 moles of helium, so there is double the amount of hydrogen, or 18 more metric tons