Al is added to water, and oxidizes. This is the initial reaction. We need 6 moles to be the "base" for this.
3x[2Al + 3H20 --> Al2O3 + 3H2]
That's 18.18g of H2, from 162.2g (162.2mL) of water used up in that one reaction.
Oxidized Al is "eaten" away by the NaOH:
6Al2O3 + 6NaOH --> 6Al + 6O2 + 6Na + 3H2
Converting moles to mass: 6 mol Al2O3= 611.76g , 6 mol NaOH= 40g, 3 mol H2= 6.06g (seems low, but don't worry), 6 mol O2= 192g
But wait, there's also the reactions which release more H2, Al regenerating its oxide layer, and Na reacting to form NaOH again.
2Al + 3H20 --> Al2O3 + 3H2
Remember, we had 6 moles of Al initially, so everything is x3. That's another 18.18 g (9 moles) of H2 released!
And:
4Na + 4H2O --> 4NaOH + 2H2
Again, x1.5 to get equal to 6 initial moles of Na. That's 6.06g of H2 more.
Then the reaction starts over, but this is one complete cycle.
Total H2: 30.3g= 15 moles
An ideal gas (like H2) takes up 24.8L per mole.
24.8(15)
Gives us 372L of H2 gas produced, at 101.3 kPa. Convert that into psi and imperial units yourselves, and figure for higher pressures, lower temps, etc. using the gas laws. That's a lot of gas.
But... The Al, when the oxide layer is gone, will react again to form another oxide layer, which will be eaten again by the NaOH, also newly formed using water. Some Al will be left out of the reaction, from losses of NaOH. Off of a Al block (not the fastest way, but it'll last a longer time), the Al that is "eaten" off will gather on the bottom. What stops the waste Al from reacting again and again with the NaOH, and using up the water? If it doesn't react, it can be gathered, and smelted into more bars or blocks.
Edit: Note: That's from 161.88g of Al (not counting the already oxidized layer on it), converted to 611.76g of Al2O3.
Edit, Edit: Added inital oxidation reaction. Counting that first one, we have 24 moles of H2, for 595.2L of H2 at SATP. That's if the last oxidation reaction applies, otherwise, we just have 372L. This is all totals, and it'll take a long time to get this much gas. Over a week for a pound (and we have 0.35lb of Al, or 1.35lb of Al2O3), so this could last a while. Divide by number of hours the aparatus is run, water usage (and NaOH usage), and we have gas production per hour. Hopefully, it's high enough Still, that's a ton of gas. All of the above reactions are going on constantly, so yields can change if some created H2 or O2 is used in regenerating the NaOH and Al2O3.
Edit, Edit, Edit: I gotta stop thinking of new things to add after submitting it...
But... All this depends on the concentration of NaOH in the water (reaction speed), and the purity of all of the substances involved (aluminium, for example, probably will have a decent amount of contaminants).
