# How much sodium hydroxide, water, and aluminum are needed to make hydrogen?

Discussion in 'Chemistry' started by kingcarrot, Jan 22, 2012.

1. ### kingcarrotRegistered Senior Member

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2 Al + 2 NaOH + 2 H2O → 2 NaAlO2 + 3 H2

How much sodium hydroxide, water, and aluminum (by weight) would I need to produce 100kgs of hydrogen lift from a balloon?

3. ### TrippyALEA IACTA ESTStaff Member

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10,880
Calculate the molecular weight of dihydrogen, and each of the reactants.
Calculate how many moles of dihydrogen is in 100kg.
Using the 2:3 reaction stiochiometries of the various reactants and dihydrogen, calculate the number of moles of each of the reactants, and multiply it by the molecular weight of that reactant, to calculate how many grams of each reactant are required.

M[sub]w[/sub](Al)=26.9815386
M[sub]w[/sub](Na)=22.98976928
M[sub]w[/sub](O)=15.9994
M[sub]w[/sub](H)=1.00794

5. ### Captain KremmenAll aboard, me Hearties!Valued Senior Member

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If I've understood this properly
http://en.wikipedia.org/wiki/Lifting_gas

Every kilo of Hydrogen will lift 13.36 kilos of weight.
So to lift 100kg would require 7.48 kilos Hydrogen.
I think you can work out the amounts of reagent using Molecular Weights.

You are going to need a very big test tube though.
And you need to coat the inside of the balloon with Aluminium, or the Hydrogen will all leak out.

and don't produce any hydrogen indoors or it will blow you up.

7. ### TrippyALEA IACTA ESTStaff Member

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Oh yeah :Face palm: I misread the question. I thought he wanted 100kg of Hydrogen.

Modify this:
From 100kg to the appropriate mass of hydrogen.

8. ### araucaBannedBanned

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H2O ---- > 44.00 kg
NaOH--- > 99.78 Kg
Al------- > 61. 0 Kg ?

9. ### Captain KremmenAll aboard, me Hearties!Valued Senior Member

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Wouldn't you be better to produce the Hydrogen by Hydrolysis?
It would probably take far less energy than the production of the Aluminium required.

Last edited: Jan 23, 2012
10. ### kingcarrotRegistered Senior Member

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92
Okay, I'll tell you my secret plan. I am looking for the cheapest way to build a lifting balloon that will allow me to run in a field and simulate being on the moon (perhaps two so I can simulate sweet ninja battles). I have a harness and I weigh about 85kgs with it on. Any thoughts?

11. ### TrippyALEA IACTA ESTStaff Member

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Ferrosilicon might be cheaper to obtain, and easier to work with.

12. ### AsguardKiss my dark sideValued Senior Member

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then isn't your calculations wrong? if you want to simulate moon gravity shouldn't you need only 50kg of lift? and if that's all you want to do wouldn't it be easier to use helium which can be bought easily rather than hydrogen which is flammable?

13. ### billvonValued Senior Member

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11,101
I think you will rapidly find yourself approaching 100,000 feet. This will make you rather unhappy so I'd try something simpler.

Bungee cords tied to trees work and are a lot cheaper. And a lot safer if the wind comes up. However I'd point out that they are far from totally safe - it one breaks near the top end it will blast into you with a great deal of force.

And if you want to fight with someone there's always the Mad Max approach. They do this every year at Burning Man.

14. ### kingcarrotRegistered Senior Member

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I'm pretty set on balloons with the obvious safety measures (ropes) to prevent floating away. Plus the extra weight from said safety measures will need to be lifted too and I assume there will be loss of hydrogen during its production and storage - and 100 is an easy number to work with. Does anyone know a cheap way to hydrolysis? Or ferrosilicon?

15. ### billvonValued Senior Member

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11,101
If you are set on hydrogen - why not just rent a few tanks of hydrogen? It's commonly available at welding supply shops and it's going to be far cheaper than trying to make it yourself.

16. ### AsguardKiss my dark sideValued Senior Member

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a) why are you set on hydrogen?
b) that weight is a fair assumption but you need to reduce your target Why are you aiming for compleate cancilation of ALL weight? you said you want moon gravity which according to this http://www.moonconnection.com/moon_gravity.phtml is 83.3% (or 5/6). Therefore you need 13.7% lift

17. ### kingcarrotRegistered Senior Member

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92
Because a bungee cord is lame and does not mimic the effect of consistently reduced weight.
Never said I was set on hydrogen, but it should require only half the space of helium, right?
That would be really dumb to want to cancel all the weight... I didn't mean to imply that. I don't really care what I actually weigh. I just want to be able to jump up 20 feet. Probably using two or three weather balloons in case one pops. I'm not really into broken bones...

18. ### AsguardKiss my dark sideValued Senior Member

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just out of interest, why do you think NASA uses a plane to simulate lower or zero gravity rather than this sort of method?

Answer, watch the mythbusters episodes helium raft and the one with the girl with a massive of helium balloons.

19. ### Captain KremmenAll aboard, me Hearties!Valued Senior Member

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To fill a balloon with Helium would cost a lot of money.
50,000 litres of Gas to lift 50kg.
Filling a balloon with hot air would be best.

@kingcarrot
You could make a giant Chinese Lantern out of Chicken wire and Newspaper.
Then fill it over a small fire. You would need to tether it while it was filling.
Once it was full, you would lash yourself to a trapeze strung beneath it.
Cut the tethers with a knife and up! up! and away you would go!
While in the air, you could use a small blowlamp to keep the air hot.
It you painted it with Japanese characters it would look very Ninja.

Launch the Ninja Chinese lantern on a hillside clear of trees.
Perhaps a field with sheep in it would be best, as they are soft to land on.
Wear lots of layers of clothes, so you don't break too many bones.

You don't want to break any bones?
Why not? That's not the attitude to take.
I would do it myself, but it is your idea and you should get all the glory.

Last edited: Jan 23, 2012

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21. ### billvonValued Senior Member

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11,101
Actually, a long one mimics it extremely well - much better than a big balloon will.

No. It's not the weight of the gas that matters but the weight of the air displaced. The difference is less than 10%.

You can't do that with a balloon.

A 100kg lift force will require a balloon that's about 6 meters (18 feet) across. That's a lot of drag. As soon as you push off drag will stop you dead. If there is even a little wind you will go with the wind; trying to stop yourself will require tens or hundreds of pounds of force.

If you want to do "ninja" stuff with someone else you will need long swords; you won't be able to get closer than about 9 feet to them.

A much simpler approach is get a SCUBA system, weight yourself down so you weigh 20 pounds underwater and hop around that way.

22. ### Captain KremmenAll aboard, me Hearties!Valued Senior Member

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I'm not sure what you mean by this.
Are you are saying that the difference between the weight of Hydrogen and Helium in a specific volume is only 10% of the weight of the air displaced from that volume?

Not a huge degree of difference then.
Do you know the difference between hot and cold air.

Last edited: Jan 24, 2012
23. ### billvonValued Senior Member

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11,101
Basically yes. The ideal balloon is a perfect vacuum inside, but they are hard to build. So we use light gases instead. In all cases the air displaced is the important weight, so the figure of merit is the difference in displaced weight.

Some numbers:

Weight of air 1.2kg/M3 at STC

Weight of helium .175kg/M3 - so available buoyancy is 1.03kg/m3
Weight of hydrogen .089kg/M3 - so available buoyancy is 1.11kg/m3
Perfect vacuum = zero weight - so available buoyancy is 1.2kg/m3

PV=nRT so the hotter gas would occupy 115% of the space the cold gas did. (Or to put it another way, the same volume of gas would weigh 87% less if it were 100C instead of 50C.)

So perhaps a hot air balloon!