To continue the chemistry lesson:

A mole is an expression of a specific number of particles. Since Atoms are so tiny, to humans doing any sort of significant calculation, we need something a bit more tangible. 1 Mole is defined as 6.023 X 10^23 particles (this can be atoms or molecules which are combinates of atoms). It is also equal to the formula mass of a substance expressed in grams. For example:

1 mole of H2O = 6.023 X 1023 molecules of H2O = 18 grams H2O

So, for chemistry, you want to know both the physical weight and the numeric count of those atoms. You want to be able to count out the atoms by tare weight since you cant really pick them out individually except in high-end research.

It's not much different from saying, I know that there are a dozen eggs in a standard carton, and based on that number can calculate what those dozen eggs weigh if I know how much an egg weighs. A mole would be the count and in our case, the weight of an atom is MUCH more predictable than the weight of any given egg, so we can calculate it's weight to a high degree of certainty.

H2SO4 is the formula you want for sulfuric acid

The mass of H2SO4 can be calculated by the atomic weight of its constituent atoms.
2 x 1.00794 (Hydrogen)
1 x 32.065 (Sulfur)
4 x 15.9994 (Oxygen)

Thus 98grams. It just so happens that those thoughtful people who brought you the periodic table of the elements also brought you the weight in grams of 1 mole of each atom. That's what that strange number with all the decimal places is.

So, 1mole H2SO4 = ~98.1g H2SO4

Neat huh?

Blast already told you that you need 8.5 moles of H2 to fill a 55gal drum (volume by liters) and that H2SO4 gives off 1 mole of hydrogen gas.

So 8.5 moles of H2 are produced by reacting 8.5 moles of sulfuric acid with iron under nominal conditions.

You have the weight of H2So4, so you multiply it by the number of moles needed.

You get 833g or .833kg

Not bad for a pound and a half of acid.

Haven't touched on the iron side of the equation yet, but the SO4 reacts on a 1:1 basis with Fe. So you'll need the same number of moles of pure (non-oxidized) iron.

Oh, and H2SO4 has a relative density of 1.8 compared to water (1.0). This oily looking acid (oil of vitriol is it's ancient name) has a density of 1.83kg/L at a 17.6molar (near 100%) concentration. I don't recommend carrying a half liter of full concentration Sulfuric Acid under any circumstances. But I can think of a ready source of H2SO4 when traveling. Make sure to bring some steel wool and use it with a different kind of battery (9V for starting a fire and 12V for the balloon) *wink*

So, how much iron will you need to fill that drum?