H2SO4 into H2O? Another "Facts for fiction" question.

I hope this doesn’t skate too close to the edge of “question with a factual answer”. I’m writing a story that involves terraforming Venus. I’d like to maintain some semblence of scientific substance. So, in that light, how might I convert Venus’ sulfuric acid into water?

Or maybe more specifically, given a test tube of sulfuric acid, how would I go about obtaining water from it, and what other chemicals would be produced by the reaction? Neither Google nor “Chemistry for Dummies” have been very helpful up to this point.


assuming it is concentrated sulfuric acid it is almost impossible to get the “water” out again. Sulfuric acid is made from the reaction of sulfur trioxide and water. However, I know of no way of going backwards.

It is possible to add something to react with the sulfuric acid (e.g. sodium hydroxide) which would produce water and salt (care extremely violent reaction). However, most of the “water” formed came in essence from the sodium hydroxide.

If it was dilute sulfuric acid, then a large amount of water can be distilled from the sulfuric acid (though a little acid may codistill over).

According to a problem we did in chemistry yesterday Mn0[sub]2[/sub] + 2H[sub]2[/sub]SO[sub]4[/sub] Mn(SO[sub]4[/sub])[sub]2[/sub] + 2H[sub]2[/sub]O

Not sure if that answers your question. :wink:

Well, I was a chemist in a former incarnation, although I have forgotten a load of what I learnt…

Anyway, as I understand it, you can’t really “convert” H[sub]2[/sub]SO[sub]4[/sub] into water per se, but you can react it with a base (alkali).

The general equation is acid + base = salt + water.

For example, you could perform the following reaction:

H[sub]2[/sub]SO[sub]4[/sub] + Ca(OH)[sub]2[/sub] —> H[sub]2[/sub]O + CaSO[sub]4[/sub]

where Ca(OH)[sub]2[/sub] is calcium hydroxide, or slaked lime. The products are water and CaSO[sub]4[/sub] is calcium sulphate. However this is complicated by the fact that calcium sulphate exists in both anhydrous and hydrated forms (the hydrated form is known as gypsum)… and I couldn’t tell you whether it would precipitate out and leave water, or just incorporate the water into its crystals. Hmmm.

I can tell you that the reaction products (sulphates) will get less soluble as you go down the group in the periodic tabel, so using barium hydroxide might be a better bet.

This wouldn’t be too practical on a planetary scale, though, unless you have some extremely large antacid tablets to hand…

As its for an SF story, maybe you could use genetically engineered bacteria? They could photosynthesise sulphuric acid into oxygen and hydrogen sulphide. From this page other organisms (or maybe the same one) could use photosynthesis to combine CO2 with the H2S to form sugar and sulphur. Still leaves you with the problem of what to do with the sulphur though.

Little Willie was a chemist
Little Willie is no more
For what he thought was H20
Was H2SO4

On the general topic of terraforming Venus, it should be noted that even if you convert all the sulfuric acid to water plus something else, it will do little to alleviate the basic dryness of Venus. There’s just not that much sulfuric acid in the Venusian atmosphere. The planet needs a few thousand comets’ worth of water. The sulphuric acid is just a drop in the bucket compared to that.

Didn’t Carl Sagan discuss “terraforming” Venus (in "The Cosmic Connection) by employing algae of a very rugged nature ? According to Dr Sagan, these algae already existed (and needn’t be ‘engineered’) and have been shown to survive in very harsh environments of heat, radiation, pH levels, etc.

Just a little nitpick here, but you have 4 hydrogens on the left side of the equation so the right side should read:

2H[sub]2[/sub]O + CaSO[sub]4[/sub]

ISTR calcium sulfate has more than one possible number of molecules of water of crystallization, including CaSO[sub]4[/sub]·6H[sub]2[/sub]O and CaSO[sub]4[/sub]·12H[sub]2[/sub]O. It’s been a while so maybe someone more up to date will correct me. OTOH, all that gypsum falling to Venus’ hot surface might be heated enough to drive out all the water anyway.