Am I reading this reaction right?

[JeffEvarts]

In the late 19th early 20th century, sulfuric acid production was a huge deal, and even today, conversion of SO2 to SO3 (contact process) is something that people take great pains to optimize.

But I also see references here on physics forums as well as elsewhere which assert that sulfur dioxide and water will reduce elemental iodine. This seems (to me) like a weak acid producing a stronger one, so my intuition says that this runs the other way. Likewise, if SO2 and water reduced iodine and produced sulfuric acid, the contact process (and the Glover tower before it) would have been pointless.

What am I missing?
-Jeff

 

[SteamKing]

Just because a reaction involving iodine may produce sulfuric acid does not necessarily mean that that reaction may be the most economical means of production. As an industrial chemical, sulfuric acid is produced by the ton, and securing enough iodine for production in those quantities may be wildly expensive. Even today, most elemental iodine is produced from salts in the ocean and a few mineral deposits from places like Chile.

Initially, sulfuric acid was made in small quantities in glassware containers. When that method could not be scaled up economically to produce larger amounts of acid, the lead chamber process was developed:

http://en.wikipedia.org/wiki/Lead_chamber_process

Again, further development led to the contact process, which was even more economical at producing large amounts of acid cheaper than the previous method:

http://en.wikipedia.org/wiki/Contact_process

The key to success in any chemical production process is to not only make the chemical, but to make money as well.

 

[JeffEvarts]

SteamKing,

Are you answering my question one way or the other? Does SO2 + 2H2O + I2 = H2SO4 + 2HI at reasonable temperatures and pressures?

I am very familiar with both the chamber and contact processes. I referred to both of them in my original post, and have practical knowledge of how they work.

So... does the reaction work the way they say it does, or were you just tossing out some loosely related links to get my query off the "new query/unanswered" list?

-Jeff

 

[Bystander]

weak acid producing a stronger one

It's not a question of a weak acid producing a stronger one, it's a question of a redox reaction; iodine oxidizes sulfur dioxide to sulfur trioxide as you have it written.

 

[JeffEvarts]

Bystander: Thank you! I am enough of a chemistry novitiate that I'm not sure when which rules apply or take precedence. Thanks for explaining.

Perhaps a reasonable conclusion is that if I had a mixed stream of SO3/SO2 (from calcination of FeSO4, for instance) and I washed the gas first with water, and then with water containing iodine, the SO3 would be directly absorbed in the first wash, while the SO2 would (more slowly) pass to the second, be reduced, and thence be absorbed in the water, giving H2SO4 in both, albeit with some hydrogen iodide impurities in the second.

That sounds like a good lab experiment, provided you can calcine the sulfate (450-600C) reasonably.

-Jeff

 

[Bystander]

second, be reduced oxidized, and thence be

 

[Borek]

This seems (to me) like a weak acid producing a stronger one, so my intuition says that this runs the other way.

Why should the strength of the acid matter? This is not an acid/base equilibrium, this is a redox process, driven by redox potentials.

 

[JeffEvarts]

second, be <s>reduced</s> oxidized, and thence be

*Facepalm*

Yes, of course.

-Jeff

 

[SteamKing]

So... does the reaction work the way they say it does, or were you just tossing out some loosely related links to get my query off the "new query/unanswered" list?
-Jeff

It worked, didn't it?