WCL (Wet Chemistry Lab) sample |
WCL (Wet Chemistry Lab) sample |
Jun 25 2008, 12:18 AM
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#1
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
We'll soon know what kinds of crops we can grow on Mars! Bonus, the fruits will be already freeze-dried!
Handy list of preferred pH's of common garden plants. -Mike -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Jun 27 2008, 06:40 PM
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#2
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Merciless Robot Group: Admin Posts: 8785 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
Hmm. What does this tell us (if anything at all) about the existence of superoxides at the site? Straining my memory of ancient high-school chemistry here, I would expect such compounds to be aggressive electron donors & therefore acidic.
(Okay, now tell me I got that backwards. Plus, I know it's a subsurface sample, but you'd expect this stuff to get circulated down at least a couple of cm due to wind action over time.) -------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Jun 27 2008, 11:16 PM
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#3
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Member Group: Members Posts: 384 Joined: 4-January 07 Member No.: 1555 |
Hmm. What does this tell us (if anything at all) about the existence of superoxides at the site? Straining my memory of ancient high-school chemistry here, I would expect such compounds to be aggressive electron donors & therefore acidic... As you feared, you actually have it a little reversed. An oxidizing agent like oxygen gas, peroxide ion, or superoxide ion wants to gain electrons (be an electron acceptor) - all want to turn into the oxide ion, O2-. A reducing agent like iron metal wants to lose electrons (be an electron donor), to either the ferrous ion Fe2+ or the ferric ion, Fe3+. Combine them and you get either FeO (wustite) or Fe203 (hematite). Oxidizing and reducing are clearly relative terms, because an ion like Fe2+ can either be oxidized to Fe3+ or reduced to Fe metal. Regarding acids, by the electronic (Lewis) definition of acids and bases, an acid is electron pair acceptor, generally with a large charge to radius ratio (the ultimate acid is the tiny naked proton H+), whereas a base is an electron pair donor (e.g., the oxide ion, O2-, which has a pair of electrons to donate). Combine them and you get neutral H2O or water. In aqueous solution, these two ions are unstable - the proton combines with a water molecule to form H3O+ (hydronium) and the oxide ion takes on a proton to form OH- (hydroxide). By common convention (acidic and basic, like reducing and oxidizing, being relative terms in a continuum), an aqueous solution with an excess of hydronium is called acidic and one with an excess of hydroxide is called basic. As you correctly recalled, there is some overlap between the definitions of oxidized and acidic, and between reduced and basic, inasmuch as both definitions involve electrons and ionic charge. This is accounted for in the so-called Usavovich definition, only rarely used by geochemists, which does not differentiate between oxidizing agents and acids, or reducing agents and bases. A familiar example of its importance is to compare the acid strength of reduced hydrogen sulfide H2S (very weak) with that of oxidized sulfuric acid H2SO4 (very strong). That is, if it's oxidized, its generally more acidic, as you correctly you pointed out. Relevance to Mars? That's a longer story, and this post is already too long. -- HDP Don |
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