Alien pH question

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Alien pH question

Post by NuclearVacuum on 25th August 2008, 1:44 pm

This question has been bothering me for a bit now. I can't think of any other way to ask it without making it into a story.

Lets say that an alien visitor comes to the Earth. However, he's home world is a planet with ammonia oceans (which is a base to humans). Ammonia and water have a pH difference of about 4. Would water feel to the alien as acid would feel to a human? And vise versa: would an alien from a planet with acidic oceans think water would feel like a base?

I know, this is a stupid question.
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Re: Alien pH question

Post by Sirius_Alpha on 25th August 2008, 10:10 pm

Yeah, probably.

As you know, pH just measures hydronium ions. If they base the dividing line between acid and base on their most abundant material, in this case, ammonia, then sure, water would be relatively acidic.

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Re: Alien pH question

Post by NuclearVacuum on 26th August 2008, 9:29 pm

Sirius_Alpha wrote:Yeah, probably.

As you know, pH just measures hydronium ions. If they base the dividing line between acid and base on their most abundant material, in this case, ammonia, then sure, water would be relatively acidic.

Would that also work vise versa? The main reason for me asking this is for story-lines. My alien species is used to acidic conditions. So I wanted to know how they would react to watery Earth.
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Re: Alien pH question

Post by Sirius_Alpha on 28th August 2008, 8:49 pm

Yeah, I'm sure it would. If I base my pH scale on something that is usually a pH of 9. Then I would consider water basic, at two below what I define as the dividing line.

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Re: Alien pH question

Post by Juramike on 1st September 2008, 1:37 am

Yup.

To get all anal-technical about it, the solvent can affect the measured pH. Most of the stuff we are used to are measured in water, so ammonia in water, H2S in water, etc.

Another common solvent used to measure the pKa's and pKb's is DMSO.

To get really anal about it, it is probably easiest to use the pka's and pkb's. pKa measures at above what pH is necessary to rip a proton off, and pKb measures at below what pH is necessary to stick a proton on. (It's a log scale, so at the pH things will be at 50% protonated/50%deprotonated. At 1 log unit below, you get about 10%/90%, and at 2 pH units below/above you get 1%/99%.)

[Medicinal chemists gotta worry all the time about what state molecules are in to get absorbed in the stomach or duodenem, or transported in the bloodstream (physiological pH 7.4).]

Here's a real example about pH: Your eyeball is at about pH 7.2-7.4. You can tolerate eyedrop formulations down to about pH 5, but anything below 6.5 will start to sting. On the basic side, if you get around pH 8 or pH 9, the basic conditions can actually cause hydrolysis of key stuff in the eye and can cause permanent damage - not good. Most eyedrop therapeutics avoid basic formulations and shoot for acidic formulations if they can't use a pH "neutral" formulation.

Depending on the biochemistry of your alien (especially the skin or other sensitive membranes), an different solvent or a different pH could cause damage. [A salt-dude visiting from the surface of Titan might not be too happy in his first terrestrial rainstorm.]

-Mike

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Re: Alien pH question

Post by Pfhreak on 18th October 2008, 2:27 pm

From http://www.daviddarling.info/encyclopedia/A/ammonialife.html which has a lot of information regarding the probability and nature of ammonia-based life:


In the ammonia system, water, which reacts with liquid ammonia to yield the NH+ ion, would appear to be a strong acid quite hostile to life. Ammono-life astronomers, eyeing our planet, would doubtless view Earth's oceans as little more than vats of hot acid.

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