Reef Chemistry Question of the Day #2

Randy Holmes-Farley

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Now this one has to be from memory since it is too easy to look up. Don't cheat...


Part 1. Name the four most abundant ions in seawater, in decreasing order of weight-based concentration (that is, decreasing order of ppm).

Part 2. Same question, but in decreasing order of the number of ions in seawater.


I'd rate it fairly hard since the majority of reefers may not have memorized this list.

Good luck and feel free to guess. That's part of the fun. We won't belittle any guesses.
 

TruRacr314x

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Weight Based

Hydrogen
Oxygen
Sodium
Calcium

No idea really...just guessing! On the ion side, not even gonna try to guess!
 

ScottyMcReefer

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Lol, it was a rough class but I graduated with a zoology degree somehow! Lol. This question has me absolutely stumped.
 

TruRacr314x

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I paid no attention in chemistry as show by my answer. A quick google check showed me I have no clue what I'm talking about!!
 

cope413

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Decreasing order? Meaning highest to lowest?

If so, I think leptang is right
Cl
na
so4
mg

And #2
Cl
Na
Mg
so4

Reason being mg is a lot lighter than so4 so higher number?
 

cope413

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Actually, I'm now wondering if cl and na are flipped for the same reason... It would also make sense why you would pose the question. Or maybe you wanted us to over think it... Cripes
 
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Randy Holmes-Farley

Randy Holmes-Farley

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Actually, I'm now wondering if cl and na are flipped for the same reason... It would also make sense why you would pose the question. Or maybe you wanted us to over think it... Cripes

:lol:

Yes, I wanted people to think it over. It's always good to know what's in your seawater. There have recently been discussions of what sorts of industrial salts might work as a cheap substitute in aquaria (none that I know of) and what it might mean that some manufacturers claim that their mix is mostly dried sea salt.

I'll give folks that might not check the forum on weekends a bit more time before posting the answer, but you folks are doing great!
 
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johnanddawn

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I don't know the answer, I would have to look it up. But guessing off the top of my head I would say
By weight and number Cl has to to be the most

The others Na, Ca, Mg I would think that because Ca and Mg ppt out Na has to be next again in both weight and number

The last two I would guess Mg by number and Ca by weight just cause you asked there has to be a difference

And since cope mentioned SO4 I didn't even consider that so know I have to look it up
 
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Randy Holmes-Farley

Randy Holmes-Farley

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Good work, everyone!

Cope had it exactly right.

The big four ions in seawater by weight are roughly:

chloride 19,400 ppm
sodium 10,800 ppm
sulfate 2700 ppm
magnesium 1300 ppm

But sulfate weighs more than all the others combined, so it moves down in rank when just counting the number of ions:

chloride 546 mM
sodium 468 mM
magnesium 53 mM
sulfate 28 mM
(mM = millimoles/liter; one millimole = 6 x 10^20 ions)

Certainly, oxygen is the largest mass in seawater, followed by hydrogen since they comprise the water, but I asked for ions, and water is not an ion. :)

Calcium just misses the list at 420 ppm, followed quickly by potassium at about 400 ppm.

Happy Reefing. :)
 

cope413

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Very cool. Always interesting to see numbers to things you don't often pay close attention to.

I have to ask, when you get a PhD from Harvard in Chemistry, do they give you a pass on shortening Avogadro's constant? It's been about 12 years since my last chem class, but my professors couldn't have used enough red ink if I had ever written 6 instead of 6.023 (if not .02214). One professor (he may have sniffed too many 'reagents' in the 60's) even took 10/23 as a personal holiday every day for over 20 years.
 
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Randy Holmes-Farley

Randy Holmes-Farley

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Very cool. Always interesting to see numbers to things you don't often pay close attention to.

I have to ask, when you get a PhD from Harvard in Chemistry, do they give you a pass on shortening Avogadro's constant? It's been about 12 years since my last chem class, but my professors couldn't have used enough red ink if I had ever written 6 instead of 6.023 (if not .02214). One professor (he may have sniffed too many 'reagents' in the 60's) even took 10/23 as a personal holiday every day for over 20 years.

Yes, I get too shorten Avagadro's number. I even get to call it Av's number for short. I don't get any special holiday's, however. :D

Seriously, I figured most reefers have so little interest in math that anything past the first digit just makes them hit the "next page" button. :)
 
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