Reef Chemistry Question of the Day 290: Zwitterions

[Randy Holmes-Farley]

Reef Chemistry Question of the Day 290

Ions can come with a variety of charges on them, including one or more positive charges, one or more negative charges, and some of each.

An ion with some of each type is called a zwitterion,

In seawater at pH 8.2, which of the following materials exists as a zwitterion? (note, for this question, we are not considering the more complicated issue of what sorts of ion pairs or complexes these ions may make with other ions in seawater).

A. Phosphate
B. Nitrate
C. Calcium
D. Glycine (the amino acid)
E. Acetate (such as from dosing vinegar)
F. Ethanol (such as from dosing vodka)

Good luck!

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Reef Chemistry Question of the Day 289: What is H+?

Reef Chemistry Question of the Day 289 There are a variety of ways that H+ is important in reefing. pH is a measure of the concentration of H+ in the water. Total alkalinity is the amount of acid needed to raise the H+ concentration to a specific value. A CaCO3/Co2 reactor uses carbon...

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[taricha]

I remember reading about zwitterions. They sounded very made-up. Now... what was I reading about? I don't remember.

 

[Dan_P]

I remember reading about zwitterions. They sounded very made-up. Now... what was I reading about? I don't remember.

HINT: Zwitter in German can mean hermaphrodite, like an earthworm, you know +/- in the same individual.

 

[taricha]

Now... what was I reading about? I don't remember.

Now I remember. I was reading some stuff trying to figure out why aspartic acid was so annoying to dissolve, and figure out if there was a simple solvent that would help.

 

[Dan_P]

Now I remember. I was reading some stuff trying to figure out why aspartic acid was so annoying to dissolve, and figure out if there was a simple solvent that would help.

Yes, the solubility is a pain.

 

[biom]

Most zwitterions are generally quite soluble in water.

Now I remember. I was reading some stuff trying to figure out why aspartic acid was so annoying to dissolve, and figure out if there was a simple solvent that would help.

Just neutralize it with a base to have 150 times more soluble aspartate

 

[taricha]

Just neutralize it with a base to have 150 times more soluble aspartate

Zapping the solution in the microwave for a few minutes was the least annoying way I found to dissolve it in a small amount of water.

 

[Randy Holmes-Farley]

And the answer is:

In seawater at pH 8.2, which of the following materials exists as a zwitterion? (note, for this question, we are not considering the more complicated issue of what sorts of ion pairs or complexes these ions may make with other ions in seawater).

A. Phosphate
B. Nitrate
C. Calcium
D. Glycine (the amino acid)
E. Acetate (such as from dosing vinegar)
F. Ethanol (such as from dosing vodka)

D.. Glycine. Glycine looks like the drawing below, with a positive charge on the nitrogen and a negative charge on the oxygen. All amino acids exist primarily as zwitterions at pH 8 in seawater.

Glycine - Molecule of the Month - April 2010 (HTML version)

http://www.chm.bris.ac.uk/motm/glycine/zwitterion-ph.gif

A. Answer A is wrong because phosphate only carries negative charges (from 1 to 3 in seawater at pH 8) PO4---, HPO4-- and H2PO4-.
B. Answer B is wrong because nitrate only carries one negative charge. NO3-
C. Answer C is wrong because calcium only carries two positive charges. Ca++
E. Answer E is wrong because acetate only carries one negative charge. CH3CO2-
F. Answer F is wrong because ethanol carries no charges (CH3CH2OH).