Reef Chemistry Question of the Day #199 Trace element form

[Randy Holmes-Farley]

Reef Chemistry Question of the Day # 199

Trace elements in seawater are wonderfully complicated beasts. Despite most being metals, they come in all sorts of different chemical forms, and some come in several forms at the same time.

Most metals are present in seawater in a positively charged form, such as sodium (Na+), copper (Cu++), iron (Fe++ and Fe+++), etc.

Some, however, are present in a negatively charged form.

Which of the following is NOT negatively charged? To help, I have written the name of the chemical form present in seawater.

A. Chromium as chromate
B. Vanadium as vanadate
C. Cobalt as cobaltous ion
D. Molybdenum as molybdate

Good luck!





































.

 

[cginter]

C?

 

[DamianOZ]

C

 

[JimWelsh]

I'm going with "C" also, because I associate the "-ate" suffix with anions, as in sodium carbonate, sodium nitrate, potassium chromate, etc., and "cobaltous" sounds a lot like the "-ous" suffix used with the cation in ferrous sulfate, for example.

 

[DamianOZ]

ate = bound with O atoms, all ates and ites are -'ve charged.
Cobalt is a metal, all metals have a +'ve charge, since its an ion it is not bound to another elements, so it remains +

 

[Lynn52]

C

 

[jimymin]

C

 

[Bruce Burnett]

C

 

[jsker]

I am joining the C's

 

[john.m.cole3]

C, b/c it's the only one that doesn't end with an "ate"

 

[KingBlingTX]

Well, I'm jumping on the "C" bandwagon as well. The -ous suffix gives it away (like Ferrous Oxide where the iron is the cation).

 

[Randy Holmes-Farley]

And the answer is...C. Cobalt as cobaltous ion

Not that most reefers will not know or need to know this, but here are some interesting (maybe ) things to note about chemical names:

Names ending in "ate" are negatively charged and contain oxygen, like phosphate (PO4---), nitrate (NO3-), and silicate (various forms, such as Si(OH)3O-). The reverse is not necessarily true, since other forms with oxygen and a negative charge do not end in "ate" when there are multiple possible forms with the same central atom (such as N or P). An example is nitrite (NO3-).

Ions that end in "ous" are usually metals with a positive charge. They are often those with multiple possible forms, and the "ous" has a lower positive charge and the "ic" end has a higher positive charge, such as ferrous (Fe++) vs ferric (Fe+++).

Knowing what forms trace elements are in is needed to know what things can mix with other things in additives mixtures, for example.

Happy Reefing.