Bi weekly discussion---- Chemistry 101

[tims]

Yup thats right.. it is time to roll up those sleves and dust of the brain..
Chemistry 101

Lets start off with the the very basic Reef chemistry. , then move in to the more heavier things including making your own kalk...

So tell me what your parameters are and why, and whatyou know about them?
Do you have a good defintion of something? post it here, when we are all done i will cut and paste it on to one long post so you can find it a bit easier...

[tdwyatt]

Chemistry?

[gwen_o_lyn]

I have a question about measuring ALK- my test kit measures it in meg/L and if I get between 4-6, then thats a good number, however other test kits measure it another way and numbers like 9-11 are good... what are those differences?

[tdwyatt]

Originally Posted by gwen_o_lyn

I have a question about measuring ALK- my test kit measures it in meg/L and if I get between 4-6, then thats a good number, however other test kits measure it another way and numbers like 9-11 are good... what are those differences?

Hardness Units: .................. Eq in PPM CaCO3:
1 mEq/l...................................... 50 ppm
ppm CaCO3................................. 1.0 ppm
1 grain CaCO3/US gal.................... 17.1 ppm
Clark (eng) 1grain/impGal............... 14.3 ppm
10ppm(france) CaCO3................... 10.0 ppm
1 dKH (Germany) 10ppmCaO........... 17.9 ppm

and

If you want to do the conversions:

(mEq/l) X 50 = ppm CaCO3

(mEq) X 2.8 = dKH

(dKH) divided by 2.8 = mEq/l

(dKH)X 1.25 = Clark ( English hardness units)

(Clark) X 14.3 = ppm

(Clark) X 0.8 = dKH

ppm X 0.07 = Clark



The definition of Carbonate hardness is that amount of alkalinity in seawater due to the Carbonate (sigma-CO2) content of the water column. This includes all the species of the carbonate/bicarbonate buffer system, and as CARBONATE hardness does not include that alkalinity attributed to boron and it's differing species (boric acid/borate) BY DEFINITION (in practice, this is often intended to mean total alkalinity, although this is not correct). Boron levels in seawater are there mostly as boric acid, and at a pH of 8.0-8.1, are present as approximately 25% as the Borate ion. The TRUE concentration of HCO3- and CO3-- are determined by measuring at least two parameters of the carbonate system (pH; the total alkalinity called A sub t (AT; the total CO2, sigma CO2;or the partial pressure of CO2, [pCO2]), and plugging these values into Frank Millero's formula for total alk. However, when we wish to measure total alkalinity of the water column, we can titrate it with an acid, using an indicator dye to detect the point where all the carbonate is utilized to accept protons (, as indicated by the color change of the indicator) to meaasure true TOTAL ALKALINITY. This method of evaluating AT, including both borate and carbonate and miscellaneous other minor species, is the method used by most good home seawater test kits (Salifert, etc., titraation kits) for alkalinity. Determination of Borate is possible using permanganate to oxidize all the organic borate to a meaurable inorganic form, then using a complex with mannitol and glycol in the presence of a strong acid, then titrating with a base (Salifert makes a borate/boric acid test kit using a similar methodology). Seachem salts are unusually high in Boron, which, according to Leo Morin of Seachem, is because they (Seachem) feel that pH stability of the ASW made from this product is more important that the drawbacks of using high levels of Borate (open to debate; true for FO systems, not true for coral systems). Unless you are measuring both total alk and your boron alkalinity, (and subtracting the value for the boron alk from total alk), then your test kit is testing for total alkalinity of all proton acceptors. The units of the values reported will be determined by which product you use. Conversion is as per the above chart.


HTH

[tdwyatt]

Originally Posted by gwen_o_lyn

I have a question about measuring ALK- my test kit measures it in meg/L and if I get between 4-6, then thats a good number, however other test kits measure it another way and numbers like 9-11 are good... what are those differences?

Using 1 mEq/l X (2.8dKH/l)/(1 mEq/l) = 2.8 dKH/l...

4 mEq/l x 2.8 mEq/l = 11.2 mEq/l
6 mEq/l x 2.8 mEq/l = 16.8 mEq/l (a bit high, but these ARE just approximations)

a better goal in terms of mEq/l would be 3.5 to 4.5 mEq/l


HTH

[2003mikem]

uh what ??????

[gwen_o_lyn]

Originally Posted by tdwyatt

a better goal in terms of mEq/l would be 3.5 to 4.5 mEq/l


HTH

Wow Tom- that was very helpful, now if you could just explain that all over again and pretend you are talking to a kindergardener!! I like your goals for ALK better. *taking notes* My seachem test kit says that ASW measures between 2-3 mEq/l and that my tank should read between 4-6, however most the time I am reading around 3-4.

Another question... you are saying mEq/l- what does that mean? the L is for liter I think? but what about the rest of it. And what does DKH stand for?

[tims]

hhehhe Tom, i knew i could drag you in here sooner or later

since this is going to be Chem 101.
what are the main things we think about with our tanks and chemistry?

what are the defintions you think of when you talk about it?

Chemistry
n. pl. chem·is·tries

1. The science of the composition, structure, properties, and reactions of matter, especially of atomic and molecular systems.
2. The composition, structure, properties, and reactions of a substance.
3. The elements of a complex entity and their dynamic interrelation: “Now that they had a leader, a restless chemistry possessed the group” (John Updike).
4. Mutual attraction or sympathy; rapport: The chemistry was good between the partners.

Alkalinity
n. pl. al·ka·lin·i·ties The alkali concentration or alkaline quality of an alkali-containing substance
n : pH values above 7

phosphate

1 a : a salt or ester of a phosphoric acid
b : the trivalent anion PO₄⁻⁻⁻ derived from phosphoric acid H₃PO₄
2 : an organic compound of phosphoric acid in which the acid group is bound to nitrogen or a carboxyl group in a way that permits useful energy to be released (as in metabolism)

[tims]

Dkh is german for Degrees of Carbonite hardness
Kh is just carbonite hardness

over all i think we shoudl think of Dkh as total alkalinity

[tims]

Originally Posted by 2003mikem

uh what ??????

Mike welcome to the BI weekly..
that is the total reason why i am calling this Chem 101.....
dont understand something please ask!

[ski1297]

This is a must read for me!

[drsyme]

Originally Posted by gwen_o_lyn

Another question... you are saying mEq/l- what does that mean? the L is for liter I think? but what about the rest of it. And what does DKH stand for?

milliequivalents per liter.

This is measurement is a concentration. An amount of something per something.

Now what are milliequivalents you ask? If you dont really want to know, dont read any further.

First you need to be familiar with Avagadro's number. This is a very large number it is 6.023 x 10^23. If you want to know how it is derived I could tell you but it isnt important now how it is derived. But when you have a certain number of some substance that is equal to that number you have what is called a mole.

In this case we are talking about moles of hydrogen ions. Specifically a milliequivalent/liter is the same as a millimole per liter. That is (6.023 x 10^23 divided by 1000)hydrogen ions. So a millimole of ions in 1 liter of water is 1 meq/liter.

So...... The alkalinity in meq/l is the same as the number of millimoles of hydrogen ions. So an alk of 4.0 meq/l is 4 millimoles. or )6.023 x 10^23 / 1000) X 4.

This is important because as Tom was saying, the alkalinity kits used for home measurement, the good ones anyway, measure the number of hydrogen ions needed to convert all of the carbonate/bicarbonate species to carbonic acid. Which in seawater occurs at about pH 4.2. Tom's point is that other species absorb hydrogen ions too, so the actual number of hydrogen ions that titrate the test kits to completion is actually higher than the number of ions that convert carbonate/bicarbonate.

Now. Bicarbonate can accept one hydrogen ion, but carbonate can accept 2 hydrogen ions. so a 1 millimolar concentration of bicarbonate will be converted by 1 millimolar of hydrogen ions, or 1 millimolar concentration of bicarbonate is equal to 1 meq/l. But since carbonate accepts 2 hydrogen ions 1 millimolar concentration of carbonate is equal to 2 meq/l.

Why is this important? Well one of the other units is given in terms of how much calcium carbonate would it take to neutralize the number of hydrogen ions in this sample? It just so happens that the weight in grams per mole of calcium carbonate is 100. (A happy coincidence for reefers, like polaris is a happy coincidence for astronomers.) In other words a mole of calcium carbonate weighs 100 grams or 100 milligrams/millimole.

So sometimes, by convention, alkalinity is measured in terms of ppm. That is how many parts per million of calcium carbonate would it take to convert they hydrogen ions present in the sample. Since each molecule of calcium carbonate converts 2 hydrogen ions. And since the weight is 100 mg/millimole 100/2 = 50. The conversion to convert from meq/l to ppm multiply by 50.

[110galreef]

I thought this was the 101 class not the Doctorate's of CHEMISTRY!

[tdwyatt]

Originally Posted by drsyme

milliequivalents per liter.

This is measurement is a concentration. An amount of something per something.

Now what are milliequivalents you ask? If you dont really want to know, dont read any further....

...sometimes, by convention, alkalinity is measured in terms of ppm. That is how many parts per million of calcium carbonate would it take to convert they hydrogen ions present in the sample. Since each molecule of calcium carbonate converts 2 hydrogen ions. And since the weight is 100 mg/millimole 100/2 = 50. The conversion to convert from meq/l to ppm multiply by 50.

Nice post, Jack!

I was just discussing this with Mel, I was trying to decide just how deep into the topic to go This was just enough information to keep from bogging down in trying to explain the issues of two receptor slots for divalent ions vs one without throwing out too much theory.


BRAVO! GOOD POST!

[three90s&125sump]

Well, now I'm embarassed to post. I was just asking Tom about posting some info on this stuff. The Whats and Whys of tests and the such. I'm glad I just stumbled onto this.