Converting mg/L into mEq/L
 

I've been searching online for how to do this but my head is starting to hurt. :p I've never been good at math and forget chemistry! I found a conversion formula but it was for Ca and you have to know the valence or something like that so I thought I'd try looking up "valence of CaCO3" but that didn't work. I probably wasn't even on the right track. This is what I was looking at;

milliequivalents per liter (meq/L) - meq/L is another method of expressing concentration, when the analytes are dissolved and disassociated in solution. meq/L is also equal to millimoles of charge per liter (mM+/L or mM-/L depending on valence). To calculate meq Ca/L from the reported value in mg/L, we must know something about calcium.


Calcium has a molecular weight of 40.08 grams/mole
Calcium has a valence of +2
The equivalent weight = (40.08grams/mole)/(2 equivalents/mole) = 20.04 grams/eq
To convert to mg/meq you simply multiply g/eq by 1000 mg/g and divide by 1000 meq/eq, thus g/eq = mg/meq
If your sample contains 30 mg Ca/L, what is the concentration in meq/L?

Meq Ca/L = (30 mg Ca/L)/(20.04 mg/meq) = 1.50 meq Ca/L

Anyways, I just want to know if you have alkalinity test results of 110 mg/L, what is that in meq/L? (I'd like to know how to solve the problem too for future reference)

mg/L is about the same as ppm, so divide by 50 for ppm CaCO3 equivalents. That's about 2.05 meq/L. The valence isn't critical; the atomic weights are what's used. This article covers a lot of units of measurement:

http://reefkeeping.com/issues/2005-08/rhf/index.php

Jon

The valence is critical when dealing with ions with a charge of more than 1.

I mol with a valence of 1 = 1 meq / l

1 mol with a valence of 2 = 2 meq / l

1 mol with a valence of 4 = 4 Meq /l

10 mmol of Ca++ = 20 meq /l Ca++

1 mmol of HCO3- = 1 meq / l

1 mmol of CO3-- = 2 meq / l

Mol / L x MW = ppm or mg / l

It all depends on what your are calculating

If your sample contains 30 mg Ca/L, what is the concentration in meq/L?

Mol / L x MW = ppm or mg / l

So, 30 ppm / 40 MW = .75 mmol

.75 mmol x its charge of 2 = 1.5 meq/ l

In this hobby the only thing we use in meq/ l is Alk. So forget about everything else unless you have a reason for it.

I was assuming she wanted ppm CaCO3 equivalents.

I know but I just wanted CaCO3 equivalents clarified. And now I will have to clarify this CaCO3 equivalents

This is really not a REAL value. It is an expression conversion and the value does not really give you a true value of how much Ca++ there is.

It goes like this. IF water could hold 150 ppm CaCO3, which it absolutely can not, it would yield a concentration of 150 ppm CaCO3 if all the CO3-- was attached to a Ca++ ion. It is a poor expression from long about that gave the "potential" of you much CaCO3 could leave solution. Be it FW or SW only a very small amount of CaCO3 can held in solution. It is only a few ppm. Remember here we are talking about CaCO3 in solution and NOT Ca++ and CO3-- in solution. The Ksp in FW is only 8.3 and vs the Ksp for Kalk which is 5 and something like KCl is 0.98. The lower the # the more it can hold. Dolomite is like 15

Thank you Jon, you make it so simple. I was kind of hoping you'd post some big, long formula and I wouldn't feel so bad for not getting it on my own. :)

Boomer, for now I'm just worried about what is used in this hobby but hey, who knows when you might run in to the need for the other info!

Thanks!

I wanted to be simple Rachel like Jon but you made if difficult :D. See the other post.

I make simple things difficult on a pretty regular basis! ;) Thank you both for your time!

isn't 1 meq/l = 50ppm = 2.8 dKh and not 2.05?

That equation is correct. The 2.05 is the conversion of 110 ppm by incorrect division. :) I must have been tired. 110 ppm is about 2.2 meq/L. :)