Chemical Purity

[SaltyWaitress]

First real post!

How many impurities are in common reef additives? Is the difference in purity between a reef marketed sodium bicarbonate supplement and USP or even reagent sodium bicarbonate big enough that it could make a difference in the long run? Maybe some impurities aren't so bad and that's the reason we do not care as much? I was thinking about it and thought that maybe through difference sources and purification processes that certain additives might be more likely to have bad impurities than others. Which could those be, including trace additives like strontium or anything at all?

 

[Randy Holmes-Farley Verified Community Expert]

First real post!

How many impurities are in common reef additives? Is the difference in purity between a reef marketed sodium bicarbonate supplement and USP or even reagent sodium bicarbonate big enough that it could make a difference in the long run? Maybe some impurities aren't so bad and that's the reason we do not care as much? I was thinking about it and thought that maybe through difference sources and purification processes that certain additives might be more likely to have bad impurities than others. Which could those be, including trace additives like strontium or anything at all?

Welcome to Reef2Reef!

How many impurities? Probably about a hundred (meaning every inorganic ion likely to be stable in seawater).

Certainly the key to impurity concern is what impurity and what concentration.

There are several approaches to this concern.

One good option is to use only grades like FCC (food), USP (pharmaceuticals) or ACS reagent grade. IMO, that's the best bet.

Second option is to use only materials that have either been analyzed for purity (very, very few), or which have a wide range of reefers using them OK.

Last option is to wing it and hope for the best using whatever grades you can buy. lol

Reefers do all of these, and for some additives, option 3 is still OK since other options are not easily obtained.

 

[SaltyWaitress]

Thank you. I thought ACS and reagent grade was the same but some stuff says reagent grade but is not ACS, looks like ACS is even better?

 

[SaltyWaitress]

Say I am looking at bromine. Sometime I see it measured in ppm like an ICP I saw that said 55 ppm. Other times I see people talking about it in mg/L. How do I convert between the two, can you show me the math and what I need to know to do it? Then if I have sodium bromide, how do I calculate how much I dissolve in water and dose to say bring it from 55 to 70 and also what is that in ppm, thank you again

 

[Randy Holmes-Farley Verified Community Expert]

Thank you. I thought ACS and reagent grade was the same but some stuff says reagent grade but is not ACS, looks like ACS is even better?

ACS and reagent grade are generally the same thing.

To convert from ppm to mg/L impurity in a liquid you need to know the density of the liquid. If the density is 1.000, those units of measure are the same. mg/L is never a unit of measure for impurities in a solid.

here's the general process for doing calculations, but for many things we use, online calculators are available.

If bromide is 50 ppm (very close to 50 mg/L) in a reef aquarium and you want to raise it to 60 ppm, then you need to add 10 mg for each liter of water volume.

Sodium bromide has a molecular weight of 102.9 g/mole, with sodium accounting for 23 g/mole and bromide accounting for 79.9 g/mole. Sodium bromide is thus 79.9/(102.9) = 77.6% bromide by weight (assuming it is anhydrous meaning no water in it).

Since sodium bromide is only 77.6% bromide, to get 10 mg of bromide you need 10 mg/0.776 = 12.9 milligrams of sodium bromide.

Thus you will add to your aquarium 12.9 mg of NaBr for each liter of water volume.

 

[Randy Holmes-Farley Verified Community Expert]

On the topic of purity, you may find this question of the day interesting:

Reef Chemistry Question of the Day #253 Purity, what does it mean?

Reef Chemistry Question of the Day #253 Purity means different things to different people. We use products that have purity grades (such as pharmaceutical grade (USP), food grade (FCC), reagent grade), some that give numbers (e.g., 99%) and many that say nothing. For example, let's take one...

www.reef2reef.com

 

[SaltyWaitress]

Great, very clear but one question. You mentioned purity, I did not think that related to converting units like mg/L to ppm or vice versa.

So I would google what the density of sodium boride, if it's one then mg/L and ppm is the same for all compounds, and if its not one?

 

[Randy Holmes-Farley Verified Community Expert]

Great, very clear but one question. You mentioned purity, I did not think that related to converting units like mg/L to ppm or vice versa.

So I would google what the density of sodium boride, if it's one then mg/L and ppm is the same for all compounds, and if its not one?

There will never be a purity of a compound listed as mg/L unless it is a liquid.

If you did want to convert from mg/l to ppm of something in a liquid, especially one that isn't water, you will have to account for the density.

That said, for nearly all reef purposes, assuming that mg/L and ppm are the same will almost always be accurate enough for our purposes. We rarely use liquids that deviate greatly from the density of pure water, which is 1 g/mL.

 

[SaltyWaitress]

I was doing the math on your improved two part Ca recipe one and kept getting about 47500ppm Ca which I got wrong, it's 37000. Is this because ESV CaCl is really calcium chloride dihydrate and I need to account for the weight of the dihydrate so the CaCl is really just 78% of it (other 22% is dihydrate)? When I order BRS CaCl is that pure or is that also dihydrate?

I was also reading your alk pages and but am still confused on some stuff. I don't see why soda ash provides more alk than sodium bicarbonate because sodium carbonate just has an extra sodium, so a lesser percentage of it's mass is HCO3 as compared to sodium bicarbonate with only one Na. I also read this post "sodium carbonate has 2 equivalents but sodium bicarbonate only has one" which makes no sense to me for the same reason, only difference is one Na. The only reason I can understand is that you can dissolve more sodium carbonate and that is why it's stronger.

 

[SaltyWaitress]

And how can I calculate how much alk I get from Sodium bicarbonate, sodium carbonate, and calcium hydroxide? I can get to ppm or mg/L just like with other examples but it's in meq/L or DKh.

Is there a quick weight in grams per L provides this much alk for each one of those and if I did want to do the calculations how would I do that?

Thank you

 

[Randy Holmes-Farley Verified Community Expert]

I was doing the math on your improved two part Ca recipe one and kept getting about 47500ppm Ca which I got wrong, it's 37000. Is this because ESV CaCl is really calcium chloride dihydrate and I need to account for the weight of the dihydrate so the CaCl is really just 78% of it (other 22% is dihydrate)? When I order BRS CaCl is that pure or is that also dihydrate?

I was also reading your alk pages and but am still confused on some stuff. I don't see why soda ash provides more alk than sodium bicarbonate because sodium carbonate just has an extra sodium, so a lesser percentage of it's mass is HCO3 as compared to sodium bicarbonate with only one Na. I also read this post "sodium carbonate has 2 equivalents but sodium bicarbonate only has one" which makes no sense to me for the same reason, only difference is one Na. The only reason I can understand is that you can dissolve more sodium carbonate and that is why it's stronger.

Yes, you need to account for the dihydrate.

I believe the BRS product is also the dihydrate. In general, the 2 water molecules in it are no drawback for adding into water, and the dihydrate is generally cheaper since the typical industrial process involves drying the dihydrate to make anhydrous calcium chloride.

 

[Randy Holmes-Farley Verified Community Expert]

And how can I calculate how much alk I get from Sodium bicarbonate, sodium carbonate, and calcium hydroxide? I can get to ppm or mg/L just like with other examples but it's in meq/L or DKh.

Is there a quick weight in grams per L provides this much alk for each one of those and if I did want to do the calculations how would I do that?

Thank you

1 meq/L equals one millimolar (1 millimole/L) of alk added

For bicarbonate and hydroxide, the alk added is equal to the millimolar concentration of the bicarbonate ions or the hydroxide ions present (some chemicals, such as calcium hydroxide, add two hydroxide ions, so you need to account for that).

Carbonate adds two units of alkalinity for each carbonate ion, so 1 millimolar carbonate = 2 meq/L of alkalinity.

 

[SaltyWaitress]

OK so to see if I did the math right I took the recipe 2 where you tell us the answer is 2660, but then I did it a different way yet still got the same answer:

297g/gal x gal/3.78L = 78.57g/L x mol/84g = .935 mol/L x 1000mmol/mol = 935mmol/L = 935meq/L x 2.8 = 2618 dkh which is pretty close to your answer of 2660dkh.

Then I realized I used the mass for the whole NaHCO3 (84g) and NOT just for HCO3 bicarbonate ion (61g) so did I do this wrong? Your post said “millimolar concentration of bicarbonate or hydroxide ions” so do I use the % of NaHCO3 that is CO3 and it’s mass?

297g x 61g/84g = 215.7 grams of carbonate ion /gal x gal/3.78L = 57.06g/L x mol/61.02g= 0.935mol/L x1000mmol/mol = 935mmol/L = 935meq/L x 2.8 = 2618 dkh.

OK got the same answer but don’t understand why, when doing this for CaOH or NaOH can I just do take the molar mass (whole CaOH) of those and don’t need to % out the OHs like I did the carbonate ions in the second problem I did?

Thanks a lot hope you dont mind if I keep asking you these, I will get it eventually

 

[Randy Holmes-Farley Verified Community Expert]

No problem!

Since you weigh out the whole thing (sodium plus hydroxide, for example), you have to divide by the molecular weight of the whole thing to get the molar concentration of any of the parts.

You could do the percent thing you mention then divide by the weight of the hydroxide alone, but that's just extra steps.

Calcium hydroxide is Ca(OH)2.

 

[SaltyWaitress]

But I would think that different molecules would provide different percentages of alkalinity related to their total weight.

1. Will 1 mole of NaOH provide the same amount of alk as 1 mole of NaHCO3?

2. Does 1mmol/L = 2meq/L hold true for both Na2CO3 and CaOH2. If not how to account for 2 OHs in CaOH2?

3. Na2CO3 only has 1 CO3, just like NaHCO3, why does it have double the alk?

 

[Randy Holmes-Farley Verified Community Expert]

But I would think that different molecules would provide different percentages of alkalinity related to their total weight.

1. Will 1 mole of NaOH provide the same amount of alk as 1 mole of NaHCO3?

2. Does 1mmol/L = 2meq/L hold true for both Na2CO3 and CaOH2. If not how to account for 2 OHs in CaOH2?

3. Na2CO3 only has 1 CO3, just like NaHCO3, why does it have double the alk?

1. Moles (weight divided by molecular weight) are numbers of molecules, and molar concentration is moles per unit volume so number of molecules per unit volume, so it translates directly to alkalinity.

2. Yes.

3. Goes back to the definition of alkalinity. I discuss that in detail here:

Chemistry and the Aquarium: What is Alkalinity?

Randy provides an overview of alkalinity as to why it's important, how it's measured, and how can it be tested.

reefs.com

The article explains why, but this is the definition of total alkalinity (TA):

TA = [HCO3–] + 2[CO3--] + [B(OH)4–] + [OH–] + [Si(OH)3O–] + [MgOH+] + [HPO4--] + 2[PO4---] – [H+]

[A] means the molar concentration of chemical A

 

[SaltyWaitress]

Great, then If I understand 1 mole of NaOH will provide the same amount of alk as 1 mole of NaHCO3 just like your answer in 2. where one mole of CaOH2 and one mole of Na2CO3 provide the same amount.

 

[SaltyWaitress]

I am on a roll of learning here! Snowed in and coronad' in

I read that 96g of NaHCO3 can be dissolved in 1 L of water, is this RODI or tap and isnt it different?

96g x 3.78 = 362 grams, any reason why I should not dissolve the max possible? Why do you only call for 297g/gal in recipe 2?

Recipe one has you cooking the NaHCO3, you simply make Na2CO3 from this right?

 

[Randy Holmes-Farley Verified Community Expert]

Great, then If I understand 1 mole of NaOH will provide the same amount of alk as 1 mole of NaHCO3 just like your answer in 2. where one mole of CaOH2 and one mole of Na2CO3 provide the same amount.

Yes!

 

[Randy Holmes-Farley Verified Community Expert]

I am on a roll of learning here! Snowed in and coronad' in

I read that 96g of NaHCO3 can be dissolved in 1 L of water, is this RODI or tap and isnt it different?

96g x 3.78 = 362 grams, any reason why I should not dissolve the max possible? Why do you only call for 297g/gal in recipe 2?

Recipe one has you cooking the NaHCO3, you simply make Na2CO3 from this right?

Pure fresh water, but tap will be close. Tap may already have some sodium or bicarbonate or both in it, which reduces the amount more that will dissolve.

Max possible can be hard to attain, and if it gets cool, some will precipitate back out. That's the main reason I backed off on concentrations. Low dose volume if not usually a main goal, except perhaps if trying to use an existing dosing pump.

Right on the baking.