Reef Chemistry Question of the Day 293: Let's Count Ions!

[Randy Holmes-Farley]

So dosing phosphate can raise the total alkalinity (just like silica), but won’t effect the amount of bicarbonate an’s carbonate?

It’s complicated. lol

But rest assured the effects are very small even with 1 ppm phosphate.

1 ppm phosphate will provide less than 0.03 dKH.

The reason it is complicated whether phosphate dosing impacts carbonate/bicarbonate has to do with the fact that one can dose PO4 - - - or HPO4- - or H2PO4 -. It then converts into the range of forms of phosphate present as a function of pH in seawater, and if the dosed forms do not match the final forms, some bicarbonate/carbonate may be added or removed.

 

[Miami Reef]

It’s complicated. lol

But rest assured the effects are very small even with 1 ppm phosphate.

1 ppm phosphate will provide less than 0.03 dKH.

The reason it is complicated whether phosphate dosing impacts carbonate/bicarbonate has to do with the fact that one can dose PO4 - - - or HPO4- - or H2PO4 -. It then converts into the range of forms of phosphate present as a function of pH in seawater, and if the dosed forms do not match the final forms, some bicarbonate/carbonate may be added or removed.

Thank you, Dr. Holmes-Farley. I really appreciate it.

 

[CoralB]

Reef Chemistry Question of the Day 293

The number of ions in a reef tank is truly mind boggling.

In 100 gallons of seawater, there are about 255,000,000,000,000,000,000,000,000 individual ions.

Let's count them one by one!

Someone had to do it, right? How else would we know?

OK, we'll assign that to a newbie and try a different exercise.

Counting by numbers of ions, not by weight of ions, which are there more of in seawater?

A. Calcium ions
B. Ions that contribute to alkalinity
C. All trace elements added together
D. Potassium Ions

PS, this is an open book test, unless you are truly a chem wizard!

Good luck!

Previous Reef Chemistry Question of the Day:

Reef Chemistry Question of the Day 292: Fireworks

Reef Chemistry Question of the Day 292 In honor of the Fourth of July (Independence Day, sorry, Great Britain), let's have some fireworks fun. Which of these favorite reefing chemicals provides the orange color in many fireworks? A. Calcium B. Magnesium C. Phosphate D. Nitrate Good luck and...

www.reef2reef.com

No fair , I tried turning the tablet upside down and couldn’t find the answer . My cereal box has more respect for me lol !!
My answer is “A “ because I just tuned in and you already gave the answer !!

 

[Randy Holmes-Farley]

Thank you, Dr. Holmes-Farley. I really appreciate it.

You're welcome!

Happy reefing.

 

[Randy Holmes-Farley]

No fair , I tried turning the tablet upside down and couldn’t find the answer . My cereal box has more respect for me lol !!
My answer is “A “ because I just tuned in and you already gave the answer !!

Better late than never. lol

 

[FrugalReefer]

None of the above. The correct answer is algae ions.

 

[taricha]

I would've guessed K (lighter than Ca, so maybe more ions) and been wrong btw.

Total ions adding up to give alkalinity (bicarbonate, carbonate, borate, phosphate, silicate, hydroxide) together are about 5x lower than calcium and potassium.

So if you had added answer choice F. "Ions contributing to pH" where would that rank? Fewer than ions contributing to alk?

 

[Randy Holmes-Farley]

I would've guessed K (lighter than Ca, so maybe more ions) and been wrong btw.

So if you had added answer choice F. "Ions contributing to pH" where would that rank? Fewer than ions contributing to alk?

This is perhaps a surprisingly complicated question to answer with real accuracy.

When you say contributing to pH, that could mean a number of things.

1. Add it in some form, does that addition impact pH?

2. When in the water, does it contribute to pH buffering against small changes up and down?

3. Truly contributing to pH while in the water is only H+ since that's the actual definition.

Discussion:

1. Some things one might add in one form will take a different form in the water. That includes obvious ones like hydroxide, carbonate, bicarbonate, borate, and boric acid. But also some nonobvious and small contributors such as magnesium.

From one of my articles:

A small portion (about 10%) of the magnesium is present as a soluble ion pair with sulfate (MgSO4), and much smaller portions are paired with bicarbonate (MgHCO3+), carbonate (MgCO3), fluoride (MgF+), borate (MgB(OH)4+), and hydroxide (MgOH+).

Those pairings tend to use up some of each of those (e.g., removes them). When the system re-equilibrates, there will be a small change in pH. The up or down effect is not trivial to determine overall:

When you remove some carbonate, some bicarbonate splits into H+ and carbonate to replace it, buy Le Chatlier's principle:

HCO3- --> H+ + CO3--

That lowers pH.

The reverse happens with bicarbonate removal

H+ + CO3-- ---> HCO3-

That raises pH.

Binding borate lowers pH. Binding hydroxide also lowers pH.

My expectation is that adding bare magnesium ion tends to lower pH a small amount, but does not alter alkalinity because each of those things will fall off during an acid titration.

Other ions do this as well, such as calcium. From the definition for total alkalinity in seawater:

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

we see that someone has already determined that all of these are pretty minor in normal seawater concentration, except MgOH+.

2. The same discussion as above would relate to pH buffering. The big boys are carbonate/bicarbonate and borate/boric acid, but many other things give very minor contributions.

 

[taricha]

I was going back and forth arguing with myself that "Ions contributing to pH" was bigger or smaller than "ions contributing to alk"
1) all it takes to define pH is H+ and/or OH- making it smaller than "ions contributing to Alk"
and
2) seawater pH is a function primarily of Alk and CO2, meaning that I need to include more ions than alkalinity to determine pH.

Your answer confirms that I can still give myself headaches anytime I think about pH long enough.

 

[Randy Holmes-Farley]

I was going back and forth arguing with myself that "Ions contributing to pH" was bigger or smaller than "ions contributing to alk"
1) all it takes to define pH is H+ and/or OH- making it smaller than "ions contributing to Alk"
and
2) seawater pH is a function primarily of Alk and CO2, meaning that I need to include more ions than alkalinity to determine pH.

Your answer confirms that I can still give myself headaches anytime I think about pH long enough.

On #2, assuming normal seawater concentrations of all ions, and at fixed salinity, those other ions are already baked into the standard calculations. But for water that deviates significantly (and magnesium differences might be among the most important here since it varies a lot), there will be deviations.