Using vinegar vs muriatic acid to clean aquarium

[AlanM]

I got 2 gallons of muriatic acid from Lowes to etch doo-doo off some old live rock. In addition I'd like to use it to remove coralline and calcium deposits off an old aquarium. I know a lot of people use vinegar to clean off equipment of calcium deposits and old coralline and make it all shiny, but I only have vinegar in salad size quantities, so I'd like to use the HCl I bought already.

 

I took chemistry too many years ago, so maybe someone can help me out with this. I know HCl is considered a strong acid, meaning it dissociates completely in water, so if you know the molarity of HCl then you also know the molarity of hydronium ions. My muriatic acid is 30% HCl, so by my math that's a molarity of about 8.61 mols of hydronium per liter.

 

I read somewhere that storebought vinegar is about 5% acetic acid, which comes out to 0.85M, and it has a dissociation constant of 1.8e-5, so that seems like store bought vinegar would have a molarity of about 1.5e-5 mols of hydronium/liter.

 

Does that mean that to get the same "dissolving power" of straight vinegar when using muriatic acid from Lowes I would have to dilute it by a factor of 8.61 / 1.5e-5 or 574,000? This comes out to 6.6 microliters per gallon, that's like a tenth of a drop.

 

Seems like I must be doing something wrong. Are there any chemists around that can set me straight? I put a cup of the stuff into a 5 gallon bucket of water, hung a crudded up aquaC Remora on the edge and set it running. Seems to be working.

[Dan]

not sure, but i always heard to dilute muriatic acid 1:10 for cleaning up a tank. just remember to always add the acid to water, and not the water to the acid (but you probably already knew that).

[AlanM]

Yep, that and don't breathe the vapors.

 

I had heard to dilute muriatic acid 1:10 for cleaning live rock at which concentration it will fizz like crazy for a while as it dissolves calcium off the outer parts of the rock, but thought it was maybe different for doing a tank and equipment.

[Origami]

I got 2 gallons of muriatic acid from Lowes to etch doo-doo off some old live rock. In addition I'd like to use it to remove coralline and calcium deposits off an old aquarium. I know a lot of people use vinegar to clean off equipment of calcium deposits and old coralline and make it all shiny, but I only have vinegar in salad size quantities, so I'd like to use the HCl I bought already.

 

I took chemistry too many years ago, so maybe someone can help me out with this. I know HCl is considered a strong acid, meaning it dissociates completely in water, so if you know the molarity of HCl then you also know the molarity of hydronium ions. My muriatic acid is 30% HCl, so by my math that's a molarity of about 8.61 mols of hydronium per liter.

 

I read somewhere that storebought vinegar is about 5% acetic acid, which comes out to 0.85M, and it has a dissociation constant of 1.8e-5, so that seems like store bought vinegar would have a molarity of about 1.5e-5 mols of hydronium/liter.

 

(Close. Take the square root of your 1.5e-5 to get ~3.87exp-3 [H+] -Tom)

 

Does that mean that to get the same "dissolving power" of straight vinegar when using muriatic acid from Lowes I would have to dilute it by a factor of 8.61 / 1.5e-5 or 574,000? This comes out to 6.6 microliters per gallon, that's like a tenth of a drop.

 

(8.61 / 3.87exp-3 = 2225. But, as you'll see below, the HCl is actually more concentrated. -Tom)

 

(Density was a minor oversight in both prior calcuations. Density is used to get the number of grams and, thus, the number of moles per liter. -Tom)

 

Seems like I must be doing something wrong. Are there any chemists around that can set me straight? I put a cup of the stuff into a 5 gallon bucket of water, hung a crudded up aquaC Remora on the edge and set it running. Seems to be working.

 

I dilute muriatic at a 1:100 ratio for cleaning equipment. This is still faster and more effective than vinegar.

 

That said, assume 5% acetic acid in store bought distilled vinegar. I'm assuming this is by volume, not by weight. That's 50 ml acetic acid per liter. Applying a density factor of 1.049 grams/ml, this yields 52.45 grams acetic acid per liter. At 60 grams per mole, that's 0.874 molar. pKa for acetic acid is 4.76, or Ka = 1.738exp-5. Ka for this is [H+][CH3COO-]/[CH3COOH]. For simplicity, since the dissociation constant is so low, assume [CH3COOH] = 0.874 (that is, not much of it is dissociating) to get a first order approximation for [H+]. Now calculate SQRT((1.78exp-5)(0.874)) = 3.94exp-3. This is approximately [H+], or 0.00394 moles/liter.

 

The HCl from Lowes is 20 Baume, or 31.45% HCl by weight. Density of this solution is 1.159 kg/l. Molarity is 10.17 molar. Dissociation is assumed complete,so you get 10.17 moles/liter [H+].

 

10.17 / .00394 = 2581. That's about how many times more H+ ions you'll get from 20 Baume muriatic acid than from an equal amount (by volume) of store-bought distilled white vinegar. [edit: Assuming both are sitting in a flask, unconsumed. This changes a bit as the acetic acid continues to dissociate as hydrogen ions are consumed in a tank-cleaning scenario.]

[DaveS]

I dilute muriatic at a 1:100 ratio for cleaning equipment. This is still faster and more effective than vinegar.

 

That said, assume 5% acetic acid in store bought distilled vinegar. I'm assuming this is by volume, not by weight. That's 50 ml acetic acid per liter. Applying a density factor of 1.049 grams/ml, this yields 52.45 grams acetic acid per liter. At 60 grams per mole, that's 0.874 molar. pKa for acetic acid is 4.76, or Ka = 1.738exp-5. Ka for this is [H+][CH3COO-]/[CH3COOH]. For simplicity, since the dissociation constant is so low, assume [CH3COOH] = 0.874 (that is, not much of it is dissociating) to get a first order approximation for [H+]. Now calculate SQRT((1.78exp-5)(0.874)) = 3.94exp-3. This is approximately [H+], or 0.00394 moles/liter.

 

The HCl from Lowes is 20 Baume, or 31.45% HCl by weight. Density of this solution is 1.159 kg/l. Molarity is 10.17 molar. Dissociation is assumed complete,so you get 10.17 moles/liter [H+].

 

10.17 / .00394 = 2581. That's about how many times more H+ ions you'll get from 20 Baume muriatic acid than from an equal amount (by volume) of store-bought distilled white vinegar.

 

Ok if I glazed over this correctly, at 1:100 dilution of muratic acid, it's still 25x stronger than straight household vinegar?

[Origami]

Ok if I glazed over this correctly, at 1:100 dilution of muratic acid, it's still 25x stronger than straight household vinegar?

Yes. In terms of acidity, it is.

[AlanM]

Thanks for straightening out my math! Missed that square root in there and got some of the densities a bit wrong.

 

If it's 25x stronger at a 1:100 dilution in terms of acidity is it also 25x stronger at dissolving the reef tank calcium precipitates and coralline algae (and live rock surfaces) we're interested in dissolving?

[Origami]

Thanks for straightening out my math! Missed that square root in there and got some of the densities a bit wrong.

 

If it's 25x stronger at a 1:100 dilution in terms of acidity is it also 25x stronger at dissolving the reef tank calcium precipitates and coralline algae (and live rock surfaces) we're interested in dissolving?

Not quite. It gets a little more complicated as the hydrogen ions are consumed, the remaining undissociated acetic acid should begin to dissociate. However, not to the same extent as the acetate component will not have been consumed (and remains in solution). Thus, less hydrogen ion will be released and consumed, raising the level of acetate even further. And so on. Eventually, all of the acid will dissociate (if the hydrogen ions continue to be consumed), but it could take a very long time as exponentially lower and lower concentrations of hydrogen ion are in solution because of the limit imposed by Ka.

 

From a practical standpoint, it dissolves calcium carbonate and coralline algae just the same, only quicker and without the organic residue (acetate) of vinegar.

[swffan]

I personally would need a translator for this conversation!

[Rosco's Reefs]

Why did you buy 2 gallons? That sounds like a load of that stuff. Is that the only way the sell it?

[Origami]

It's sold in 1 gallon jugs at a cost of around $7 per gallon at Lowe's. Personally, I always have at least a spare gallon on hand as it's not worth a special trip just to pick up another gallon when you need it. For most, though, one gallon will last a long while.

 

BTW, this stuff is about as concentrated as muriatic acid (hydrochloric acid) can get. At this concentration, it fumes with chlorine gas. When I use it, I have the water at the ready when I uncap and pour it. (Always add strong acids to water, not the other way around as it can splatter if you add it the wrong way. Memory aid: A before W. Acid to Water.) Once diluted, it doesn't fume. This is pretty much the high-potency stuff that your HS chemistry teacher had on the shelf that most students didn't touch.

[AlanM]

From a practical standpoint, it dissolves calcium carbonate and coralline algae just the same, only quicker and without the organic residue (acetate) of vinegar.

 

Right. Sounds like a win. And it doesn't waste the salad vinegar.

[Origami]

Right. Sounds like a win. And it doesn't waste the salad vinegar.

Not only is the muriatic a lot less tasty than salad vinegar, it's a whole lot cheaper, too.