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neutralizing muriatic acid

popawheelie's picture

If I use a gallon of muriatic acid to etch a slab how much baking soda should I use to neutralize it? Thanks!

______________________________________________________________ ______________________________________________________________ There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves. Will Rogers

(post #106683, reply #1 of 13)

Do not add baking soda to acid!!!!


You are correct that baking soda will react and neutralize acid.  But if you dump a bunch into say a pail of acid, you could have a foamy dangerous mess.  A better way would be to dissolve a bunch of soda into water, and then add acid to that.


In all honesty, I would think that you could find an area of sand and rocks near Fort Collins, and as long as the area was not near a aquifer, that the calcium cements in the sediments would react with the HCl.  I have also dump a limestone rock into HCl, and used that to neutralize the material by the reaction


HCl + CaCO*3 = H*2 O + CaCl + CO*2

(post #106683, reply #9 of 13)

"HCl + CaCO*3 = H*2 O + CaCl + CO*2"

Aha! So you're the source of all that global warming. :)

BruceT
BruceT

(post #106683, reply #10 of 13)

No, I thought we went over this.
It's all the methane from those cows.

(post #106683, reply #2 of 13)

muriatic acid to etch a slab


simple answer - none


The alkalai in the cement neutralizes the acid, that is why the acid etches the cement! 

(post #106683, reply #3 of 13)

As Mcmark says, there are better ways.


Water is your best choice for diluting the effects.  Then, IF you must, dissolve some (not a lot) baking soda in a gallon of water and dilute it further.  Or ammonia.


But begin slower.  Don't use the straight acid.  Dilute it (A is before W in the alphabet - therefore acid goes into the water) first with water.  If'n the results aren't enuff, do it again, with a slightly stronger solution.


Acid staining requires this type of technique.  There, you'll want to stop the reaction at a certain point.  Of course, that acid is weaker that straight HCl, but the applier needs to have a spray bottle of dilute ammonia in his back pocket.  Followed by copius quantities of water.


 


Edited 7/19/2008 10:52 am by peteshlagor

(post #106683, reply #4 of 13)

Let me explain what I'm doing a little better. With a garden sprayer I'm spraying muriatic acid on my slab to open up the top and expose the sand.


I then wash the slab thoroughly with water.


Then I wash out the sprayer with water and then put in water and baking soda. I spray that on the slab to neutralize the acid.


I want to stop acid and am concerned about the acid in the soil around the slab.


If I don't need to neutralize the acid I won't.


I'm just about done etching it but need to even it out a bit. So another gallon will go on.  

______________________________________________________________ ______________________________________________________________ There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves. Will Rogers

(post #106683, reply #5 of 13)

At that point, you got little to worry about.  As earlier pointed out, the ceement will do whatever additional neutralization necessary.


The additional acid in the soil probably will do it good if you gots soil like mine.  I just got the soil tests back from CSU telling me that the average pH of the 5 samples is 7.7. 


They tell me most plants like it below 7.0.

(post #106683, reply #6 of 13)

I'll put some baking soda on it. I allready have put some on. I guess a soil analisis is in order. It's just right next to the slab though.


I just don't know how much.


I live a stones throw away for CSU. All sorts of ejemicated folks around here.


Edited 7/19/2008 1:23 pm ET by popawheelie

______________________________________________________________ ______________________________________________________________ There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves. Will Rogers

(post #106683, reply #7 of 13)

Save your money.  If the grass doesn't die, you're OK.

(post #106683, reply #8 of 13)

Sounds good to me.

______________________________________________________________ ______________________________________________________________ There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves. Will Rogers

(post #106683, reply #11 of 13)

There is no need to neutralize it.

The way it works on the masonry ( a base alkaline element) is a chemical reaction that is trending towards neutral as it works. Then you rinse,

 

 


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(post #106683, reply #12 of 13)

Thanks! I'm just about done etching it. It came out great imo.


Here are some pics of where I sprayed on a little sugar water to expose the pea gravel and one that shows the sand exposed by the acid.


The next step is to seal it in a while. A 28 day wait was suggested by the guy at Red Cap.

______________________________________________________________ ______________________________________________________________ There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves. Will Rogers
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and the answer is.... (post #106683, reply #13 of 13)

"It depends".

As others correctly point out, your acid will most likely be fully (or nearly so) reacted by contact with the alkaline cement, as long as it was well wet with a solute (h2O) long enough to facilitate its reaction.  But for fun, lets do the chemistry any way....

The real "it depends" is given you fail to mention the strength of your muriatic.  So I'll assume you meant the common "pool grade", which is 31.45% and 20°baume.  If you do the molar convert, one liter of this strength is 10 mols of HCL.  So for every liter of this strength HCL you need 10 mols of sodium bicarbonate to balance the reaction.  The mass of 1 mol of NaHCO3 is about 84g...so to get 10 mol you need 840gram for every liter of 10M HCL ... or 1.84 pounds /liter or 7 pounds per gallon.  7 one pound boxes of good ol' arm & hammer.  

Of course, you really won't need anything near this much, given the acid has been greatly spent.  (I typically use baking soda in etching to help protect downstream cement that is not to be etched....for even if you dilute the acid, it still has hcl...and the water dries, its concentration rises till it is either spent or crystalizes.)