[BigJohnny]

Hi guys, long time no chat (since 2007), But I'm into some other hobbies now and I need some more chemical advice.

First of all I want to make it clear on this subject that I do not take this lightly, I understand all risks involved, to wear proper safety gear and to store and label chemicals properly.

What I want to do is make an etchant for PCB's. A simple formula can be found on the web for muriatic acid and hydrogen peroxide.

That's all fine and good, but the solution is resuable so long as you maintain the level of acid in the solution.

This would be easy if one could obtain hydrochloric acid off the shelf.

I found a video that showed a simple way to make reagent grade HCL with distilled water

Two smaller containers inside one large container, one containing muriatic acid, and the other containing distilled water.
After about a week the HCL ions end up converting the distilled water to reagent grade HCL. (Please forgive my laymans way of putting it.... I'm an engineer, not a chemist)

So here are my questions;

My muriatic acid says "20° Baume Commercial (31.45%), what exactly does this mean?? (I get the percent part)

What is "Reagent grade" how pure is this?

How should I go about labelling and storing this refined HCL and etchant material?

Is there a better way to refine the muriatic acid into pure hydrochloric acid?

I'm only looking to refine my muriatic acid for topping up my etchant without having to do a bunch of math to figure out the measurements with 68.55% water.

By refining the acid it will be much easier to add the needed amount to "refresh" my etchant.

And this is why I come here, to the people with the real knowledge on the subject to inform me of the need to knows and things I may be overlooking. Help me be safe guys, I know this stuff is super dangerous (I think I'm understating it)

Thanks for any info.

[Arkcon]

The muriatic acid you buy at the hardware store is pretty impure.  It's also very strong, so it constantly fumes off pure HCl gas.  This will then redissolve in any moisture available.  This is a pretty "cute" way of getting the purest hydrochloric acid you'll ever find on your own, but by definition, some will be lost, so it will be weaker.  Again, a cute trick, but I don't know what strength you need.  Its probably more reliable to buy the correct acid.

[Borek]

My muriatic acid says "20° Baume Commercial (31.45%), what exactly does this mean?? (I get the percent part)

http://en.wikipedia.org/wiki/Baumé_scale

Chances are muriatic acid is pure enough for etching.

[BigJohnny]

It's fine for etching.

It's the topping up of the etchant that requires pure acid.

[billnotgatez]

I assume you have read the WIKI on Hydrogen Chloride
http://en.wikipedia.org/wiki/Hydrogen_chloride
and the WIKI on Hydrochloric acid
http://en.wikipedia.org/wiki/Hydrochloric_acid

Are you saying you want to maintain a concentration of 31.45% Hydrogen Chloride for the etching solution?
Or, is there a recipe' for your etching solution that reduces the concentration.
Can you give a link for the etching process you are using.

[BigJohnny]

Sorry, I was a bit unclear.

The etchant is made from 2 parts hydrogen peroxide and 1 part muriatic acid.

as it gets used it gradually becomes weaker. It can be refreshed by adding more acid, but will make chlorine gas if it isn't mixed right or has too much peroxide as I understand it.

by adding pure HCL (or with as little impurities as possible) you can make the solution strong again without making more or dumping out the "used" product.

The page is HERE

from that page

"The Hydrogen Peroxide (H2O2) system of replenishing has been popular in the Photochemical Milling industry. Using this system requires a reliable control system, for both components required to replenish the system, Hydrogen Peroxide, and Hydrochloric Acid.

The use of Hydrogen Peroxide also produces a purer Cupric Chloride, without Sodium Chloride (NaCl) impurities, but the Hydrochloric Acid level must be carefully monitored, as it is consumed in the regeneration part of the reaction. This replenishment method also suffers from the fact that over-replenishing with the Hydrogen Peroxide can generate free Chlorine gas."

[Tittywahah]

I sincerely hope by offering some input I will not complicate things for you; but I have been doing etching for a few years now and would never move away from the copper chloride system.  It has these advantages:
No need for H2O2
No fuming in that you can do it indoors
Self regenerating no need to throw anything down the sink (at least I have not for a couple of years now)
Cheaper I think than the above since I do not need to keep adding HCl that much, just keep the right Molarity (concentration). 
Nothing wrong with your method but thought that I would throw this one in.
Regards

[BigJohnny]

I sincerely hope by offering some input I will not complicate things for you; but I have been doing etching for a few years now and would never move away from the copper chloride system.  It has these advantages:
No need for H2O2
No fuming in that you can do it indoors
Self regenerating no need to throw anything down the sink (at least I have not for a couple of years now)
Cheaper I think than the above since I do not need to keep adding HCl that much, just keep the right Molarity (concentration). 
Nothing wrong with your method but thought that I would throw this one in.
Regards

I'm under the impression that the muriatic/h2o2 method is much safer than ferric chloride for etching. And also a little bit more environmentally friendly when it comes to disposal.

[Hunter2]

Additinal to say muratic acid / peroxide has also maintained, because the copper content will rise during the etching process. It get thick as a pudding at the end. So some dilution and removal oft he copper is necessary. In industy application these kind of etching solution are in common use and companies existing who do recycling of it.

[Tittywahah]

BigJohnny:  Copper chloride I use not ferric chloride, and yes copper chloride is by far much safer than ferric chloride, less obnoxious, and with copper chloride I have no need to dispose anything after two years.

Hunter2:  The amount of dilution is negligible really plus one never needs to remove copper content since this is useful, there are two copper species in solution  the CuCl2 species does that actual etching and produces an insoluble CuCl but this can remain in the solution due to the HCl, if there is not enough HCl to keep the insoluble CuCl in solution then it precipitates out as a sludge, but this CuCl will be oxidized back to CuCl2 and this is why it is self regenerating, the only thing you need is a source of oxygen - I use an air pump.  This is over simplified but you can see that there is never any point in removing copper even if you could.

[Hunter2]

Yes I know that.  Cu + CuCl₂ + 2 HCl => 2 H[CuCl₂] equal 2 (CuCl*HCl)

4 H[CuCl₂] +  O₂=> 4 CuCl₂ + 2 H₂O

But your amount of CuCl₂ will rise and the acid will be consumed as well. So I dont agree you dont have to dilute or remove some of your solution and add fresh acid.

[BigJohnny]

You do need to add fresh acid as it is consumed during the regeneration process.

That's why I wanted pure acid, so as not to further dilute with water the initial solution.

I think this did get a little off topic somewhere though.

Would someone simply explain what the difference in molarity is between acids?

In the video I watched to refine it, he starts with 10M 31.45% Muriatic acid, and says that after the process you have very pure 5M hydrochloric acid.

Does that mean the reagent grade 5M is weaker?

[Hunter2]

HCl 37% w.w is a common grade to buy. But it smokes from HCl fumes. Better handling ist 25% w.w.

[Tittywahah]

Dilute yes but I did say little, very little.  But this all depends upon how much of the etchant solution you require, sorry.  I etch very deep and often 8 inch long pieces my etch solution is 1.5 litre and rising, but this is fine for me.

Differences in molarity?  5 moles of HCl in 1 litre has the same amount of Gas dissolved in it as 5 moles in 10 litres , the only difference is the BIG M the molarity.  This is the concentration,  if you have a 5 moles in 1 litre at a 5M (molarity) concentration then you have 5x86mLs = 430mLs of HCl and 570mLs water.  If you have this same 430mLs HCl in 10 litres then you have 9570mLs water and 430mLs HCL.  the first one has a Molarity of 5M the second one here has a molarity of 0.5M . 

I always pour in 37% neat, this is approx 12M. And it can range from 5mLs to 20 Mls at a time I do calculations to determine how much to get to the desired concentration/molarity.  If you can titrate your solution of etchant to be between 1 and 3M maximum then you will have no fuming that is obnoxious or harmful if in a ventilated room, ie a window slightly open is all you need.  May I ask how you are kick-starting your etch solution?

[Hunter2]

Your calculations are not understandable.

5 moles of HCl in 1 litre has the same amount of Gas dissolved in it as 5 moles in 10 litres

Big???

Molecular weight of HCl 36,5 g/mol

a 5 M HCl contains 5 times 36.5 g = 182.5 g/l pure HCl

Specific gravity is 1,082 g/cm³ that means 1 l  has a weigth of 1.082 kg minus the 182.5 g pure HCl gives 899.5 g water.

5x86mLs = 430mLs of HCl and 570mLs water

where does this calculation comes from???

And at least in summery of all chemical reactions gives:

2 Cu + 4 HCl + O₂ => 2 CuCl₂ + 2 H₂O

You add copper and HCl to your tank and create copper-II-cloride. This amount will rise. There will nothing dissappear.