Chemical Forums
Specialty Chemistry Forums => Citizen Chemist => Topic started by: BigJohnny on April 04, 2014, 06:59:01 PM
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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.
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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.
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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 (http://en.wikipedia.org/wiki/Baumé_scale)
Chances are muriatic acid is pure enough for etching.
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It's fine for etching.
It's the topping up of the etchant that requires pure acid.
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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.
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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 (http://mad-science.wonderhowto.com/how-to/create-pcb-etchant-automatically-improves-after-each-use-0135192/)
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."
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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
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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.
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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.
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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.
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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.
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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?
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HCl 37% w.w is a common grade to buy. But it smokes from HCl fumes. Better handling ist 25% w.w.
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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?
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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.
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Assuming a 36% or near a 12M starting point: To make a 1M solution in 1 litre is 86 mLs. So 5x86 is a 5M solution in 1 Litre. Since I was working in mLs and not Gaseous equivalents I said 5moles in 1 litre and 5moles in 10 litres contains the same amount of dissolved gas.
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Ok agreed.
But it doesnt solve the problem copperchloride will rise with every etch treatment. And if you add your 5 M in 10 liter of course the cocentration is 0.5 M but the etching strength also will go down. It takes only longer.
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Ok back to beginnings. I said earlier that I never use diluted HCl that is absolutely pointless. I always put in the 12M when my calculations and titrations indicate the need. Copper chloride needs to be at a certain density to work efficiently. 1.2 is my average bench mark, the density increases as the copper 1 and 2 species increases. This dissolved copper 1 and 2 takes quite some time to increase in volume, we are talking a 2 litres in 18 months as I use it every 2 to 3 weeks for etching large pieces around 4 to 8 inches at some considerable depth. Etches can take 3 to 16 hours at a time for me. If the density (Specific gravity, this is the dissolved copper whether it be in the form of CuCL or CuCl2) rises above 1.3 all I have to do is to add distilled water But this is so minimal as to be negligible, you shgould not need to add water for many many weeks as this only decreass the Specific gravity which has an influence on etch speed. It takes weeks before I need to add water, I think I have only ever added water about three times in two years. As I mentioned I have 1.5 litres after a year and half but I began by making a 800 mL solution mixing copper oxychloride and HCl, this is how I kick-started my second operation. My first operation was through copper metal, HCl and Air.
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if you have a 5 moles in 1 litre at a 5M (molarity) concentration then you have 5x86mLs = 430mLs of HCl and 570mLs water.
No, it is NOT 430 mL of HCl, it is 430 mL of HCl solution.
I am ignoring the fact that it doesn't make sense even if explained this way, as 12 M solution of HCl already contains water so the final solution contains more water than 570 mL that you added.
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if you have a 5 moles in 1 litre at a 5M (molarity) concentration then you have 5x86mLs = 430mLs of HCl and 570mLs water.
No, it is NOT 430 mL of HCl, it is 430 mL of HCl solution.
I am ignoring the fact that it doesn't make sense even if explained this way, as 12 M solution of HCl already contains water so the final solution contains more water than 570 mL that you added.
Honestly Borek, a little bit of nit picking. I think it was obvious what I meant: To make a 1 litre 5M solution from a 12M concentration HCl you place 430mLs HCl and top up with 570mLs water. Of course I know that 37% HCl contains 63% water, just as 98% sulphuric acid contains 2% water. Now what on earth was wrong with what I said previously? really.
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ok well all of the debate aside, I still don't understand the strength of the final product when making reagent grade.
If you start with 10M 31.45% muriatic acid in one container, and in the other you have distilled water, after a week you end up with a solution of 5M muriatic acid (at what percentage now??) and 5M reagent grade HCL.
So how does the molarity come into play here? Which of the two end products is stronger? Wouldn't this effectively mean I'm making 2 solutions of 5M, 15.72% muriatic acid??
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I think it was obvious what I meant: To make a 1 litre 5M solution from a 12M concentration HCl you place 430mLs HCl
No, it is not obvious. "430 mL of HCl" doesn't unambiguously mean 430 mL of 12 M HCl. First meaning is "430 mL of gaseous hydrogen chloride", second meaning is "430 mL of some uknown solution of HCl".
Besides, you can't say that the diluted solution contains 570 mL of water. 1L of 5 M solution weighs 1082 g, and contains 182 g of HCl, so it contains 900 g of water. 900 g of water is 900 mL, not 570 mL.
This is not about being nitpicking, this is about being precise without risk of misinforming/confusing others.
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Borek this is stupid. We are NOT doing analytical chemical analysis of empirically derived products in a sanitized bio-chemical lab! For the purposes of BigJohnny's needs there is absolutely Nothing wrong at all with my directions - if there were then every experiment and mixture I have performed over the last 2 years would never have worked and I have made at least 50 chemicals from crystals to new acids to plain inorganic dry chemicals. What you are showing does not benefit bigjohnny. What I have shown is correct and is simply practical. If you want to get analytical then yes do this, but this analytical is irrelevant and has absolutely no practical use whatsoever in this thread so far. Sorry Borek, I respect your wealth of knowledge and expertise, I do, so I am not disagreeing with your perspective, simply the application of your perspective is not relevant in this context..
BigJohnny: If you start with 10M and in the other you have distilled water? What do you mean by two containers - sorry do not get this. Anyway, if you have a 10M HCl solution in one litre and this is 31.45% a 5M will be 15.7% in one litre. When you are working with your HCl work in either Percentage Or Molarity. They mean both the same thing. For example a 95% sulphuric acid is approx 17.6M in one litre 10% would be 1.76M. This molarity and percentage is always expressed as in One litre, not 500 mLs or gallons. Molarity and Percentage is an expression of concentration. If the consumer would read 2.58M on the package they would not have a clue what it meant. Hence percentage since we all relate to percentages. 5M and 10M is Not the same thing. Please do not hesitate to ask questions, we all have to start somewhere, and no one was born with a PHD in chemistry, so no question is too stupid.
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If you start with 10M 31.45% muriatic acid in one container, and in the other you have distilled water, after a week you end up with a solution of 5M muriatic acid (at what percentage now??) and 5M reagent grade HCL.
Right. 5 M hydrochloric acid is about 16.9%
So how does the molarity come into play here? Which of the two end products is stronger? Wouldn't this effectively mean I'm making 2 solutions of 5M, 15.72% muriatic acid??
Once the system is in equilibrium concentration of acid is identical in both beakers, so they have both exactly the same strength. Whether their concentration is exactly half of the initial concentration, depends on the amount of distilled water put in the second beaker.
Actually this is kind of calculations where being precise about "amount of water" is paramount.
Let's assume we start with 1.000 L of 10 M HCl. It contains 10 moles (364.6 g) of HCl. Solution density is 1.1569 g/mL, so the mass of the solution is 1157 g, of this 1157-364.6=792.4 g is water.
After the procedure we want to end with 2.000 L of 5 M acid (in separate beakers, but we can treat them combined here). Density of 5 M acid solution is 1.0819 g/mL, so the total mass of the solution needs to be 2164 g. We already have 1157 g of the solution and all HCl we need is there, so we need to add 2164-1157=1007 g of water.
Things get tricky when we try to calculate volumes of both acids - the pure one (reagent grade) and the leftover (muriatic, technical, stock, whatever you want to call it). New beaker contained 1007 g of water, now it contains 5 M HCl solution with a density of 1.0819 g/mL. How much HCl does it contain? Let's call HCl mass mHCl - then the mass of the solution is
[tex]1007+m_{HCl}[/tex]
volume of the solution is mass over density
[tex]\frac {1007+m_{HCl}} {1000 \times 1.0819}[/tex]
(1000 is a conversion factor between mL and L) and number of moles of HCl is
[tex]\frac {m_{HCl}}{36.46}[/tex]
(36.46 g/mol being molar mass of HCl).
By definition molar concentration is
[tex]C = \frac n V[/tex]
We know concentration to be 5 M, so we can write
[tex]5 = \frac {\frac {m_{HCl}}{36.46}}{\frac{1007+m_{HCl}}{1000\times 1.0819}}[/tex]
solving for mHCl yields 204 g, so mass of the reagent grade solution is 1007+204=1211 g (or 1211/1.0819=1119 mL), the other beaker contains now 1157-204=953 g (or 953/1.0819=880 mL) of the technical, 5M solution.
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Borek this is stupid. We are NOT doing analytical chemical analysis of empirically derived products in a sanitized bio-chemical lab! For the purposes of BigJohnny's needs there is absolutely Nothing wrong at all with my directions
It is not recipe that I am disagreeing with, it is your explanation of what is going on that is wrong and confusing. Sorry to say that, but you don't understand what you are doing and that means you are a danger to yourself and others.
For example a 95% sulphuric acid is approx 17.6M in one litre 10% would be 1.76M
No, 1.76 M solution of sulfuric acid is 15.6 %, 10% acid is 1.09 M.
This molarity and percentage is always expressed as in One litre
No, concentration is an intensive property and doesn't depend on the volume. Molarity is defined PER liter, so it is sometimes easier to think about it this way, but percentage is defined as ratio and doesn't require any particular units.
Amount of substance is an extensive property, so it depends on the volume.
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On the two parts where you quoted me I made mistakes due to edit typing. I know that percentage is Not an expression of how much in a litre, that was a typo error in my second edit when I added something. 1.76 as 10% yes I made a thoughtless mistake in my haste. I am not a danger to myself just because I mis-calculated. I do not make mistakes when I am doing stoiochemetry, I take my time. It's just that I was eager to stress that your perspective and argument with me has no practical purposes for bigjohnny. With all your instructions his question has not been answered still. So I give up since my input got lost in an array of in-precise reasoning and mathematical calculation. I will leave the answer to the PHD'ers.
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With all your instructions his question has not been answered still.
Which question was not answered? I believe I addressed all questions from his last post (plus some).
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Borek, I really do not want to appear an antogonist, neither disrespectful nor in-polite, I hope I have not been. I just feel there has been a little misunderstanding perhaps on my part about exactly what the OP needs to know, maybe I have completely missed the point, and maybe I have cross wired with hunter2's questions and it became a bit confusing. The only thing I would like to say is that I was trying to keep things absolutely simple, though a bit anethema to the professional, because I was not pedantically observant in my calculations. Yes I made a mistake with one percentage - honestly I should have spent an extra few seconds with a calculator instead of typing off the top of my head. My fault. If the OP is happy now with your answers then great, if not I will leave him to you to clarify.
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BigJohnny: If you start with 10M and in the other you have distilled water? What do you mean by two containers - sorry do not get this.
Sorry,my bad, I was referring to this video that I didn't even link to.
https://www.youtube.com/watch?v=jv1Ms6Subg4
Anyway, if you have a 10M HCl solution in one litre and this is 31.45% a 5M will be 15.7% in one litre. When you are working with your HCl work in either Percentage Or Molarity. They mean both the same thing. For example a 95% sulphuric acid is approx 17.6M in one litre 10% would be 1.76M. This molarity and percentage is always expressed as in One litre, not 500 mLs or gallons. Molarity and Percentage is an expression of concentration. If the consumer would read 2.58M on the package they would not have a clue what it meant. Hence percentage since we all relate to percentages. 5M and 10M is Not the same thing. Please do not hesitate to ask questions, we all have to start somewhere, and no one was born with a PHD in chemistry, so no question is too stupid.
thanks, that pretty much cleared up most of my confusion.
In respect to the above video, what the hell is he talking about then? if I understand this topic correctly he isn't purifying anything, nor is he making any stronger acid....so what exactly is he doing?
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Sorry,my bad, I was referring to this video that I didn't even link to.
Funny thing is, I have seen this video in the past and I know what he is doing, so I knew what it is all about and I have not noticed you didn't link to the video.
In respect to the above video, what the hell is he talking about then? if I understand this topic correctly he isn't purifying anything, nor is he making any stronger acid....so what exactly is he doing?
He is purifying the acid by a quite clever method, ending with an acid that is about half concentrated as the one he started with.
Hydrochloric acid is a solution of HCl (hydrogen chloride, which is a gas at room temperature) in water.
Hydrochloric acid - when concentrated - is quite volatile (which means - HCl fumes are present over the solution).
When you put an open jar with a concentrated acid in the room, you will be able to smell HCl everywhere.
He puts two separate, open jars in a closed container. One initially contains 10 M HCl solution, the other contains pure water.
What is happening next is that the HCl from the concentrated solution gets airborne and saturates the container. Then, it dissolves in the pure water that is present in the other jar.
This process continues until concentrations in both containers are identical (which we call an equilibrium).
What the exact final concentrations are depends on the initial amount of acid and initial amount of pure water used. I have explained how to calculate it in my earlier post.
Note, that it is HCl that is volatile - most impurities are not, so they stay in the original solution, and only HCl is transferred to the new solution. That's why the purification works.
After you correctly wrote
Wouldn't this effectively mean I'm making 2 solutions of 5M, 15.72% muriatic acid??
I assumed you got it.
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Yes I made a mistake with one percentage - honestly I should have spent an extra few seconds with a calculator instead of typing off the top of my head.
Please recheck your calculations. I believe even after you correct what you think your error is, you will still not get the correct result.
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I assumed you got it.
I mostly do now, I understood the process of what's happening in the video, just not what the resulting end products would be. Now I know that it is a weaker, but more pure acid correct??
This leaves me with the question of; If I was able to purchase high strength/lab grade/pure/etc (not sure what it would be called) as would be used in a true scientific environment by licensed people, how strong would that acid be??
IE, are actual chemists able to purchase 100% HCL, or does that even exist?
What impurities would be in a bottle muriatic acid?? I figured it would be just acid and water.
If I boiled/distilled this muriatic acid, what would I end up with?? (No, I don't think I'll be doing this, just curious)
At this point my original topic has pretty much become moot, but now I'm very curious about this subject.
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The impurities in HCl vary
For trace metal analysis there are around 30 impurities but their amounts are extremely small indeed. Then you have lab quality impurities, about anywhere between 20-30, once again impurities are kept to between 0.001 up to 0.1 parts per million.
Impurities can consist of so many chemicals that I care not to list them all, but these are acceptable under the above circumstances and are I Presume? a natural consequence of the manufacture under the strictest conditions.
One example is chlorine, that is not in a product of lab quality, but in a lesser quality it can be 2ppm, this is one of many examples. But for etching, no need to worry about this at all.
36% - 38% at a specific gravity of 1.16 to 1.18 is considered the de facto standard concentration for most purposes. But as for the professional scientists and their work, I have no idea what is possible. We do not use the term muriatic here in Europe, I presume it is American, you certainly would never find it for sale to the general public in a store.
I have never distilled HCl but heated up on a number of times in order to concentrate a particular reaction, for example making ferric chloride, heating gently will of course evaporate water, no harm in this, but I would never boil it.
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I mostly do now, I understood the process of what's happening in the video, just not what the resulting end products would be. Now I know that it is a weaker, but more pure acid correct??
Weaker and purer in one jar, weaker and containing all original impurities in the other, yes.
This leaves me with the question of; If I was able to purchase high strength/lab grade/pure/etc (not sure what it would be called) as would be used in a true scientific environment by licensed people, how strong would that acid be??
IE, are actual chemists able to purchase 100% HCL, or does that even exist?
No, the strongest stock HCl available is around 38%. That's because at this concentration it becomes so volatile it doesn't want to stay in the solution. It is possible to prepare more concentrated solutions using increased pressure, but then even just storing the acid requires pressure resistant bottles.
What impurities would be in a bottle muriatic acid?? I figured it would be just acid and water.
Depends on how the acid was made. Typically there will be some dissolved salts and whatever was present in the water used for preparation, as technical acid is not made using distilled water.
If I boiled/distilled this muriatic acid, what would I end up with?? (No, I don't think I'll be doing this, just curious)
Distillation is another way of purifying and concentrating the acid. I am not sure about exact numbers (and too lazy to check them), but you won't get past 38 or 40% (40+?) for reasons stated earlier.
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If I may chip in, the term muriatic acid = hydrochloric acid is still used in Europe.
it means pertaining to brine or salt.
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wow, a wealth of excellent information has been put forth here.
Tittywahah: Muriatic acid is just what they call it here I guess, another name is pool acid. It's also used for cleaning concrete and stuff, so that's why it's publicly available.
What I didn't realize is how close to 'full strength' it actually was.
it wouldn't be hard to evaporate 6% of the water out, but the dangers of having it build pressure are far too great to even attempt anything like that home.
However I now have a far greater understanding of this subject than when I first made the post.