# Is it possible to increase HCL concentration by boiling?



## w0lvez (Jun 19, 2011)

What are the ways to increase HCL concentration? I tried boiling it but I'm not sure if the concentration increase because I can't get the exact weight cause my digital scale is broken.


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## jimdoc (Jun 19, 2011)

Why are you wanting to increase the concentration?
How high are you trying to concentrate it?

Jim


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## w0lvez (Jun 19, 2011)

jimdoc said:


> Why are you wanting to increase the concentration?
> How high are you trying to concentrate it?
> 
> Jim



I'm trying if a more concentrated HCL will deposit better than less concentrated HCL if use as activator.

I got 19% and 29% HCL I would like to increase it's concentration where I can see and compare if there's a difference using more concentrated HCL


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## goldsilverpro (Jun 19, 2011)

> I'm trying if a more concentrated HCL will deposit better than less concentrated HCL if use as activator.


No offense, but I have absolutely no idea what you're talking about.

Unlike sulfuric, you can't increase the concentration of either hydrochloric or nitric by simple evaporatiion. In both cases, the acids will tend to evaporate off before the water.


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## butcher (Jun 19, 2011)

Study azeotropes of acids, dilute acids can be concentrated up to that point, then acid will vapor off.

Depending on concentration the boiling point changes, so temperature is an important factor when concentrating your acid.

Example 35% HNO3 can be concentrated to about 68% HNO3, then you are just vaporizing off 68% acid if heating any further.

boiling point and boiling a solution should not be confused, 
boiling a solution you will surely loose your acid, and even metals the acids contain.


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## goldsilverpro (Jun 21, 2011)

butcher said:


> Study azeotropes of acids, dilute acids can be concentrated up to that point, then acid will vapor off.
> 
> Depending on concentration the boiling point changes, so temperature is an important factor when concentrating your acid.
> 
> ...



Richard,

I must embarrassingly admit that I have never studied azeotropes until recently (but, so far, only briefly), thanks to you. Quite interesting and usable. I wish I had known about them when I was using that rotary evaporator. Here's the way I understand it. Please correct me if I'm wrong. I'll only get into the HCl azeotrope.

All this assumes an open evaporation vessel.

(1) The HCl/water azeotrope occurs at about 20% HCl. At this point, the boiling point (109C) remains constant and both the evaporation fumes and the solution concentration of HCl remains constant at 20%.

(2) If the HCl starts at less than 20%, the fumes will contain less than 20% HCl and more than 80% water.

(3) If the HCl starts at more than 20%, the fumes will contain more than 20% HCl and less than 80% water.

(4) In either case, as the solution concentration of HCl approaches 20%, the fume concentration approaches 20% HCl and 80% water.

So, with open evaporation, I would think that the answer to wOlvez's question would still be no, unless 20% were as strong as he needed. Even then, a good portion of the HCl could be evaporated off and wasted by the time the HCl reached 20%. This is unlike sulfuric, which comes off very slowly, until the concentration approaches 93.3%. Unlike HCl, H2SO4 is not a gas dissolved in water

I read that there are certain distillation methods and methods using pressure that will increase the HCl higher than 20% and that there are certain things that can be added to the solution to break the azeotrope. I also read that the saturation point of HCl in water is about 40%. Above that, things start getting extremely dangerous for metals and living creatures. I also read that very strong HCl will readily attack most plastics. Also, since pure HCl boils at -84C, I can't imagine anyone working around it and still being alive.

I hope that wOlvez sees the futility and the inherent dangers in this. I wish people would just go with the flow and quit trying to reinvent the wheel, at least until they have mastered the workable accepted processes in the real world.

Chris


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## butcher (Jun 24, 2011)

Boiling solutions, I think we need to consider evaporation when we read that sentence, I think many times, we read boiling solution when we should have read evaporation at lower than a rolling boil, temperature of solutions has a lot to do with what stay's in our pot and what goes’ up in smoke. These terms seem to be used interchangeably to a fault as we have learned.


Let’s look at nitric acid and water.

very dilute nitric mostly water, if we heat below the "boiling point for that concentration we will vapor off mostly water in vapor's very little loss of acid as long as we do not heat too high, now the acid in solution is concentrating and the " boiling point of this solution is yet higher, we could raise our temperature, but there is really not much need to as water will still vapor off (we really do not want a boil as this is gases forming from deep in solution forming gas bubbles which POP and carries acids with them, what we want is a hot still solution and gases just forming from the surface VAPORIZING just from the surface, what we call evaporation), the boiling point for nitric acid is highest at its azeotrope, and this is the highest we can concentrate nitric acid by this method, about 68%, further heating or evaporation will just vapor off 68% nitric till the pot is dry. 

Now if we had 98% HNO3 and we evaporated it we would just have nitric in vapors untill we reached 68% then we would just vapor off 68% till pot was dry,
here our boiling point for 98% acid raises as we get closer to azeotropic nitric acid 68%,

So yes he can heat his dilute HCl to vapor off water until he reaches 20%, but with metals he is also concentrating the metal salts in solution, the metals in solutions would give different boiling points than just acids and water, and sometimes if elemental metals are in solutions the reactions with acids form gasses of the acids and salts of the metals in solution, this starts changing the whole picture of what we are discussing.

If anybody interested I have a lot of notes on nitric acid and can make some posts with some of that info. Although I do not think we should discuss anything over 68% HNO3 here on the forum, no need for anything stronger with what we do with metal recovery and refining.
edited to use spell checker


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## goldsilverpro (Jun 25, 2011)

Richard,

I'm really trying to get a mental grasp of this, so please bear with me. In the following, I am assuming pure systems of only HCl/pure water or HNO3/pure water. I am also assuming that things like humidity aren't affecting this and that the evaporation is being done in an open container.

It is my contention that, if the acid percentage is far below that of the azeotropic concentration, the fumes will contain mostly water. However, as the solution evaporates, whether at room temp or by applying heat below the boiling point, the acid concentration in the fumes will gradually increase until the azeotropic concentration is reached (20% for HCl; 68% for HNO3). The opposite would occur for acid concentrations above the azeotropic level. It would start out with mostly acid coming off but the acid/water ratio would gradually decrease until the azeotrope were reached. 

You said:


> Now if we had 98% HNO3 and we evaporated it we would just have nitric in vapors untill we reached 68%


Please don't take offense, but this makes little sense to me. It sounds like you're saying that, at 69%, the vapors are 100% nitric with no water and then, magically, at 68%, the vapors suddenly contain 32% water. I can't believe that this is the way it works. It just has to be a sliding ratio, probably not linear, from where you start (whether above or below the azeotrope), until you reach the azeotrope.



> So yes he can heat his dilute HCl to vapor off water until he reaches 20%


Of course, I would agree to this. My point is, how much acid would he lose in doing so. It would probably be little if he started with 19% but I would bet it would be quite a bit if he started with 5%.

I spent about 2 hours this morning looking for graphs or equations depicting these relationships, to no avail.

If I had a lab, I would start evaporating various solutions, titrating the acid and measuring the changing volumes along the way, and then plotting the results.

BTW, I read, on a science forum, a discussion on the concentrating of battery acid by evaporation. Some guy said that sulfuric acid doesn't appear in the fumes, significantly, until the [H2SO4] reaches about 70%. At 80%, he says quite a bit fumes off. This increases to the azeotrope of 93.3%, where the vapor concentration reaches 93.3% H2SO4. Most all references gave the H2SO4/water azeotrope as 93.3% (one guy said 98%?), so I assume it's 93.3%. In any case, all should USE A FUME HOOD, to do this.


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## butcher (Jun 25, 2011)

My understanding, 10% nitric can be concentrated (evaporating the water , basically min acid in vapor, almost like none)to 68% HNO3 with very little loss of original acid, as long as evaporation is from surface not boiling and splashing acid, or from carrie over in fumes, ( I operate steam boilers, we can make almost pure water, chemicals and minerals stay in solution, but if we get chemicals too high or too much contamination we can have what we call carrie over, then we have contaminates in the steam and even water),

and yes I did not explain evaporation from 98% very well, you are right (we could not magically get 32% water all of a sudden) let me try again, 98% when evaporated acid fumes off till azeotrope is reached (we wont gain water, but fume can be 68% or more acid at this point, and pot is dry, this Idea is normally used in distillation (when you are capturing and or condensing)the acid vapors, but is also used to show how if acid was more than 68% evaporation would bring your stronger acid in solution down to 68% and then your just holding that concentration of acid in the pot and fumes both.

it has been some time since I studied this and without a teacher I may have some misunderstanding of it, but as far as I remember or know thats how I see it, maybe you'll show me different.

It is great you are interested GSP, as I know when your on the trail we can tree this coon.


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## butcher (Jun 26, 2011)

Like makin moonshine, ethanol (which is more volatile than water) will vapor off as gas first, if condensed you will have stronger shine in condenser, and more water in the boiling pot than ethanol, basically you can vapor off most of the water leaving a watery mush, if this condensed shine was run again through the still we would again get a stronger vapor of alcohol, higher proof, leaving more water behind in the still, up until we reach azeotrope, then we just vapor off that proof, we can no longer get it any stronger.

Sometimes we can add something to the pot that will break the azeotrope,
in nitric acid (the water being more volatile than the acid) sulfuric will break the azeotrope, sulfuric acid will act as dehydrator and keep water from vaporizing and keeping it in reaction boiling vessel.

Look also into non ideal mixtures of liquids and fractional distillation of acids.
You may see this differently than I do?


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## qst42know (Jun 26, 2011)

Can HCL be concentrated by freezing as some other acids can be?


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## Palladium (Jun 26, 2011)

http://www.resistoflex.com/hci_graphs.htm#2
The freezing point curve indicates that partial freezing can only concentrate a 33% HCl solution to 40%; a composition corresponding to an HCl.3H2O complex.


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## pesco (Jun 27, 2011)

w0lvez said:


> What are the ways to increase HCL concentration?




You could try to dehydrate your 19% HCL with anhydrous CuS04. If you have CuSO4*5H2O (pentahydrate - usual blue crystals) you can dehydrate it by heating dry crystals till they become pale/gray/white powder.

Take one airtight glass/polyethylene container (bottle) and fill it with your HCL solution, connect it using tube with other airtight container filled with dehydrated CuSO4. Then leave it for some time, hours, days? Dehydrated CuSO4 is a strong desiccant and should suck the water out of your weak HCL/HNO3. You might have to do it few times replacing blue crystals of CuSO4*5H2O with freshly dehydrated CuSO4.
You could use concentrated H2SO4 instead of CuSO4, but it would be more dangerous.

Interesting (and worth to remember!) thing about concentrated H2SO4 - never leave it in open container especially if there is not much room left in this container - it will such moisture in from the air around and will overfill the container


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