itb2003
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Cupric chloride etchant titration question
I'm trying to find out the molarity of hcl in my etchant tank...I tryed using the following example http://members.optusnet.com.au/~eseychell/PCB/etching_CuCl/i...
Where he titrates the solution with 1M NaOH and waits for it to become cloudy. When I tried I also measured the ph and it was still acidic when it
was cloudy. It took quite a bit more NaOH to go past a ph of 7.
So I guess my question is what's the correct way to perform a titration on the cupric chloride? If my way is correct and wait for it to pass a ph of
7 then that article would be very wrong or maybey I measured something wrong in the process....
Also curious how professional detectors that measure hcl concentration are made? Are they just mini titrators or something better?
[Edited on 9-12-2012 by itb2003]
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CHRIS25
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Hi, I did a lot of etching with copper chloride. Here is one example from my notes where I titrated copper chloride. The aim is to keep the specific
gravity of the solution between 1.2 and 1.4 and a ph between 1-3. But in my experience if time is not an issue then these rules are very flexible
indeed. So titration: I made 0.5 mole solution of NaOH: I put 50mLs distilled water into a beaker. I added 5Mls of my copper chloride solution. I
dripped a total of 13.8mLs of NaOH into the solution until copper ions no longer dissolved and you start to see copper hydroxide precipitate, ie,
until the cloudiness would no longer disappear. (tip, keep shaking or stirring the beaker after each drip).
Now I did the following: Mole of NaOH/Vol of CuCl x Number of mLs of NaOH titrated.
0.5/5 = 0.1; then 0.1 x 13.8 = 1.38
1.38 is the molarity/concentration of acid HCl. Or, the PH so to speak. Ultimately it is the amount of free acid in solution that is not bound up
yet with the copper ions.
As far as the PH is concerned litmus paper is useless because the copper chloride itself is acidic and the litmus really tells you nothing except that
you should not put your hands in it. Truth is litmus paper does not give an
accurate indication of anything in this instance, too many variables involved and the litmus paper itself might be cheap or whatever.
Specific gravity can best be determined with a hydrometer, I bought one and they are not expensive at all, a very useful instrument. But make sure
you get one with a measurement parameter of between the 1 and 3 that is needed for this situation as they come in many different measurement ranges.
I hope this helps as well:
http://home.exetel.com.au/adam.seychell/PCB/etching_CuCl/tit...
I did not use this, but you might find some useful info here:
http://www.piclist.com/techref/pcb/etch/CuCl2Calc.htm
[Edited on 9-12-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
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itb2003
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Hi thanks for the response! I was curious does the amount of water put into your titration beaker matter? I'm guessing it's just so you can see the
visible cloudiness? Also curious why you use so much etchant to do your titration...does it give more accurate results or not matter?
That's starting to make sense so after the NaOH combines with all the HCl it starts making Cu(OH)2 which is end of titration assuming of course NaOH
and HCl want to react first.
I bought a hydrometer but it's long and my tank is dinky lol so I think I will make a better one for pcbs that's deeper. Unless someone knows of a
different method to determine specific gravity.
Here's another very nice article on cupric chloride if anyone's interested: http://www.chemcut.net/pdf/Cupric-Chloride.pdf
The only thing I'm still interested in is how do you determine HCL normality in the form of a sensor so you know how much hcl is in there all the time
and just add some when it's low.
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watson.fawkes
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Quote: Originally posted by itb2003  | | I bought a hydrometer but it's long and my tank is dinky lol so I think I will make a better one for pcbs that's deeper. Unless someone knows of a
different method to determine specific gravity. |
Take out clean graduated cylinder from
cabinet.
Take some etchant out of the tanks and put it into the graduated cylinder.
Use hydrometer to take specific gravity reading within the graduated cylinder.
Pour etchant back in tank.
Wash graduated cylinder. Let dry. Put back in cabinet.
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CHRIS25
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Hi, I have no idea about the sensor question sorry. HCl levels do not need to be kept at a critical exactness, unless your work requires. What are
you etching?
As for the amount of water, I do not believe that it matters how much you put in. But 30mLs is also a good amount, not less, and above 50mLs is not
needed By the way, make sure the water is a bit warm to start with. As for the hydrometer issue, I simply drew out a whole load and put it into a
narrow container and then put the hydrometer in that - no need to use the actual tank, just find a tall narrow container - even as thin as your
hydrometer will allow is sufficient, well not that thin - but you get the idea. The reason I used so much CuCl2 (2 liters in my tank) was because the
average size of my copper pieces were usually 6 inches by 6 inches and sometimes bigger,plus I needed a support system that was even bigger - hence a
big tank. Actually the more you have the better it is I found, required less titrating and sample taking. Also I used an air pump to deliver oxygen
into the solvent every time, and sometimes kept the pump going just a little while after the etch was complete. Thanks for that article, I have not
read it yet but will look tomorrow.
Another tip, depending of course on what you are doing, if you keep the outlet of the air pump underneath the piece to be etched this will give you
two distinct advantages, the etch will be even; and also the surface of the copper will be kept at a very constant pace of regeneration, no time for
the surface of the copper to build up with those ??? ions, and that is what I have forgotten, all those + and - ions and oxidation states and Cl ions
lose me totally on this one, I have read it a hundred times and never can remember it. Anyway the point is there is no uneven build up of those
ions??? which prevent the copper from being etched evenly.
Please forgive my lack of chemical accuracy/exactness/notation here - a bit tired right now.
Just something else I had: http://www.sciencemadness.org/talk/viewthread.php?tid=22646#...
[Edited on 9-12-2012 by CHRIS25]
[Edited on 9-12-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
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itb2003
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Wow lol graduated cylinder...sometimes the simplest things are overlooked lol...as for what I'm etching it's just pcbs but it works nice so far I've
been able to etch pcbs with around 5 mil seperation easily so I'm very happy. Only other thing I"m struggling with is that my container doesn't seem
to have the best seal on it so I"m pretty sure fumes are coming out...that's why I was busy with the titration wondering if there was a high hcl
concentration still left. I'm going to be making a new container with the works....bubbler and heater and plus put the container in a polyethelene
bag when not in use if my container still doesn't seal as well as I'de like.
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