Sciencemadness Discussion Board

Titration of Copper chloride solution

CHRIS25 - 16-5-2012 at 01:52

Hi Gentlemen,

Re: HCl + Cu + H2O2 for etching

I left my large piece of copper in the tank overnight and the solution was still a medium green, the copper was not covered with a black copper oxide but with a light brown, so the reaction did interact and not allow copper oxide to develop too much. Dissolving of various parts took place but not deep enough.

As per what I have read: A 1m NaOH solution is prepared. And small amount of warm tap water. Then 1mL of the copper chloride is extracted and put into the warm water. Then 1mL of the NaOH extracted and slowly inserted into the water with the CuCl whilst stirring. If the water stays clear, it first turns green where the NaOh meets the water at the point of the syringe, then goes clear (dissolves), then there is sufficient HCL in the solution still. Also my PH indicator gives a PH of 1 for the actual green copper chloride solution that I have, so plenty of acid then.

All this indicates that to kick start the reaction I simply need to add either H2O2 or Ammonium chloride.

Question: On his website (http://techref.massmind.org/techref/pcb/etch/CuCl2.htm) he mentions that specific gravity is dependent on copper concentration between 1.22 and 1.38. Now Etch rate is dependent upon HCL concentration I am not bothered with this one because time is not an issue here. I am more concerned with etch depth and quality and so am eager to understand the specific gravity, only I do not have a hydrometer at the moment. I am presuming that specific gravity is basically eyeballed so to speak, that is that if the solution is kept from reaching a dark green then we are at a reasonably good Copper concentration?

watson.fawkes - 16-5-2012 at 05:53

Quote: Originally posted by CHRIS25  

Re: HCl + Cu + H2O2 for etching
[...]
All this indicates that to kick start the reaction I simply need to add either H2O2 or Ammonium chloride.
[...]
I am more concerned with etch depth and quality and so am eager to understand the specific gravity, only I do not have a hydrometer at the moment.
The actual etchant, chemically speaking, is the Cu2+ ion. It's the reaction Cu2+ + Cu0 --> 2 Cu+ that's the actual etch. When you start with just HCl and H2O2, you have to get some Cu2+ first before the etch gets going. The best way, long term, to kick start the reaction is to take out your work piece and put in some copper in some form and get the etch solution prepared in advance, rather than relying on copper from the work piece to provide the etching Cu2+ species. After the etching solution is prepared, it works much faster than overnight. If you use metallic copper, be prepared to be patient, as it's got all the surface area issues that bulk metals have. Powdered copper oxide is faster; it's available as a glaze ingredient from pottery suppliers.

Specific gravity is pretty easy to measure, and you don't need a hydrometer. You can do it with a scale and a small graduated cylinder; for more accuracy, use a volumetric flask. The specific gravity of water is 1, by definition, and that's 1 g in 1 ml of water. Just measure out some solution by volume and weigh it.

CHRIS25 - 16-5-2012 at 06:15

Once again WatsonFawkes, thankyou for your tips and advice. I thought that with the amount of copper that is not under a resist I should be able to kill two birds with one stone, good preparation is probably important. I could make copper oxide simply by heating pieces of copper to their maximum, when they turn red, and this turns the pieces black, an idea?

The brown gunge precipitate that falls to the bottom, I suppose this is the insoluable copper +1 gathering as a direct result of depleting HCL, which, could serve as an indicator to add more HCL?

watson.fawkes - 16-5-2012 at 08:25

Quote: Originally posted by CHRIS25  
I thought that with the amount of copper that is not under a resist I should be able to kill two birds with one stone, good preparation is probably important. I could make copper oxide simply by heating pieces of copper to their maximum, when they turn red, and this turns the pieces black, an idea?

The brown gunge precipitate that falls to the bottom, I suppose this is the insoluable copper +1 gathering as a direct result of depleting HCL, which, could serve as an indicator to add more HCL?
There's likely not enough copper not-under-resist to give you a good etch solution.

You can get some copper oxide by surface oxidation with a torch, but it really won't be much by volume. If you want to use a heat mechanism, but a bunch of copper wire into a crucible in the fire. Direct a gentle stream of air over the crucible and you'll oxidize the copper. You'll want to preheat the air so as not to thermally stress the crucible. You want the air stream to be gentle so as not to blow your copper oxide away.

Using bulk metal, as always, has surface area issues to deal with. It's a bigger issue with fire processes, because extra time also means extra fuel. You can use mechanical means to increase the surface area. If you've got a ball mill, for example, you can make some high-surface area powders which will oxidize readily. As you work metal, I'm sure you figure this one out.

If you get insoluble Cu+ falling out, you don't need more acid so much as you need an oxidizer. The (partial) reaction you want is Cu+ --> Cu2+. You can dissolve the Cu+ with more HCl, but it won't etch until the 1+ copper species is oxidized. You could use hydrogen peroxide. You could also sparge air through the solution. This oxidation step is the "regeneration" of the etching solution, the word used in the web site you cited.

CHRIS25 - 16-5-2012 at 08:58

Right...it's so much clearer now what is going on, getting the background info from a web site, or in my case many web sites sometimes is not enough. But when someone as yourself begins to answer the questions that seem to hang around like irritating mosquitoes, the bits fall into place and I think now I have a very complete picture of what is going on and how to adjust things.

A big Thankyou for your help, I could have just thumbled on, but I actually like chemistry and want to understand, so I guess I am walking two paths, they go together quite nicely actually. I never found the idea of just buying in ready made products appealing, even the patinas I won't buy, stubborness or perfectionism - no idea - maybe I just like to do what a friend of mine does, he makes his own pigment paints from scratch, just like the old days, that makes his paintings unique. Anyway, back to ion exchange mechanisms.....

CHRIS25 - 17-5-2012 at 06:55

Hi, Just aerated a bath of copper chloride with copper inside. 400ml of solution for two hours. The pump delivers 50 I/L , a small fish tank pump. Right my confusion now seems to be the following: The solution went from bright clear emerald green to a very dark almost black. Now this was what I expected except and untill I read the following on Cu +1 control which says:

=="To decrease Cu1+ concentration the bath must be aerated. See chemical equation [4]. If you want to be pedantic then the solution can be aerated after each etching job until the color is a completely transparent bright green, i.e. Cu1+ concentration << 1 g/L"==

What surprised me here was the speed at which the colour changed within two hours, what I summize is this: That this is a saturated solution of Cu +1 and that there IS more than sufficient Oxygen in this solution and so I need to add concentrated HCL which will supply the Cl ions to get the Cu+1 turned into Cu+2. Am I working this correctly now? Thankyou.

Forgot to say. I just did two tests on this solution.
1. At the start of reaction For specific gravity I took 3ml of solution and it weighed 3gr; by the end of the reaction I had 3ml at 2.8grams??
2. The NaOh test with a 1ml sample of solution and 1ml NaOh showed plenty of acid in solution. Hence the confusion with my above beliefs that more HCL needs to be added?

[Edited on 17-5-2012 by CHRIS25]

watson.fawkes - 17-5-2012 at 07:53

Quote: Originally posted by CHRIS25  
The solution went from bright clear emerald green to a very dark almost black.
[...]
1. At the start of reaction For specific gravity I took 3ml of solution and it weighed 3gr; by the end of the reaction I had 3ml at 2.8grams??
2. The NaOh test with a 1ml sample of solution and 1ml NaOh showed plenty of acid in solution. Hence the confusion with my above beliefs that more HCL needs to be added?
My first thought is to ask a question: What means did you use to introduce the air into solution? If the material wasn't compatible, the dark color could be contamination from the aerating apparatus.

The density numbers you state don't make sense. 3 g / 3 ml is a specific gravity of 1, and 2.8 g / 3 ml is less than 1. Even at SG 1.05 you should be getting masses of 3.15 g for 3 ml, and this is greater than the resolution even of the cheapest scales. Something's wrong with those numbers. I don't know what.

For the NaOH test, 1 ml of solution doesn't mean much to others without knowing the concentration of the NaOH in solution.

CHRIS25 - 17-5-2012 at 08:19

Sorry. The NaOh was a 1 mole solution. As for the Air, I just bought a fish tank pump and pushed a glass rod into the end of the Flexi hose and switched it on (Only the glass was inside the solution). Yes I agree, the SG results made no sense. But I triple checked the weight of the plastic gradation cylinder each time to make sure there was consistency. also while I used as much accuracy as I could I think that maybe the syringe levels were off by a miniscule, even though it measures mils. But this is unlikely. I will have to do it again and double check I'll do it now......now I am getting a 3gr reading. i think that thescales are to blame, I have had one or two issues when the scales weigh in 0.1 increments, accuracy seems to be within a 0.2 range instead of 0.0 as no doubt professional scales would be.

[Edited on 17-5-2012 by CHRIS25]

I have just done a calibration check, I used this sight: http://www.ecb.int/euro/coins/common/html/index.en.html and checked loads of coins. There were some very tiny errors on a couple of coins by 0.1 and 0.2 grams, but after checking three of the same coins in each category I have to say that they were accurate.

[Edited on 17-5-2012 by CHRIS25]

watson.fawkes - 17-5-2012 at 10:11

Quote: Originally posted by CHRIS25  
i think that thescales are to blame, I have had one or two issues when the scales weigh in 0.1 increments, accuracy seems to be within a 0.2 range instead of 0.0 as no doubt professional scales would be.
The way of dealing with this sort of problem is to measure closer to full scale, the maximum capacity of the measuring device. In this way the ratio between the scale resolution and the measurement becomes smaller. For example, measuring 30 ml instead of 3 ml of solution will give you an extra digit of in your answer. A typical capacity of small scales is 500 g, so you might be able to get a 250 ml measurement, if your scale goes that high and you've got an appropriate measuring vessel.

CHRIS25 - 17-5-2012 at 10:40

Yes, I had actually considered that about an hour ago, measuring up to 200ml or something. I will do that the scales are up to 500 so I'll pick a figure around the 350 mark otherwise it is a bit inpractical.

Just done it, now I have measured 200ml in a accurate beaker andthe weight was 219.4. So this translates into 19 grams of copper chloride 1?

[Edited on 17-5-2012 by CHRIS25]