[Tittywahah]

I have been titrating copper chloride thus:
EG 4mLs of a 0.5M NaOH neutralized 1mL CuCl2 in 30mLs water (ignore the water)
So, 0.5/1 = 0.5
0.5 x 4    = 2M is the CuCl2 solution (free H+ Ions)

However I was stupid enough to forget this:  2NaOH + CuCl2 = Cu(OH)2 + 2NaCl

I should be Halving the 2M to 1M?

Thankyou.

[Borek]

This is making no sense to me at all.

NaOH doesn't neutralize CuCl₂. At best it can precipitate Cu(OH)₂.

[Tittywahah]

Ok Ok - I meant, as I was writing, that copper Hydroxide is precipitated at the moment that there no more Free Cl- ions in solution.  At this point I know what the molarity of the copper chloride solution is in terms of HCl, IE free Cl-  ions. 

[Borek]

Ok Ok - I meant, as I was writing, that copper Hydroxide is precipitated at the moment that there no more Free Cl- ions in solution.

This is ever worse - copper precipitation doesn't change amount of Cl^- in the solution, they freely float before and after the reaction.

[Tittywahah]

Borek,  I really think you are misunderstanding something here.  I did not say that any amounts of Cl- ions or copper or whatever were changed.  I said that there are free Cl- ions in solution, when NaOH is added it will dissolve back into the CuCl solution.  BUT, at the point where there are no more FREE Cl- ions from the HCl which has been added to the CuCl solution, in solution, the NaOH no longer dissolves, you will get a copper hydroxide precipitating out of the solution. Hope this clarifies things.  But it has digressed from my original question about titration.  Nevermind.

Oh and yes my titration is wrong.  I need to halve the end result, just found my notes from over a year ago....

[Borek]

Either I am misunderstanding what you wrote, or what you wrote is a word salad. I can't make any sense out of the chemistry you are describing.

[Tittywahah]

I etch copper as well as other things.  CuCl2+HCl+Source of oxygen dissolves copper.  The copper that is dissolved becomes copper chloride 1.  This is insoluble, but The acid that is in the etch solution oxidizes this copper 1 back into copper 2.  The copper 2 then digs away at the copper and the process is constantly regenerating itself ad finitum.  All you need to do is to keep an eye on Specific Gravity of copper in solution and most importantly the amount of HCl that is NOT tied up, bonded with copper chloride complexes keeping them dissolved.  This would be the Cl-, the chloride ion that is important.   The minute that all the HCl is exhausted you then get precipitation of Copper 1 and an etch solution that no longer etches because the copper 1 can not be oxidized back into copper 2.

This is where titration comes in, one checks that Amount of Free Cl- ions in solution (These would be the Cl- ions that are donated by the HCl and are not tied up with copper chloride 1 and 2 complexes and possibly 4 as well) and keeps the copper chloride solution at about a molarity of around 1.8 to 3.

Hope this clarifies - if not please do not hesitate to let me know.  Happy to oblige.

[Borek]

It becomes clearer now, still, the chemistry you describe is awfully off.

The copper that is dissolved becomes copper chloride 1.  This is insoluble, but The acid that is in the etch solution oxidizes this copper 1 back into copper 2.

It is not acid that oxidizes Cu(I) to Cu(II), but air oxygen (or hydrogen peroxide, used in some of the recipes).

All you need to do is to keep an eye on Specific Gravity of copper in solution

No such thing as "specific gravity of copper in solution". Either "specific gravity of copper" (which doesn't make sense here, as you don't have metallic copper), or "specific gravity of solution" (which is most likely what you want, as it is a simple way of checking that the solution composition is within some predefined limits).

This is where titration comes in, one checks that Amount of Free Cl- ions in solution

You can't check level of Cl^- in the solution titrating with NaOH. You can check how much H⁺ is left. My bet is that the dissolution consumes H⁺, and when pH goes up too high process stops. Titration with NaOH would be just checking how much acid (but not free Cl^-) is left.

[Tittywahah]

Hallo Borek.  Well I very much appreciate the corrections.  It's hard teaching yourself and having nobody to ask questions.  So Iam not surprised I get  it wrong.  Although I must say that I did realize that it was the O2 that does the oxidizing, this was a word error.  Still thankyou.  Regards the SG.  I thought that this was the amount of dissolved copper in solution that I was measuring?  Since after all more and more Metallic copper is certainly being dissolved in solution every week?  As for the H+ that is what I had written down, I should have re-read my notes before posting.  However, as you say yes HCl is consumed during the process and this gas is released in tiny quantities that are safe for indoors in a ventilated area, no smells at a Molarity under 3. 
Regards this H+, a little instruction here if you could, I am measuring free hydrogen ions then and not Cl ions? I thought that the Chloride ion is what is necessary to the solution not the H+, do you mean that I am actually measuring the H+ and by this measurement I am then seeing how much free Cl- there is left.  I think this is the point of the titration, to measure the H+ in order to get a measurement of the Cl-? Which is what is needed right, the chloride ion is what is important not the Hydrogen ion, which has no ultimate purpose in the solution.?

[Borek]

Regards the SG.  I thought that this was the amount of dissolved copper in solution that I was measuring?

No. Amount of copper can be estimated from the solution density (assuming you have all other things under control!), but what you are measuring is just a proxy for the copper amount.

Regards this H+, a little instruction here if you could, I am measuring free hydrogen ions then and not Cl ions? I thought that the Chloride ion is what is necessary to the solution not the H+, do you mean that I am actually measuring the H+ and by this measurement I am then seeing how much free Cl- there is left.  I think this is the point of the titration, to measure the H+ in order to get a measurement of the Cl-? Which is what is needed right, the chloride ion is what is important not the Hydrogen ion, which has no ultimate purpose in the solution.?

My bet is that the overall copper dissolution reaction is

2Cu + O₂ + 4H⁺ 2Cu²⁺ + 2H₂O

As you see when all H⁺ are consumed, solution will stop to work.

[Tittywahah]

Hallo Borek.  Well I do not quite know what you mean by proxy here, but all I know is that I measure the density of the solution with my hydrometer and this tells me how 'dense' the solution is with regards to 'copper content'. 

When the the Cu 2 species reacts and liberates Cu 1 species the Cu 1 species can only remain dissolved because of the Cl- ion. and then the Oxygen dissolved in the solution oxidizes this Cu 1  back into Cu2 and that does the etching.  So I am sorry, and my ignorance here or failure to understand something is apparent, I can not see the role of the H+ ion.
Regards

[Borek]

Think about Cl^- as a catalyst - it is necessary, but it doesn't get consumed in the reaction. H⁺ gets consumed.

Solution density can change because of many factors, copper presence is just one of them. Depending on the exact solution composition, solution that has density 0f 1.1 g/mL can contain 0.86 M of copper (solution of CuCl₂), 0.65 M of copper (copper sulfate), 0.59 M of copper (copper chlorate), or even no copper at all.

[Tittywahah]

Ok Thankyou.