I have read so much and have watched videos, unfortunately I am having trouble finding answers so need some help to understand how to interpret my
results:
30mils water + 1mil NaOH (1 mole) +1mil copper chloride solution with Unknown amount of HCl i(probably depleted) in this solution = Blue Copper
Hydroxide precipitate and NaCl in solution.
Now I added to a separate beaker the exact same amounts as above EXCEPT I added 36% HCl 1 mil at a time to this separate solution, 15mils later and
the solution just only began to turn a slight blue.
I understand what is happening here but I want to be able to translate this data so that I can ascertain how much HCl I would need in my CuCl etchant
solution in order to replenish it. Too much HCl would have an adverse effect. So I need to work out what the required amount is so that there are
enough chloride ions in solution to convert the CuCl1 back into CuCl2. I am sure there is maths involved here but I have no clue where to find or how
to search for the formulas in books or on the web. thankyou.Migratory - 11-6-2012 at 07:11
When you say "1mil copper chloride solution with Unknown amount of HCl i(probably depleted)" do you mean that you had previously added HCl, and expect
most it to have reacted out?
Once you know how much HCl is in your solution, you should be able to handle it with stoichiometry. A good chemistry book should have a chapter or two
on stoichiometry.CHRIS25 - 11-6-2012 at 07:32
Hi, no problem with stoichemetry - and yes the solution had HCl in it. All I need to know is if there is any maths, or equation or possibility that I
can determine how much HCl I need to add to continue the reaction without overdoing it, based upon what the NaOH titration exercise is telling me? watson.fawkes - 11-6-2012 at 08:55
All I need to know is if there is any maths, or equation or possibility that I can determine how much HCl I need to add to continue the reaction
without overdoing it, based upon what the NaOH titration exercise is telling me?
Yes and no.
The problem is that spent etchant has a mixture of Cu1+ and Cu2+ ions. For a neutral chlorine balance with copper you need twice
as much Cl- for one than for the other. In other words, unless you know what the ratio is between Cu1+ and Cu2+ in
your solution, the titration doesn't give you enough information to just start adding HCl.
Probably the easiest way of dealing with this situation is oxidize all the Cu1+ to Cu2+before titrating. Then the
ratio is 0:1 and you can derive numbers reasonable. Oxidization is done either by sparging oxygen through the solution, usually from the atmosphere,
or with hydrogen peroxide. The acid itself won't oxidize the copper; its job is coordinate around the copper and keep it in solution. The one problem
with this is that if the etchant is seriously depleted, you may need to add some HCl just to get the oxidation to proceed.
CHRIS25 - 11-6-2012 at 09:54
Hallo watsonFawkes, right ok then. Yes I use pumped air all the time now, cheaper than H2O2 and with that 6% that I can only get there is too much
water.
Ok I see that knowing the Cu(1+) in solution makes things a bit uncertain but I have two guidelines that at least give me an idea about the amount.
Firstly if the colour of the solution starts to become yellow brown or even dark brown then I know that there is quite a concentration of Cu(1+) ions
in solution (I drop a droplet of solution on white paper for this). Also if there is blackened gunge at the bottom of an etchant then this is Cu(1+)
that could not be dissolved. Since neither of these states has been reached Plus the colour of the solution against white paper is a nice emerald
green I can be confident that there is more Cu(2+) than Cu(1+), admittedly I can not know the ratio as you suggest and that would be handy, (I will
try and find a way to see if there is a separate experiment to determine this).
I am a little bewildered here about this:"Probably the easiest way of dealing with this situation is oxidize all the Cu1+ to Cu2+ before titrating"
What I don't understand is how you know when this has happened, because I thought you could only know the opposite, ie, when HCl is depleted and the
solution becomes really dark almost black then Cu(+1) is in excess almost because there can be no more oxidation, ie no more etching will occur.
I have read so much about this and yet all that reading raises more questions than answers,....
[Edited on 11-6-2012 by CHRIS25]CHRIS25 - 12-6-2012 at 01:17
Answer is that at the moment I have 1.5 moles of acid in 1litre of solution. So I have just discovered that when I add 1.5 NaOH to my 30 mil solution
of "CuCl in water" The copper hydroxide will not redissolve. Therefore 1.5mil is the same as 1.5 cm3, why people use the term cm3 seems ridiculous
really if it is the same as mililitres??
Since neither of these states has been reached Plus the colour of the solution against white paper is a nice emerald green I can be confident that
there is more Cu(2+) than Cu(1+), admittedly I can not know the ratio as you suggest and that would be handy
Qualitatively, this sounds like there's no more Cu1+ left. If there's a tiny amount, it won't matter at the precision
you're working to. You may assume that the ratio Cu2+:Cu1+ is 1:0.
Answer is that at the moment I have 1.5 moles of acid in 1litre of solution. So I have just discovered that when I add 1.5 NaOH to my 30 mil solution
of "CuCl in water" The copper hydroxide will not redissolve. Therefore 1.5mil is the same as 1.5 cm3, why people use the term cm3 seems ridiculous
really if it is the same as mililitres??
I can't make sense of this enough to know what's happening. In part
it's because you're not using standard unit names. In part it's because there aren't units at all where there should be.
"mil" is not a scientific unit name. It is an informal name only. In the USA it means one-thousandth-of-an-inch. I understand that elsewhere it means
milliliter. There are two standard abbreviations for milliliter: "ml" and "mL".
The liter is simply a unit of volume. It's a convenience unit, avoiding writing superscript-three so much. It's also a colloquial one, going back to
the French revolution. In any case, see the Wikipedia page on the liter for more information.
The phrase "when I add 1.5 NaOH" is meaningless. "1.5" of what? Are these solid grams of NaOH? Is it 1.5 ml of some solution? If it's a solution, what
is it's concentration? For a solution, you need to specify both the volume and concentration to know what's happening. See Wikipedia on molar concentration. The unit abbreviation for molarity is "M". Like any unit, you leave a space between the number and the unit abbreviation. So
perhaps you have "1.5 ml of 1 M NaOH solution (in water)", but you haven't said that.
The endpoint of titration of the etchant with NaOH solution is just as the solution starts to turn cloudy. The cloudiness are tiny particles of copper
hydroxide. When then endpoint is reached, it means that there's a tiny excess of OH- ions. What that means is that you've neutralized all
the H+ ions. (You may see people write this as H3O+; that's more the physical form of the ion. Sometimes that's
relevant, but not so much here.) The relevant reaction for the titration is just the ionic neutralization reaction: OH- + H+
--> H2O. The molar amount of OH- in the titrant is the same as the amount of H+ neutralized in the test solution.
Given the volume of test solution, this allows calculation of the molarity of H+ in the test solution. From this you can calculate its pH.CHRIS25 - 14-6-2012 at 11:23
Hi watsonFawkes. Just returned from Galway. need a bit of time on your reply to work things out, just to let you know that I am not ignoring what
you have said.
