Homebrew PCBs

I've been thinking about switching to CuCl etching, to avoid having to
deal with FeCl any more.  I've started collecting the bits and pieces,
and have my HCl (Lowes had it, Home Depot and Ace didn't).  I've found
a place that has a suitable hydrometer (the local auto parts store
only had 1.1-1.3).  I've considered the venting issue.

My current question is about pH or HCl molarity.  Adam Seychell's page
says that pH strips won't work because the copper messes up the
reading.  What about the cheap digital pool pH meters?  They claim
they support 0-14, but (1) will the copper mess those up? and (2) how
does the molarity translate to pH in a CuCl solution?

I don't think PH meters will work.
You don't want to measure PH, you want to measure molarity
(concentration of HCl).

I can only explain my understanding with an electrical analogy: Take
measuring the state of charge in a NiCd battery.
Can't be done with a voltmeter (PH meter), unless you discharge the
battery. While you discharge it, you can look how much energy you can
take before the voltage drops to some point.

The same is done with CuCl. You take a sample of CuCl (say 10 drops),
and you add a PH indicator to it. Now you slowly add NaOH solution of
known concentration. This is the same as discharging the battery - the
two chemicals neutralise each other. The indicator will show when the
NaOH has neutralised all Acid and the PH reverses. The amount of NaOH
you used directly gives you the concentration of HCl. I suppose the PH
meter could replace the indicator, but i see no reason to do that
unless you have such a meter the indicator is far cheaper and easier
to use.

ST

On Dec 9, 2007 6:26 AM, DJ Delorie <dj@...> wrote:
>
> I've been thinking about switching to CuCl etching, to avoid having to
> deal with FeCl any more.  I've started collecting the bits and pieces,
> and have my HCl (Lowes had it, Home Depot and Ace didn't).  I've found
> a place that has a suitable hydrometer (the local auto parts store
> only had 1.1-1.3).  I've considered the venting issue.
>
> My current question is about pH or HCl molarity.  Adam Seychell's page
> says that pH strips won't work because the copper messes up the
> reading.  What about the cheap digital pool pH meters?  They claim
> they support 0-14, but (1) will the copper mess those up? and (2) how
> does the molarity translate to pH in a CuCl solution?
>
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBs
> Yahoo! Groups Links
>
>
>
>
>

Your method is what works for me, except I use the
solution itself as an indicator.

First off, mix 40 g NaOH to 1 liter of water to make a
1 molar standard solution (even 4 g in 100 ml will
last you a lifetime).

Place 10 drops of CuCl2 in a test tube or other
similar container. Add some water to increase the
volume a bit, quantity isn't critical but don't make
it too transparent. Double or triple is fine.

Fill the dropper with the standard solution (wash it
off first). Add it to the test tube one drop at a
time. A darkish cloud forms where it hits. Shake the
tube to dissolve it. As you keep dropping it will
start forming tiny white flakes. Keep shaking it. Stop
when the flakes refuse to dissolve. Divide by 10 (or
however many drops of CuCl2 you used) to find the
molarity.

The NaOH at first reacts  with the HCl forming NaCl
and H2O. The initial darkish cloud is due to a
momentary  formation of CuCl which reacts with the
remaining HCl back to CuCl2. When the HCl is exhausted
the reaction forms CuOH which is only weakly soluble
making it cloudy.

As for density you can weigh 100 ml in a tared
container and multiply by 10.

You can also use a tared container of unspecified
volume by first weighing the solution and then the
same volume of plain water. Divide the former by the
latter to find the density directly.

The methods above are ballpark only, but should be
within 10% tolerance. CuCl2 itself is pretty tolerant
about variations as long as they stay within limits.

- YD.

--- Stefan Trethan <stefan_trethan@...> wrote:

> I don't think PH meters will work.
> You don't want to measure PH, you want to measure
> molarity
> (concentration of HCl).
> 
> I can only explain my understanding with an
> electrical analogy: Take
> measuring the state of charge in a NiCd battery.
> Can't be done with a voltmeter (PH meter), unless
> you discharge the
> battery. While you discharge it, you can look how
> much energy you can
> take before the voltage drops to some point.
> 
> The same is done with CuCl. You take a sample of
> CuCl (say 10 drops),
> and you add a PH indicator to it. Now you slowly add
> NaOH solution of
> known concentration. This is the same as discharging
> the battery - the
> two chemicals neutralise each other. The indicator
> will show when the
> NaOH has neutralised all Acid and the PH reverses.
> The amount of NaOH
> you used directly gives you the concentration of
> HCl. I suppose the PH
> meter could replace the indicator, but i see no
> reason to do that
> unless you have such a meter the indicator is far
> cheaper and easier
> to use.
> 
> ST
> 
> 
> 
> 
> On Dec 9, 2007 6:26 AM, DJ Delorie <dj@...>
> wrote:
> >
> > I've been thinking about switching to CuCl
> etching, to avoid having to
> > deal with FeCl any more.  I've started collecting
> the bits and pieces,
> > and have my HCl (Lowes had it, Home Depot and Ace
> didn't).  I've found
> > a place that has a suitable hydrometer (the local
> auto parts store
> > only had 1.1-1.3).  I've considered the venting
> issue.
> >
> > My current question is about pH or HCl molarity. 
> Adam Seychell's page
> > says that pH strips won't work because the copper
> messes up the
> > reading.  What about the cheap digital pool pH
> meters?  They claim
> > they support 0-14, but (1) will the copper mess
> those up? and (2) how
> > does the molarity translate to pH in a CuCl
> solution?
> >
> >
> > Be sure to visit the group home and check for new
> Links, Files, and Photos:
> > http://groups.yahoo.com/group/Homebrew_PCBs
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> 



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DJ Delorie wrote:
> 
> 
> 
> My current question is about pH or HCl molarity. Adam Seychell's page
> says that pH strips won't work because the copper messes up the
> reading. What about the cheap digital pool pH meters? They claim
> they support 0-14, but (1) will the copper mess those up? and (2) how
> does the molarity translate to pH in a CuCl solution?

pH is nothing more than a logarithmic scale of hydrogen ion activity. 
Some of your HCl will be exists as HCl molecules while the remainder 
dissociates as hydrogen ions and chloride ions. To further mess up pH, 
not all of these hydrogen ions are active at such high concentrations. 
Since pH only responds to active hydrogen ions you will get a false low 
acid reading.

At very low HCl concentrations < 0.01 molar then the pH begins to gives 
better indication of HCl concentration.

Adam Seychell <a_seychell@...> writes:
> pH is nothing more than a logarithmic scale of hydrogen ion
> activity.  Some of your HCl will be exists as HCl molecules while
> the remainder dissociates as hydrogen ions and chloride ions. To
> further mess up pH, not all of these hydrogen ions are active at
> such high concentrations.  Since pH only responds to active hydrogen
> ions you will get a false low acid reading.

Ok, that seems obvious enough with that explanation.  Thanks!

In article <255096.97029.qm@...>,
   YD <yd_br@...> wrote:
> Your method is what works for me, except I use the
> solution itself as an indicator.

I was wondering about that. With a strongly coloured solution it would be
difficult to see the colour of most indicators.

lists <stuart.winsor.lists@...> writes:
> I was wondering about that. With a strongly coloured solution it
> would be difficult to see the colour of most indicators.

http://members.optusnet.com.au/%7Eeseychell/PCB/etching_CuCl/titraion_images.html

Yes, it's a good idea that.
Since i already have the indicator, i use that. I rather stupidly
bought quite a large amount (for an indicator), which will last me for
the next two million years or so. The day after i got it i was
wondering if i had an eyedropper bottle somewhere, so i got out my old
chemicals set. Guess what, in there was an eyedropper bottle filled
with just that same indicator. Haven't even opened the one i bought,
how stupid is that?

Anyway, you don't need it, but it makes things easier to see.

ST

On Dec 10, 2007 1:22 AM, lists <stuart.winsor.lists@...> wrote:
> In article <255096.97029.qm@...>,
>   YD <yd_br@...> wrote:
> > Your method is what works for me, except I use the
> > solution itself as an indicator.
>
> I was wondering about that. With a strongly coloured solution it would be
> difficult to see the colour of most indicators.
>
>

Not to thread-jack, but what is the proper method of disposal of the 
CuOH precipitate following this procedure?

--- In Homebrew_PCBs@yahoogroups.com, YD <yd_br@...> wrote:

>
> Your method is what works for me, except I use the
> solution itself as an indicator.
> 
> First off, mix 40 g NaOH to 1 liter of water to make a
> 1 molar standard solution (even 4 g in 100 ml will
> last you a lifetime).
> 
> Place 10 drops of CuCl2 in a test tube or other
> similar container. Add some water to increase the
> volume a bit, quantity isn't critical but don't make
> it too transparent. Double or triple is fine.
> 
> Fill the dropper with the standard solution (wash it
> off first). Add it to the test tube one drop at a
> time. A darkish cloud forms where it hits. Shake the
> tube to dissolve it. As you keep dropping it will
> start forming tiny white flakes. Keep shaking it. Stop
> when the flakes refuse to dissolve. Divide by 10 (or
> however many drops of CuCl2 you used) to find the
> molarity.
> 
> The NaOH at first reacts  with the HCl forming NaCl
> and H2O. The initial darkish cloud is due to a
> momentary  formation of CuCl which reacts with the
> remaining HCl back to CuCl2. When the HCl is exhausted
> the reaction forms CuOH which is only weakly soluble
> making it cloudy.
> 
> As for density you can weigh 100 ml in a tared
> container and multiply by 10.
> 
> You can also use a tared container of unspecified
> volume by first weighing the solution and then the
> same volume of plain water. Divide the former by the
> latter to find the density directly.
> 
> The methods above are ballpark only, but should be
> within 10% tolerance. CuCl2 itself is pretty tolerant
> about variations as long as they stay within limits.
> 
> - YD.
>

You must of course collect it and bring it to the proper disposal facility ;-)

Or you could just dump it down the drain, we are talking about minute
amounts for this analysis.

In the end you must wash boards too, which leaves you with lotsa
slightly dirty water. You can hardly drink it.

The solution to pollution is dilution :-)

ST

On Dec 14, 2007 6:29 PM, persnickimmon <dexter.kline@...> wrote:
> Not to thread-jack, but what is the proper method of disposal of the
> CuOH precipitate following this procedure?
>
>
> --- In Homebrew_PCBs@yahoogroups.com, YD <yd_br@...> wrote:
> >
> > Your method is what works for me, except I use the
> > solution itself as an indicator.
> >
> > First off, mix 40 g NaOH to 1 liter of water to make a
> > 1 molar standard solution (even 4 g in 100 ml will
> > last you a lifetime).
> >
> > Place 10 drops of CuCl2 in a test tube or other
> > similar container. Add some water to increase the
> > volume a bit, quantity isn't critical but don't make
> > it too transparent. Double or triple is fine.
> >
> > Fill the dropper with the standard solution (wash it
> > off first). Add it to the test tube one drop at a
> > time. A darkish cloud forms where it hits. Shake the
> > tube to dissolve it. As you keep dropping it will
> > start forming tiny white flakes. Keep shaking it. Stop
> > when the flakes refuse to dissolve. Divide by 10 (or
> > however many drops of CuCl2 you used) to find the
> > molarity.
> >
> > The NaOH at first reacts  with the HCl forming NaCl
> > and H2O. The initial darkish cloud is due to a
> > momentary  formation of CuCl which reacts with the
> > remaining HCl back to CuCl2. When the HCl is exhausted
> > the reaction forms CuOH which is only weakly soluble
> > making it cloudy.
> >
> > As for density you can weigh 100 ml in a tared
> > container and multiply by 10.
> >
> > You can also use a tared container of unspecified
> > volume by first weighing the solution and then the
> > same volume of plain water. Divide the former by the
> > latter to find the density directly.
> >
> > The methods above are ballpark only, but should be
> > within 10% tolerance. CuCl2 itself is pretty tolerant
> > about variations as long as they stay within limits.
> >
> > - YD.
> >
>
>
>
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBs
> Yahoo! Groups Links
>
>
>
>
>

The amount is small, milligrams at most, and of low
toxicity. Just pour it down the drain.

- YD.

--- persnickimmon <dexter.kline@...> wrote:

> Not to thread-jack, but what is the proper method of
> disposal of the 
> CuOH precipitate following this procedure?
> 



      ____________________________________________________________________________________
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