Homebrew PCBs

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:
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