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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