Homebrew PCBs

I built an autotitrator with a chemistry student some years back. It
used a syringe pump driven by a stepper. We were dropping NaCl
solution into silver nitrate IIRC (I supplied mechanical/electronic
assistance, he did the chemistry). The probe was expensive but he
borrowed it from the school. Would there be a probe which would
detect the endpoint in this case? Or would visual inspection be just
as good - in terms of time required?

Grant

--- In Homebrew_PCBs@yahoogroups.com, Adam Seychell <a_seychell@y...>
wrote:
> grantfair2001 wrote:
> > 
> > Hi Adam -
> > 
> > An automated process would take the tedium and time out of it. But do
> > you know of sensors up to the job? A SG sensor might not be too hard
> > to improvise. But molarity?
> 
> A simple float might be done with a block of polyethylene plastic
with a 
> small stone tied to it somehow. But the S.G is fairly slow changing and 
> doesn't require frequent measurement so using hydrometer will not be a 
> problem, and you know its accurate. The hydrometer will be essential 
> when mixing/making your first batch of etchant.
> 
> Acid molarity is best done by titration. You don't need indicator since 
> your end point is the first signs of the copper precipitate. In fact 
> one of the technical staff at http://www.oxfordvue.com  told me in a 
> email that titration of copper chloride etchant should only be done 
> using the copper hydroxide precipitate for end point detection. He said 
> the high copper levels interfere with pH and causes most indicators not 
> to work. I tried eye dropper method but the drop size of etchant is 
> about 1.5 times volume that of sodium hydroxide. Counting drops is very 
> inaccurate. Instead I use a 1.0 cm^3 measuring pipette and a pipette 
> sucker. Take 1.0 mil of etchant into about 20 cm^3 tap water, then 
> titrate with 1M NaOH solution, until I see first signs of precipitate. 
> Note that towards the end point the solution must be mixed and the NaOH 
> added slowly so make sure all the acid has reacted. I sometimes heat in 
> a microwave oven for a few seconds before doing the titration to speed 
> up the reaction of last traces of acid towards the end point.
> 
> Glass measuring pipettes and the suckers are about $2 to $3. The
problem 
> is only lab supplies have this kind of stuff.