grantfair2001 wrote:
>A chem student tells me the pH of the solution outlined in:
>
>http://www.dnai.com/~rexa/Projects/CuCl_ech.html
>
>would be just as good an indicator of needed chemical additons as the
>lengthy lab methods in the above article. A pH probe is more
>convenient and much cheaper than the lab equipment the article says is
>necessary. For example, Corning sells a pH probe for $40.
>
>Does anyone know if the student is right? What pH level would be
>optimum, and what would variations mean need to be added to the brew?
>
>Grant
>
>
pH isn't a good indication for HCl concentration of this etchant. pH will be very insensitive to acid concentration because HCl is a strong acid. (almost all HCl goes to H3O+ and Cl-). i.e pH will always be very very low, even for a small amounts of acid. Acid/bace titration is the only reliable method.
However the article below mentions that a very sensitive conductivity meter is often used to automate HCl addition on commercial etching equipment. My guess this isn't so straight forward. At the very least the probe would require careful calibration across temperature and HCl concentration.
http://www.pcbfab.com/iepart3.htmlI have the glassware to do acid/bass titrations and it isn't that difficult or expensive as it may sound (class-B 50 ml burette AUD$55). One good thing about this equipment is it will last you forever and doesn't require maintenance unlike pH probes. The most difficult part would be making up your standard solutions of sodium hydroxide. Best bet would be to visit your local university chemistry department and ask for some.
I made the mistake buying some cheap glass/plastic equipment from a school science supply. It was total rubbish, errors greater than 10% and wasn't even that much cheaper than the proper German made stuff that I later got from a laboratory supplier.
good luck