I use a very common methyl orange indicator which I don't think is a
food dye, but available from any lab supplier (at premium price) or some
industrial dye suppliers as samples.
You can go to the supermarket and look for food dyes. I'm sure some
common dyes can make satisfactory indicators for titration of HCl with
NaOH. I don't know of any off by hand sorry. Tatrazine (yellow) ? I've
used turmeric power once before but it is lot less accurate than methyl
orange.
If you want a quick answer then try post an article on USENET
news://sci.chem asking what common food die can be used as an indicator
for HCl titrations. The choose of indicators is flexible since HCl is a
strong acid and NaOH is a strong base which means pH ramps very steep
towards the end point.
grantfair2001 wrote:
>Adam- thanks very much for the information and link.
>
>What kind of indicator do you use? My chem student friend seemed to
>think that Bromphenol Blue was some kind of throwback to the dark ages
>and very difficult to find.
>
>Grant
>
>--- In Homebrew_PCBs@y..., Adam Seychell <adam_seychell@y...> wrote:
>
>
>>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.html
>>
>>I 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
>>
>>
>
>
>
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