Grant,
Its been interesting listening to your progress on copper
chloride makeup over the past few weeks. I agree with you about
it all this chemistry being fun while learning new things.
I'm not sure what you know about molar mass and working in
concentrations represented in moles per liter (or "Molar" or just
"M" for short).
http://www.cards.anoka.k12.mn.us/projects/HTML_98/sievert/Sievert.htmlWorking with percent by mass of HCl is not very popular because
its a lot more difficult to calculate accurately, when doing
analysis. Concentrations are almost always given in the mass of
the active species per volume of liquid. If you know the molar
mass of the compound then you can easily convert in to number of
moles per liter. Where molar mass of NaOH and HCl compounds are;
NaOH = 40.00 grams per mole.
HCl = 36.45 grams per mole.
You prepare 0.1 moles/liter of NaOH solution by placing 4.000
grams of NaOH into a flask and add water until its exactly 1 liter.
You added 17.5 cm^3 of 0.100 M NaOH and it reacted with 1 cm^3 of
etchant of unknown concentration. The equation to calculate
concentration of the unknown is
[HCl] = 17.5cm^3 ∗ 0.100M / 1.00cm^3 = 1.75 moles/liter
This is a bit higher than necessary, but definitely not too high
to worry about. You should aim for 0.5 to 1 moles/liter of HCl.
Note the symbol N ("normality) is sometimes used for
concentrations. The normality is equal to the molarity when the
compound has one atom available for the reaction (this is not a
good definition). Sulfuric acid has 2 hydrogen atoms and each one
reacts with a NaOH molecule. So you need two moles of NaOH to
react with one mole of H2SO4. The normality of a 1 mole per liter
concentration of sulfuric acid is 2 N. The normality of a 1 mole
per liter concentration of hydrochloric acid is 1 N.
What type of hydrometer did you end up getting ?
I think 1.245 is ok. My solution measures around 1.29
I don't know the copper concentration, but going by the mass of
copper dissolved during makeup and its final volume, its should
be around 150 g/l.
Adam
grantfair2001 wrote:
> Hi Adam - (and interested list members).
>
> All (I hope)of my equipment and most of my chemicals are now on hand.
> The specific gravity of my etchant is 1.245.
>
> I did a trial titration. First I tried titrating until I reached
> "turbidity" (whatever that is, I didn't see anything which I thought
> might be it.) So I started over.
>
> I put 1 ml of etchant in 20 mL distilled water, and added 4 drops of
> Methyl orange. I then dripped 0.1 N NaOH solution into the beaker
> until the color changed from orange to yellow. About 17.5 mL of
> titrant were used to get to the end point.
>
> Assuming .31% HCl corresponds to 1 mL of titrant, the acid
> concentration is about 5.4%, which is a bit high I guess, but some
> etching will bring it down.
>
> I had fun playing mad chemist. When a couple more chemicals arrive I
> will try to determine the copper content and see how (if?) it matches
> up with the specific gravity. (Luckily I found a photographer with a
> 100 pound bag of sodium thiosulfate who was happy to send me 100 grams
> for the price of stamps. While it is a consituent of some current
> photographic "fixers" (to fix the silver structure of the photgraph so
> it doesn't change), there are lots of other chemicals included in all
> the fixers I found, so I had to go looking for someone who had the
> pure stuff.
>
> I do have one question: is this the appropriate way to titrate with
> methyl orange indicator? Are these calculations right?
>
> The only other problem I see is all the grunge bits floating on my
> etchant - I think this is the dissolved bits of the "airstone" I tried
> until it mushed out. I'll try coffee filters to get rid of it.
>
> I will be etching some boards eventually <g>. All this chemistry is
> more than what is needed to use this approach, but I find it a fun bit
> of learning.
>
> For anyone interested in trying this approach, don't let it scare you
> off. The "quick, cheap and dirty" analysis mentioned on the website
> (in the links) on Etching with Copper Chloride Etching Systems is
> likely all you need.
>
> www.pacificsun.ca/~robert/pcb/pcb.htm
>
> My next focus (I hope) will be trying to get a fairly even etch.
>
> Grant
>
>
>
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