Acid neutralization addendum ... sulfuric acid.

John Shott shott at snf.stanford.edu
Thu Jan 18 11:51:41 PST 2001


SNF labmembers:

Two additional points related to acid dumping and neutralization that I forgot
to mention:

1. You do not need to nofify us of use of dump rinsers or use of SVG
developers.

2. We have to be particularly careful when dumping sulfuric acid.  If we
compare dumping equal hot pot volumes of 5:1:1 H2O:H2O2:HCl vs. 9:1 H2SO4:H2O2
we find that the amount of neutralization that has to be done in the case of
the HCL hot pot is proportional to 1/7 * 0.37 which is about 0.05. The 1/7 is
due to the fact that only one part in seven of the total mixture is actually
HCL and the HCl that we use is about 37% concentration.

One of the 9:1 H2SO4:H2O2 pots, however requires total neutralization that is
proportional to 9/10 * 0.96 *2 which is about 1.7.  In this case, the volume
of our mixture is about 90% sulfuric acid, plus the strength of sulfuric acid
straight out of the bottle is approximately 96%.  Finally, because there are 2
hydrogen ions in each H2SO4 molecule, we have to neutralize each of them. In
other words, dumping one of our sulfuric hot pots requires approximately 35
times more neutralization "effort" than an equivalent 5:1:1 HCl hot pot.  So
be extra careful to warn us if you are about to dump a sulfuric hot pot!

Thank you for your continued support ...

John



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