I recently picked up some ACS grade potassium hydrogen phthalate for use as a primary standard in titration and it came with an assay reporting the
purity as (you guessed it!) 99.5-100.5% pure.
I rarely buy ACS grade reagents as I enjoy sourcing/purifying my own whenever possible, but for a primary standard a high (and known) purity is worth
spending a few monies. Only now I'm left with the conundrum of how to handle 99.5-100.5% when calculating error in titrations. Clearly the chemical
isn't over 100% pure, that'd be witchcraft, but the python uncertainties library I've used in the past assumes linear distribution around a central value.
Calculating with the provided value of 1.000(5) is the obvious answer, but it seems like an unnecessary addition of uncertainty when I'm quite certain
the purity isn't over 100%. Calculating with the value of 0.9975(25) is another possibility, but I don't rightly know if this would make the situation
better or worse. Any help/advice would be appreciated.
It's worth noting that my mathematical skills do not (yet) extend to calculus, so answers of that nature may help other people who have similar
questions, but won't be of much use to me.Heptylene - 2-8-2019 at 12:41
They give a few worked examples, one of which is the titration of NaOH with potassium hydrogen phthalate (KHP). Their KHP is 100.00(5) % pure, so they
use that in their formulas. See page 46.Felis Corax - 2-8-2019 at 14:33
Well, that makes this easy. Thanks for the highly applicable answer, and the book!wg48temp9 - 2-8-2019 at 23:21
I didn't know we had a library. Very interesting stuff!
Its an option on the first page of sciencemadness.org
I don't know how items gets added to the library.
By linking an item it tends to decay (becomes invalid) with time. The alternative is to up load for example Attachment: QUAM2012_P1.pdf (1.9MB) This file has been downloaded 315 times that way it will not decay.
