inspector071
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Acid densities with a hydrometer
I just got a 1.000-2.000 specific gravity hydrometer. I wanted one specifically for checking the densities of concentrated nitric and sulfuric acids,
however the one that I got is pretty big, and frankly, I don't have enough acid to even use the thing! It's about a foot long and maybe 3/4 inch wide.
For checking the density of small amounts of liquid, say 50-100 mL, what should I be using?
Edit: it appears as though hydrometer test cylinders are specially made just for this application! Who would have thought? At any rate, how much are
the hydrometer cylinders normally filled prior to putting the hydrometer in?
[Edited on 7-3-2012 by inspector071]
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UnintentionalChaos
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get a good thermometer and a 10, 25, or 50ml class A volumetric flask. let everything come to a known temperature. Take the weight of the empty flask,
fill carefully to the line, avoiding making bubbles, and measure again. divide the difference in mass by the volume of the flask. The better your
scale, the more accurate your density, though at some point, slight variations in temperature or the error inherent in the flask will become dominant.
For the truly anal, you can account for the mass of the air displaced in the empty flask, but an excellent approximation for any typical usage is that
it has no mass.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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inspector071
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Alright, that method would work just fine, but alas I don't have a scale that would be suitable for weighing that mass between a 500g spring scale
(not accurate) and my Mettler Toledo mechanical microbalance. The microbalance might actually be able to weigh that much, but I don't have it set up
currently as I don't have a sturdy lab table to put it on. Would a pycnometer be an improvement over the volumetric flask?
There is always of course the trusty titration to determine the concentration of my acids, but I don't have a burette yet.
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zoombafu
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You don't need a burette to preform titrations. If you have a graduated cylinder you can just pipette the liquid.
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inspector071
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Quote: Originally posted by zoombafu  |
You don't need a burette to preform titrations. If you have a graduated cylinder you can just pipette the liquid. |
That's true, though my graduated cylinders are not very accurate. Getting a burette shouldn't be hard though, and it would be a nice piece of lab
equipment to have.
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White Yeti
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You can dilute a sample of your acid with a known amount of water and add to it a known concentration of a NaOH solution. The more dilute your
samples, the less accurate your measuring equipment has to be.
I'm guessing you have phenolphthalein indicator, if not try using NaHCO3 solution as titrant, the reaction reaches equivalence when the mixture stops
fizzing.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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