measuring concentrations

[Chainsaw]

I've thought alot about ways of measuring concentration of different liquids (HNO3, H2SO4) and my latest idea would be this:

buy alcoholometer (device that measures concentration of ethyl alcohol)
nice ascii art <img border="0" title="" alt="[Wink]" src="wink.gif" />

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">code:</font><hr /><pre style="font-size:x-small; font-family: monospace;"> _______________
/o o|| \_______________________________________
|oo || __|_|_|_|__|____|______|______|________&gt; &lt;-saw here
\o_o||__________/</pre><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">o = lead balls for weight
|| = paraffin that holds these balls
|_|__|____| = scale

now the idea is to saw it open, add more lead balls and then paraffin again so it gets heavier.
Then make new paper scale. I believe it's logarithmic (i have to look into it) - so we know where water level is with 1.00g/cm3 water and we know where level is with battery acid 1.27g/cm3, so we should be able to calc. where it should be with 1.84 mixture or whatever (with some math. function). Then replace your own scale with original, and then seal the top of device with silicone.

EDIT: hydrometer for ethanol won't work for this. It has too small measuring scale, because of its narrow neck. You have to make it out of old thermomether or some other glass tube.

<small>[ March 17, 2003, 09:21 PM: Message edited by: Chainsaw ]</small>

[Tuatara]

Its a very good idea. The device is called a hydrometer. Mine goes from 0.90 to 1.16 s.g. Hydrometers used to be available for measuring battery acid to assess the state of charge - in the good ol' days before maintenance free car batteries. If you can find one it may not need any alteration.

I'd thought of using a hydrometer for measuring the rate of nitric acid production from an electric arc.

<small>[ March 12, 2003, 05:28 PM: Message edited by: Tuatara ]</small>

[Anthony]

Anywhere that sells basic home brewing equipment will sell hydrometers. As-is their range isn't nearly high enough for concy HNO3, H2SO4 etc. So the idea of modificated is a good one.

[Chainsaw]

... i am making scale for one right now, and i want to add percentages of acids there, but i am not sure about relation of percentages and spec gravity.

Percentages of acids are measured by weight, right?
What confuses me is that on 'special project: nitric acid' forum main page, there are some numbers that i can't get by calculations. Take for example 40g H2O + 60g HNO3 (60% by weight)

60 + 40
----------------- = 1.25 g/cm3
40/1.00 + 60/1.51

but on that page is 60% =&gt; 1.37 g/cm3

[vulture]

You can't just calculate the density of a mixture of liquids by accounting the percentages and the density of the components.
Alot of interactions like hydrogen bonding have severe effects on density.

[Al Koholic]

As well as temperature and ambient pressure.
Solutions being similar to gases at least in some respects might (anyone help me out here?) obey a similar density relationship like gases do ie: d = m/v = (P(Molar Mass))/(RT).

Obviously R will be useless for solutions but I'd imagine that the rest of the relationship should be somewhat applicable.

<small>[ March 24, 2003, 03:58 PM: Message edited by: Al Koholic ]</small>

[frogfot]

This ideal gas equation is only used at low pressures, some gases wouldn't obey it even at 10 atm. It's maby because of molecules getting closer together? :confused: And in liquid they're as close together as they can be, so it wouldn't work, i suppose..

<small>[ March 24, 2003, 04:59 PM: Message edited by: frogfot ]</small>

[vulture]

In an ideal gas the molecules are at any time such a distance from eachother away at which there are no more intermolecular forces present. This usually means pressures lower than 0,5 atm. For realistic gases there are approximations like the Van der Waals equation for realistic gases.
In liquids and solids gas law does not apply, it doesn't even come close because of the very strong interactions.

[Al Koholic]

Good point. I neglected to think about the decreased distance between the molecules and the higher molecule size : distance ratio.

Regardless however, T should still affect the measurements of the hydrometer due to its effect on V.

[Tuatara]

Who here hasn't done the little experiment where your mix 50ml of water with 50ml of ethanol and end up with ~95ml mixed?

And if it wasn't for Hydrogen bonding, water would boil around the same temperature as Nitrogen!

T definitely has an effect - my hydrometer specifically states on the side that it is only accurate at 20C.

[Chainsaw]

Interesting...
anyway, could somebody then post some percentages (90%,80%,70%,...)with corresponding densitys in g/cm3 for H2SO4.

[shrek]

A quick search at google gave me the following:

<a href="http://web1.caryacademy.org/chemistry/rushin/StudentProjects/CompoundWebSites/2000/SulfuricAcid/density.htm" target="_blank">http://web1.caryacademy.org/chemistry/rushin/StudentProjects/Compou ndWebSites/2000/SulfuricAcid/density.htm</a>

Percent Mass Sulfuric Acid to Water

Density per g cm-3

100.0 % --- 1.8305
94.0 % --- 1.8312
90.0 % --- 1.8144
84.0 % --- 1.7693
80.0 % --- 1.7272
74.0 % --- 1.6574
70.0 % --- 1.6105
64.0 % --- 1.5421
60.0 % --- 1.4987
54.0 % --- 1.4351
50.0 % --- 1.3952

There is more.. but I got lazy

Edit: Fixed formating problems... Still not perfect but...

<small>[ March 25, 2003, 12:57 AM: Message edited by: shrek ]</small>