Liquor treatment - dilution confirmation - 98% w/w Sulfuric - 25% sulfuric

[Gadjobrinus]

Just looking for a dilution confirmation for 98% w/w sulfuric to 25% w/w sulfuric for liquor treatment (alkalinity and SO4 addition).

No advisements against using for safety or "not good for brewing - build up from RO" please.

98% w/w H2SO4 = 18.35 M
25% w/w H2SO4 = 3.18 M

To get 1 L of 25%/3.18 M sulfuric acid, by c1v1 = c2v2,

v1 = (3.18 * 1000)/18.35 = 173.3 ml sulfuric acid, with enough chilled DI water to make up 1 L, roughly 826.7 ml cold DI water, acid to water in small increments, to ease the exothermic reaction.

Thanks.

 

[AlexKay]

Shooting from the hip here, but I’d expect partial molar volume errors to be unusually large for this mixture. That is, adding 826.7 mL of water to 163.3 mL of acid will not, in fact, give you a liter total. Better to weigh things.

 

[Gadjobrinus]

double post

 

[Gadjobrinus]

Ah, crap, post tanked. Basically thanks on the volume thing. A British brewer I know indicated the same thing to me, but as I'm playing catchup still working on understanding the loss of volume issue - is it due to the exothermicity of the reaction?

At any rate, I did use the Sigma-Aldrich calculator and it's a bit interesting because they use slightly different values from the SDS given by the vendor of the concentrated H2S04 (Science Direct). Science direct gives 96% w/w, Sigma defaults to 95%. I also don't know where I got 98% w/w, so that threw things off.

If I use the Sigma default, they give 178.4 ml stock (concentrated) acid (first to 250 ml DI, then enough DI to reach 1 L). If I use the SDS w/w from Science Direct and override the default w/w, they give 176.6 ml H2SO4 for 1 liter 3.18 M acid. So, pretty close. I do get the idea of using mass but am still working it out (reacquainting myself on the fly with relationship between densities, formula weights, molarity, etc.).

Thanks again.

 

[AlexKay]

If you want a hand-waving explanation, it has to do with how the molecules arrange themselves when they’re clumped together in a condensed phase. In water, molecules have a strongly preferred distance and orientation due to hydrogen bonding; in water ice (Ih) this gives you tetrahedral hydrogen bonding, a hexagonal lattice, and is the reason for the characteristic density. Solid, pure sulfuric acid will make its own crystal structure, again based upon fixed-length, directional hydrogen bonds. Mix the two together, and you might be able to imagine more complicated ways of packing them, and because the arrangement changes, the density does as well, and it need not be a weighted average of the two components.

This is less intuitive for liquids if you think of liquids as a disordered mess, but in fact most liquids have a surprising amount of structure, and look pretty similar to solids at short range.

Strong hydrogen bonding makes the effect of structure on density much larger, which is why I said I guessed it would be relatively more important for water/sulfuric acid. Strong hydrogen bonding is also the explanation for the large enthalpy of mixing, but other than that, there isn’t a direct connection.

From what you’ve posted, it seems this is still an issue of a few percent, though it did seem (for some reason) you were concerned with accuracy at that level.

If you’ve got a table of density versus composition, you can do the calculations you need.