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If i keep adding sulfuric acid into water, will it keep dissolving forever?

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  • $\begingroup$ Sulfuric acid and water are miscible. Does this answer your question? en.wikipedia.org/wiki/Miscibility $\endgroup$
    – aventurin
    May 10, 2018 at 23:05
  • $\begingroup$ Yes, it will continue to dissolve the water. $\endgroup$
    – A.K.
    May 11, 2018 at 3:37

3 Answers 3

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If you remove the last two or so percent of water from concentrated $\ce{H_2SO_4}$, it starts fuming, giving off SO3 until it again contains enough water to be stable.

$\ce{H_2SO_4 <-> SO_3 + H_2O}$

Pure sulfuric acid does not exist, so there is no clear yes/no answer to your question. Also $\ce{H_2SO_4}$ (like all other mineral acids) does not just mix with water, but strongly reacts. So it's clear there can be no miscibility gap like with water/ether or similar pairings.

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When you dissolve a small amount of sulfuric acid in water then a chemical reaction occurs. The sulfuric acid dissociates into hydrogen cations (H+) and hydrogen sulfate anions (HSO4-). At very low concentrations of sulfuric acid in water the conductivity of the water is proportional to the sulfuric acid concentration.

When the sulfuric acid concentration is increased then the activity coefficents of the ions will decrease, the ions will be less free to move independently of each other. If we use the Bromley equation then the ion pairing term will become more and more important. One can regard the specific ion interaction of the hydrogen and the hydrogen sulfate ions as a reversal of the dissociation of sulfuric acid.

As the concentration climbs higher and higher, the fraction of the sulfuric acid which is dissociated into seporated ion pairs will decrease. The ions will be in the form of contact ion pairs where the two might be touching. At this point the electrical conductivity of the solution will be less than what would be predicted if we made the assumption that the conductivity is proportional to the concentration (and used low concentration data to make the prediction).

These contact ion pairs will be part way between the truely solvated ions and the intact sulfuric acid. As the concentration of the sulfuric acid goes even higher I think we will get to a situation where the majority of the sulfuric acid is in the form of molecules of sulfuric acid where a covalent bond exists between the hydrogen atoms and the oxygens of the sulfuric acid molecules. The mixture will be very viscous and it will have lots of hydrogen bonds in it.

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Yes, there is no chemical reaction between H2S04 and water. it is just a dilution of H2S04. If u want to add 1000 liter water in 1ml H2SO4 , U can add and there will be clear solution without an solid or layer

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