If sulfuric acid barely evaporates, why we can smell it? Or does it give off sulfur dioxide gas?
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2$\begingroup$ Are you talking about laboratory-grade 98% sulfuric acid? As one of the largest volume production chemicals in the world, it comes in all kinds of grades and mixtures, so that whatever else is in it may be responsible for the odor. $\endgroup$– Nicolau Saker NetoFeb 22, 2020 at 7:38
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1$\begingroup$ You can smell salt at the sea shore even if salt does not evaporate at all. $\endgroup$– PoutnikFeb 24, 2020 at 6:56
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4 Answers
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There are at least two plausible explanations for why an odorless compound with very low vapor pressure could nevertheless generate an odor:
Sulfuric acid is highly reactive. If you are pouring or dispensing sulfuric acid, you are probably generating some mist. This is a concern in industrial settings where sulfuric acid is used:
https://www.cdc.gov/niosh/docs/81-123/pdfs/0577.pdf
Thus, even if the sulfuric acid itself has neither a significant vapor pressure nor an odor, as the mist enters your nose it could react with substances in your nasal passages to create compounds that have an odor. Some studies have reported the perception of odor from sulfuric acid mists: https://www.epa.gov/sites/production/files/2014-09/documents/sulfuric_acid_interim_dec_2008_v1.pdf
And even without misting, particulates in the air, as they fall into an open container of sulfuric acid, could react with sulfuric acid to generate compounds that create a smell. This effect is seen with metals -- the metallic "smell" is not from the metals themselves (which have an extremely small vapor pressure at room temperature), but from reaction products of the metals:
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According to wikipedia:
Sulfuric acid (alternative spelling sulphuric acid), also known as vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with molecular formula $\ce{H2SO4}$. It is a colorless, odorless, and viscous liquid that is soluble in water and is synthesized in reactions that are highly exothermic.
Hence, you can't smell it.
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2$\begingroup$ But then why it is said: If you are exposed to concentrated sulfuric acid in air, your nose will be irritated and it may seem like sulfuric acid has a pungent odor (atsdr.cdc.gov/phs/phs.asp?id=254&tid=47). $\endgroup$ Feb 22, 2020 at 6:54
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1$\begingroup$ As conc sulphuric acid is a strong dehydrating agent, I think it would absorb the water or the mucus in your nose and you will feel irritated $\endgroup$ Feb 22, 2020 at 7:05
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1$\begingroup$ But the issue is how the sulphuric acid molecule gets into the air and into my nose? $\endgroup$ Feb 22, 2020 at 7:32
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1$\begingroup$ Welcome to the site! I would urge you to go through this and this. Please try to familiarize yourself with this MathJax and $\LaTeX$ tutorial for proper formatting in posts. Additionally, plagiarism is a serious offense: when copy-pasting from Wikipedia, make sure you add a reference. And also enclose quoted text in block-quotes using
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2$\begingroup$ Sulfuric acid can get into your eyes and nose as fine droplets, or in a water-based mist depending on how a spillage occurs. $\endgroup$ Feb 22, 2020 at 8:32
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Most of the sulfuric acid in the air is formed from the sulfur dioxide released when coal, oil and natural gas are burned. The sulfurous anhydride that is released forms sulfuric anhydride slowly, and it reacts with water in the air forming sulfuric acid. Sulfuric acid dissolves in water present in the air and can remain suspended for varied periods of time; It is removed from the air in the rain. Sulfuric acid in the rain contributes to the formation of acid rain. Sulfuric acid in water separates resulting in hydrogen and sulfate ions. The ability of sulfuric acid to change the acidity (pH) of water depends on the amount of sulfuric acid and the ability of other substances in the water to neutralize hydrogen ions (buffer capacity).
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It may reach our nose due to a varietyof reasons. The sensation of smelling is it probably because sulfuric acid absorbs water from the nose and irritates it. Similar to how eyes are irritated while cutting onions due to formation of sulphuric acid. Also, it isn't necessary for it to vaporize. It can be just fine droplets that reach the nose and cause irritation.
