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145

This is a nice question, as it confronts a very replicable and common experience with a well established yet seemingly contradictory fact. As you expected, the smell of metal has nothing to do with the metal actually getting into your nose, as most metals have far too low of a vapor pressure at ordinary temperatures to allow direct detection. The ...


78

The odour threshold for HCN is in fact quite a bit lower than the lethal toxicity threshold. Data for hydrogen cyanide can be found in many places, but here and here are a couple of good references. That subset of the human population that can detect bitter almonds do so at a threshold of 0.58 to 5ppm. The lethal exposure dose is upwards of 135ppm. That's a ...


55

I'll quote from$\ce{^{[1]}}$: The general requirements for an odorant are that it should be volatile, hydrophobic and have a molecular weight less than approximately 300 daltons. Ohloff (1994) has stated that the largest known odorant is a labdane with a molecular weight of 296. The first two requirements make physical sense, for the molecule has ...


48

The "fishy" odor that you're familiar with is brought about by a whole bunch of compounds, and not any single one. Then again, if we were to narrow this down a bit, we could say that simple nitrogen compounds are the main culprits. But suppose we want to blame only a single compound for the delightfully pungent odor of rotting fish, and we couldn't be ...


46

This is a very interesting question. Provided that the materials used in making papers aren't the same around the globe, this is a very broad case of study. However, a study has been conducted in which the main goal was to identify the compounds that are the cause of the smell; VOCs:[1] Volatile organic compounds (VOCs) are organic chemicals that have a ...


41

Hair is largely (~90%) composed of a protein called keratin, which originates in the hair follicle. Now, keratin is composed of a variety of amino acids, including the sulfur containing amino acid, cysteine. All these amino acids are joined to each other by chemical bonds called peptide bonds to form these long chains that we call polypeptide chains. In the ...


35

There are 2 cases, both related to the acid-base reactions. Both are also partial reasons why so many fish recipes use lemon juice. Fish, especially sea fish, naturally contain trimethylamine-N-oxide $\ce{(CH3)3N-O}$ that, after death, gets enzymatically reduced to trimethylamine $\ce{(CH3)3N}$, the source of ammonia-like fish odour. Trimethylamine N-...


31

Recognize that a whiff of most toxins, even in high concentration, will probably not kill you. You need a sufficient concentration in your blood - which means you have to actually get a certain number of HCN molecules to penetrate across the mucosa of the lung and into the blood stream. Typical breathing volume is about 500 mL (tidal volume), about 1/40th of ...


28

Sugar is made by repeatedly boiling and cooling cane syrup (or sugar beet syrup). After each cooling, the solution becomes supersaturated with respect to sucrose, causing sucrose to crystallize out of the "mother liquor" (the industrial term for the liquid solution from which crystals form). These crystals of "raw" sugar are heavily processed (washed in ...


21

My first guess was that it was putrescine and other polyamines---but the smell of putrefying potatoes actually comes from methyl mercaptan, dimethyl sulfide, and dimethyl trisulfide. Check it: Source: A. Kamiya, Y. Ose, Study on offensive odor (Report IV): A Consideration of Putrefaction and Offensive Odor of Solid Waste, Journal of Japan Society of Air ...


21

Smell works because your nose detects substances in the air. Everything you can smell is the result of a molecule carried by air interacting with complex proteins in the nose/mouth (smell and taste are related but taste copes with solids and liquids as well as volatile airborne stuff). We broadly understand how smell works but the exact details are often a ...


17

If the stench is caused by putrescine or cadaverine, then you are in luck! Both putrescine and cadaverine are amines ($\ce{RNH2}$), which react with acids to form water-soluble ammonium salts ($\ce{RNH3+}$). Most soaps, surfactants, and other cleaning products are basic to help remove fats and oils (by hydrolysis). Try white vinegar, which contains acetic ...


17

Water in its pure form, i.e. $\ce{H2O}$ does not have a smell, or at least no smell that we can distinguish because the receptors in our nose (and mouth) are continuously exposed to it. What you smell are dissolved gases and other volatile impurities. The nature of these chemicals will vary mainly by location/source of the water, and might also be a bit ...


16

Dissenter is correct about aromatic compounds and that the basic requirement for a compound to be detected by smell is for it to be volatile enough to reach the nose. This is why things like dry salt don't really smell like anything. Once they reach the nose, things become more complex. Why many esters smell fruity while most thiols smell rather unpleasant ...


16

Hydrogen cyanide $(\ce{HCN})$ is variously described as smelling of bitter almonds, marzipan, ratafia, or peach kernels. While some people can smell $\ce{HCN}$ at very low concentrations, many people cannot perceive the odour at all. The odour threshold is about $1{-}6\ \mathrm{mg/m^3}$ for people who are actually sensitive to the odour of $\ce{HCN}$. ...


16

Almonds smell like they do mostly due to the presence of benzaldehyde: This colorless liquid has a characteristic almond-like odor. Benzaldehyde is the primary component of bitter almond oil and can be extracted from a number of other natural sources. Hydrogen cyanide also has an almond-like odor, but it is not as pronounced as that of benzaldehyde. From ...


15

Gatterman reports (Org. Synth. 1927, 7, 50, as a footnote) that people who smoke regularly have enhanced sensitivity to the smell of cyanide gas, and he recommend smoking while preparing it! Organic Synthesis Collective Volume 1 1941 314-315 Just opening the NaCN container, most regular (and former regular) smokers can smell the trace amount of HCN formed ...


13

If you are right, and the smell is coming from an amine, then you may need to clean a lot more than you have. Even if you think you've done a thorough cleaning, amines have very low odour thresholds. I can't find specific numbers for putrescine and cadaverine; however, another amine generated in decaying animal protein, trimethylamine, has an odour ...


12

Since odour is generally coming from vapour / gas form of a material, and NaCl has zero vapour pressure, it should be odourless. However: Moving around solid materials, dust, small particles can fly around that can be dissolved in the nose and interact with the odour sensors. You almost always have something else together with salt. And if it is not pure, ...


12

Without a sample and a gaschromatograph it is hard to say what exactly it can be but... there are at least three well-known sources of odour in plastics: Some residual of the monomer that makes up the plastic (that is a polymer). Some residual of some other substance used during the manufatcturing process (catalyzer, co-polymers, modifiers and so on). For ...


12

I think that there are two reasons: the sulfur is quite common in biochemistry and at the same time a lot of sulfur compounds are toxic. The bio-degradation of sulfur compounds mostly leads to some sulfides which very strongly bind transition metals, i.e. they can destroy/block Metalloenzymes. If you add some millions years of evolution it's a v.good feature ...


12

Interesting question. I actually had to look up the definition of petrichor. After getting a little nostalgic about rainfall, I decided to go ahead and forage around for an answer for you. I found a nice summary article here for those that are interested, and then a really nice bit of history here with a link to a great video about how rainfall helps to ...


11

The food that you eat regularly is something that you are used to. You know exactly which smell combines with which taste ... but that does not imply that the chemicals you smell are the same that you taste. If you had been eating your whole life long fragrant soap with apple smell, you would wonder about the taste of real apples as you wonder right now ...


10

Smell is what you feel when molecules of some compound (and not any kind of radiation, mind you) touch the olfactory nerves deep inside your nose. It is just another property of a compound, like molecular weight, or melting point, or color, only different. Unlike molecular weight, it can't be calculated from molecular formula by simple rules. Unlike ...


9

I've never heard of onions, lemons or vinegar removing a paint smell, but I would guess that they'd just cover up the unpleasant odor with something nicer. As to your later comment: I wouldn't want to remove the smell but leave the VOC or other bad elements there. VOC stands for "volatile organic compound." (See the Wikipedia page on VOCs) Volatile ...


9

While car engines might look simple there is a vast amount of technology installed to ensure as complete a combustion as possible. Complete combustion according to the equation $$\ce{C_{$m$}H_{$n$} + \frac{2$m$ + $n$}{2} O2 -> $m$~CO2 + \frac{$n$}{2} H2O}$$ (not accounting for oxygen, nitrogen or other elements present in the fuel) requires a precise ...


8

The term aromaticity originated with the discovery of unusually stable hydrocarbons that also happened to have strong smells. Many hydrocarbons smell, but not all are aromatic. Nowadays, a compound being classified as "aromatic" has little to nothing to do with its smell and everything to do with its electron configuration. There are also non-aromatic ...


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