# Is sodium chloride really odourless? If yes, what do I smell?

I just had to read some general descriptions of sodium chloride and it was always classified as odourless (e.g., by Wikipedia). However, large amounts of table salts (around 1 kg) have a clearly perceptible odour to me. By table salt I mean salt sold for the purpose of cooking – I have not been taking notes or making experiments, but as I had the experience on dozens of different occasions, I would guess that the salt does not need to be iodised.

If I had to describe the smell, I would first say salty. It’s somewhat similar to the smell of the seaside, but the latter is much richer and has additional components. From the ten smell categories proposed here, only sweet and chemical fit somehow. It also has something of petrichor.

Is the classification as odourless just an approximation or do I smell additional ingredients (such as iodide) or impurities that cause table salt not to be pure sodium chloride? In the latter case: What causes the odour?

• I see the same thing, too. Especially when I come near to sea. – Huy Ngo Mar 26 '17 at 3:17
• What kind of smell do you detect? Can you describe it? – Yashas Mar 26 '17 at 7:31
• @YashasSamaga: See my edit. Now I have to explain, why I have a bowl of salt next to my computer. – Wrzlprmft Mar 26 '17 at 8:04
• The smell of the sea is due to the presence of dimethyl sulfide. I am not quite sure why someone would add dimethyl sulfide to common salt. – Yashas Mar 27 '17 at 10:29
• @YashasSamaga: I am not saying that it’s precisely that smell. It’s just something my brain associates with it. – Wrzlprmft Mar 27 '17 at 10:43

Your table salt is not just $\ce{NaCl}$; there are countless other compounds which make up the table salt.

Here are a few:

1. $\ce{NaCl}$ - the main component
2. Iodine in the form of $\ce{I-}$ and $\ce{IO_3^-}$ salts (salts of potassium and sodium usually).
3. Iodine Stabilizers: $\ce{I2}$ sublimes at room temperature; therefore, stabilizers are added to prevent the loss of iodine. A commonly used stabilizer is dextrose.
4. Iron is added in the form of ferrous fumarate.
5. Folic acid and other vital vitamins are also added.
6. Fluoride salts are also added in many countries.
7. Anti-caking agents such as $\ce{Na4[Fe(CN)6]}$, $\ce{CaCO3}$, $\ce{MgCO3}$, $\ce{Ca3(PO4)2}$ and fatty acids are added.

From the big list above, fatty acids usually have an odor. While solids have a negligible vapor pressure, some molecules do leave the surface. Therefore, you can still smell solids.

The main component of the sea smell is dimethyl sulphide ($\ce{CH3-S-CH3)}$. In the ocean, dimethyl sulphide is produced as a byproduct by the bacteria which decompose phytoplankton.

The manufacturer of the common salt you use might be using sea water as the raw material. The sea water might not have been thoroughly cleaned which could have left traces of compounds found in sea water in your salt. You might want to try buying salt manufactured by a different company.

• The manufacturer of the common salt you use might be using sea water as the raw material. – I observed this with many salts, some of which are explicitly not made from sea water. – Wrzlprmft Mar 27 '17 at 10:47
• My salt smells too but it smells like some chemical (and I need to get very close to it to recognize the smell). It does not have the distinct strong smell of the sea water, however. – Yashas Mar 27 '17 at 10:51

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, you cannot be sure what makes the odour, the salt or the impurity. Eg. sea salt often contains remains of algae.

• If the dust particles moving in space are the cause of the smell, then shouldn't the OP detect that smell everywhere? Since OP is specifically asking about the odor of common salt, that should imply that random air particles aren't the source of smell in their case. – Yashas Mar 26 '17 at 5:07
• I am talking about small particles of salt and the impurities of salt in the particular case. Maybe it was not clear, sorry. – Greg Mar 26 '17 at 7:56
• Of course NaCl has no vapor pressure (a property of liquids), but it does have some sublimation pressure (a property of solids). These are often conflated, but looking at the NIST property data the point seems moot: webbook.nist.gov/cgi/… – Gavin Kramar Mar 27 '17 at 19:33
• @GavinKramar , the link you gave gives the Antoine equation parameters for the vapor pressure of NaCl. The CRC Handbook gives both sublimation pressure and vapor pressure for ice. I've rarely seen the term sublimation pressure used. Is there is an official, say IUPAC, preferred terminology? – airhuff Mar 27 '17 at 21:19
• @GavinKramar Since it is an ionic material, we can agree that sublimation pressure is effectively zero for room temperature, too. Odor arising from sublimation is much more typical to molecular materials, like iodine or fats, organic acids. – Greg Mar 27 '17 at 23:48

## protected by orthocresol♦Nov 9 '18 at 17:43

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