174

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 ...


101

Toothpaste is what is called a non-newtonian fluid, more specifically toothpaste is a Bingham plastic. This means that the viscosity of the fluid is linearly dependent on the shear stress, but with an offset called the yield stress (see figure below). This yield stress is what makes it hard to say whether it is liquid or solid. The fact that toothpaste is ...


89

Hydrofluoric acid is toxic and corrosive, but actually isn't that strong of an acid compared to other hydrohalic acids; the fluorine has a very good orbital overlap with hydrogen and is also not very polarizable, therefore it resists donating its proton, unlike other hydrohalic acids which are good proton donators. It will break down some tissues, but it ...


80

Combustion of small materials, such as a match or birthday candle, actually involve the release of volatile vapours, which themselves burn. It is not the solid material that burns. There needs to be a minimum amount of volatile material present in this combustion zone (just above the burning match) for the ignition to occur. As the combustion process ...


79

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 ...


71

The hydrochloric acid in the stomach is already quite dilute; its pH is in fact no less than 1.5 so that at the extreme maximum there is only 0.03 molar hydrochloric acid. And even that small amount is, of course, stabilized by being dissociated into solvated ions. There is just not enough stuff to react violently.


70

The other answers here, describing oxygen toxicity are telling what can go wrong if you have too much oxygen, but they are not describing two important concepts that should appear with their descriptions. Also, there is a basic safety issue with handling pressure tanks of high oxygen fraction. An important property of breathed oxygen is its partial pressure....


66

Where is the sugar? When you freeze a dilute aqueous sugar solution pure water freezes first, leaving a more concentrated solution until you reach a high concentration of sugar called the eutectic concentration. Now you have the pure water that's frozen out, called proeutectic water, and the concentrated eutectic sugar solution from which the sugar is ...


60

There are different angles this question can be answered: Chemical point of view: A full analysis of a totally unknown mixture is painful and extremely costly. It is always helpful to know how many components you are looking for; what types etc. In this case, it is not enough to analyse the elemental composition or some pure elements, but Coke contains a lot ...


55

What would be the effect if someone were to drink ultra-pure, 18 M-ohm water? Not much, although if they drank many gallons of the water it could be a problem. Would they immediately die? No. Would they just need to pee more? Probably. Would $\ce{CO2}$ from the air (after the bottle is opened) and whatever's in saliva dissolve into the water ...


53

Probably the biggest drivers behind using methane as a fuel is that it is abundant in natural gas and is (currently) mostly useless as a chemical feedstock. Ethane makes up a few percent of natural gas and can also be obtained as byproducts of petroleum refining, but the big difference from methane is that ethane is extremely useful in chemical synthesis (...


52

As Nilay Ghosh said, nitrogen is cheap. Very cheap. Neon is expensive. Argon is cheaper than neon, but considerably more expensive than nitrogen. Helium is also expensive and needs to be used wisely, for important things, e.g., cryogenics. And hydrogen! I can just see the ads: “Buy our chips: they are lighter than air! But avoid open flames and sparks unless ...


51

The starch forms a loosely bonded network that traps water vapor and air into a foamy mass, which expands rapidly as it heats up. Starch is made of glucose polymers (amylopectin is one of them, shown here): Some of the chains are branched, some are linear, but they all have $\ce{-OH}$ groups which can form hydrogen bonds with each other. Let's follow some ...


49

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 ...


49

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 ...


48

In most countries, cosmetic product labels use the International Nomenclature of Cosmetic Ingredients (INCI) for listing ingredients. The INCI name “AQUA” indeed just describes water (which is used as a solvent).


47

First of all, it depends on how the tap water was treated before it was piped to your house. In most cases, the water was chlorinated to remove microorganisms. By the time the water arrives at your house, there is very little (if any) chlorine left in the water. When you fill you container, there is likely to be some microorganisms present (either in the ...


47

First I'd locate the bottle which causes the problem. Usually HCl is #1 suspect, but to be sure you can put a vial with smelling salts (aqueous solution of $\ce{(NH4)2CO3}$) or ammonia in the box with acids; white coating of $\ce{NH4Cl}$ on the bottle signifies the leak. It's also a good practice to store acids in glass bottles with a proper joint (teflon ...


45

Alle Dinge sind Gift, und nichts ist ohne Gift, allein die Dosis macht dass ein Ding kein Gift ist (The dose makes the poison) - Paracelsus Poisons (I'm going to use this as an umbrella term for "toxins" and "venom" as well. Bear in mind though, they are not the same thing) have been known since antiquity. Back in the good old days, you figured out if ...


44

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 ...


44

Not mentioned yet: nitrogen is entirely non-toxic, environmentally friendly, does not contribute to global warming or ozone depletion. In very good approximation, nitrogen is just air with the oxygen removed that would oxidize the contents. The usual production process consists of liquefying air, distilling it, and then selling the gases separately. This ...


42

Here's a genchem-level answer for a genchem-level question about the classification of matter: Toothpaste is a sol: a stable suspension of tiny solid particles in a liquid. When the toothpaste dries out you can see what the solid part alone looks like. Mixtures with more than one phase often have interesting properties and behaviors that the components ...


41

First off, may I say that I applaud your decision to test this through an experiment. It's rare to see that than I would like. Now, on to the matter at hand. It's fairly well known from industrial chemistry that non-polar solvents degrade latex quite heavily. I work with latex seals a lot, and the hexanes we use routinely break the seals down in under a ...


41

The $\mathrm{pH}$ of pure water (rain as well as distilled water) in equilibrium with the atmosphere ($p_{\ce{CO2}}= 10^{-3.5}\ \mathrm{atm}$) can be calculated as follows. $$[\ce{H2CO3^*}]=K_\mathrm H\cdot p_{\ce{CO2}}$$ where $[\ce{H2CO3^*}]$ is the total analytical concentration of dissolved $\ce{CO2}$, i.e. $[\ce{H2CO3^*}]=[\ce{CO2(aq)}]+[\ce{H2CO3}]$, ...


39

In both cases, there appears to be a confusion of terminology between common and technical uses. We commonly use methane and propane for cooking (and home heating), but not ethane. I would expect ethane to be suitable for this, being in between the two, but I've never heard of anyone using it for this purpose. Why is that? In reality, anyone using ...


39

Upon reading the answers on Quora (thanks S007 for pointing that out) I realized this trick question is a lousy play upon two somewhat peculiar features of sulfur: When submerged in water (not "dissolved", mind you, for sulfur does not dissolve), its apparent weight becomes less, thanks to Archimedes and the buoyancy force. This is indeed true of any ...


39

There are two ways to efficiently make an aerosol product: Use a gas that liquifies under the pressure inside the can. For example, butane lighters. Nitrogen is one of the "fixed gases", meaning it's a gas under most conditions (but take a look at the temperatures and pressures needed for liquid nitrogen—it's not going to ever be found in consumer products)....


39

According to the Intergovernmental Panel on Climate Change (IPCC): "Greenhouse gases are those that absorb and emit infrared radiation in the wavelength range emitted by Earth." In order for a molecule to absorb and emit in the infrared (IR) region, its chemical bonds must rotate and vibrate in a manner that affects something called the molecule's ...


38

I cannot think of anything in tap water that would make the water undrinkable after a couple of days already. Tagging the question with biochemistry probably points in the right direction. The only effect I can think about is growth of anaerobic microbes, e.g. Escherichia coli, causing diarrhea. There's good chance to keep the water from 'going bad' and ...


37

From explainthatstuff.com: Why doesn't glue stick to the tube? Adhesives are designed to work when they leave the tube—and not before. Different adhesives achieve this in different ways. Some are dissolved in chemicals called solvents that keep them stable and non-sticky in the tube. When you squeeze them out, the solvents quickly ...


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