Here’s also an experiment you can do at home. Take some Hibiscus flowers (any color) and dip some into an acidic solution and some into alkaline solution. You can use vinegar for acidic and sodium hydroxide based drain cleaner for alkaline. You will get the hibiscus to change color and become a tie dyed flower 
Hibiscus flowers are natural pH indicators.
So is the juice from Red Cabbage
Anthocyanin is responsible
Responsible for the characteristic smell of canned berberechos; google translates that as cockles but google seems to translate a bunch of different bivalves as “cockles” 
Copper’s salts tend to be brightly colored. Verdigris (lit. “grey green”) refers to several of its salts; the greenish color on bronze statues comes from that kind of compounds. Copper sulfate is a gorgeous blue: in solution it is used as a fungicide, notably on grapes; I don’t know if that gets a specific name in French, but in Spanish we call it sulfatear or sulfatar - note that the actual fungicide is the copper half of the salt. Copper paint is used as a protective coat on ships for the same properties.
Dihydrate, and what a big difference a little letter makes. At least this one isn’t one of those cases where, as my Orgo teacher put it, “in Chemistry, misspellings kill”.
When I was a student working in a lab we used to dry electron microscope specimens using, among other things, amyl acetate which smelled just like ripe bananas. There was another organic solvent, amyl nitrate, IIRC, that smelled like strawberries.
One of the products we make at work is a Schiff base, with benzaldehyde as one of the raw materials. Benzaldehyde smells very strongly of Maraschino cherries. Indeed, I think it’s often added to enhance the cherry smell. It’s also used as a food additive because it tastes like almonds.
I once dropped a gallon jar of benzaldehyde in the lab, and the whole place smelled like cheap cocktails for almost a week. As we make products that produce hydrogen sulfide, mercaptan, and other fun odors, this was a marked improvement.
Damn, I thought I typed “dehydrate”
How about sulfur? As an element it’s a strange yellow. According to wikipedia, “When burned, sulfur melts to a blood-red liquid and emits a blue flame.” Also, “Sulfur burns with a blue flame with formation of sulfur dioxide, which has a suffocating and irritating odor.” It’s toxic too.
Ijen Caldera in Indonesia with its bright blue sulfur flames is a tourist attraction
Interesting, I’ve been wondering how they get the sea breeze smell in shampoos, lotions etc
You did.
The various sulfur compounds have their own brand of stench - my PhD supervisor used to call thiophenol an ‘honest’ smell. Honest meaning a brutal, headache-inducing smell you can almost see in the air. The lighter thiols are often absolutely rancid smelling but it’s a less onerous smell IMHO.
There’s a common reaction in chemistry called a Swern oxidation, reliable method for taking an alcohol to a ketone or aldehyde. One of the reagents used is dimethylsulfoxide (weakly smelling), which forms a byproduct in the reaction of dimethylsulfide (absolutely wretched smelling of rotting cabbages, very volatile). If you can do a Swern reaction in your lab fume hood and no one else is aware of it then you’ve got some skills as a practical chemist.
Hydrogen sulfide is a highly toxic gas encountered in a lot of industries / environments that absolutely reeks of rotten eggs. This is a helpful property, from a H&S perspective (compared to CO, say), but it has the insidious property of numbing the sense of smell above a certain concentration. Apparently makes it the leading cause of gas inhalation deaths in the US workplace - although CO posioning must surely kill more people in general.
Worst smelling compounds I’ve worked with, though, are not sulfur based but a class called isonitriles. Like being jabbed on the nose by a middleweight boxer, but on top of that they linger something fierce. Go home at night and you imagine you can still smell them.
I’ll try and think of some nice smelling compounds I’ve encountered in the organic chemistry lab - must have been at least one or two in the past 25 years…
Talking about pungent smells, I’m reminded of how I absolutely hate ammonia.
I’m sure that you guys have experienced worse, but it has a very specific quality that I have a hard time putting into words. Let’s say that where some nasty organic compounds call to mind the decay of something that was once alive, ammonia smells alien to me, like the sort of thing that you’d only encounter on a far-away, dead planet.
Are there any compounds based on ammonia that actually smell nice or at least ok ?
I’ve been told that C17H21NO4 has a very exhilarating smell.
Very true. H2S is weird - Humans can detect H2S well below 1 ppm with the wrotten egg smell. Above about 30 ppm, it smells sweet and above about 100 ppm - humans can’t smell it at all.
CO can also give you hallucinations. There are cases where people reported having a religious experience or feeling a ghost which turn out to be CO poisoning.
I do a lot of work in chemical plants, and this (phosgene smells like freshly cut grass) was one of the things I was going to say. The other is that cyanide smells like bitter almonds. They usually warn you about these smells as part of the safety training if you do any work in a chemical plant that uses these chemicals.
The safety training in a couple of plants I have worked in was also basically “there’s no such thing as a good siren” and “follow guys wearing company shirts because they know where to go.”
I wasn’t there at the time, but some people I work with had the fun of hiding out in a control room for several hours, watching through the windows as one of those pale green clouds made its way around the chemical plant. The control room was sealed so it was one of the safe places in the plant during a leak or a spill.
Butyric acid smells exactly like vomit.
Odd thing is, somehow I discovered that by accident as a kid. Not with hibiscus, but some random purple colored flowers we had growing in the garden. I just always called them “violets,” due to their color, but I’m not entirely sure if they were violets or not. Anyhow if you steeped them like tea, the liquid become a natural ph indicator. Same with red/purple cabbage mentioned above. Acid turns red cabbage from a purple color to red, and base changes it to green. With flowers, I think it was just purple, blue and pink for the colors it would change to, but this was like 35 years ago. If anybody knows what purple flowers do this, let me know. It wasn’t something like hydrangea. It was a weed of some sort that grew in our backyard in clumps. I’m not sure how I came across it, but I guess at some point I must have been playing with a chemistry set and some kind of experiment with purple water turning pink in the presence of a base, so I just decided any purple water changes color in the presence of a base or some faulty thinking like that. Oddly, I don’t remember experimenting on grape juice—probably because it wasn’t around the house, But purple cabbage nd those weeds were!
normally I wouldn’t even try to contribute among our experts on this subject, but I happen to be rereading John Clark’s IGNITION. That history book is the only place I have ever seen FOOF mentioned matter-of-factly and without histrionics. Just another oxidizer they tried.
To give a small taste of the subject matter from his chapter titled “Exotics”:
“Boranes are unpleasant beasts. Diborane and pentaborane ignite spontaneously in the atmosphere, and the fires are remarkably diffi- cult to extinguish. They react with water to form, eventually, hydro- gen and boric acid, and the reaction is sometimes violent. Also, they not only are possessed of a peculiarly repulsive odor; they are ex- tremely poisonous by just about any route. This collection of proper- ties does not simplify the problem of handling them. They are also very expensive since their synthesis is neither easy nor simple.”
This book describes a history from the late 40’s to the early 60’s where the Gov’t was spending large amounts of money trying to find the best rocket fuels for missiles and rockets. Some truly amazing things were tried-almost all of which didn’t work for some spectacular reason.
If you have ever seen liquid oxygen, its a beautiful blue color
You’ve probably seen the Belousov-Zhabotinsky reaction?
Yes and of all the chemical plants I have been through, liquid oxygen plants scare me the most. Because around liquid oxygen, you are the fuel, the asphalt road is the fuel and your clothes can be the fuel.
There is an old military video (sexist in my opinion) but it shows the dangers of liquid oxygen (LOX). Warning : it has graphic pictures near the end.
