Many members of SM have a lot of Chemistry Knowledge.
Gimme some !
You'll not lose any knowledge in the process, and you might learn something new yourself (see the small print).
All (haha) you have to do is prepare the Teaching Material and present it here - All SM members will benefit.
To kick things off, i have a Perl of wisdom to impart:
Leaving an iron pot on a glass table in the rain Will leave a rust mark, generally circular, which is impossible to remove using mechanical means
without damaging the glass.
Rubbing the mark with a cloth (or tissue) dampened with hydrochloric acid removes it in seconds. No damage.
The 'rust' is iron oxide(s) mostly FeO2/ hydroxide.
HCl reacts with it to make FeCl2FeCl3 which is soluble in
water.
HCl generally comes as 20% around here, so that other 80% is water, which is where the FeCl2FeCl3 ends up, in the cloth or tissue.
Now, that's kinda lightweight, but so is my understanding of Chemistry.
Is anyone up for doing a Lesson on the mechanism behind the reaction of KMnO4 and Glycerol ?
That's just a suggestion. Pick your own.
Teach !
1. you might get it wrong and be ridiculed
2. some tosser will probably heckle a lot
3. Knowledge might be imparted to the masses.
4. There is a risk that you are a great teacher
Edit:
Corrected glaring errors according to the wisdom of masters ninhydric1 & Melgar. (see below)
[Edited on 17-3-2018 by aga]ninhydric1 - 16-3-2018 at 15:33
Actually, the rust produced is an iron oxide-hydroxide (FeO(OH)) in the 3+ oxidation state, and if dehydrated, will produce Fe2O3. The HCl then
dissolves it, turning it into FeCl3, in the 3+ oxidation state. Fe2+ isn't really produced from rust often, as FeO rapidly disproportionates at RT
(under 500 degrees Celsius) into Fe and Fe2O3.Melgar - 16-3-2018 at 15:44
Well, if we're going to be a proper skool...
Rust-colored iron oxide stains are usually iron oxide-hydroxide, and contains Fe in the (III) oxidation state. I don't think FeO2 actually exists.
Fe2O3 exists, but is black-colored. And hydrochloric acid will convert it to yellow FeCl3, which is indeed water-soluble.
I guess I can lecture about candles and fat biochemistry:
Candles are surprisingly complicated from a chemistry perspective. Candle wax isn't just any mix of hydrocarbons, they have to all be saturated, which
makes them very unreactive compared to other organic compounds. Most candles are made out of paraffin wax, which comes from oil. That name came from a
Latin phrase, "para affinis", meaning "next to no reactivity".
Saturated hydrocarbons burn cleaner in a candle, because their single bonds can be broken by lower temperatures, meaning that they're less likely to
escape a candle flame as carbon particles (soot).* They can be pyrolyzed with a carbon catalyst though, to make a flammable mix of gases. Cellulose
string, when burnt, forms a porous mass of carbon at the end that can catalyze this decomposition. It does this when you light a candle, with the
flame growing as it liquefies more and more wax. But eventually the catalytic tip is overwhelmed by molten wax and slows down, creating an
equilibrium. If you blow out a candle, you'll often see a glowing bit on the tip that's releasing smoke. This is the catalytic carbon part of the tip,
oxidizing the candle wax into the mix of smaller molecules that are found in smoke.
So, why are some natural oils saturated and some unsaturated, anyway? It all comes down to what temperatures they experience, of all things. Birds and
mammals have high enough body temperatures to keep saturated fat from solidifying. Fish, on the other hand, do not. So their fat molecules have kinks
in them, in the form of carbon-carbon double bonds, to keep them liquid at cold temperatures. This goes for plants too. Most plants grown in temperate
climates have kinks in their fat molecules, to keep them from solidifying. But plants that grow only in tropical climates, like coconuts and other
palms, have saturated fat molecules that solidify when they get cold.
Soy candles, though, are solid at room temperature, even though soy grows in temperate climates. That's because soy candles are actually made from
hydrogenated fats like margarine and shortening are made from, except fully-hydrogenated as opposed to partially hydrogenated. These have had the
kinks chemically removed from their fat molecules, so they're solid at room temperature. This type of fat is supposed to be slightly bad for you if
you spend your life eating it, but there's certainly no harm in burning it in a candle.
* Double bonds can release more energy, but also require more activation energy.j_sum1 - 16-3-2018 at 19:00
Nice Melgar. Some new stuff for me there. I had not associated plant lipid saturation with climate before.
Faraday famously presented a series of lectures to the public on the topic of candles. People were fascinated. The lectures are reproduced here by
engineerguy and are still interesting.
Cleaning precious metal jewellery (gold, silver, or alloys of such) can be easily achieved without damaging the item in the slightest.
1. In a saucepan is placed a folded up piece of aluminium foil.
2. The jewellery is put on top of the foil. For a piece like a chain, it is arranged in such a way that the highest surface area is present (don’t
just dump it in a pile).
3. The pot is filled with aqueous NaCl or bi/carbonate until the piece is submerged.
4. Turn on the heat, and watch as the aluminium foil (which is obviously more reactive than silver) magically darkens with sulphides from the
jewellery! This will only take 10 minutes or less, and you can clean a whole bunch of jewellery at once.
Now for the science. Silver can tarnish in air by forming a layer of Ag2S, which darkens it and causes it to lose its lustre hence is not
very pretty. By heating it with a more reactive metal in electrolyte solution, aluminium metal will be oxidised to Al3+ and silver ions are reduced to
Ag metal: 2 Al + 3 Ag2S -> Al2S3 + 6 Ag
Seems like something relatively simple and worthy of being mentioned here?
[Edited on 17-3-2018 by LearnedAmateur]aga - 17-3-2018 at 01:01
That's the Spirit !
Fat/oil composition being linked to a species/habitat seems so obvious now Melgar said it, yet never occurred (at least to me) before.
'Simple' is fine LearnedAmateur, so long as it's accurate That's a nice, concise
and do-able post you made there.
It might be an idea to add a title to opening posts with 'lessons' to make them easier to google.
Rainbow Potassium Chloride Snow
18thTimeLucky - 17-3-2018 at 02:38
Now settle down children, it is skool story time.
When purifying some potassium chloride by recrystallisation I found it made cube crystals, similar to sodium chloride, but once agitated, long
needle-shaped crystals form and occasionally some rhombus-shaped crystals. After further experimentation, I found under bright white light these seem
to reflect and refract the white light as they fall, forming a colourful disco.
You get every colour imaginable: blues, greens, purples; and if done correctly can yield dozens of sparkling colours a second. As far as I'm concerned
though, nobody has made any videos or wrote anything about this. The only hit on Utubes I get is a show named KCL with a band The Snow Globes playing
on it... KCL The Snow Globes... Potassium Chloride Snow Globe... so I took their unintended advice and did just that.
I packed some solution into little jars to act as snow globes which you heated in a microwave and let cool for the rainbow snow effect - great, cheap,
non-toxic Christmas presents for skool mates when you spent too much of your parent's pocket money on sweets and stink bombs. The video attached is a
short clip of the beautiful demonstration.
(Which I thus deemed the Rainbow Snow Globe Demonstration and wrote a blog post on it although the restriction to pictures did not do the rainbow
effect justice https://18thtimelucky.wordpress.com/2018/01/02/the-rainbow-s...)
dihydroxymalonic acidWouldSynthesizeForFood - 18-3-2018 at 04:28
Not exactly sure if this fits in here but fatty acid diethanolamides can be used to inhibit corrosion in iron and its alloys.MrHomeScientist - 19-3-2018 at 06:03
I researched the permanganate reaction many years ago (in 2011!) and this is what I came up with:
14KMnO4 (s) + 4C3H5(OH)3 (aq) == 7K2CO3 (s) + 7Mn2O3 (s) +
5CO2 (g) + 16H2O (l)
Being that long ago, I can't reproduce the reference unfortunately.aga - 19-3-2018 at 06:52
Manganese(III)oxide doesn't sound anywhere near as sexy as dihydroxymalonic acid.
Oh well - you live and learn.
Anyone got any good, simple synths that clearly demonstrate some principle or other ?
Nothing like a good Practical to get the students excited/fighting/slightly damaged.Sulaiman - 19-3-2018 at 06:53
Links aren't really what i had in mind - we can all google.
Something more akin to blogfast25's awesome Quantum thread, where the information is contained in the thread for all to see, now and in the far
distant future, when no other website exists.Magpie - 19-3-2018 at 07:39
from dihydroxymalonic acid in Wiki:
"Synthesis
Dihydroxymalonic acid can be obtained synthetically by hydrolysis of alloxan with baryta water,[2] by warming caffuric acid with lead acetate
solution,[4] by electrolysis of tartaric acid in alkaline solution,[7] or from glycerin diacetate and concentrated nitric acid in the cold. The
product can be obtained also by oxidation of tartronic acid [8] or glycerol.[9]"
Reaction products of a hydrocarbon with KMnO4 can vary greatly depending on dilution, temperature, and pH.
[Edited on 19-3-2018 by Magpie]
[Edited on 19-3-2018 by Magpie]Melgar - 21-3-2018 at 18:25
So why is carbon chemistry such a big deal, anyway? And why not its neighbors on the periodic table, like nitrogen and silicon?
First, carbon can form really stable, complex structures with other carbon atoms. Tetrahedral shapes are incredibly stable in chemistry, and carbon
has exactly four valence electrons. With each valence electron occupying a point on the tetrahedron, carbon is well-protected from many types of
reactions when it adopts this bonding pattern. Nitrogen can form complex compounds to some degree, but is hampered by the fact that many of these
compounds are explosive. This is because nitrogen gas forms very easily and is quite stable, whereas carbon has the highest boiling point of any
element. This occurs mainly because triple bonds form fairly easily and are stable, but quadruple bonds are impossible. And when nitrogen
triple-bonds to itself, it then forms a gas which is very difficult to get to react with anything.
Second, carbon and hydrogen have very similar electronegativity. Unlike with silicon, there is virtually no polarity in the bond between hydrogen and
carbon, making hydrocarbons essentially nonpolar and alkanes virtually unreactive at normal temperatures. This allows complex carbon-based molecules
to have some parts be unreactive, which is really important if you want the molecule to be stable. Silicon is too metallic to form covalent bonds with
itself, and silicone polymers have to have the silicon atoms separated by oxygen in order to counteract that tendency. Since oxygen can only form two
bonds, this means that silicone chains can’t have any double or triple bonds, or conjugated systems, and thus can’t form the wide variety of
structures that carbon is capable of.
Third, carbon is produced in stars via the CNO cycle and triple-alpha helium fusion, along with nitrogen and oxygen. So these three elements (carbon, nitrogen, and oxygen) get disproportionately produced
via stellar fusion. Lithium, beryllium, and boron all get burned up as soon as they get anywhere close to stellar temperatures, by comparison. So
they’re a lot more rare in the universe.
That's a nice, concise
and do-able post you made there.