170 replies to this topic

[Destiny]

How can a normal human tell the difference between anything? It sure looks fun, though. Can't imagine the fun of being a chemist

[Chyros]

Oh yeah, for sure!

Time for another experiment. The synthesis of potassium dichromate, which is an extremely orange solid that is green during synthesis. For this, we use almost alchemical equipment; two Bunsen burners and a metal crucible.

First, the chemicals are added to the crucible and heated quite a lot. The heat is enough to actually melt some of the crucibles every time despite them being mate out of cast iron which can take quite a lot:


The chemicals then change colour and start to rise and fall as if it were alive:



Finally the crucible is cooled down and an aqueous extraction is performed.


The result is deep orange crystals that look like this:

[Admiral FCS]

Alright, I have some rather elementary questions here, and since there is this wonderful chemistry thread, I don't really want to open another thread, and I'm hoping that this don't count as a necro.

Do salt crystals form following a certain pattern, or do they randomly grow? I'm doing a geometric study of salt crystals and small-scale salt formations, formed as evaporites in a seasonal desert lake, and the salts I'm investigating are presumably (from wiki) sodium chloride, sodium carbonate and sodium bicarbonate.

[Chyros]

 Admiral FCS, on 13 September 2013 - 22:45, said:

Alright, I have some rather elementary questions here, and since there is this wonderful chemistry thread, I don't really want to open another thread, and I'm hoping that this don't count as a necro.

Do salt crystals form following a certain pattern, or do they randomly grow? I'm doing a geometric study of salt crystals and small-scale salt formations, formed as evaporites in a seasonal desert lake, and the salts I'm investigating are presumably (from wiki) sodium chloride, sodium carbonate and sodium bicarbonate.

More than happy to oblige!

That depends. Some salts are crystalline, which means they have an ordered structure, others are amorphous, which means they grow in random directions and are unordered. Most salts are crystalline, the structure of which can be described by one of the Bravais Lattices (http://en.wikipedia....Bravais_lattice) which describe a crystal system (http://en.wikipedia..../Crystal_system); a few, like sand-like silicates, are amorphous, which can't be described with any crystal structure. The salts you describe are all crystalline under normal conditions; NaCl is isometric hexoctahedral (O_h), sodium carbonate is monoclinic domatic (C_1h) and sodium bicarb is monoclinic prismatic (C_2h). When solutions of these salts evaporate, a process called "nucleation" occurs: as the solution becomes supersaturated; tiny crystals crash out of solution. As these are thermodynamically bound to form the most energetically favourable conformation of atoms, these tiny nuclei are ordered in geometry. Then, according to a principle called Ostwald ripening, instead of more small nuclei forming, these tiny crystals will instead grow, because this is more thermodynamically favourable. As such, these crystals will grow, and in the same geometry as the mother nucleus, because this is the only thermodynamically allowed arrangement for crystals. As such, if you grow any of these materials carefully, they will form nice, big crystals according to the minerals' respective Bravais Lattices. The experiment is commonly done in schools as the "crystals on a string" experiment: http://www.scienceco...tring-W140.aspx . A great example was in our lab back in Utrecht, where a dish filled with a copper sulphate dip (a useful indicator for certain reactions) was forgotten and found years later. Because the dip had very carefully dried out, under very gentle conditions, a beautiful, big single crystal had grown out of the solution:



Hope this makes it clear; if you need further explaining or want more info, don't hesitate to ask .

[Admiral FCS]

Thanks for the fast reply! And yeah, although a bit late, I do have some follow-up questions.

When I google image'd "salt formation", there are many kinds of different salt formations, and although I do know that at a microscopic level they are indeed more or less cubic crystals, at the macro level they have various appearances, such as spikes and needles; I was just wondering if it's because of the forces of natures that shaped them or are the forces still related to chemistry.

[Chyros]

 Admiral FCS, on 15 September 2013 - 20:37, said:

Thanks for the fast reply! And yeah, although a bit late, I do have some follow-up questions.

When I google image'd "salt formation", there are many kinds of different salt formations, and although I do know that at a microscopic level they are indeed more or less cubic crystals, at the macro level they have various appearances, such as spikes and needles; I was just wondering if it's because of the forces of natures that shaped them or are the forces still related to chemistry.

Ehhh, from a scientific point of view, all forces of nature are defined as being physical or chemical in nature, without exception. From a microscopic-macroscopic perspective, crystals tend to be the same irrespective of scale; crystals will "try to be" the same at macroscopic level as on a microscopic level as this is thermodynamically more favourable (this isn't as simple as "cubic space groups will form cubic crystals" though). The degree to which macroscopic crystals resemble their microscopic crystal structure and which form they take on is a factor of many things including impurities, co-crystals and the temperature and pressure at which they are formed. Some materials form crystals so small that their macroscopic ordering is practically nihil; a well-known example of this is hematite, the main ore of iron. This appears as a mass of silvery bubbles; these bubbles are not actually "round crystals" but rather a bubbly collection of crystals that are actually tiny thin plates jutting out in all directions, the structure of which is invisible to the naked eye.

[Admiral FCS]

 Chyros, on 15 September 2013 - 23:46, said:

 Admiral FCS, on 15 September 2013 - 20:37, said:

Thanks for the fast reply! And yeah, although a bit late, I do have some follow-up questions.

When I google image'd "salt formation", there are many kinds of different salt formations, and although I do know that at a microscopic level they are indeed more or less cubic crystals, at the macro level they have various appearances, such as spikes and needles; I was just wondering if it's because of the forces of natures that shaped them or are the forces still related to chemistry.

Ehhh, from a scientific point of view, all forces of nature are defined as being physical or chemical in nature, without exception. From a microscopic-macroscopic perspective, crystals tend to be the same irrespective of scale; crystals will "try to be" the same at macroscopic level as on a microscopic level as this is thermodynamically more favourable (this isn't as simple as "cubic space groups will form cubic crystals" though). The degree to which macroscopic crystals resemble their microscopic crystal structure and which form they take on is a factor of many things including impurities, co-crystals and the temperature and pressure at which they are formed. Some materials form crystals so small that their macroscopic ordering is practically nihil; a well-known example of this is hematite, the main ore of iron. This appears as a mass of silvery bubbles; these bubbles are not actually "round crystals" but rather a bubbly collection of crystals that are actually tiny thin plates jutting out in all directions, the structure of which is invisible to the naked eye.

Well... as much as I "expected", thank you.

[Chyros]

There you go, more SCIENCE!

I found a chemical that is two different colours at once. Theorise.

[Wizard]

 Chyros, on 22 October 2013 - 20:20, said:

Theorise.

Magic?

[Chyros]

 Wizard, on 23 October 2013 - 07:16, said:

 Chyros, on 22 October 2013 - 20:20, said:

Theorise.

Magic?

Personally I think it's caused by angular diffraction effects and/or the nature of the light reflecting off of it. I've only ever seen one other chemical system exhibit this kind of effect, which was blue and yellow at the same time; I'm fairly sure that was due to absorption/emission effects.

[Wizard]

 Chyros, on 23 October 2013 - 10:59, said:

 Wizard, on 23 October 2013 - 07:16, said:

 Chyros, on 22 October 2013 - 20:20, said:

Theorise.

Magic?

Personally I think it's caused by angular diffraction effects and/or the nature of the light reflecting off of it. I've only ever seen one other chemical system exhibit this kind of effect, which was blue and yellow at the same time; I'm fairly sure that was due to absorption/emission effects.

So Magic then?

[Chyros]

 Wizard, on 23 October 2013 - 13:21, said:

 Chyros, on 23 October 2013 - 10:59, said:

 Wizard, on 23 October 2013 - 07:16, said:

 Chyros, on 22 October 2013 - 20:20, said:

Theorise.

Magic?

Personally I think it's caused by angular diffraction effects and/or the nature of the light reflecting off of it. I've only ever seen one other chemical system exhibit this kind of effect, which was blue and yellow at the same time; I'm fairly sure that was due to absorption/emission effects.

So Magic then?

Ehhh, in short, I guess, yeah .

[Chyros]

Liquid defies gravity!

[Chyros]

Compound that is different colours in solution and outside of it, gogogo!

[Alice Brown]

Hi Chyros, I spent half an hour reading your thread. Indeed very interesting and instructive, especially the part you mention about the synthesis of potassium dichromate (the orange powder)-“the chemicals then change color and start to rise and fall as if it were alive”, very vivid description, but I’ve got a very basic question: how to keep safe while doing experiments as potassium dichromate is poisonous even when touched by skin according to my limited knowledge?

[Chyros]

 Alice Brown, on 05 July 2017 - 07:01, said:

Hi Chyros, I spent half an hour reading your thread. Indeed very interesting and instructive, especially the part you mention about the synthesis of potassium dichromate (the orange powder)-“the chemicals then change color and start to rise and fall as if it were alive”, very vivid description, but I’ve got a very basic question: how to keep safe while doing experiments as potassium dichromate is poisonous even when touched by skin according to my limited knowledge?

We performed all the experiments in a fumehood. With proper safety measures, it is a very safe experiment - I did it in my second year of uni (which is many years ago now ).

[Admiral FCS]

Long time no see lol

I remember back in '10 or something when I wrote a little bit of a fan fiction about RA3, and there was that part where I think I wrote that the Japanese used alkali metals in their power plants. Do you think that's actually possible?

[Chyros]

 Admiral FCS, on 09 July 2017 - 03:04, said:

Long time no see lol

I remember back in '10 or something when I wrote a little bit of a fan fiction about RA3, and there was that part where I think I wrote that the Japanese used alkali metals in their power plants. Do you think that's actually possible?

Yes, liquid sodium is a common coolant in nuclear power plants.

[Admiral FCS]

 Chyros, on 09 July 2017 - 09:26, said:

 Admiral FCS, on 09 July 2017 - 03:04, said:

Long time no see lol

I remember back in '10 or something when I wrote a little bit of a fan fiction about RA3, and there was that part where I think I wrote that the Japanese used alkali metals in their power plants. Do you think that's actually possible?

Yes, liquid sodium is a common coolant in nuclear power plants.

Uhh, I think I was rather referring to using just the metal's reaction with water itself. Didn't the alkali metals produce a certain amount of hydrogen - or something - when reacting with water?

[Chyros]

 Admiral FCS, on 09 July 2017 - 18:05, said:

 Chyros, on 09 July 2017 - 09:26, said:

 Admiral FCS, on 09 July 2017 - 03:04, said:

Long time no see lol

I remember back in '10 or something when I wrote a little bit of a fan fiction about RA3, and there was that part where I think I wrote that the Japanese used alkali metals in their power plants. Do you think that's actually possible?

Yes, liquid sodium is a common coolant in nuclear power plants.

Uhh, I think I was rather referring to using just the metal's reaction with water itself. Didn't the alkali metals produce a certain amount of hydrogen - or something - when reacting with water?

Yes: 2Na(s) + 2H2O → 2NaOH(aq) + H2(g)

There's not that much use in that however, as it's already very easy to liberate hydrogen from water. It's kind of a shame to use two equivalents of sodium to produce the same thing.

[BennieGeorge]

This is amazing, can't wait to get through your posts. Looking forward to them!