Hot ice~

       This week I gonna share a experiment called "hot ice" with you guys~ Let's see the video first~

Wonder what is happening? The experiment just shows an interesting feature of superstation (過飽和). The colorless solution is actually water supersaturated with sodium acetate (醋酸鈉). Most of you probably have heard of supersaturation, which means that there are more solutes (in this case, sodium acetate) than normal in the solvent. Supersaturated solution is not thermodynamically stable but there is no proper way for it to transform into the more stable crystal phase since the energy barrier is too high.


However, once you put a “seed” (or nucleus, 晶種) into a supersaturated solution, the crystal will form rapidly because the seed has decrease the energy barrier considerably (btw this phenomenon is called heterogeneous nucleation).  

  What’s more, the reaction is exothermic—it generates a large amount of heat at the same time. So that’s why it is called “hot ice”! Here’s a video about how hot it could be. Though hilarious, you should take it seriously! (I have no idea why he wanted to put his hand inside it@@ why not just put a thermometer......)

     Never try to do that stupid thing at home, but here's something you can try. Some hand warmers  just make use of this phenomenon. You are supposed to “crush” them before use and them can be reused by putting them into hot water. Interestingly, the crush you do is actually providing a seed for the crystal to grow. By using these hand warmer, you can directly feel the heat produced when forming sodium acetate crystal, in  a more gentle way of course!

reference:

1.http://www.amazingrust.com/Experiments/how_to/Hot-Ice.html

2.https://en.wikipedia.org/wiki/Nucleation

3.https://en.wikipedia.org/wiki/Sodium_acetate

sandwich and hamburger molecule

  

  I think there are too much organic compounds in the previous posts; though organic compounds indeed have a much greater variety and flexibility in structure, inorganic compounds do also have something to show! So this week I would like to introduce some classes of inorganic compounds with interesting structures. The first class is sandwich compound, they have structure like this:

   The dash lines between the metal and the ring up and down are not actually chemical bonds, they are  just simplified symbols to represent a special type of coordination bond. 

   Still one thing worth mentioning is that though the “bread” of the sandwiches are different (pentagon, hexagon, octagon…), they are all aromatic (芳香). This property stabilizes the overall compound structure.

   If you have no idea what previous sentences are talking about, don't be afraid, just appreciate their structure~

Of course there is “half sandwich” compound, which is also called "piano stool" compound due to their structure. Here’s one example:

And this is piano stool haha:

    What’s more, there is "mutlidecker sandwich" compound, just like big mac! Take a look at the structure:

  However, there are more classes of compound, as the image below shows, and I only mention a narrow range of them today! Hope you can have a deeper insight into molecular structure after reading my post~

Explosive experiment

    This week I want to introduce something sensational and explosive~

The first experiment is the chemical volcano. Literally, it is a experiment that have a volcano-like product. Let’s check out the video first:

 

  The reaction is the heat decomposition of ammonium dichromate [(NH₄)₂Cr₂O₇], and during the decomposition, it will produce lots of ashy Cr₂O₃ and accumulate into a mountain. The total reaction equation is (NH₄)₂Cr₂O₇ → Cr₂O₃ + 4 H₂O + N₂

  

  Another similar reaction is the Pharaoh’s serpent (法老之蛇). It is the decomposition of Mercury(II) thiocyanate, while in this reaction, the decomposed product resembling a snake rather than a volcano.

The reaction can be described as below:

2Hg(SCN)₂ → 2HgS + CS₂ + C₃N₄

HgS + O₂ → Hg + SO₂

2C₃N₄ → 3(CN)₂ + N₂

CS₂ + 3O₂ → CO₂ + 2SO₂

Here’s the video:

*Warning: the experiment would be a little bit disgusting…

   Last one will be the experiment of dehydration of carbohydrate. Simply, the “de”hydration of carbo”hydrate” will produce “carbon”! Sulfuric acid (H₂SO₄) is often used as a strong dehydrating agent, so we can see black carbon forms after we mix the sugar (carbohydrate, C₆H₁₂O₆) with sulfuric acid. The reaction equation is C₆H₁₂O₆ → 6C + 6H₂O

Here’s the video:

Reference:

1.      http://chemistry.about.com/cs/demonstrations/a/aa033003a.htm

2.      http://chemistry.about.com/od/fireworksprojects/a/pharaohs-snakes.htm    

Molecules in daily life

  Chemistry is everywhere, and it is an essential part of our world. So let’s look up some molecules in our daily lives!

  Here come the molecules in chocolate—phenylethylamine, tryptophan, and theobromine. Scientists used to believe that phenylethylamine and tryptophan make us feeling good after having some chocolate, however, latest research suggested that it could only be a placebo effect since these compounds would undergo metabolism(代謝) when we consume them. Theobromine is harmful to dogs, so never let your dog try chocolate!

  There are countless kinds of smell in our lives, have you ever wonder what molecules are interacting with your nose? Let’s consider the scent of flowers first. Here’s a list of compounds behind the smell of flowers:

  Another interesting topic is the smell of books. The distinct aroma of new books comes from the inks, papers, and adhesives while that of old books comes from oxidation products of polymers which make up the papers.

  Do you remember the refreshing smell after rain? It is caused by the compound geosmin and volatile fat molecules, as shown below. By contrast, the beyond-description smell before rain is arisen from ozone.

    All information is retrieved from http://www.compoundchem.com/ .You can also search “compound interest” on FB to follow their pages. The website talk about the chemistry behind everything in our lives, and it is really worth reading!

Blue bottle, red bottle, and traffic light reaction

   This week I want to show three reversible color changing reaction, and they are blue bottle, red bottle, and traffic light reaction. They are often used on magic shows or to perform demonstration experiments. However, though it seems to be complex and the ingredient should be the magician’s secret, I will reveal the secret to you today.

In fact, the mechanisms behind these amazing experiments are similar and easy to understand. When the bottle is shaken vigorously, one species in the solution would be oxidized (氧化) by the oxygen dissolving into the solution, and the color would change due to the different color that oxidized species has form the original one. After we put it aside and wait for a while, we could observe the color gradually return to the initial one. That is because the oxidized species has been reduced by the reductant (還原劑), usually glucose, in the solution.

Here are some videos:

 blue bottle

 red bottle and blue bottle (they are combined to make purple bottle)

traffic light

 In the blue bottle reaction, the species being oxidized is methylene blue (亞甲藍); in the read bottle reaction, that would be resazurin (刃天青); in the traffic light reaction, that would be indigo carmine (靛胭脂). The indigo carmine has three oxidation states with different colors so the color depends on which level it has been oxidized. 

methylene blue:

resazurin:

                            colorless                                                                                       red

  

indigo carmine:

Reference:

1.http://ncsu.edu/project/chemistrydemos/Kinetics/Blue%20Bottle.pdf

2.https://en.wikipedia.org/wiki/Blue_bottle_(chemical_reaction)

3.http://case.ntu.edu.tw/magichem/blog/wp-content/uploads/2010/09/NTUCASEChemdemo_example.pdf

Molecular toy building blocks

    I would like to introduce some geometrically interesting compounds this week. I think they are interesting because they have all kinds of structure—whatever you can imagine. They are just like tiny toy building blocks in microscopic world.

    The compounds that I want to talk about is “Platonic hydrocarbon”(柏拉圖烴). There are five Platonic solids: tetrahedron (正四面體), cube(正六面體), octahedron (正八面體), dodecahedron (正十二面體), icosahedron (正二十面體). But acutally only tetrahedron, cube, and icosahedron have their counterparts in hydrocarbon (due to the nature of carbon in bonding¹), and they are tetrahedrane, cubane, and dodecahedrane respectly.²

tetrahedrane, cubane, and dodecahedrane

   

  

    Of course there are piles of derivatives (衍生物) of Platonic hydrocarbon.For example:

Octanitrocubane, which is very explosive thus can be used in bomb and fuel:

Pagodane, an isomer of dodecahedrane:

  

Prismane, an isomer of bezene:

Fullerene (C60), which we are more familiar with:

However, chemist synthesis these compounds not only for fun but to collect data of these molecules. Chemistry behind these odd molecules is different form that behind ordinary molecules since they usually suffered from huge angle strain and are quite unstable. The data help chemist to develop and improve the existing theories (such as theoretical chemistry, computational chemistry, molecular modeling… and so on) and move further in chemistry.  

What’s more, molecule structure has no boundary so there are more left for us to explore!

1.The nature of carbon in bonding is that it merely has four valence and the angle shouldn't deviated from 109.5 degree too much.

2.Actually, tetrahedrane has not been synthesized yet, but lots of its derivatives have been published and the theoretical calculation also supports its stablity.

Reference:

1.https://en.wikipedia.org/wiki/Platonic_hydrocarbon

2.http://sites.northwestern.edu/scheidt/files/2011/11/012004_Galliford_Pltsolids.pdf

3.https://www.scripps.edu/baran/images/grpmtgpdf/Shenvi_Jan_06.pdf

Elephant's toothpaste

This week, I would like to talk about a common classroom demonstration—elephant’s toothpaste. The reaction behind this experiment is quite simple. It’s just about the spontaneous decomposition of hydrogen peroxide (H₂O₂) and the equation is showed below:

Here is the “recipe”:

1. 100 mL 30% hydrogen peroxide

2. 2.5 g KI

3. 20 mL surfactant

4. 3 mL fod coloring (or watercolor) in any color you like

    Put these things all together in a cylinder or something is long and has an upward opening than there will be a amazing show like this:

           So… it’s obvious why it gets its name “elephant’s toothpaste” ~~

           I want to talk about the role of each agent now. Hydrogen peroxide, is the main reagent while potassium iodide (KI) serves as catalyst (催化劑) and can be replaced by yeast or ferric cation (Fe³⁺). The present of catalyst makes the reaction much faster. Surfactant is used to retain the oxygen produce by decompose and makes bubbles. Finally, the coloring is optional because they are merely used to make the experiment colorful XD

    Enjoy yourself with this easily-conducted experiment!

*Attention

1. The decomposition reaction is exothermic and will make the container quiet hot!

2. 30% hydrogen peroxide is a strong oxidant which may cause serious result, please handle it with care!

Reference:

1. http://pubs.acs.org/doi/pdf/10.1021/acs.jchemed.5b00037

2. https://en.wikipedia.org/wiki/Elephant_toothpaste