Catalyst

I've always heard the term catalyst and wondered how they work. The most common term people know is probably catalytic converter (a thing in your car that improves emissions) which uses Platinum and/or Palladium as catalysts. People used to steal them to try to extract the precious metals. Maybe they still do.

I generally understood what a catalyst is, but wanted to experiment and see them in action. I thought I would pick the very well-known and widely understood metal oxide added to hydrogen peroxide to speed its decomposition into water and oxygen.

    2H2O2 -> 2H2O + O2

It turns out that it is very well known, especially with MnO2, but remains an active area of research for the exact series of reactions involved. The best-looking answer I found on the internet initially for MnO2 was completely wrong as it left MnO as a product. A true catalyst speeds the reaction but is unchanged; it is not modified by the completed process even thought it may be temporarily modified during the reaction. You should be able to reuse the catalyst. Luckily, I don't have to take my car down to Jiffy Lube for a refill of Platinum.

For kicks, I had some Fe2O3 (hematite) laying around, and decided to bake-off the natural decomposition of H2O2 vs. with MnO2 vs. with FeO3. I had done no research on hematite as a catalyst for the reaction - I just thought it might work. In retrospect that was probably silly as Fe2O3 is abundant and cheaper than MnO2, so I would probably have found more on iron oxides as a catalyst than manganese oxides initially if it worked just as well.

OK, so I dumped some hydrogen peroxide into two beakers. Not much happened. There was an occasional bubble. Not enough for me to have even thought a reaction was occurring, but sloooowly. Then I dumped some MnO2 into one and it went crazy making oxygen gas. The beaker also became very warm. This is clearly an exothermic reaction! Next, I dumped a bit of red iron oxide into the control beaker. I didn't observe much. There was some bubbling, but I'd have to compare to video to try to determine if it was any faster than before.   

What is going on with the MnO2 reactions?? I was a bit disappointed to find no good reference on this on the internet. The ones I did find were vague or detailed but clearly wrong. A catalyst creates a series of reactions that end up with the catalyst unchanged, the same products (water and oxygen here), but has a lower activation energy so that the reaction can be done faster with the same energy or with less energy. In my case, I was adding no energy to the system beyond room temperature (which is what the hydrogen peroxide was stored at in the first place). I expected the rate of reaction to change.

Here is a handy artwork I made to show the H2O2 reactant, it's formation enthalpy, the normal activation energy, and the products with the exothermic release of energy (delta H) calculated from the formation enthalpy of liquid water. Since the activation energy with MnO2 is known, I charted that as well and tried to approximate a couple of reactions along the way in a second line on the diagram. But later I read that there could be five reactions involved.

After trying much math and good searches, I did feel better to finally find a recent academic paper which states that the exact series of reactions is unknown and proposes five reactions as a possible solution. When you are having trouble finding a solution, it is always nice to know what you thought should be easily discoverable is actually unknown to science. I feel less stupid. One thing I so know is the "slowest" of that series of reactions must have an activation energy of 58KJ/mol to match overall lab results for the catalyst. But I'm not going to repeat the research in detail here.

So what about my iron oxide (with Fe(III) ions instead of Mn(IV) ions)? Further research uncovered that this is also being actively studying for potential performance in different environments (temperature, pH level, etc.). It does seem that the effectiveness of iron oxide is not nearly as good as that of MnO2. I noticed what appears to be some bubbling at a greater rate than before, but nothing worth writing home about.

I once visited a vast field of manganese oxides in New Mexico. I have been to mines in California and other places. The ocean floor is littered with manganese oxide nodules. I would love to have collected some of these natural minerals (pyrolusite - MnO2 - among others) and try them out. But these things are mostly just ugly black and so I didn't bring much back or keep track of it. Maybe some day I'll run to the Quick-E-Mart and buy some hydrogen peroxide if in the areas again. Like taking ore to the coal mine, or Mohammad to the mountain, it seems that taking a bottle of liquid to the ore field is the easier task. I would pour it on the black ground and it should fizz wildly. In the process I water any plants and add oxygen to the New Mexico sky.

Thanks for reading,

Paul

It's a Liquid, it's a Solid, it is Ferrofluid!

I attempted to make my own ferrofluid. I failed. First I bought some printer toner but it was not magnetic enough. So then I bought more toner, this time magnetized for check printing (MICR toner). I mixed with vegetable oil at different thicknesses. I made a magnetic suspension fluid but it did not form cool shapes quite like I expected. I'm not sure what the problem was, but I made a HUGE mess and spent a week trying to recover my beaker and magnets, etc. I decided that I would break my personal rule and buy the stuff ready-made. I will not share my formulations as they all failed to impress me and made a massive mess. If you have never dealt with printer toner, I don't recommend you start now. It is ink, and simply opening a bottle of it causes and ink cloud to form and settle on everything around it. Someone once joked that if you sneeze, you may have to buy a new house.

What is ferrofluid? Well, as NASA envisioned it, it is a liquid that can be controlled by magnetic fields. So it has properties of two phases, liquid and solid. In order to make ferrofluid, you need very small (10nm or so) particles of magnetite (magnetic iron oxide), polarized in a surfactant (like soap) and suspended in a carrier liquid. The carrier and surfactant can be one substance in the case of thin oils like mine, but NASA's formulation was hopefully more sophisticated.

Since I skimped on cheap toner, maybe my particles were too big. 10nm is really small. Again, I'm not really sure. I know from a job I had once that growing consistently small crystals on that scale is quite hard. You have to stop growth before the crystals are even visible.

Here is a picture of my new purchased fluid above a medium sized rare earth magnet:

It is a big hard to see black against black, so here is a view of the same picture where I edited the light and contrast:

Note the characteristic spikes arranged in a beautiful 360-degree flower shape. The shape corresponds perfectly with the magnetic field, as expertly drawn by me below. Note the field follows this pattern in 3D, not just to the right and left of the magnet as in my drawing.

And here is another picture with a smaller and therefore weaker magnet:

Note the field is weaker, so it can sustain fewer spikes and they are tending to bend down according to gravity and the smaller shape of the magnetic field.

You may be wondering why the spikes form so precisely. I did, so I looked it up. The particles are so small as to move about and bounce off each other randomly in the same way molecules do in liquid. This is known as Brownian motion. Thus the liquid can arrange itself perfectly with force fields according to probability's directions. As we showed in the magnetic field diagram, the spikes correspond to these magnetic field lines in 3D. However, they are limited by gravity and surface tension. The tips of the spikes are the point when the opposing forces are equal. The spikes grow longer with a stronger magnetic field. The direction of gravity can affect them. The largest and sharpest spikes are formed when surface tension of the liquid is minimized. 

If you wish to try something similar and not buy the stuff or figure out how to make it, a quick and easy thing to do is to dump some iron filings on paper or glass above a rare-earth magnet. Don't let the filings get on the magnet! The much-bigger filings align with the magnetic field in a similar way, generally showing the magnetic field shape. They cannot reposition themselves ideally because they are not small enough, not suspended in a fluid, and make physical connections with each other (like little magnets stacking themselves upon each other).

One last thing. What is magnetism? I am oversimplifying this because it is kind of complicated and honestly I don't fully understand it yet. For our purposes here, some materials have unpaired electrons. Iron is one such substance. Another is Magnetite (due to a combination of both Fe(ii) and Fe(iii) cations in its molecular makeup). Paired electrons cancel out a magnetic property known as spin. Unpaired electrons retain this property and are attracted to electromagnetic fields. While electromagnetic fields are usually the realm of physics, I guess my point here is it all comes from the chemistry of the substance.  

Thanks for reading, 

Paul

p.s. I kind of butchered some of the science for simplicity. In reality, what I am calling magnetic is paramagnetic (other than the magnets themselves). Paramagnetic material like iron filings and this ferrofluid can be attracted to magnetic fields spontaneously. Paramagnetic material has one or more unpaired electrons. Paired electrons oppose each other's "spin," and therefore magnetic properties. This means the bonding of molecules and even between molecules in crystal lattices makes a difference in whether electrons are paired, and therefore, whether they are paramagnetic. O2 is paramagnetic but N2 is not. Without getting into Molecular Orbital Theory (MOT), it is easiest to determine the elements and ions. Iron has four unpaired 3d-shell electrons (according the Hund's law). Iron +2 or (or Fe(II)) also has four. Iron +3 has 3 unpaired electrons. In a compound, note iron oxides hematite (diagmagnetic) and magnetite (strongly paramagnetic) are determined by MOT and not just their metal ions by themselves. A common question is why copper, silver, and gold are not paramagnetic. All three line up in group 11, meaning they have one unpaired electron, but the large size of the atoms means the many filled shells' diamagnetic properties overcome the attraction of the one unpaired electron. I believe MOT is beyond AP-level Chemistry.

      

 

The Black Snake

I wanted to make the Pharaoh's Serpent, but then I read how toxic it is and I had no plan to manage that properly. In researching this, I saw the much less cool Black Snake experiment as another type of intumescent reaction. An intumescent is a substance that swells with heat exposure. These can come in handy as fire retardants. Both "snake" reactions are of this type where a substance appears to grow out of a hole as it expands. I have never been to Diwali in India, but apparently this is one of their favorite firecracker types. Personally, I have no recollection of these fireworks at all (but also am not that experienced). 

The way the reaction goes, sucrose (powdered sugar)and sodium bicarbonate (baking soda) are mixed in a  4:1 ratio, added on top of sand soaked in a fuel such as lighter fluid (butane), and then the fuel is ignited. In my case, I used isopropyl alcohol as the fuel. Fairly quickly, several reactions start at once:

1) The fuel combusts, making carbon dioxide and water vapor and - most importantly - heat.

2) As the baking soda heats up, it releases carbon dioxide gas and water vapor as it decomposes to sodium carbonate. This is known as thermal decomposition, and is a key reaction in baking.  

3) The sucrose combusts much like the alcohol, again creating carbon dioxide and water vapor; however, some of the sucrose forms carbon. Remember burning creates lots of different reactions. See below.  

C12H22O11 + 12O2 -> 12CO2 + 11H2O

C12H22O11 + 11O2 -> 12C + 11H2O

So what happens is pure carbon and sodium carbonate are formed as solids, but pushed up and out by the carbon dioxide gasses. It cools as a long continual "ash" that can look like a black snake slipping crawling out of a hole.

I tried this, but it wasn't hugely impressive. I think my dish was too small and after a while the flames were choked out by the sand losing its exposure to air. It could be that I just did not use enough reactants to get a long reaction and product. I went for a relatively small effect as I didn't necessarily want a huge long pile of ash and I had limited 91% alcohol to conserve. Perhaps I ran out of that and lost the chain of exothermic reactions.

Note that this is super kid-friendly except for one big caveat: the fire. The biggest mistake made is people add alcohol to the flame and it splashes and spreads flames which have been known to badly injure people. Never do that! Of course, in general it is easy top burn yourself or something else with fire. That much is obvious. I'm not sure it is much more dangerous that barbecuing, however. The only real difference is we are adding gasses from within to expand the ash.

This is what my snake looked like when it went out after about 10 minutes.

As you can imagine it would look better if longer and thinner. I think my dish was too small. The video is not quite impressive enough to share. Some videos online are sped up. Nevertheless, you can probably play with the process a bit and get much better results.

I thought about using my new ash for gunpowder, but it contains a fair amount of sodium carbonate, I think. I'm not sure what that would do to the reaction. All of these experiments involving an oxidizer and sugar or charcoal are very similar reactions. I might be better off just burning sugar directly to get carbon. The only twist we really added here, chemically, is the decomposition of baking soda. I think it might have also slowed the burn rate a bit by displacing some oxygen with carbon dioxide.

Thanks for reading,

Paul

 

 

 

Battle of the Exothermic Redox Reactions

We've covered both thermite and "rocket candy." Here is a video of each, with 5g of thermite and 6g of rocket candy.

Here is the thermite (iron oxide with aluminum for fuel).

And here is the rocket candy (potassium nitrate with sugar for fuel):

A few things jump out at you:

1) The thermite is very hard to ignite (24s), but the sugar candy is pretty easy to ignite (<1s).

2) The thermite releases more energy in general.

3) The thermite releases more energy in the form of light.

4) The sugar candy has a longer burn (4s). The thermite is done in 2s.

5) The sugar candy releases many more gasses. 

6) If you can see in the videos, the thermite melts its aluminum cup and the sugar candy does not.

It goes without saying that sugar candy is a better propellant. Thermite actually is not a propellant at all; solids react to create solid products. Sugar candy has a longer burn with more emissions. This is what you want for thrust. Additionally, the thermite is just too hard to ignite and burns too hot to propel an actual vehicle.

That being said, the thermite can be used for welding because it leaves molten iron as a product. Since it carries all of its own oxygen in the iron oxide, burns so hot, and has no gas propellants, it can even be used underwater.

The application of chemistry is using the right tool for the job. Changing an atom here or there creates very different chemical properties and reactivity. 

Thanks for reading,

Paul

Yes I did it, Plasma Pt II

I mentioned that my daughter was home.  I wanted to show her the grape plasma, bit it did not work because the grapes were a little ripe and just split immediately upon heating. It took some convincing, but my wife allowed a quick and simple creation of a much more impressive plasma display. If my daughter were not home, she would probably have not agreed. So thanks for that! 

Let's go straight to the video because it is impressive:

We have created much more plasma that the grapes did! I have a lit match on a watch glass, held in the air by a toothpick (so it did not go out immediately), contained in a beaker. Then I pressed go on high and filmed. The plasma jumps around inside the beaker as the microwave goes through hot and cold spots of radiation. Make sure the volume is on as this makes an impressive hum. 

I analyzed the audio from the plasma and it seems to be regenerating exactly 420 times per second. I had expected 120 time per second based on NileRed and some other internet content. Yes, 120Hz is the frequency of rectified AC power but I don't think that matters. The microwaves themselves are in the gigahertz range. It seems to me that the principle of the microwave is that hot spots will form standing waves of electromagnetic energy according to the resonant frequency of the mechanical chamber itself. Perhaps that is around 420Hz. What really surprised me was how truly consistent the frequency (to the Hertz). See this analysis for one:

It is wonderful that I can analyze the audio with a free app on my smartphone. Ten years ago I would need a lab full of equipment for much of what I do on my phone now.  The number at the top is the peak. Every time I play the video I get audio playback up to 10KHz. That number may just be a cutoff given the sampling frequency of my video. I'll skip the math and physics lecture here. The point is that the dark red line is the peak signal during the plasma generation. It is a pretty narrow and strong band of sound. Two video playbacks are shown above, with ambient noise in between. For whatever reason, I get very little sound at 120Hz and a clear and consistent peak corresponding with the plasma generation at 420Hz.

Luckily I cut the experiment pretty short. I saw no real purpose in keeping my plasma alive for multiple rotations. I did not want to risk fire or any other damage. The plasma can easily reach 10,000 degrees F and much, much higher. Let's just say that my breaker cracked from the heat in only a few seconds, and it should be good up to 1000 F or so. I often use a blow torch directly on the special glass at that temperature. I don't recommend it, just like I can't recommend this experiment for others. If my beaker had fallen apart instead of just cracking, the plasma would have been free to roam the microwave and melt anything it came near. The fire risk was probably low because I had my hand on the off button, but microwaves are built out of materials that quickly melt at these temperatures. NileRed demonstrated this, so I don't need to.

To paraphrase a baseball announcer, my beaker died a hero. My microwave still works and I am still married.

Now, what was the gas that we heated to the fourth state of matter? 

Old matchheads (not safety matches were made of mostly white phosphorus). I, however, grabbed whatever free book of safety matches was available in the drawer next to the microwave. I didn't really plan this experiment, per se. I did the whole thing in just a few minutes. Wikipedia says safety matches are mostly potassium chlorate. Perhaps I'll do a whole experiment on match heads now. Chemistry begats more chemistry. I figure there was a fair bit of air that was ionized as well as some carbon gasses from the paper of the match. 

Whatever, I had neutral gasses from the flame, and I zapped it to kingdom come with a strong electric field (apparently 420 times per second). I ripped the electrons off of potassium ions and/or carbon ions and/or whatever else there was in air, including Nitrogen, to create a free cloud of electrons that emitted yellowish photons in the form of light energy. Most likely the dominant yellow color is from sodium ions that came from sodium borosilicate beaker glass. Shout out to NileRed for doing some good experiments to indicate this.

If you saw his video, I was thinking the beaker glass was causing his Na spike while he went super-technical in search of chemoluminescent reactions and so forth.  I don't know 1% of what he does, so I figured that beaker glass is somewhat related to soda-lime glass. He knew enough to seek far more complicated theories before determining the simpler truth. When you are at this high a temperature, all of the normal rules don't necessarily apply. Your beaker may not be inert. Super strong Nitrogen triple bonds break and this mostly "inert" gas reacts with oxygen to form NO2. Weird, wild stuff.

I declare success and a truce in the plasma war before things become too heated.

Thanks for reading,

Paul

    

Jump Up!

My daughter was home briefly and told me she wanted to do an experiment she saw from coolchemistryguy. Unfortunately he explained nothing in his video but looked cool doing it. So I made her do six experiments. This is the one she wanted to do, starring her. I'll explain it.

First, we melt the bottom of a birthday candle and affix it in place at the bottom of a plastic tub. We fill the tub with water, but not above the candle wick, and add some food color for a better viewing experience. Then we take an empty wine bottle and add a little bit of 70% isopropyl alcohol, the same used for hand sanitation everywhere. This time 90% is not required. We roll the alcohol around a bit in the bottle, just enough for vapors to fill and coat the inside. With the candle lit, we place the bottle over the candle and into the liquid. You don't want the bottle to form a seal at the bottom, so if possible keep it down in the liquid but not completely against the bottom. The liquid should rush into the bottle with surprising force, especially if you have done this without the alcohol.  

Here she is doing the honors:

 

Pretty cool! The reason this works is that the candle heats the air in bottle, and that causes it to expand, when placed into the water the bottle cools quickly and pressure drops. As the Ideal Gas Law states, PV = nrT, or more simply, pressure and volume are proportional to temperature. As temperature rises, volume expands and pressure increases. As temperature falls, volume and pressure reduce. So as the pressure drops back down and volume of air in the bottle reduces, it creates a suction that brings the water into the bottle.

Normally this is slow and a bit boring, but alcohol spices things up. The vapor in the bottle is flammable, and when exposed to the flame of the candle, expands rapidly and forcefully (although mostly unnoticed and unseen). This forces most of the gas out of the bottle, which in turn creates a much stronger suction when it cools. 

I could not see the gas in the bottle ignite until I looked frame-by-frame. This picture captures a hot (blue) flame shooting momentarily into the neck of the bottle.

I believe the wine bottle worked better than others we tried because the thin neck creates a venturi, speeding the liquid into the bottle. The other way to think of it is that the suction is the same, just over a much smaller area than a mason jar or similar.

This is a great thermodynamics (and fluid dynamics) experiment suitable for kids (well, without the alcohol it is about as safe as a 1st birthday cake).

Thanks for reading,

Paul

The Fourth State - Grape Plasma

We are going to make plasma, the fourth state of matter after solid, liquid, and gas. I have seen vast machines use plasma etching and vapor deposition when touring LCD factories making TVs and computer displays, but I wasn't up on the science of it and didn't fully understand that part of it. So I have wanted to better understand the states of matter and their transitions. In math and science and computer programming, the diagram below is known as a state machine, and may be used to design a vending machine or calculator for example. In this case we are mapping out the known states and transitions of matter. I assume by now you are generally familiar with melting, freezing, boiling (vaporizing), and condensing (like fog or dew). We talked about sublimation in the cloud chamber experiment when frozen carbon dioxide went directly to a gas without passing Go and collecting $200. Here is the diagram which I labored over for many hours with precision tools:

Not everyone is familiar with plasma. You may have heard of plasma televisions. You definitely know the glow of neon lights and bright flash of lightning. The sun and other stars contain plasma. You have definitely seen it but likely did not process it as a fourth state of matter. When a neutral gas is superheated it can change into ions (atoms with electrons removed) and free electrons, which is basically a conductive substance that can be controlled with magnetism and electricity. The formation of plasma is called ionization. When it cools back to a more stable gas state, that is known as deionization.

Trivia: some scientists suspect that plasma is the most abundant form of matter in the universe. Nobody really knows.

More trivia: St. Elmo's Fire is a glob of plasma that hangs about occasionally and is known to pilots and mariners.

Thanks to a video from NileRed, I decided to make my own plasma in the microwave. My wife would not be happy if I destroyed the microwave or burned the house down, so I went for 'small but visible' plasma using two grapes which she had just bought. There are other more impressive way to form big bright balls of it, but we will stick with grapes for now. I should say don't try this at home...  

It has actually taken science awhile to explain grape plasma. Original theories were wrong. I'll try to explain very briefly what scientists currently say is happening. The grapes being full of mostly water absorb the microwaves and heat up quickly. Two of them very close to each other (touching in my example) form one single heat center in between the grapes. This spot get incredibly hot, so hot that it ionizes hot gasses escaping from the grapes. We see sparking much like metal in a microwave, and this is the plasma shooting its free electrons out like little bits of lightning.

In case anyone ignores my admonition, don't do this to the point that the grapes catch on fire. Thirty seconds on high is probably more than enough. Trust me, the grapes get really hot quickly. Be careful touching them after the experiment. Use a watch glass or similar dish to hold them. You can eat them if you want (for some reason this is a common question) but wait til they cool. Use a rotating plate as microwaves have hot and cold spots due to microwave superposition (just like our light being cancelled out in the bismuth posts). The physicist Faraday says you can cut a small hole in your microwave for better filming, but I don't think it is worth it. Don't let your dog eat the grapes, cold or hot. Yes, that is my dog reflected off of the microwave in the video, hoping to get food out of this somehow.

This is what the (very hot) grapes (with a little juice splatter) looked like when done. You can easily see the heat center where the plasma was generated.

Thanks for reading,

Paul