Pharaoh’s snakes or pharaoh’s serpents are a type of small firework in which a lighted tablet exudes smoke and ash in a growing column which resembles a snake. The modern version of this firework is the non-toxic black snake. Pharaoh’s snakes produce a more spectacular display, but they are toxic so now this firework is only produced as a chemistry demonstration. If you have the materials and a fume hood, you may wish to make your own Pharaoh’s snakes.

Making Pharaoh’s Snakes

This is an extremely simple firework demonstration. All you need to do is ignite a small pile of mercury(II) thiocyanate, Hg(SCN)₂. Mercuy thiocyanate is an insoluble white solid which can be purchased as a reagent or can be obtained as a precipitate by reacting mercury(II) chloride or mercury(II) nitrate with potassium thiocyanate. All mercury compounds are toxic, so the demonstration should be performed in a fume hood. Typically the best effect is obtained by forming a depression in a shallow dish full of sand, filling it with mercury(II) thiocyanate, lightly covering the compound, and applying a flame to initiate the reaction.

Pharaoh’s Snakes Chemical Reaction

Igniting mercury(II) thiocyanate causes it to decompose into an insoluble brown mass that is primarily carbon nitride, C₃N₄. Mercury(II) sulfide and carbon disulfide are also produced.

2Hg(SCN)₂ → 2HgS + CS₂ + C₃N₄

CS₂ + 3O₂ → CO₂ + 2SO₂

The heated C₃N₄ partially breaks down to form nitrogen gas and dicyan:

2C₃N₄ → 3(CN)₂ + N₂

Mercury(II) sulfide reacts with oxygen to form mercury vapor and sulfur dioxide. If the reaction is performed inside a container, you will be able to observe a gray mercury film coating its interior surface.

HgS + O₂ → Hg + SO₂

 

Although Pharaoh’s snakes are considered a type of firework, they do not explode or even emit sparks. They burn on the ground and release smoky vapors. All aspects of the reaction can be hazardous, including handling the mercury thiocyanate, breathing the smoke or touching the ash column, and contact with the remains of the reaction during clean-up. If you perform this reaction, use appropriate safety precautions for dealing with mercury.

1. My Scariest Moment

When a package came into the stockroom, I checked the DOT labels to determine how to open the container. It was too cumbersome to open everything in the hood, so if it had no labels I just opened it on the receiving table. On a particular day, like any other, a single package came in. No labels. I put on my nitrile gloves and opened the container. I removed a small bottle nestled in Styrofoam and immediately noticed that my glove was drenched. Annoying. It happens. I look at the bottle and I immediately lose my shit. The first word I see is Dimethylmercury. I had taken lab safety classes and was aware of the tragic death of Karen Wetterhahn. My mind was racing. My wife was pregnant and hadn’t finished grad school. What if I died and wasn’t there to raise my child? Awful thoughts ran through my head.

I took off my gloves and placed them into a secured waste container. I calmed down and walked to our most experienced Organic professor and told him what was happened. His jaw dropped and he muttered, “Fuck.” We walked to the stockroom and I showed him the container. I saw relief in his face, which then turned to anger. The substance was a standard used by the biology department for a mercury analysis machine used to determine Hg concentration in fish. I believe it was either a 1ppm or 1ppb standard. I really can’t remember. I thought he was pissed at me for overreacting, but he was really mad at the professor who ordered it. Never understood why. Either way, I left work early to be with my pregnant wife and wind down.

1. Most Embarrassing / Saddest Thing I Witnessed.

I was actually taking Organic Chemistry Lab to improve my practical chemical knowledge. We were performing an extraction using dichloromethane. Nothing fancy. There was a real dunce in the class who had horrible lab technique. It was obvious from the first lab. The dunce went to pour his organic layer back into his sep funnel, but forgot to close the stopcock. In addition, he was doing this outside of the hood with the glassware aimed right at his crotch. After drenching his genitals with dichloromethane, he stood at his hood, too embarrassed to move. I heard him go up to the TA and say, “I think I messed up.” By this point, his penis had started itching and burning and he was really worried. I brought him down to the stockroom and had him strip down to his boxers while he stood underneath the safety shower. I made him stand there for the whole recommended 15 minutes. Sadly, the professor in charge of the lab heard about the accident and came in and bitched him out as he was standing there in his boxers. I felt awful for the kid. He dropped the class the next day and switched majors. I don’t think he was cut out to be a chemist, but I still felt awful for how he found out.

The Golden Book of Chemistry Experiments: How to Set up a Home Laboratory-Over 200 Simple Experiments

The Golden Book of Chemistry Experiments was a children’s chemistry book written in the 1960s by Robert Brent and illustrated by Harry Lazarus and published by Western Publishing in their Golden Books series. Many of the experiments contained in the book are now considered highly dangerous for unsupervised children, and would not appear in a modern children’s chemistry book. OCLC lists only 126 copies of this book in libraries worldwide. It was said that the experiments and information contained herein were too dangerous for the general public.

The book was a source of inspiration to David Hahn, nicknamed “the Radioactive Boy Scout” by the media, who tried to collect a sample of every chemical element and also built a model nuclear reactor, which led to the involvement of the authorities.

Copies of this book often sell for prices between $100 to over $700 (USD), or higher, depending on condition. You can own a copy of this rare book for only a fraction of the cost of the original!

Illustrated Guide to Home Chemistry Experiments: All Lab, No Lecture (DIY Science)

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About the Author

Wet Deposition

Wet deposition refers to acidic rain, fog, and snow. If the acid chemicals in the air are blown into areas where the weather is wet, the acids can fall to the ground in the form of rain, snow, fog, or mist. As this acidic water flows over and through the ground, it affects a variety of plants and animals. The strength of the effects depends on several factors, including how acidic the water is; the chemistry and buffering capacity of the soils involved; and the types of fish, trees, and other living things that rely on the water.

Dry Deposition

In areas where the weather is dry, the acid chemicals may become incorporated into dust or smoke and fall to the ground through dry deposition, sticking to the ground, buildings, homes, cars, and trees. Dry deposited gases and particles can be washed from these surfaces by rainstorms, leading to increased runoff. This runoff water makes the resulting mixture more acidic. About half of the acidity in the atmosphere falls back to earth through dry deposition.

History

The corrosive effect of polluted, acidic city air on limestone and marble was noted in the 17th century by John Evelyn, who remarked upon the poor condition of the Arundel marbles.^[2] Since the Industrial Revolution, emissions of sulfur dioxide and nitrogen oxides to the atmosphere have increased.^[3][4] In 1852, Robert Angus Smith was the first to show the relationship between acid rain and atmospheric pollution in Manchester, England.^[5] Though acidic rain was discovered in 1852, it was not until the late 1960s that scientists began widely observing and studying the phenomenon.^[6] The term “acid rain” was coined in 1872 by Robert Angus Smith.^[7] Canadian Harold Harvey was among the first to research a “dead” lake. Public awareness of acid rain in the U.S increased in the 1970s after The New York Times promulgated reports from the Hubbard Brook Experimental Forest in New Hampshire of the myriad deleterious environmental effects demonstrated to result from it.^[8][9]

Occasional pH readings in rain and fog water of well below 2.4 have been reported in industrialized areas.^[3] Industrial acid rain is a substantial problem in China and Russia^[10][11] and areas down-wind from them. These areas all burn sulfur-containing coal to generate heat and electricity.^[12] The problem of acid rain not only has increased with population and industrial growth, but has become more widespread. The use of tall smokestacks to reduce local pollution has contributed to the spread of acid rain by releasing gases into regional atmospheric circulation.^[13][14] Often deposition occurs a considerable distance downwind of the emissions, with mountainous regions tending to receive the greatest deposition (simply because of their higher rainfall). An example of this effect is the low pH of rain (compared to the local emissions) which falls in Scandinavia.^[15]

History of acid rain in the United States

In 1980, the U.S. Congress passed an Acid Deposition Act. This Act established a 10-year research program under the direction of the National Acidic Precipitation Assessment Program (NAPAP). NAPAP looked at the entire problem. It enlarged a network of monitoring sites to determine how acidic the precipitation actually was, and to determine long term trends, and established a network for dry deposition. It looked at the effects of acid rain and funded research on the effects of acid precipitation on freshwater and terrestrial ecosystems, historical buildings, monuments, and building materials. It also funded extensive studies on atmospheric processes and potential control programs.

In 1991, NAPAP provided its first assessment of acid rain in the United States. It reported that 5% of New England Lakes were acidic, with sulfates being the most common problem. They noted that 2% of the lakes could no longer support Brook Trout, and 6% of the lakes were unsuitable for the survival of many species of minnow. Subsequent Reports to Congress have documented chemical changes in soil and freshwater ecosystems, nitrogen saturation, decreases in amounts of nutrients in soil, episodic acidification, regional haze, and damage to historical monuments.

Meanwhile, in 1990, the US Congress passed a series of amendments to the Clean Air Act. Title IV of these amendments established the Acid Rain Program, a cap and trade system designed to control emissions of sulfur dioxide and nitrogen oxides. Title IV called for a total reduction of about 10 million tons of SO2 emissions from power plants. It was implemented in two phases. Phase I began in 1995, and limited sulfur dioxide emissions from 110 of the largest power plants to a combined total of 8.7 million tons of sulfur dioxide. One power plant in New England (Merrimack) was in Phase I. Four other plants (Newington, Mount Tom, Brayton Point, and Salem Harbor) were added under other provisions of the program. Phase II began in 2000, and affects most of the power plants in the country.

During the 1990s, research continued. On March 10, 2005, EPA issued the Clean Air Interstate Rule (CAIR). This rule provides states with a solution to the problem of power plant pollution that drifts from one state to another. CAIR will permanently cap emissions of SO2 and NOx in the eastern United States. When fully implemented, CAIR will reduce SO2 emissions in 28 eastern states and the District of Columbia by over 70 percent and NOx emissions by over 60 percent from 2003 levels.^[17]

Overall, the Program’s cap and trade program has been successful in achieving its goals. Since the 1990s, SO₂ emissions have dropped 40%, and according to the Pacific Research Institute, acid rain levels have dropped 65% since 1976.^[18][19] However, this was significantly less successful than conventional regulation in the European Union, which saw a decrease of over 70% in SO₂ emissions during the same time period.^[20]

In 2007, total SO₂ emissions were 8.9 million tons, achieving the program’s long term goal ahead of the 2010 statutory deadline.^[21]

The EPA estimates that by 2010, the overall costs of complying with the program for businesses and consumers will be $1 billion to $2 billion a year, only one fourth of what was originally predicted.^[18]

Chemical processes

Combustion of fuels creates sulfur dioxide and nitric oxides. They are converted into sulfuric acid and nitric acid

Gas phase chemistry

In the gas phase sulfur dioxide is oxidized by reaction with the hydroxyl radical via an intermolecular reaction:^[5]

SO₂ + OH· → HOSO₂·

which is followed by:

HOSO₂· + O₂ → HO₂· + SO₃

In the presence of water, sulfur trioxide (SO₃) is converted rapidly to sulfuric acid:

SO₃ (g) + H₂O (l) → H₂SO₄ (l)

Nitrogen dioxide reacts with OH to form nitric acid:

NO₂ + OH· → HNO₃

Chemistry in cloud droplets

When clouds are present, the loss rate of SO₂ is faster than can be explained by gas phase chemistry alone. This is due to reactions in the liquid water droplets.

Hydrolysis

Sulfur dioxide dissolves in water and then, like carbon dioxide, hydrolyses in a series of equilibrium reactions:

SO₂ (g) + H₂O SO₂·H₂O

SO₂·H₂O H⁺ + HSO₃⁻

HSO₃⁻ H⁺ + SO₃²⁻

Oxidation

There are a large number of aqueous reactions that oxidize sulfur from S(IV) to S(VI), leading to the formation of sulfuric acid. The most important oxidation reactions are with ozone, hydrogen peroxide and oxygen (reactions with oxygen are catalyzed by iron and manganese in the cloud droplets)

…………..

http://en.wikipedia.org/wiki/Acid_rain

Single-wall carbon nanotubes are usually about a nanometer in diameter, but they can be millions of nanometers in length. It’s as if you took a one-atom-thick sheet of carbon atoms, arranged in a hexagonal pattern, and curled it into a cylinder, like rolling up a piece of chicken wire. If you’ve tried the latter, you know that there are many possibilities, depending on how carefully you match up the edges, from neat, perfectly matched rows of hexagons ringing the cylinder, to rows that wrap in spirals at various angles — “chiralities” in chemist-speak.

Chirality plays an important role in nanotube properties. Most behave like semiconductors, but a few are metals. One special chiral form — the so-called “armchair carbon nanotube”* — behaves like a pure metal and is the ideal quantum wire, according to NIST researcher Xiaomin Tu.

Armchair carbon nanotubes could revolutionize electric power systems, large and small, Tu says. Wires made from them are predicted to conduct electricity 10 times better than copper, with far less loss, at a sixth the weight. But researchers face two obstacles: producing totally pure starting samples of armchair nanotubes, and “cloning” them for mass production. The first challenge, as the authors note, has been “an elusive goal.”

Separating one particular chirality of nanotube from all others starts with coating them to get them to disperse in solution, as, left to themselves, they’ll clump together in a dark mass. A variety of materials have been used as dispersants, including polymers, proteins and DNA. The NIST trick is to select a DNA strand that has a particular affinity for the desired type of nanotube. In earlier work, team leader Ming Zheng and colleagues demonstrated DNA strands that could select for one of the semiconductor forms of carbon nanotubes, an easier target. In this new paper, the group describes how they methodically stepped through simple mutations of the semiconductor-friendly DNA to “evolve” a pattern that preferred the metallic armchair nanotubes instead.

“We believe that what happens is that, with the right nanotube, the DNA wraps helically around the tube,” explains Constantine Khripin, “and the DNA nucleotide bases can connect with each other in a way similar to how they bond in double-stranded DNA.” According to Zheng, “The DNA forms this tight barrel around the nanotube. I love this idea because it’s kind of a lock and key. The armchair nanotube is a key that fits inside this DNA structure — you have this kind of molecular recognition.”

Once the target nanotubes are enveloped with the DNA, standard chemistry techniques such as chromatography can be used to separate them from the mix with high efficiency.

“Now that we have these pure nanotube samples,” says team member Angela Hight Walker, “we can probe the underlying physics of these materials to further understand their unique properties. As an example, some optical features once thought to be indicative of metallic carbon nanotubes are not present in these armchair samples.”

* From the distinctive shape of the edge of the cylinder

Journal References:

1. Xiaomin Tu, Angela R. Hight Walker, Constantine Y. Khripin, Ming Zheng. Evolution of DNA Sequences Toward Recognition of Metallic Armchair Carbon Nanotubes. Journal of the American Chemical Society, 2011; : 110728080027017 DOI: 10.1021/ja205407q
2. Xiaomin Tu, Suresh Manohar, Anand Jagota, Ming Zheng. DNA sequence motifs for structure-specific recognition and separation of carbon nanotubes. Nature, 2009; 460 (7252): 250 DOI: 10.1038/nature08116

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