Thursday, February 26, 2015

Chemicals in fireworks (2)

In addition to the chemicals mentioned the previous post,  there are other chemicals in fireworks and support their functions

Combustion agents, which generate high temperature after the fireworks are ignited. The major chemical component of combustion agents include fuel and oxidants that support combustion. Besides black powder, some metals (Al, Mg, Fe, Zn), petroleum components, phosphor, sulfur organometal also serves as fuels of fireworks. The combustion of these fuels requires the support of oxygen. However, at the fast rate of combustion with fireworks, the oxygen in air is consumed faster than can be refilled by surrounding air. Therefore, different oxidants are also added to fireworks to support the abrupt chemical reactions.

The most common oxidizer is potassium nitrate, which decomposes to potassium oxide, nitrogen gas, and oxygen gas.

decomposition of potassium nitrate

Sometimes more explosive oxidizers, which produced temperatures of 1700 to 2000°C and made possible the creation of much more intense colors. These oxidizers are the chlorates and perchlorate

reaction of chlorates
reaction of perchlorates

decomposition of potassium nitrateThe chemicals as oxidants generally involve nitrate, chlorate, bromorate, and perchlorate.

Fireworks use chlorate and perchlorate as the oxidizer often include catalyzers . The function of catalyzers is to decrease the required temperature for certain chemical reactions. Catalyzers often include some transition elements, for example, CoO2, Cr2O5, CuO, TiO2, PbO2, Pb3O4.

Besides the chemical components that take part in chemical reactions during firework combustion, there are also other inner component such as sulfate, phosphate, carbonate and natural resin that make the different chemicals stay together.

Sometimes fireworks are used during the day time. In such case, smoke from fireworks plays a more important role than the light from fireworks. Such fireworks used during the day time also includes smoke generating agents which forms many aerosol particles with different sorption and refraction on the light to give different colors. Such chemicals that form aerosol particles include yellow phosphor, white phosphor, hexachloroethane, alumimum powder, zinic oxide, and dyes

With so many chemicals in fireworks, what's the environmental impact caused by these chemicals in fireworks? Let's continue next time.

Saturday, February 21, 2015

Chemistry of fireworks

This week unfolds the Lunar year of Sheep.  Lunar new year has been celebrated with fireworks for almost a thousand years. What's the science in fireworks. Let's explore by starting with black powder. 

Black powder was one of the greatest inventions of ancient China. It was invented  by alchemists experimenting with a naturally-occurring salt, potassium nitrate while looking for an elixir of immortality. But in handling and heating the sensitive substance they inevitably discovered its explosive properties. 

ancient book documenting how to make black powder

Although the first known account of the use of gunpowder as a weapon dates to 1046 in China, the use of black powder to make fireworks was documented during the Song Dynasty around the 1200s. 

There are various chemical components in fireworks. The major chemical component is the lighting agent. The ideal lighting agent requires a long time of lighting from chemical reactions. Flare of firework needs to be supported with heated solid and liquid microparticles that release energy via chemical reaction. The temperature of flare from lighting agents can be over 2000 Celsius. The effieciency of lighting agent depends on the content of magnesium. The most commonly used lighting agent in fireworks contains 55% magnesium, 40% sodium nitrate and ~5% synthetic resin. The time of lighting can last from 30 seconds to a few minutes.

Besides lighting agent, there is also a component called flashing agent in fireworks. Flashing agent generate bright light in a short time (0.1 s).  One type of flashing agent include aluminum-magnesium alloy, which is relatively safe. Another type of flashing agent additionally include potassium perchlorate (KClO4).

The other component of firework is called coloring agent. Coloring agents are comprised of different metal salts. Chemical reaction by the lighting and flashing agent generate large amount of heat. Such energy will excited the electrons of metal elements.  This high-energy excited state does not last for long, and the excited electrons of the elements quickly release their energy. The amount of energy released can be characterized by a particular wavelength of light and varies from element to element.  Higher energies correspond to shorter wavelength light, whose characteristic colors are located in the violet/blue region of the visible spectrum. Lower energies correspond to longer wavelength light, at the orange/red end of the spectrum.

The colors you see exploding in the sky are produced by the elements with the characteristic emissions listed in the table (source:

ColorCompoundWavelength (nm)
strontium salts, lithium salts
lithium carbonate, Li2CO3 = red
strontium carbonate, SrCO3 = bright red

calcium salts
calcium chloride, CaCl2
sodium salts
sodium chloride, NaCl
barium compounds + chlorine producer
barium chloride, BaCl2
copper compounds + chlorine producer
copper(I) chloride, CuCl
purplemixture of strontium (red) and
copper (blue) compounds
silverburning aluminum, titanium, or magnesium

More coming in the next post. ..

Friday, February 20, 2015

Chemicals associated with E-Cigarettes

Electronic cigarette is also referred as e-cig or e-cigarette, which is a battery-powered vaporizer which has a similar feel to tobacco smoking.

Third generation of e-cigarette that have organic light-emitting diode displays and buttons to adjust wattage or voltage.
Credit: Shutterstock/C&EN

Electronic cigarettes do not contain tobacco, although they do use nicotine from tobacco plants. They do not produce cigarette smoke but rather an aerosol. In general, they have a heating element that atomizes a liquid solution known as e-liquid.  E-liquid, also referred as e-juice or simply "juice", is a liquid solution that when heated by an atomizer produces vapor. The main ingredients of e-liquids are usually a mix of
propylene glycol (PG),

glycerin (G)

and/or polyethylene glycol 400 (PEG400),

sometimes with differing levels of alcohol mixed with concentrated or extracted flavourings;

E-cigarette fluid or “e-juice” comes in thousands of flavors, including pineapple custard and Scooby snack.
Credit: Associated Press

and optionally, a variable concentration of tobacco-derived nicotine.ingredients but without nicotine.

The solution is often sold in bottles or pre-filled disposable cartridges, or as a kit for consumers to make their own eJuices. Components are also available to modify or boost their flavour, nicotine strength, or concentration of e-liquid. Pre-made e-liquids are manufactured with various tobacco, fruit, and other flavors, as well as variable nicotine concentrations (including nicotine-free versions). Surveys suggested that the most liked e-liquids had a nicotine content of 18 mg/ml, and largely the favorite flavors were tobacco, mint and fruit. The flavorings may be natural or artificial.

Flavoring substances not identified in a natural product intended for human consumption, whether or not the product is processed. These are typically produced by fractional distillation and additional chemical manipulation of naturally sourced chemicals, crude oil or coal tar.

Most artificial flavors are specific and often complex mixtures of singular naturally occurring flavor compounds combined together to either imitate or enhance a natural flavor. These mixtures are formulated by flavorists to give a food product a unique flavor and to maintain flavor consistency between different product batches or after recipe changes. The list of known flavoring agents includes thousands of molecular compounds, and the flavor chemist (flavorist) can often mix these together to produce many of the common flavors.

Isoamyl acetate
Bitter almond
Ethyl propionate
Methyl anthranilate
Ethyl decadienoate
Allyl hexanoate
Ethyl maltol
Sugar, Cotton candy
Methyl salicylate

References and more to read:

Saturday, February 14, 2015

Caffeine chemistry

Caffeine, a methylxanthine alkaloid  closely shares chemical structural features with the adenine and guanine contained in deoxyribonucleic acid (DNA).


adenine                                     guanine

Caffeine is the world's most widely consumed psychoactive substances, but unlike many others, it is legal and unregulated in nearly all parts of the world.  Caffeine is classified as "generally recognized as safe" (GRAS) with toxic doses, over 10 grams per day for an adult. A cup  of coffee contains 100–200 mg of caffeine.

Caffeine can have both positive and negative health effects. It may confer a modest protective effect against some diseases, including Parkinson's disease and cardiovascular disease such as coronary artery disease and stroke. On the other hand, caffeine can cause sleep disruption, headaches, irritability, increased blood pressure and heart rate.

Decaffeination (decaf) is applied to remove caffeine from coffee beans, cocoa, tea leaves and other caffeine-containing materials. Decaffeinated drinks contain typically 1–2% of the original caffeine content, and sometimes as much as 20%.

In all decaffeination processes, coffee is always decaffeinated in its green, unroasted state. The greatest challenge to the decaffeination process is to try to separate only the caffeine from the coffee beans while leaving the other chemicals such as sucrose, cellulose, proteins, citric acid, tartaric acid, and formic acid at their original concentrations.  Since caffeine is a polar, water-soluble substance, water is used in all forms of decaffeination. However, water alone is not the best solution for decaffeination because it is not a selective solvent and therefore removes other soluble substances, including sugars and proteins, as well as caffeine. Therefore decaffeination processes use a decaffeinating agent such as methylene chloride, activated charcoal, CO2, or ethyl acetate.

Plastic Pollution in the World's Oceans

Plastic Pollution in the World's Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea.

A paper published in Science today on the estimation of mass of land-based plastic waste entering the ocean by linking worldwide data on solid waste, population density, and economic status. It is estimated that 275 million metric tons (MT) of plastic waste was generated in 192 coastal countries in 2010, with 4.8 to 12.7 million MT entering the ocean. Population size and the quality of waste management systems largely determine which countries contribute the greatest mass of uncaptured waste available to become plastic marine debris. Without waste management infrastructure improvements, the cumulative quantity of plastic waste available to enter the ocean from land is predicted to increase by an order of magnitude by 2025.

More information in the Report published in Science:
source of the graph:

Tuesday, February 10, 2015

Chemicals used for vector control

DDT has been used in malaria vector control because of its long residual efficacy when sprayed on walls and ceilings (6–12 months depending on dosage and nature of substrate).

Vector control is a method to limit or eradicate the mammals, birds, insects or other arthropods which transmit disease pathogens. The most frequent type of vector control is mosquito control using a variety of strategies.

DDT has been listed in the Stockholm Convention for persistent organic pollutants for international control. Recognizing that total elimination in many malaria-prone countries is currently unfeasible because there are few affordable or effective alternatives, the convention exempts public health use within World Health Organization (WHO) guidelines from the ban.

Today, about 3,000 to 4,000 tonnes of DDT are produced each year for vector control. DDT is applied to the inside walls of homes to kill or repel mosquitoes. This intervention, called indoor residual spraying (IRS), greatly reduces environmental damage. It also reduces the incidence of DDT resistance.
DDT (dichlorodiphenyltrichloroethane)


Saturday, February 7, 2015

Chlorofluorooctane sulfanate (ClFOS or Cl-PFOS) : metabolites or by-product during the production of perfluorooctane sulfanate?

Researchers from the National Research Centre for Environmental Toxicology of Australia used liquid chromatography quadrupole time-of-flight tandem mass spectrometry found some novel fluorinated surfactants in firefighters. The study was published this week at Environmental Science and Technology.

One of the novel chemicals is chlorofluorooctane sulfanate (ClFOS or Cl-PFOS), or one F atom in PFOS get replaced with Cl.

One hypothesis for the origin of Cl-PFOS is due to metabolism of PFOS-related compounds in human body.

On the other hand,  I think it is plausible that the novel chlorofluorooctane sulfanate is a by-product during the production of PFOS.  Check the analysis of chemical reactions during the production of PFOS: