Science Makes Sense-Week 27: Esters, pheromones, artifical flavorings.

March 7, 2016

I remember that corner store near our house in New Delhi, India. There was a glass bottle with colored sweets: the one shaped like an orange tasted like an orange, the one looking like a banana tasted almost like eating a banana. I loved staring at those candies and once in a while my mother would relent and get me some!
Years later I learnt about artificial flavorings and how fast-food companies spend millions on researching different chemicals to enhance flavor and entice us all to buy them. Those candies in that shop were just sugar, water and artificial flavoring.
Most of the chemicals that enhance flavor are esters. An ester is nothing more than an organic molecule created by a reaction between an alcohol and an organic acid of general formula RCOOR’. Just like in inorganic chemistry when an acid reacts with a base you get a salt and water, when an organic acid, say like acetic acid reacts with an alcohol like methyl alcohol you get methyl acetate and water. The methyl acetate, or correctly called methyl ethanoate,(Ref.1) is the ester, akin to the ‘salt’ in the field of inorganic chemistry. The IUPAC name for acetic acid is ethanoic acid so the ester is methyl ethanoate. Of course the methyl part comes from the alcohol. Low molecular weight esters are soluble in water, but as the molecular weight becomes bigger, as in the case of fats, they are insoluble in water.
(Ref.2))
There are many common esters that are used for artificial flavoring, but methyl ethanoate is not one of them. Even though it has a fruity odor, it is a colorless solvent, used in lacquers and paint thinners and in pharmaceuticals.(Ref.3) The common esters that are used for artificial flavoring include the following. I am not using the IUPAC names, but the familiar names:

Ester Flavor
Ethyl formate Rum
N-amyl acetate Pears, bananas
N-octyl acetate Oranges
Methyl butrate Apples
Ethyl butrate Pineapples
N-amyl butrate Apricots
Methyl salicylate Oil of wintergreen
Linalyl acetate Lavender, sage(Ref.4)

The food industry is so beholden to esters and strange, unknown flavors are being discovered by playing around creating new esters. Our attraction and desire to eat inexpensive fast-food is enhanced by the flavors they have and some food chemists are focused in the world of esters.
Some esters may be found in pheromones. What are pheromones? They are chemicals that could be released by insects, bacteria or animals to elicit a response from another of its species. It is a means of communication and the response could be territorial,cooperative or sexual in nature.(Ref.5) Amyl acetate, an ester that can mimic the flavor of bananas or pears is also produced as an alarm pheromone in honeybees.(Ref.6)
Esters are also big in the polymer industry. A few weeks back we looked at polymers and polyester, the fabric that does not need to be ironed is here to stay. This is a polymer of an ester. Dacron, another material used to make clothing is made from esters.(Ref.6)
When some esters have the element nitrogen, they form explosives, while phospho-esters are the building blocks for DNA. Some large chain esters are also fats.
Truly esters play a significant role in our lives from creating flavor to causing love!(Ref.6)
Activities for Middle School Teachers
Using model kits for making organic molecules, create simple ester structures starting with acids like formic acid and different molecules of alcohols like methyl, ethyl, propyl alcohols. Introduce isomers wherever possible. How many isomers can you obtain with ROH (general formula of an alcohol) where R is a carbon chain from 1 to 10? How many esters have different flavors when formic acid is replaced by, say, acetic or higher carbon chain acids?
Take a field trip to the supermarket and focus on processed foods. How many of these foods contain flavorings, etc in their ingredients? How many can the students recognize as esters? Look at the perfume/ cosmetics section as well for esters.
Learn the difference between natural and synthetic perfumes. There are perfumes like oil of sandalwood using sandalwood obtained from sandalwood trees in South India; at the same time there are many perfumes synthesized in the laboratory by reacting an organic acid with an alcohol.
Nuggets of Information
Pineapple flavoring contains 20 ingredients that cause that flavor along with ethyl butrate, an ester.(Ref.7)
More about pheromones and esters:(Z)-6-dodecen-4-olide, a circular(12-carbon with a double bond) ester, is associated with the black-tailed deer and is called a “social scent”. Circular esters (called lactones) are also found in the oily poisonous secretion of termites..(Ref.7)
Actually making an ester is not as easy as making a salt. You need a catalyst like sulfuric acid to complete the reaction.(Ref.8) Sometimes, even with the catalyst, the products formed may be 70%. In order to make it 100%, it is advisable to keep removing the other product formed which is water.(Ref.9)
It is interesting to note that while esters are fragrant and responsible for many flavors, the alcohols and carboxylic acids that are the starting components may not be so desirable. For example, methyl butrate gives apples that familiar taste, but methanol is poisonous, and butyric acid has a smell that gives rancid butter its odor – just goes to show how a chemical reaction can effectively change chemical properties! (Ref.4)
Many natural flavors are quite complex. For example, when you are eating a chocolate cake made with real chocolate or eating a sweet flavored with hazel nuts, your sense of smell and taste are hit by several chemicals that combine to produce that amazing, almost sensual feeling inside you as you slowly savor and relish the food! In the case of fruity odors, this can be replicated somewhat using some esters. The trick is in the exact amounts added to not overwhelm but suggest those smells and taste. (Taste and smell are closely linked; when you have a cold, nothing tastes good.) Also remember that for the smell it is important that the ester is volatile so the molecules can enter your olfactory organs.(Ref.10)
Most perfumes produced in the laboratory use esters of low molecular weight.
References:
1.http://www.ivyroses.com/Chemistry/Organic/Naming-Esters.php
2.http://chemguide.co.uk/organicprops/esters/background.html
3.http://nj.gov/health/eoh/rtkweb/documents/fs/1217.pdf
4.http://wiki.chemprime.chemeddl.org/index.php/Esters_in_Foods
5.http://www.pheromoneauthority.com/articles/how-do-pheromones-work/
6.http://www.oilsandplants.com/esters.html
7.http://orgchemistrylife.blogspot.com/2014/03/ester.html
8.http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gateway/carbon_chemistry/smellsrev1.shtml
9.http://www.chem.umass.edu/~samal/269/ester.pdf
10.http://science.howstuffworks.com/question391.htm

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Science Makes Sense-Week 26: Iron and Steel, alloys.

February 28, 2016

My mother who was born in the early part of the 20th century, was innovative and forward-thinking in many ways. She was the first among her sisters to discard bronze and lead vessels for cooking and start using stainless steel containers on a regular basis. The kitchen used to sparkle with those bright silver-like containers gleaming in the sunshine! I must say my mother loved those new vessels for cooking and storing food. We called them ever-silver, small wonder.
As we already know, iron is a transition metal and we have studied a lot of the characteristics of iron earlier. We cannot forget about the alloys of iron that include the different forms of steel which have revolutionized our lives both in the kitchen and outside. An alloy is basically a mixture of one or more elements added to the main element and melted together. The added metal or metals arrange themselves in between the rows of the main metal.
Stainless steel is an alloy of iron and mainly chromium. Iron alone is prone to oxidation and forms the reddish-brown iron oxide , familiarly known as ‘rust’. When carbon is added, you get stronger iron to use industrially as well as to make cast iron pots and pans. Stainless steel is corrosion resistant and the chromium added gives it a shine.(Ref.1)
Pure iron, like most metals is not particularly strong; the atoms of iron are too free to move around. The addition of other elements allows some of the atoms of iron to be pinned down, but too much addition might make the iron too brittle, too rigid. The trick is to add just the right amount to create a stronger metal. (Ref.2)
The fascinating fact is that this knowledge of forming mixtures with other metals, called alloys has been known to mankind for the longest time. One of the earliest steels made was by Indian metalworkers and it was called ‘wootz”(Ref.2) However, these alloys were made in small quantities and only in the 18th century did we perfect the art of creating alloys on a larger scale.(Ref.2)
Wrought iron was first made in the 18th century using a method called “puddling”: this involved the heating of iron ore and refined iron until impurities like Sulfur, S, and silicon, Si, formed a slag with Oxygen, O. (Wrought iron is a black metal that is used for railings.) After removal of most of the slag by hand, the temperature was raised to let the carbon react with the oxygen and burn. The remaining slag sits among the pure grains of iron to form a material that is stronger and more flexible than the original iron. (Ref.2)
Here are some improvements in the manufacture of alloys of iron in the 20th and 21st centuries:
Basic oxygen process (BOP): The steel is made in a giant egg-shaped container, open at the top, called a basic oxygen furnace. This is like an ordinary blast furnace, only it can rotate to one side to pour off the finished metal. The air draft used in a blast furnace is replaced with an injection of pure oxygen through a pipe called a lance. This furnace is based on the Bessemer process developed by Sir Henry Bessemer in the 1850s. (Ref.3)
Open-hearth process (also called the regenerative open hearth): Reminds one of a giant fireplace in which pig iron, scrap steel, and iron ore are burned with limestone (calcium carbonate) until they fuse together. More pig iron is added, the unwanted carbon combines with oxygen to form the slag that is removed and the iron turns to molten steel. The steel is sampled and the process is continued until the iron has the right carbon content to make the type of steel needed.
Electric-furnace process: The electric furnace, uses electric arcs (effectively giant sparks) to melt pig iron or scrap steel. Since they’re much more controllable, electric furnaces are generally used to make higher-specification alloy, carbon, and tool steels. (Ref.3)
The alloys of iron have become an essential part of our lives; we are beholden to this element,iron for thousands of years. In fact, there is more to talk about this interesting ‘d’ shell element, especially about its magnetic properties. Next time we will delve into this very exciting property of iron.
Activities for Middle School Teachers
Let students compare and contrast the periods of the Bronze Age and the Iron Age. What were the tools created out of bronze and iron mainly used for? What was happening in the world at that period? Consult with Social Studies teachers for this activity.
Nuggets of Information:
The word ‘iron’ comes from a word that means ‘metal from the sky’. Early iron was extracted mostly from meteorites.(Ref.1)
“Puddling” was very popular in the 18th and 19th centuries; one of the famous wrought iron structures built during this period is the Eiffel Tower in Paris, France. (Ref.2)
“Pig iron” is„ raw iron, the immediate product of smelting(a metallurgical process by which any metal is extracted from its ore and heated it to a high enough temperature to melt it(Ref.4)) iron ore with carbon(coke) and calcium carbonate(limestone). It has a high carbon content, around 4-5% and makes it very brittle. (Ref.5)
There are basically two kinds of alloys formed when metals are combined together at high temperatures. Sometimes, the size of the guest metal atom is almost the same as that of the host metal atom and these atoms take the place of the host atom. These alloys are called substitutional alloys like brass where zinc atoms substitute for some copper atoms in the lattice structures.
Then there are interstitial alloys like steel alloys where the manganese, chromium or carbon atoms place themselves in between the spaces around the host atoms, which in this case are iron atoms.(Ref.6)
Carbon steel with the lowest carbon content is typically called wrought iron. The metal is hard, but not brittle and is used for fences, chain links, gates and railings. The low carbon content allows this alloy to be worked into different shapes. The most commonly used carbon steel has a medium carbon content; uses of carbon steel in this category include structural steel to build buildings and bridges. It is also used for making automobile parts and in shipbuilding. High-carbon steel is hard but brittle and less easily worked. This type of carbon steel is used to create springs and high-strength wires. The increased hardness makes this category of steel ideal for cutting tools, punches, dies and industrial knives.
Finally, carbon steel with ultra-high carbon content is commonly referred to as cast iron. This type of cast iron is very hard but highly brittle. It has little to no malleability and cannot be easily welded or tooled. Often, it is used for cast iron pots, hot water radiators and certain types of lamp posts. Industrially, this steel is used for castings.(Ref.7)

References:
1.http://www.chemistryexplained.com/St-Te/Steel.html
2.Trefill, James, A Scientist in the City, p.38 (Doubleday,1994)
3.http://www.explainthatstuff.com/ironsteel.html
4.http://www.thefreedictionary.com/Smelting
5.http://chem.tamu.edu/class/majors/chem470/Steel.pdf
6.http://www.scienceiscool.org/solids/metallic.html
7.http://www.wisegeek.com/what-are-the-uses-of-carbon-steel.htm

Science Makes Sense-Week 25: Lead and Tin

February 22, 2016

The recently revealed shocking story of lead-poisoned water for the residents of Flint, Michigan for almost a year (Refs.1,2) brought back memories of lead paint poisoning of children living in poor, older inner city neighborhoods.(Ref.3) The tragedy is that this old story of lead paint has resurfaced in many African-American communities in Chicago once again.(Ref.4) Both situations could have been avoided since there is ample evidence to point out that even low level continuous ingestion of lead causes damage in hearing, learning abilities and coordination.(Ref.5)
Why has lead been used from the time of the Greek-Roman civilizations in spite of knowledge regarding its toxicity?(See Nuggets) This is because lead has a high corrosion resistance, it is soft, easy to work with and has a low melting point.(Ref.6) Furthermore, it has been durable for many uses, especially till recent times for lead-based paints and lead pipes.(Ref.5)
The word ‘plumbing’ derived from ‘Plumbum’, gave rise to the chemical symbol Pb for lead since lead was used a lot in the field of plumbing.(Ref.3)
This shiny blue-white soft metal,lead, when exposed to the air containing oxygen and carbon dioxide, becomes coated with a dull grey layer of basic carbonate that adheres to the surface and protects it from further change. A similar kind of protection takes place in the presence of sulfuric acid: it forms a layer of lead sulfate. Because of this property, lead is often used to sheathe cables, to carry tanks of sulfuric acid and to protect roofs from the atmosphere.(Ref.6)
In recent times, it is mainly used in lead-acid storage batteries.
The electron configuration of Pb is 6s2 6p2 which means there are 2 electrons each in the 6s and 6p level respectively. Lead exhibits the oxidation state +2, when it loses the ‘p’ electrons and is generally basic. However, the oxidation state +4 also exists and in it, lead is more acidic. This property where a metal exhibits both acidic and basic characteristics like another metal, aluminium, Al, is called amphoterism. Tin also exhibits this behavior in the +4 oxidation state.(Ref.6)
Lead exists as many oxides, carbonate and chromate and shows brilliant colors that were useful for paint pigments till the 20th century when the toxic nature of ingested lead was documented. The reason it was used for so long is because no one imagined that lead paints would be ingested till there was evidence to show that children were licking lead paint off frames in old homes.
The other area where lead was used extensively was in motor fuel as an anti-knock agent called tetraethyl lead. The addition of lead to the fuel reduced engine knock and so was used for years. Here the lead replaced the carbon in methane and each of the hydrogen atoms was replaced by an ethyl group, fooling the motor fuels into letting it dissolve. In the cylinder, the heat would knock the ethyl radicals off and form a cloud of PbO, lead oxide. The ethyl radicals stopped any explosions and let the fuel charge not detonate and burn smoothly. This permitted the use of less expensive straight-chain hydrocarbons as fuel versus the more expensive branched and aromatic hydrocarbons of higher octane rating.(Higher octane rating improves engine efficiency.) The lead in the air was found to be especially harmful for younger children and so leaded fuel was finally discontinued. It is important to note that most adults working with lead are not unduly affected by it, unless ingested continuously. Its widespread use in paints and in fuels made it dangerous, since children and growing young adults are particularly vulnerable to it; yet lead is not as toxic as mercury.(Ref.6)
Tin is another metal similar to lead in some of its properties, and in the same Group in the Periodic Table. Known with the chemical symbol Sn, today we mainly think it is used with other metals in alloys as well as coating other metals.
Known from the Bronze Age where tin and copper formed the very useful alloy bronze, tin like lead has an ancient history. Just like lead it has a low melting point, but its boiling point is very high. This large range where it is a solid helps in forming alloys without loss in vaporization. (Ref.7)
Tin also exists in two oxidation states having the same outermost electronic configuration like lead. This leads to its amphoteric behavior just like lead. Tin forms chlorides and stannous chloride is a reducing agent. Metallic tin is safe and is not toxic when ingested like lead. (Ref.7)
Organo-tin compounds were used as a biocide, but because of their toxicity, these compounds have been phased out. (Ref.8)
Tin and lead have much in common, both known from ancient times, both are amphoteric, low melting point solids. Lead has been less expensive and even though many of its uses have been phased out, it is still useful in certain specific areas. Tin though is coming back to be used more often than before. (See Nuggets) These two metals cannot be dismissed that easily!
Activities for Middle School Teachers:
What are the other metals in this group besides tin and lead? What are their properties and uses? How are they similar and different in their properties and uses?
Lead is toxic when ingested; what about mercury? Compare and contrast how both lead and mercury are being used in different ways today compared to earlier because of their toxicity.
Nuggets of Information:
The Roman architect, Vitruvius Pollio during the first century BC recognized the dangers of using lead.(Ref.3)
In the mid 19th century lead poisoning was called’painter’s colic’.(Ref.3)
The slightly sweet taste of lead made it a good additive in Roman wine and there is a belief that this use of lead could have been one of the causes for the fall of the Roman Empire.(Ref.3)
The relative higher density of lead, compared to copper and iron, has made it suitable in the manufacture of bullets and sinkers.(Ref.6)
Even though many European countries banned the use of interior lead paints in 1909, the US waited till 1971 to do so.(Ref.3)
Tin was also called white lead, being a soft white metal.(Ref.7)
Tin exists in three allotropic forms:Below 18 degrees C, it exists as alpha tin or grey tin with a diamond structure (like carbon, silicon and germanium)and is a semiconductor. From 18 to 161 degrees C, the stable form is beta-tin or white tin with a slightly higher density and a tetragonal crystal structure. Above 161 degrees C to the melting point is gamma-tin with about the same density but rhombic crystal form. When beta-tin is bent it emits a sound called “tin cry’ from the shearing movement between the crystal grains.(Ref.7)
Apart from being used most often in the alloy, bronze, tin is also used in several other alloy forms like pewter(tin and lead), a superconducting wire alloy of tin and niobium,and Babbitt metal which is a combination of tin,copper and antimony. The superconducting wires are used in the manufacture of very powerful magnets and Babbitt metal is used for bearings. Tin plating which is a coating of tin over steel is still used for canned goods and to prevent corrosion (Refs.8,9)
The biggest use of tin is for soldering especially electrical circuits. Molten glass used in windows is floated on tin to get a flat surface; stannous flouride is used in toothpaste and organo-tin products are needed to stabilize PVC plastics.
(Ref.9)
Indonesia and China are the largest producers of tin.(Ref9)

Chicago Tonight, April 2016, had a story about the presence of lead in service lines that could leach and enter homes and become a crisis like the Flint, Michigan water situation.(Ref.10)

References:

1.http://www.theguardian.com/us-news/2016/feb/17/flint-water-crisis-michigan-contaminated-water-bills-food-water-watch-study
2.http://www.democracynow.org/2016/2/17/thirsty_for_democracy_the_poisoning_of_an
3.http://www.toxipedia.org/display/toxipedia/History+of+Lead+Use
4.http://www.chicagotribune.com/news/watchdog/ct-lead-poisoning-chicago-met-20150501-story.html
5.http://www.dhr.virginia.gov/pdf_files/LeadPaint1.PDF
6.http://mysite.du.edu/~jcalvert/phys/lead.htm
7.http://mysite.du.edu/~jcalvert/phys/tin.htm
8.http://humantouchofchemistry.com/history-of-tin.htm
9.http://wanttoknowit.com/uses-of-tin/
10.http://chicagotonight.wttw.com/2016/02/18/chicago-s-lead-pipes-what-you-need-know

Science Makes Sense-Week 24:Chemistry and Social Justice, plastics in the environment.

February 14, 2016

Several years ago, I used to travel by train in India regularly. When we stopped at a station, we would buy tea from vendors who would serve it in little clay pots that we could throw out of the window and watch it break. Now when I come to India and drink tea, there are no clay pots that are biodegradable, only plastic cups that litter the trash and get into water bodies. Milk no longer comes in glass bottles but in plastic bags. Take-out food is no longer given in leaves stitched together and wrapped up with string; it is now given in little plastic bags! In the U.S., the amount of plastic in packaging in addition to replacing glass with plastic everywhere has led to huge amounts of plastic trash getting into lakes, seas and oceans.
We already know that plastic has been man-made using polymers of different monomers to arrive at the varieties of plastic discussed last week. We will look at how humans and other animals are affected by plastic.
Residual Monomer:
Formation of long polymer chains is never perfectly stoichiometric and can be a random process. This can lead to unreacted monomers. Some monomers like formaldehyde, styrene(from take-out containers),vinyl chloride(from PVC),and bis-phenolA(from polycarbonates) are known carcinogens.(Ref.1)
Plasticizers:
Plasticizers are added to polymers to render them more flexible. Many take up space in between the polymer chain and some are small enough to diffuse and cause health problems.(Ref.1)
Endocrine disrupters:
Many of the monomers have been found to be physiologically active. This is because they mimic the action of hormones or other signaling molecules. This is done by probably fitting and binding on to the specialized receptor sites in tissues. The health effects on adults is still not clear,but there is definite concern of its effects on fetuses.(Ref.1)
Decomposition problems:
Most polymers are not biodegradable, particularly in the anaerobic (absence of free oxygen) conditions of landfills. However, decomposition products here could combine with rainwater and contaminate nearby streams and water supplies.
Plastics with fluorochlorcarbons break down into perfluoro octane which damages aquatic animals.(Ref.1)
Effects on living beings:
Perhaps the most devastating effects has been on animals and birds and sea life. Since we know that most of the plastic trash gets into the water bodies, all life on water and near the shore are adversely affected by plastic. Animals and birds consume the plastic as food and die. Many big fish get entangled in big plastic sheets in the sea and get choked. Add to that the health hazards that animals face just like humans.(Ref.1)
Recycling is one solution, but the United States is dragging its feet to get some federal legislation passed to make it a national movement. Most countries in Europe have a viable recycling plan having bins in the neighborhood for all kinds of plastic packaging to be recycled.
When glass was replaced by plastic most of us were relieved at the light, non-brittle nature of plastic, the convenience of using trash bags that did not leak and the lunches that were so neatly packed in little plastic bags. Little did we worry about how it would impact us and other life forms around us. Today, in developing countries like India, plastic trash is everywhere, choking roadsides and canals of water. In countries like the U.S., though plastic trash is not so visible, its adverse effect on human and animal life is a daily reminder that more should be done to look for alternatives. Meanwhile, let us start cleaning up the mess created by this polymer invasion.

Activities for Middle School Teachers:
Let students go to a supermarket and list the number of products where plastic is used. Are all plastic containers the same? How are they classified? What is recyclable? (Look at Nuggets of Information also for some help)
Students should look at their own neighborhoods to see if plastic trash is around. How about in local water bodies?
Take the students to recycling centers and find out how and which kinds of plastic are recycled. Attend special green festivals where plastic is reused in innovative ways.
Teachers and Students! Do you travel for vacations to beaches in, say, Mexico, Thailand, India? When you stay at hotels/ resorts find out what happens to all the plastic trash used by tourists. Are there viable recycling programs in these countries? How are we as US tourists impacting world use of plastic? What are our ethical responsibilities?
Encourage yourself and students to use cloth bags when shopping anywhere; avoid plastic bags as much as possible. Recycle plastic bags at suitable supermarkets. Use glass instead of plastic to store food and spices.

Nuggets of Information:
Each year 8 million tons/16.6 billion pounds/7.2 billion kilograms of plastic enters the ocean. Each day two Empire Buildings (New York)full of plastic washes into the ocean. A 21-year old Dutch scientist named Boyan Slat is getting ready to clean the Pacific Ocean of its plastic trash. (Ref.2)
In India,you are charged for using plastic bags in several places where you shop.
PDFA, a monomer from which Teflon is made, was the subject of a 2004 lawsuit against DuPont when ground water was contaminated. (Ref.1)
Bis phenol A, commonly known as BPA, (actually two benzene rings with hydroxyl groups connected by a hydrocarbon link) has been found mainly in certain kinds of plastics used to make water bottles, baby bottles, sealants, medical devices and sports equipment to name a few. This kind of plastic has been shown to be endocrine- disruptors; babies and young children are especially vulnerable to this health hazard. (Ref.3)
The European Union(EU) has a far better record at recycling plastic than the United States(US);EU recycles 25%, while the US recycles only 10%.(Ref.4)
There are seven different codes for plastic found as a number and some letters at the bottom of plastic containers:
1. Coded number 1 is polyethylene terphthalate or PET/PETE. This high-impact plastic is used for beverage bottles, food jars and frozen food trays. Recycled PET is reused as bottles, as well as fleece jackets, to name a few uses.
2. Plastic code 2 is made out of high density polyethylene or HDPE which is used in milk/juice/detergent/bleach/cosmetic bottles and is recycled into garden products and buckets.
3.Code 3 is PVC-polyvinyl chloride and is used for bedding, medical equipment, pipes, etc. Recycled it is used as decking, carpet backing and for traffic cones.
4.Code number 4 is used for low density polyethylene, LDPE and is used a lot for garbage bags,bread bags and for squeeze bottles. Recycled it is used for shipping envelopes, garbage can liners, etc.
5.Number 5 plastics is made from polypropylene, or PP for yogurt, margarine, syrup containers as well as medicine bottle and auto parts. It is recycled to make garden rakes, storage bins, brooms and brushes.
6.Polystyrene or PS is coded number 6. These are short shelf-life products like take-out containers, cutlery and packing peanuts for example. This is recycled into insulation, licence plate frames and plastic moldings.
7.Code 7 is layered resins and composite materials that are very difficult to recycle and used for baking bags, ketchup bottles. It also contains BPA that is toxic: number 7 is to be avoided at all costs.
(Ref. 5)
Japan has been most successful in recycling plastics. In 2010, Japan recycled 77% of its plastic waste. Japan recycles 72% of PET bottles, while Europe recycles 48% and US is a dismal third with 29% of PET bottles recycled. (Ref.6)
‘Micro beads’ is the latest scourge in plastic contamination. This is being used mainly by the cosmetic industry and touted as a great face cleanser, but these little plastic pieces are entering our water bodies and contaminating and killing aquatic life in our seas and oceans.(Ref.7)
The latest news from January of 2016 from Germany is that several dead sperm whales washed up on the shores in Germany and a lot of plastic was found in their stomachs.
(Ref.8)

References:
1.chem.com/acad/webtext/states/polymers.html
2.http://environment.about.com/od/earthtalkcolumns/a/recycleplastics.htm
3.http://www.medicalnewstoday.com/articles/221205.php
4.http://www.plastemart.com/upload/Literature/Recycling-of-plastic-packaging-in-Europe-is-ahead-of-USA.asp
5.http://homeguides.sfgate.com/recycle-number-mean-plastic-container-79186.html
6.http://www.theguardian.com/environment/2011/dec/29/japan-leads-field-plastic-recycling
7.http://www.theguardian.com/sustainable-business/microbeads-cosmetics-gyres-plastics-pollution-makeup
8.http://www.bing.com/news/search?q=Plastics+And+Sperm+Whales&qpvt=plastics+and+sperm+whales&FORM=EWRE

Science Makes Sense- Week 23: Polymers, plastics.

February 2, 2016

What did ‘Soul Train’ and ‘ The Brady Bunch’ have in common? All the participants/actors wore polyester pants and shirts that were very popular then! The polyester came in bright shades and stayed the rage for some time in the U.S. But in India, polyester saris are available even today and is the preferred choice especially for working class women since they do not have to iron or starch their clothes every time they wear them.
Polyester is a polymer, an organic molecule made of many repeating units. A polymer can be three, two or one-dimensional. Each repeating unit is the ‘mer’ or basic unit, while ‘poly’ means the repeating unit. The units are often made of carbon,hydrogen (organic compounds) and also oxygen, sulfur, some halogens, nitrogen or silicone.(Ref. 1).
Wool, cotton, silk, wood and leather are examples of natural polymers used from ancient times. This includes bio-polymers such as proteins and carbohydrates:constituents of all living matter. Synthetic polymers (which we shall mostly look at today) generally known as plastics, became significant in the 20th century. Chemists were able to engineer them to yield different properties including strength, stiffness and heat resistance. Plastics have totally changed our way of life today.(Ref.2)
Week 7 we looked at alkenes and the first alkene was ethene or more commonly known as ethylene. This ethylene monomer combines with several ethylene molecules to form polyethylene or polythene which is what plastic bags are made of. (Ref.2) Vinyl chloride is mono-chloro-ethene where one of the hydrogen atoms is replaced by a chlorine atom. This monomer forms a polymer called Poly Vinyl Chloride which is so essential in making PVC pipes.(Ref.2)
Polyester is nothing but a polymer of an ester.(Ref.3) An ester and water are formed when an organic acid reacts with an alcohol; the reaction is similar to an inorganic acid reacting with an inorganic base to form salt and water.)
Polymers are mixtures because their molecular weights cover a range of values. Shapes of these polymer molecules are not straight chains of substituted carbon atoms. Free rotation around the C-C bonds allow long polymer molecules to curl up and tangle like spaghetti. With all these entanglements, there are regions in the polymer that could be crystalline and some that are amorphous (non-crystalline). Shorter chain lengths, less branching could lead to ordered layers; hydrogen bonding between adjacent layers also helps. (Ref.2)
We have discussed only a few polymers here, more will be mentioned under “Nuggets of Information”. Polymers have definitely revolutionized our lives in the 20th and 21st centuries. We have replaced metal and animal/plant product usage more and more with polymers. However, Week 24 we will be discussing the important question: ” Are plastics/ polymers a boon or a bane for society?”

Activities for Middle School Teachers
Let students make models of different kinds of polymers using paper clips or toothpicks with marshmallows as the monomer. Make straight chain or branched chains, even connect them at different points. Also have two or three different sized marshmallows to indicate a polymer consisting of more than one single monomer.
The students could carry out an experiment to create polymerization in the laboratory. Using Elmer’s Glue and sodium borate solution, create a plastic. Study its properties.(Ref.4)
Also study isomerism, number of isomers possible, depending on the chain length of a constructed polymer using the models indicated above.

Nuggets of Information:
The first synthetic polymer was made in 1869 as a substitute for ivory. Billiard balls had been made by ivory till then and the high demand had put a strain in obtaining it from hunting and slaughtering elephants. The problem was that it became unstable at higher temperatures. Polystyrene was the next important polymer from the 1920s used as a substitute for natural rubber as well as making toys; its one disadvantage was that it was brittle.(Ref.5)
One needs to remember that the billiard balls made not using ivory were really manufactured by modifying natural materials like cellulose and camphor. The first truly synthetic polymer was made when Bakelite was created using phenol and formaldehyde. It was invented to replace a scarce natural substance shellac that was used as an electric insulator. (Ref.6)
Thermoplastics and thermosets are two kinds of polymers. Thermoplastics are polymers that melt at a certain high enough temperature. These plastics can be injected into molds to form various shapes or extruded (drawn out) into sheets or fibers. Thermosets are polymers that are highly cross-linked, do not melt at all. It is far more complicated to form molds. Most polymers are thermoplastics, only 20% are thermosets.(Ref.2)
Thermoplastics can be further divided into homoplymers and heteropolymers. When the monomer units are the same, one forms a homo-polymer, but when the monomer units are different hetero-polymers or co-polymers are formed. Polyethylene is an example of a homo-polymer and nylon is an example of a hetero-polymer.(Ref.2)
Thermoplastic polymer structure can vary; one can have branched-chain or straight -chain homo-polymers/heteropolymers. The monomers could be joined end-to-end or cross-linked to form a harder material. If the cross links are fairly long and flexible, adjacent chains can move with respect to each other forming elastomers.(Ref.2)
In a linear polymer like polyethylene, rotations around the C-C bonds allows the chains to bend or curl up in different ways. But if one of the H atoms is replaced, say, by a halogen or a methyl group, the orientations of the monomers become significant. Now add the fact that there is a C=C bond, a double bond in the carbon chain, allowing diastereomers like cis and trans configurations. This small change can lead to profound effects in the properties of the polymer. Natural rubber is mostly cis-polyisoprene, while the trans form known as gutta percha latex has very different and inferior properties.(Ref.2)
Some objects exhibit the property of “handedness”, which means that object and mirror image are similar but not identical, like our left and right hands. This behavior is called chirality. Chiral molecules have two forms which are also called enantiomers. Polymers can exhibit chirality, depending on the arrangement of the differing groups attached. When the monomer units are aligned so that group A is attached on one side and group B is attached on the other side, the polymer is an isotactic polymer. When you have alternating groups A and B on either side it is called a syndiotactic polymer. However, when you have different groups to form the polymer, usually the placement of the two groups is random and it will be an atactic polymer. (Ref.7)
Finally, we look at 4 bio polymers:
1.Hydrocarbons/lipids, homopolymers with hydrocarbon monomer units
2.Polysaccharides,homo or hetero-polymers with sugar monomer units.
3.Proteins, hetero-polymers with amino acid monomer units
4.Polynucleotides,hetero-polymers with nucleotide monomer units. (Ref.8)

References:

1.plastics.americanchemistry.com
2.chem.com/acad/webtext/states/polymers.html
3.britannica.com/science/polyester
4.matse1.matse.illinois.edu
5.courses.sens.buffalo.edu
6.Freinkel,Susan Plastic: A Toxic Love Story(The Text Publishing Company,2011)
7.web.mit-edu/10.491-md/www/CourseNotes/Polymer/Chiral
8.brooklyn.cuny.edu/bc/ahp/SDPS/SD.PS.polymers.html

Science Makes Sense- Week 22:Transition elements, complex chemistry, d-orbitals, chelation

January 27, 2016

Have you noticed how chemists are usually depicted in magazines or advertisements? You will see serious-looking men or women in lab coats surrounded by brightly colored yellow, emerald-green or purple liquids in beakers or other containers. Nine times out of ten, most chemists pour and mix colorless, boring solutions and rarely do they create exciting-colored chemicals! The exception to this rule are those chemists who study complex chemistry and work with the transition elements.

The transition elements are the three rows or periods in the Periodic Table that are in the center between the alkaline earth metals on the left and the non- metals on the right. These are a bunch of almost 30 elements where in each row the ‘d’ shell containing ten electrons are being filled. (Ref. 1)

Most of the elements where the ‘d’ shells are being filled exhibit some interesting properties. They are metals (sometimes they are referred to as transition metals instead of transition elements), brightly colored, show different ratios in which they combine with other elements (which means they have different oxidation states) and some catalytic activity. They also combine in complex ways with metals and non-metals. (Ref. 2). In fact, the study of transition elements is a special branch of chemistry called complex chemistry. We will study why the filling up of the ‘d’ shells leads to these exceptional properties.

The definition of a transition metal is one which forms one or more stable ions which have incompletely filled ‘d’ orbitals. According to this definition, zinc, Zn, and scandium, Sc, are not really part of the transition metals, since their ions do not have any ‘d’ shell electrons.(Ref. 3)

Transition metals are good conductors of heat and electricity, less reactive than Group I alkali metals, but have high melting points, (exception is mercury,Hg, which is a liquid at room temperature), and high densities. (Ref. 4) They also form complex compounds, exhibit chelation, are good catalysts and as we already mentioned, form many colored compounds.

Let us look at four properties when we study these elements. Unlike most other metals, these transition metals do not just form simple ionic compounds like the alkali and alkaline metals. (Group I and II) Apart from the simple ionic compounds like nickel, copper, iron or cobalt chloride, they also form some complex/ coordination compounds. Many atoms or molecules called ligands, can attach themselves to these transition metals These ligands can be electron pair donor in a coordinate covalent bond. Common ligands are water, ammonia, carbon monoxide and anions (negatively charged ions) like cyanide ions, chloride ions and hydroxide ions. Sometimes these ligands are cations (positively charged ions) and electron acceptors. No wonder this branch of the study of transition metals is sometimes called complex chemistry. (Ref. 5)
Second, sometimes these ligands can be five identical carbon monoxide molecules that attach to iron, Fe, or six water ligands to nickel,Ni. These multi-dentate ligands attached to a central metal ion are called a chelating agent. ‘ Chelate’ means ‘crab-like’ and it feels like these five or six or however many ligands are like the pincers of a crab. These chelating agents have significant biological applications.(See nuggets)(Ref. 6)

 

 

image

Thirdly,transition metals are good catalysts. One of the reasons is that they can exist in a variety of oxidation states. This has the property of providing or withdrawing electrons from the intermediate stage of a reaction. For example, if a particular intermediate stage of a reaction is electron rich, the transition element could hold some of the electron density and facilitate the reaction. Or the transition metal might undergo oxidation- reduction reaction to achieve electron transfer to a substrate; this again allows the reaction to take place. In other words, a transition metal, existing in a variety of oxidation states and undergoing easy transitions between these oxidation states, can coordinate with a substrate, and also be a source or a sink for electrons, making it a good catalyst. (Ref. 7)

Finally, let us look at the reason for bright colors for transition metals. The colors of the transition metals are best described by the crystal field theory. Electrons in the d- orbital or shell are not at the same energy when there are molecules or ions attached to the metal ion. These molecules or ions are called ligands, as we already know. Ligands split the ‘d’ levels into two or more different energy levels. We see colors because the energy level differences in the ‘d’ levels is in the visible light range. When light strikes ions in solution, some of the energy with visible wavelength is absorbed by the electrons moving from a lower to a higher energy level. We see different colors because of a slight difference in energy levels that the ‘d’ levels split into. If the energy difference is greater, electrons will absorb light closer to the blue-violet end of the spectrum, and the solution will appear yellow. If the difference in the ‘d’ energy levels is less,the electrons absorb closer to the red end of the spectrum and the solution appears green; anywhere in between you will cover all the other colors. This explains why transition metals are colored. (Ref.8)

Activities for Middle School Teachers:
Before studying transition metals, students should be very familiar with the Periodic Table. They should also be able to express most elements using the electronic configuration, especially the filling up of ‘s’,’p’, and ‘d’ orbitals.
Students should understand that visible light is part of the electromagnetic spectrum and is a form of energy. They should also do research on how we perceive color in any object.
What is the role of a catalyst in any reaction? Do a comparison of enzymes and catalysts.

Nuggets of Information:
Ethylenediamine tetra acetic acid, EDTA, has 4 acetic acids,(tetra acetic acid) 2 nitrogens(diamine) on a 2 hydrocarbon chain.( Ref. 9). Chelates are biologically very signifiant. EDTA oral fluid is made up of several compounds containing transition metals and these are chelates used for curing many health issues. (Ref. 10)
Metal poisoning is treated using chelation therapy. Transition metals captures the toxic metals from the body, chelates them so that they are passed out of the excretion system of the body. (Ref. 10)
Most transition metals like iron, Fe, and chromium Cr, are key ingredients in automobiles, bridges, usually as alloys. One of the greatest applications is in cookware. They are also used in mercury thermometers, colored paints and photo reactive eye glasses. Titanium, Ti, is used to detect underwater sound, barium titanate is piezoelectric. (generates electric charge when slightly distorted)(Ref.11) Iron, Fe, along with cobalt, Co and Nickel, Ni, are magnetic and used for magnetic devices, cassette tapes, computer discs. Copper, Cu and cadmium, Cd, are used in photovoltaic cells. (Ref.11)
Human beings need two transition metals that are very essential: one is iron that is a complex compound in hemoglobin and cobalt as a complex compound in Vitamin B12.
Low iron leads to anemia and Vitamin B12 is crucial in the human diet. ( Ref.11)

REFERENCES:
1.chem-guide.blogspot.in(put in transition metals in search site)
2.chemistry-assignment.com (put in transition metals in search site)
3.hyperphysics.phy-Astro.gsu.edu
4.bbc.co.uk/schools/gcse….ansitionmetalsrev1.html
5.Britannica.com (put in ligand chemistry in search site)
6.sci-fun.chem.wisc.edu
7. madsci.org (ask the question ” why are transition metal compounds good catalysts?”)
8.answers.yahoo.com/question/index?qid=9.
9. articlesfactory.com (put EDTA in search site)
10. articlesfactory.com (put biologically significant chelates)
11.chem.uwec.edu/Chem115_F02/bat

Science Makes Sense,Week21 : The Halogens, refrigerants, toothpaste and disinfectants.

January 18, 2016

What does an older refrigerator, bleach,toothpaste and pesticides have in common?  All contain one or more halogens, the Group VII elements of the Periodic Table: fluorine, chlorine, bromine or iodine. (Astatine  is radioactive and does not behave like the other halogens.)  Today we shall study these very reactive elements, sitting so close to the most inert elements, the Noble Gases. (Ref. 1)

The word ‘ halogen’ comes from Greek, meaning ‘ salt-producing’.   The electronic configuration of all the halogens, indicate two electrons in the outermost ‘s’ shell and seven electrons in the ‘p’ shell.  This makes the halogens electrophilic and non-metals . They are ready to react with metals , which are nucleophilic. (Ref. 1)

The Halogens are diatomic molecules, i.e., they exist as two atoms sharing electrons – covalent bonding.  Astatine alone is not diatomic.  Intermolecular forces, Van der Waals forces, are very weak as one moves down the group.  This explains why the first two, F and Cl are gases.  As the forces weaken, the molecules get closer, bromine, Br is a liquid and iodine, I and astatine , At  are solids. (Ref. 2)  Since the halogens are very reactive, they are never found in the elemental form. (Ref. 1)

Flourine:

F is the most reactive of all the halogens and was a challenge to isolate it.  Even if scientists were able to get it in the elemental form, it reacted with the vessels in which it was synthesized. Finally, Henri Moisson ( 1852-1907) managed to isolate the element using electrolysis which is the process of passing an electric current to cause a chemical reaction.  Using a platinum-iridium alloy that is resistant to attack by fluorine as the electrodes, an electric current was passed through HF,which lead to the isolation of F at one of the electrodes. (Ref. 1)

Flourine is used as an oxidizing agent in rocket fuels. (Ref. 3)  As hydrogen flouride,HF, it is used to etch glass. (Ref. 1)

Chlorine:

Sir Humphrey Davy identified this gas as a greenish- yellow gas.  Chlorine, Cl, is produced by the electrolysis of brine (sodium chloride solution).  It is reactive, but not as reactive like F. (Ref.3)

The ionic compounds of Cl are used to make disinfectants for sewage, water and for pools.  The organo compounds of Cl are used to manufacture pesticides, herbicides and fungicides. (Ref. 3)

Bromine:

Bromine, Br, is a foul-smelling, reddish- brown liquid isolated in 1825 by Carl Lowing and Antoine Jerome.  It is found in deposits of brine in Israel’s Dead Sea and in the U.S. in Arkansas and Michigan. The vapors are highly irritating to the throat and eyes.  Bromine is used in dyes, pesticides,disinfectants and as a flame retardant.  One of the major uses of bromine is in the manufacture of halogen lamps.  These lamps are used as automobile headlights, floodlights, spot lights.  Tungsten is used in lamps and is considered better than carbon, since it is more durable than the latter.  However,the tungsten, W, begins to thin and break causing dimming of the light source.  But the addition of bromine or other halogens inside the bulb alleviates this problem. (Ref.1)

Iodine:

First isolated from seaweed in 1811, the word is derived from the Greek word ‘iodos’ meaning ‘ violet colored’. (Ref. 1,3)  Ultra-pure iodine, I, may be prepared adding potassium iodide to copper sulfate.  Though I as a halogen is a non- metal, it possesses characteristics of a metal sometimes.  Radioactive isotope I-131 is used to treat thyroid disorders.  Insufficient iodine leads to goiter. (Ref. 5)

Iodine was once used in photography; today it is used in chemical analyses and the synthesis of organic compounds. (Ref. 1)

Astatine:

No more than 44 mg of astatine, At, are found on the earth’s crust. It is one of the rare elements, and poorly researched.  No practical applications exist right now. (Ref. 3)

Activities for Middle School Teachers:

Students can study the chemical reactions involved in adding bleach to clothes.  Is the bleaching process an oxidation reaction or not? Please explain.

When you go down the halogen group, what makes flourine the most reactive halogen and iodine the least reactive?

Look at the different chloro-flouro carbons. Find out how many different stereo isomers there are.

Nuggets of Information:

The most characteristic feature of halogens is their distinct coloration: F is pale yellow, Cl is greenish- yellow, Br is orange to red- brown, I is dark violet and At is dark black. (Ref. 2)

Flourine reacts explosively with water and is the only element to react with Noble Gases. (Ref. 3)

Henri Moisson received the Nobel Prize in 1906 for isolating the element Flourine using electrolysis. (Ref. 1)

Teflon, which is a polymer continuing Flourine is used in non-stick cookware. (Ref. 1)

Flourine was initially added to water, to prevent tooth decay.  Now it is only added to toothpaste. (Ref.1)

‘Chloros’ in Greek indicates the color , greenish-yellow, and hence the name Chlorine, for the second halogen in the series.   Chlorine is among the top ten chemicals produced in the U.S. (Ref. 3)

Cl is a highly poisonous gas that was used in World War 1 as an agent of war (Ref. 1)

In early 19th century it was use as a disinfectant during a cholera epidemic in Europe. (Ref. 1)

The single greatest use of chlorine is in the preparation of a large variety of compounds including organo-chlorides that are the starting point of plastics like PVC, polyvinyl chloride, and neoprene, a synthetic form of rubber. (Ref. 3)

DDT which is an ogano-chloride containing two benzene rings and five chlorine atoms was used for many years as a strong pesticide. Rachel Carson, in her book written in the 60’s, called ‘ Silent Spring’ talked about the devastating environmental impact of such a pesticide and that resulted in a ban on the use of DDT in the U.S. (Ref. 4)

A series of compounds are formed by replacing the hydrogen atoms in methane by halogens. When three of the hydrogen atoms are replaced by chlorine atoms, you get the old anesthetic chloroform, or trichloromethane. When all four hydrogen atoms are replaced by chlorine atoms you get carbon tetrachloride/tetrachloro methane. This is a very common organic solvent and is also used as a refrigerant. (Ref. 3)

Chlorofluorocarbons, CFC’s, were used as refrigerants.  These are usually methane or ethane molecules where several of the hydrogen atoms are replaced by chlorine or fluorine atom/atoms.  They were given the general name Freon.  These CFC’s were found to deplete the ozone layer and were late banned. (Ref. 5)

At one time,ethylene dibromide was used by the petroleum industry as an additive to leaded gasoline. It reacted with lead to form lead bromide and cleaned out lead emissions.  In the late 70’s leaded gasoline was slowly phased out due to environmental concerns and ethylene bromide was not needed then. (Ref. 1)

Iodine, I, binds to starch and colors it deep blue; this is used as a test for iodine or starch. (Ref. 6)

Most isotopes of I are radio active, except I-127. (Ref. 6)

Solid I is blue-black and shiny, at ordinary temperatures and pressures it sublimates (converts from solid state directly to gaseous state) into a gas. (Ref. 6)

The thyroid gland uses I to make the hormones thyroxine and triodotyorine. (Ref. 6) Hormones are chemical messengers that direct cells what to do. (Ref. 7).  Insufficient iodine leads to goiter, swelling of the thyroid gland.

I deficiency is considered one of the leading causes of mental retardation. (Ref. 6)

image

References:

1.encyclopedia.com/topic/Halogen_elements.aspx

2. buzzle.com/articles/halogen- familyhtml

3. science clarified.com/Ga-He/Halogens.html

4. Carson, Rachel, Silent Spring (Houghton Miflin, 1962)

5. britannica.com/science/chloridifluoromethane

6.chemistry.about.com/od/elementfacts/a/iodine.htm

7.biology.about.com/od/molecular biology/ss/hormones.htm

 

 

Science Makes Sense: Week 20- Chemistry and Social Justice: agents of war, mustard gas, napalm, white phosphorus.

January 10, 2016

Anyone who grew up in the ’60s will never forget that horrific, poignant picture of a young Vietnamese girl running naked with her mouth open with fear. The U.S. Forces had just dropped napalm in that village where the girl lived.  That picture galvanized the anti -war movement and could have played a significant role in ending the senseless, Vietnam War.

Napalm was originally manufactured for World War 2 and was used initially as a flame thrower against German buildings . It was a mixture of naphthenic acid and palmitic acid and the name was derived from the first syllable of each acid. (Fig. 1)(Ref. 1)

By the time of the Vietnam War, napalm was made using a mixture of plastic polystyrene, benzene and gasoline.  It creates a jelly-like substance and when ignited,sticks to everything, burning up in ten minutes. (Ref. 2) (Fig.1)

The chemical reaction is quite simple. Gasoline alone can get ignited and burn/ oxidize, but the addition of benzene (inflammable material) and a plastic allows longer burning , sticking to the clothes and skin, and in addition, the carbon dioxide formed when any hydrocarbon burns, (see Week 8) is actually converted to carbon monoxide because of incomplete combustion.  This adds to lack of oxygen and death due to difficulty breathing.

Man has always looked for  chemical weapons during war.  Before World War 2, mustard gas was used in World War 1.  The structure is shown in Fig. 1; a four carbon hydrocarbon with sulfur, S, in the middle and two chlorine , Cl atoms, one at each end. (Ref. 3)

Mustard gas, is chemically known as 1,1, thio bis (2-chloro ethane).  ‘ Thio’ is for the sulfur and ‘bis’ implies 2 pieces of 2 carbon atoms, viz.,ethane each having a chlorine atom. (Fig. 1)

The chemical reaction steps of how mustard gas reacts on the human body is shown here:

Mustard gas converts due to nucleophilic attack of carbon by the sulfide to a sulfonium salt; this is attacked by water present as moisture in the human body to a hemi mustard and HCl, hydrochloride acid.  This is attacked by water to form a Thio- glycol plus HCl, and the final step has HCl once more as a by-product. Mustard gas and hemi- mustard are vesicants and the three molecules of HCl is also a strong skin irritant. (Ref. 4)

The next war weapon we will look at is White Phosphorus.  It is actually a polyatomic molecule, having four P atoms in a tetrahedral arrangement.  It is one of the three allotropes of Phosporus. (Week 17)(Fig. 1)

White Phosphorus has been used several times in war as a chemical weapon.  It is considered illegal to use this as a weapon of war. Originally, though, in World War 1, it was used as a smoke screen and for flares.  However, in the late 20th century and early 21st century, USA, Russia and Israel have been accused of illegal use. (Ref. 5)

White Phosphorus oxidizes in the presence of oxygen to form phosphorus pentoxide. (Week 17)  This oxide is extremely hygroscopic, which means it absorbs moisture very readily.  If it comes into contact with skin, it will definitely cause severe blisters. It is difficult to extinguish and keeps on burning as long as oxygen is present. (Ref. 5)  One can only imagine the horrible burns and death it can cause.

The ancient Mayas had a noble tradition, whereby they gave their enemies a decent burial. But the human race now with the use of chemical weapons like napalm,mustard gas and white phosphorus, to name only a few, are intent on bringing cruel and inhumane ways of attacking the enemy which many times includes innocent civilians.

Activities for Middle School Teachers:

Let students do a time line of chemical agents used in war.  What kinds of  such weapons were used besides vesicants and napalm?

Study how many of these chemical weapons contain chlorine.  How many contain sulfur?  What, if any is the most common element or group of elements found  in these chemical weapons?

Besides chemical weapons, there has been biological weapons used, let students make a list of these war agents as well.  How do they cause harm to humans?

Nuggets of Information: 

Dr. Louis F. Fieser created an aluminium soap mixed with naphthenic and palmitic acid.  The name napalm came from the first syllables of the two acids. This combined with gasoline, was a brutally effective weapon. (Fig. 1)(Ref. 1)

In World War 2, the German word “bombenbrandscrumpfeichen” was created in response to napalm bombing of German bunkers. Soldiers in the bunkers would be baked by the heat and the word means ” firebomb shrunken flesh”. (Ref. 1)

Kurt Vonegut’s book, Slaughterhouse Five, is about a controversial campaign where 35,000 to 135,000 German soldiers died due to napalm in World War 2. (Ref. 1)

During the Vietnam War, napalm (b) was formulated that caused even more terrible destruction of soldiers and civilians. (Ref.1)(Fig. 1)

That terrified little girl from the first paragraph, Kim Phuc, survived miraculously and is today a U.N.Goodwill Ambassador. (Ref.1)

But napalm may still have been used, despite protests and bans by the U.N., during the Persian Gulf War by U.S. forces. (Ref. 1)

Mustard gas is a vessicant, which means an agent that induces blistering. (Ref. 6)

Though this gas is always seen as a nasty poison, resulting in a slow, painful death and causes cancer, yet, ironically, it has also been used to treat cancer!  In 1919, after the first usage of mustard gas,it was noted that victims had a low blood cell count.  In 1946, nitrogen mustards (replace sulfur,S, by a nitrogen,N) reduced tumor growth in mice as well as humans.  Now nitrogen mustards have become a modern chemotherapy therapy treatment for lymph glands Hodgkin’s Disease. (Ref. 4)

White Phosphorus was also called Willie Peat during  World War 1. (Ref. 5)

image

  References:

1. science.howstuffworks.com (put in ‘napalm’ in search line)

2.  vietnamawbb.weebly.com

3.  pubchem.ncbi.nih.gov

4.mhchem.org/221/COTW/mustard_gas/mustard.htm

5.wisegeek.com (put in ‘ white phosphorus’ in search line)

6.medical-dictionary.thefreedictionary.com (put in ‘vesicant’ in search line)

 

 

 

Week 19: Science Makes Sense-Organic Chemistry-aldehydes, ketones

January 4, 2016

When my mother was young, the perfume that young women of her time would crave for was Chanel No. 5!  I remember my sister getting her first whiff of this exquisite perfume at a wealthy girlfriend’s house and raving about it.

Aldehydes played a quiet role in creating that popular perfume. (Ref. 1).     Today we shall study aldehydes and ketones and note their structure and everyday uses.

Let us start with the simplest aldehyde: commonly known as formaldehyde,but the IUPAC name is methanal.  Note the ‘al’ ending, whereas for alcohols, the ending is ‘ol’.  All aldehydes have H-C=O structure, so the first aldehyde is shown with an additional H or hydrogen atom.  The next aldehyde, ethanal or acetaldehyde has a methyl group instead of the H, or hydrogen atom. Fig. 1 has the first four in the series. (Ref. 2)

Ketones are very similar to aldehydes, but they do not have the H-C=O structure; only the C=O structure, or the carbonyl structure. The carbon atom could have two methyl groups and then could be more carbon atoms. Again, Fig.1 has the first four in the ketone series. (Ref. 2)

Since aldehydes have the hydrogen present, they are not as stable as ketones and can be oxidized.  Since ketones do not have that hydrogen atom, they are resistant to oxidation. (Ref. 3)

The carbonyl group,C=O,is characteristic of both aldehydes and ketones.      The oxygen atom is far more electronegative than the carbon atom and the presence of the extra bond (double bond) increases the pull of the electrons towards the O. The high polarity of this bond in aldehydes and ketones results in higher boiling points relative to comparative hydrocarbons. (Ref. 3)

Smaller molecules of aldehydes and ketones are soluble in water; they hydrogen bond with water molecules.  As chain length increases, the hydrocarbon ‘tails'(all hydrocarbon bits apart from the carbonyl group) of the molecule come in the way of hydrogen bonding. (Ref. 3)

Uses of aldehydes and ketones: Formaldehyde and acetaldehyde (methanal and ethanal) are used extensively in industry,resins.   Butyraldehyde or butanal,is used as a plasticizer.  Higher aldehydes are used as deodorants, favors and detergents. (Ref. 3)

Ketones are used mainly in pharmaceuticals,polymers, solvents. Ketones play a significant role in biochemistry. (Ref. 3)

So once again, organic compounds play a vital role in our daily lives.

Activities for Middle School Teachers:

Let students write straight and branched carbon groups for aldehydes and ketones for the first ten in the series.  How many isomers can you get? Are there any enantiomers, stereo- isomers? Name them all using the IUPAC nomenclature.

Nuggets of Information:

Many aldehydes are derived from the de- hydrogenation of corresponding alcohols, hence the name ‘ al-dehyde’.  (Ref. 4).  

Certain foods and flavors in our diet contain aldehydes.  Cinnamon, almonds and vanilla are examples of aldehydes cinnamaldehyde, benzaldehyde and vanillin respectively. (Ref. 5).   All these compounds have a benzene ring.

Aldehydes and ketones play an important role in the chemistry of carbohydrates.  A carbohydrate is literally a hydrate of carbon.  The sugars, glucose and fructose are carbohydrates.  Glucose is an aldehyde and fructose is a ketone. (Ref. 5)

When the body uses fat for energy,ketones are generated during fat metabolism.  The fat gets converted to A T P.  Ketones are produced as part of the process.  When people eat less carbohydrate,the bodies turn to fat for energy, naturally more ketones are generated then.  This is called ketosis. ( Ref.6)

Most cells use ketones for at least part of their energy. (Ref.6)

Ketones and aldehydes exhibit tautomerism: this is a special kind of isomerism, where the carbonyl group, C=O, converts to the hydroxyl group,OH group and a double bond.  This is called keto-enol tautomerism.  The u-tube illustrates it. (Ref. 7)image

References

1. perfume shrine.blogspit.in

2. chemguide.co.uk

3. livewebtutors.com

4. brittanica.com

5. chemed.chem.perdue.edu

6. lowcarbdiets.about.com

7.u-tube, keto-enol tautomerism, Khan Academy

 

Science Makes Sense, Week 18: Periodic Table, order

December 28, 2015

Organize, categorize, use colored stickers to mark differences.  This is how we arrange and try to understand differing groups in any subject we study. Chemistry is no different.  As soon as the definition of elements was laid out, chemists set about discovering new elements and placing them together initially based on melting points, density, and boiling point data. Today with knowledge about atomic mass, atomic number and the internal structure of an atom we have  a clear, concise way of classification called the Periodic Table.

The History of the Periodic Table is a fascinating study by itself in the field of chemistry.  Although elements like gold, silver, copper, tin, mercury, lead (Au, Ag, Cu, Sn, Hg,Pb) were known since the alchemists, the first official discovery of an element, phosphorus, P, took place in 1649 ( Week 17).  The next 200 years, 63 elements were discovered and could be classified. (Ref. 1)

Law of triads:  Initially, bunches of 3 elements were found to have similar properties.  For example,  the atomic weight of strontium,  was found to be between calcium and barium and similarly flourine, chlorine and bromine were found to be similar in properties.  So there was a theory floating about bunches of 3 elements with similar properties.  With the discovery of more elements in these bunches, one could see that the law of triads was a limited idea. (Ref. 1)

Using a special kind of cylinder, it was seen that every 16 elements showed similar properties.  This was one of the first attempts in the classification of elements. (Ref. 1)

Chancourtoisin in 1862 was the first to recognize that elemental properties recur every seven elements, but it was Dimitri Mendeleev, the Russian chemist who is credited with the first credible periodic table of 63 elements.  What was so remarkable was the fact that he was able to predict properties of elements that were in the gaps long before they were discovered, based on their possible position in the table. (Ref. 1)

The discovery of sub-atomic particles, the discovery of atomic numbers for elements in the 20th century, paved the way to organize the Periodic Table as it is today.  (Ref. 1) The presence of a certain amount of order in the electronic arrangement in different shells led to the arrangement of elements in groups of two, eight and eighteen.  The pattern of arrangement of these elements give us invaluable information; no wonder the Periodic Table is considered the backbone of Chemistry!

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Activities for Middle School Teachers:

Take a bunch of household items and categorize them like a periodic table. Justify your classifications!

During harvest season, let students bring pumpkins and carve the name of an element in each pumpkin to create a Periodic Table of pumpkins. Use other items, like leaves, pieces of different colored cloth, to do the same thing.

Do a research project on the different kinds of Periodic Tables created.

Nuggets of Information:

Each row of the Periodic Table is called a period and each column is called a Group.  For example, there are only two elements, Hydrogen,H and Helium, He, in the first period of the Periodic Table.  Elements in a group exhibit similar behavior: alkali metals, Lithium,Li, sodium, Na, potassium K, through Francium, Fr, (elements in blue) have similar properties. Again, the  Noble Gases in Group 8 ( Helium, He, Neon, Ne, Argon,Ar. etc) are inert and do not react with anything.  Elements in a Group have an identical outer shell electronic arrangement. (Ref.3)

Ninety elements in the Periodic Table occur in nature; the rest have been synthesized in the laboratory. (Ref.3)

Technitium was the first element to be made in the laboratory. (Ref.3)

The present Periodic Table has room for 118 elements. (Ref.3)

References:

1.https://www.wou.edu/las/physci/ch412/perhist.htm

2.http://fivejs.com/wp-content/uploads/2011/08/Periodic-Table-of-the-Elements-12pg.pdf

3.http://chemistry.about.com/od/periodictables/a/10-Periodic-Table-Facts.htm

 

https://www.wou.edu/las/physci/ch412/perhist.htmhttp://fivejs.com/wp-content/uploads/2011/08/Periodic-Table-of-the-Elements-12pg.pdf

https://www.wou.edu/las/physci/ch412/perhist.htmhttp://fivejs.com/wp-content/uploads/2011/08/Periodic-Table-of-the-Elements-12pg.pdf

https://www.wou.edu/las/physci/ch412/perhist.htmhttp://fivejs.com/wp-content/uploads/2011/08/Periodic-Table-of-the-Elements-12pg.pdf