Archive for March, 2016

Science Makes Sense- Week 30: Hydrogen, Helium, the very light gases

March 28, 2016

In the days of black and white photography, how can those who lived in the early part of the 20th century ever forget what happened on May 6th,1937? Today one can watch that video clip of the Hindenberg disaster that gripped the world then and is still quite dramatic and shocking to see now. The words of the reporter “Oh the humanity …..!” is something you cannot get out of your minds. This was a major tragedy that, if it had not occurred, would have changed the face of modern aviation completely.(Ref.1)
It was a chemistry blunder when hydrogen, a very inflammable gas was used to send the blimp with so many passengers up in the air. And it was not as if scientists did not know the easy burning of hydrogen. However, it was cheaper to use and had greater lift than Helium and was chosen since early test runs with the Hindenberg happened without any hitches.(Ref.2)
Hydrogen and Helium are both gases and are the only two elements on the first row of the Periodic Table. However, in spite of being gases, their properties could not be more different. Hydrogen,H, is the most abundant element in the universe, while Helium,He, is less than 0.0005%. H is very reactive and is hardly found as an element, whereas He is the first of the Noble inert gases and is not reactive.(Ref.3) The electronic structure gives us a hint; H is 1S1, whereas He is 1S2, which means the first s orbital is filled up and is a stable doublet.
Hydrogen is a colorless, odorless gas but is extremely reactive and forms myriads of compounds readily.
Let us delve into the differences of these two light gases.
Hydrogen is a gas and is the lightest element known. It is the only element with no neutrons and has 1 proton and 1 electron. However,it has two other isotopes, Deuterium that has a neutron and Tritium that has two neutrons. Hydrogen is not usually found in its elemental form on earth but is found as such in many planets especially Jupiter and is abundant in stars.(Ref.4)
Hydrogen has two oxidation states, +1 and -1. This makes it both an oxidizing and reducing agent. It is positively charged when reacting with halogens or oxygen and has a negative charge reacting with alkali metals.(Ref.4)
Helium, He, is also a colorless, odorless gas and has the second lowest atomic weight. Very little He is found in the earth’s atmosphere. Being such a light element, unconfined He immediately begins rising and escaping from the planet. However a lot of helium produced commercially is obtained from the ground. Some natural gas fields have enough helium mingled with the other gases to be extracted economically. Most of the helium recovered this way is thought to be formed as a result of radioactive decay of uranium and thorium found in granitoid rocks(See Activities for Middle School Teachers).(Ref.5)
Till World WarII, Helium was used in blimps, dirigibles, weather balloons or to fill balloons for parties and other festive occasions. Today it is used as a purging gas since it has the lowest melting and boiling point of any gas and is inert.(Ref.5) (A purging gas displaces other gases or liquids stored in tanks/containers.)
Since helium is an inert gas with low reactivity, high thermal conductivity and low density, it is an ideal gas to use in metallurgical processes, growing crystals in chemical vapors and manufacturing optical fibers, etc.(Ref.5)
Helium has very low atomic weight, high diffusion coefficient which means it escapes easily; hence it is used for leak detection. It is also used in breathing mixtures for deep water diving and medical procedures since it has a low viscosity and is easier to breathe under high pressure. A Helium atmosphere is good for welding processes since it does not react with the metals being welded.(Ref.5)
Hydrogen and Helium are both light gases; one electron and proton change causes such drastic differences in their properties and uses. One is present in almost everything but the other is hardly around us in the atmosphere. Yet both manage to play important roles in our lives.
Activities for Middle School Teachers:
Look at all the compounds in organic and inorganic chemistry that contain hydrogen. How many kinds of bonds are formed by a hydrogen atom? What classes of compounds in inorganic chemistry have to contain hydrogen? Are there compounds in organic chemistry that do not contain hydrogen? What is their number compared to those that do contain hydrogen?
Students can do a simple activity bringing everyday objects from home and figuring out if they contain the element hydrogen in them.
Look at the different kinds of rocks studied in geology. At least two types of rocks show the presence of helium. How are they formed in the earth? Where are they found on the earth?
Nuggets of Information:
Hydrogen, the lightest element of all, explodes at concentrations of 4-75%by volume in the presence of sunlight,flames or sparks.(Ref.4)
Despite being a stable element, hydrogen forms many bonds and exists in a wide variety of compounds. It is mostly found on earth as hydrocarbons and water.
The 3 isotopes of hydrogen show different properties because of the differing number of neutrons in the nucleus. Deuterium and its compounds are used in chemical experiments as well as in H-NMR Spectroscopy.(Ref.4)
In aqueous solutions the H+ ion is actually H3O+ or hydronium ion and this ion is extremely important in acid-base chemistry.(Ref.4)
The word ‘helium’ comes from the Greek word meaning sun (helios).(Ref.6)
The U.S. is the world’s largest supplier of helium, found in many natural gas fields.(Ref.6)
The balloon boy hoax on October 15, 2009 made people believe that a six-year old boy had floated away in a home-made helium balloon. But in reality, the boy was just hiding in his home.(Ref.6)
Since helium is less dense than air, when inhaled from a source, say, a helium balloon, it briefly changes the voice of the person to sound much higher. However, breathing too much helium could choke people due to lack of oxygen.(Ref.6)
Liquid helium is used for cooling metals in superconductivity experiments.(Ref.6)
Helium is a non-renewable source since the decay of thorium and uranium is slower than the rate at which it is being used. In 1925, the U.S. established a National Helium reserve and there was plenty of helium available. However, with more and more usage of helium as a purging gas and other uses and the selling of it to other countries, today we are at the stage that by 2021, the National Helium Reserve will be sold out.(Ref.5)


Science Makes Sense-Week 28: Chemistry and Social Justice, Air Pollution in India

March 14, 2016

I go to India in December to be with my siblings and spend most of my time in Chennai, a south-eastern city along the Bay of Bengal. Every year I notice that construction is booming with more and more multi-story structures and houses all over the city. Apart from that, vehicular traffic on the roads keeps increasing. This year I found myself struggling with a hacking cough and continuous throat irritation.
There is an urgent need to address air pollution here. It is important to understand the unique blend of pollutants present in India versus countries like the United States. As students of science one needs to have a general idea about measurement techniques as well. As social justice advocates it is imperative to look at the alarming health effects to the citizens and what measures are being taken to counteract this.
Even though the capital of India, New Delhi, is considered to have the worst Air Quality Index (Ref.1), or AQI, Chennai, seemed to be worse than new Delhi in 2015.(Ref.2)
What is AQI? Basically it is an index that lets one know how polluted or safe the air quality is in a particular country. Depending on the industries and the culture of daily life prevalent in the country, there are several different pollutants present in the air. One usually calculates its concentration for a 24 hour period in 3 -4 hour intervals. The AQI ranges from 0- 500+ and the higher the value the more polluted is the air. Several countries use a color code to indicate the levels of different pollutants ranging from safe to highly polluted/dangerous.(Ref.3) In the US, we often hear about ozone levels and PM2.5 and PM10 along with a few chemicals like sulfur dioxide etc.(PM2.5 is particulate matter less than 2.5 microns in diameter and PM10 is particulate matter less than 10 microns in diameter. A grain of sand is 50-70 microns in diameter. A micron is one millionth of a meter.)
In India, apart from the above mentioned pollutants the presence of nitrogen dioxide, ammonia,lead, benzene, nickel, carbon monoxide, arsenic levels are calculated to measure AQI.(Ref.4)
Why does India have all these extra air pollutants? As a rapidly industrializing country, there is a lot of coal production that leads to incomplete combustion forming carbon black(particulate matter,soot), carbon monoxide as well as lead, arsenic and oxides of nitrogen and sulfur.(Ref.5) Ammonia is present in decaying garbage, excreta as well as in pesticides.(Ref.6) Benzene and other such aromatic hydrocarbons are present because there is indoor air pollution especially in rural households where biomass, which is plant waste matter,(Ref.7) is burned during cooking, along with incomplete combustion products like carbon, carbon monoxide.(Ref.8) Nickel is present also in fossil fuel emissions as well as in the cement industry.(Ref.9)As you can see, India poses unique problems because of very severe indoor and outdoor pollutants.
The measurements of these pollutants is done using statistical analysis, gravimetric (where the element or compound being studied is isolated in a solid form and weighed)studies. In some cases, based on the chemical properties of the pollutants chemiluminescence, specroscopy as well as gas chromatography are some of the other tools utilized to do some quantitative analysis.(See Nuggets for more clarification of new terms.) All the measurements are done in terms of micrograms of the pollutant per cubic meter.(Ref.4)
Once the measurements are done for the 24 hour period, the range of pollutants present decides how safe or hazardous the air quality is for the day. 6 color codes are used in India; the safest is when the pollutants present is below 50 micrograms per cubic meter; satisfactory is around 50-100 micrograms per cubic meter; 101-200 micrograms per cubic meter is moderately polluted whereas 200 and higher will be classified under poor, very poor and severe conditions.(Ref.10)
The Air Quality Index determines the level of pollutants and as already pointed out, certain major cities in India constantly surpass safe levels many days of the year. People with asthma and other lung infections are particularly prone to severe attacks and the color codes advise them to stay indoors. However, even people with no specific health problems are prone to get headaches, coughs and throat irritations. As the threat level increases from moderately polluted to higher levels, more serious health issues are observed with the populace. There are respiratory diseases, problems during pregnancy and sometimes even death due to dangerous levels of air pollution.(Ref.11)
What is being done to combat these problems? In New Delhi, where the AQI is consistently one of the worst in the world,the government decided in early January of this year to have half the cars on the street, by having odd-even licence plate cars on the street on alternate days. Initially not much improvement was seen in the AQI, but with time and the additional factor that more people started using public transportation, the air quality has considerably improved. (Ref.1)
There is also the feeling that the Supreme court in India has the power to mandate certain reforms. Earlier in the 80’s the court mandated that compressed diesel should be used in the Delhi city buses and that did improve air quality for a while. The legislature now should go for a 30 percent tax on the sale of diesel vehicles, charge higher automobile registration and parking fees, and get more buses on Delhi’s roads. Then the Supreme Court could use its authority to order compliance with these recommendations. Finally, India’s national air-quality standards must be made legally binding.(Ref.12)
The Center for Science and Environment (CSE) is a public interest research and advocacy organisation in New Delhi. CSE researches into, lobbies for and communicates the vital need for development that is both sustainable and equitable. They believe in balancing the rural based life style of doing sustainable agriculture using biomass with the rapidly industrializing urban world in India. CSE brings out a lot of pamphlets and information articles to educate, promote the need for better air quality and care for the environment while rapidly developing.(Ref.13)
The fact that more and more people are aware of AQI is a start. There is even a smart phone app for AQI and most Indians love their smart phones!(Ref.14) Civic awareness can play a major part in a country where it was citizens who clamored for reform and created the Aam Aadmi Party(The Common man’s Party) in New Delhi to create positive change. In addition, India is cutting dependence on fossil fuels by looking seriously at alternative green sources like solar energy. But the pollution is still there, there are many deaths and severe illnesses reported in India because of poor air quality and so we have a long way to go.
Activities for Middle School Teachers
Why does New Delhi have such high AQI numbers? It could have something to do with the fact that it is landlocked and the smog presence is similar to Mexico City and Los Angeles. Study geographical reasons that might exacerbate or mitigate air pollutant levels. Would sea breezes help or hinder this process?
Look at a few major cities in the world to compare and contrast air pollutants. Why do they differ?
If students have smart phones, let them study AQI in a few regions all over the world for different months of the year and plot days from different months against AQI. Is there a correlation, any pattern seen?
Study all the quantitative techniques like spectroscopy, gravimetric analysis, gas chromatography and chemiluminescence and get to use/see those instruments either at the school laboratory or through you-tube videos.
Nuggets of Information:
A Yale University research team 2014 report shows that India ranked 174 out of 178 countries in air quality, somewhere close to China and Pakistan.(Ref.15)
World Health Organization says(2014 report) New Delhi’s air quality is the worst in the world!(Ref.15)
Air Pollution is the fifth largest killer in India.(Ref.15)
The Taj Mahal is turning yellow due to coal dust, biomass burning and high fossil fuel burning in India.(Ref.16)
Chemiluminescence simply means that certain compounds emit light due to chemical reactions just like fireflies do on long summer nights.
The number of photons (quantitative measurement of light particles) emitted can help calculate the concentration of certain pollutants like nitrogen dioxide, ozone and ammonia.
Spectroscopic studies use instruments like spectrometers that are able to assay spectral data using mathematics to calculate concentrations of different compounds.
Chromatography separates several constituents in a mixture and in a gas chromatograph, one analyses the peaks, the position of the peaks and the height of the peaks to identify compounds and analyse concentrations of the compound as well.


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.
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.