Archive for May, 2016

Science Makes Sense-Week 37: The alkaline earth metals

May 17, 2016

My grandmother was very particular that all the grandchildren who came to visit her had milk at night. She would stand with a big warm container of milk and insist that we all had a small glass before we went to bed. My younger sister hated this white liquid and would swallow it with great difficulty. Even now she dislikes the taste of milk but gets her calcium from plenty of yogurt and dietary supplements.
Calcium,Ca, is one of the alkaline-earth metals along with Beryllium,Be, Magnesium,Mg,Strontium,Sr, Barium,Ba and Radium, Ra. (Radium was covered last week) All are metals and form Group 2, next to the Group 1 alkali-metals in the Periodic Table. Like the alkali-metals, they are soft, silvery-white metals, reactive (but not as reactive as the alkali-metals) and never found as an element in the natural state. And again, like them, they glow with characteristic colors and are distinguished by the flame test. Unlike the alkali-metals which have 1 electron in the ‘s’ shell, they have two electrons in the ‘s’ shell.(Ref.1)
Some of the alkaline-earth metals except radium and beryllium were discovered by the English Chemist, Sir Humphrey Davy in the early part of the 19th century. Around this period, Sir Davy also discovered two of the alkali-earth metals, potassium and sodium.(Ref.1)
The alkaline-earth metals react easily with water to release hydrogen gas and form the metal hydroxide. Many of them react with oxygen to form oxides. In nature they are usually found as sulfates and carbonates.(Ref.1)
The most abundant of these metals is calcium, Ca. It is the fifth most abundant element in the earth’s crust as well as in the human body. Magnesium, Mg is the seventh most abundant element in the human body, whereas Ba, Be nor Ra, St are found in the body, since the first two are poisonous while radium is radioactive; meanwhile strontium is only present as 360 ppm on the earth’s crust.(Ref.1)
Beryllium is used in the health-care industry, (besides being found in precious stones)in X-ray tubes as well as in alloys for specialized electrical connections and for high-temperature uses.
Besides magnesium being important as a digestive aid and formerly used for asbestos, today it is used in the manufacture of fertilizers. Because of its property to burn in oxygen with a brilliant flame,in World War 1, magnesium was used as flares, tracer bullets and incendiary bombs. Later in World War 2, it was used to build aircraft and military equipment. Today it is used with other metals to manufacture catcher’s masks, skis, race cars and even horseshoes.(Ref.1)
Calcium has been used in buildings from ancient times. Steel, glass, paper and metallurgical industries use slaked lime(calcium hydroxide, Ca(OH)2). Acetylene used for welding is made by reacting calcium carbide(CaC2) with water. Calcium compounds are also used as a bleach, fertilizer and sometimes to melt ice on roads.
Even though strontium is not as abundantly available it still has several uses. Like magnesium, it is used for flares, tracer bullets and also for fireworks- having a brilliant crimson color. It is also used in color television picture tubes, to refine zinc and combined with iron, strontium is used to make magnets.(Ref.1)
Barium compounds are used extensively in health care applications: in enemas and also to coat inner linings of intestines so doctors can examine the patients’ digestive system.(Ref.1)
The alkaline-earth elements are used in a wide variety of ways; they are not just known for calcium and strong bones.
Activities for Middle School Teachers:
Study the boiling and melting points of the alkaline- earth elements. Is there a correlation between them and their atomic numbers as in the case of alkali-metals?
Helium,, He, has two electrons in its outermost ‘s’ shell, why then does it not behave like an alkaline-earth metal? Let the students discuss this with the teacher.
Nuggets of Information:
Beryllium is found in emeralds and aquamarines as a compound of beryllium and alumino-silicate and is called beryl.(Ref.1)
Magnesium is found as dolomite or magnesite which are carbonates of magnesium, MgCO3. (Ref.1)
Calcium is found mostly as limestone and as dolomite (calcium carbonate, CaCO3) and also as gypsum(calcium sulfate, CaSO4)
Strontium was initially discovered by Adair Crawford, an Irish Chemist in the late 18th century in witherite; it is also found in strontianite(strontium carbonate, SrCO3) and in celestite( strontium sulfate,SrSO4)(Ref.2)
Barium is found as barite(BaSO4,barium sulfate) or witherite(BaCO3,barium carbonate)(Ref.3)
Magnesium sulfate, also known as Epsom salts has been long known for their medicinal value,mainly in Epsom salts springs. It has also been used for the treatment of eclampsia, a condition that causes seizures in pregnant women.(Ref.1)
Salts of magnesium are used as a powerful laxative(Ref.1) but magnesium hydroxide,Mg(OH)2 also known an milk of magnesia is the preferred laxative.(Ref.4)
One of the most controversial uses of magnesium has been in asbestos, as a fire retardant. It is a silicate of magnesium with the formula Mg3Si2O5(OH)4. This had been used for commercial purposes 95% of the time.(Ref.5) For years it was used as a flame-retardant till it was found to be cancer-causing and had to be removed from many buildings. In spite of this, magnesium as an element is important in the health of living organisms.(Ref.1)
Magnesium plays a critical role in chlorophyll, the green pigment in plants that gets its energy from sunlight.(Ref.1)
More than magnesium, calcium is vital for living beings and is present in leaves, teeth, bones, shells and coral.(Ref.1)
We all know that calcium is essential for bone-building but it also plays an integral part in almost every cell in the body especially in the growth of muscles, the nervous system as well as the heart.(Ref.6)
Osteoporosis is caused by a loss in bone density and can be prevented by eating foods high in calcium like green vegetables and dairy products.(Ref.1)
An isotope of strontium, Sr 90, is radioactive and is a by-product of nuclear testing from the ’40’s. Once, during testing, this isotope fell to earth, coated grass and was ingested by cows. The milk from these cows was drunk by many children when the Sr 90 got into their teeth and gums causing many health problems. In the 60’s atmospheric nuclear testing was stopped. Strontium 90 affects production of red blood cells and could lead to death.(Ref.1)
Prior to receiving X-rays, patients drink a chalky barium sulfate,BaSO4 solution which absorbs radiation and adds contrast to the image.(Ref.1)

Science Makes Sense-Week 36: Chemistry and Social Justice-radiation, radium girls.

May 9, 2016

I remember when I was six or seven, my uncle came to visit us in the evening when we had a power cut in India and had no electricity. Everything turned pitch dark but I could see my uncle’s watch gleaming green in the dark! “Why is that happening? Do you have a magic watch?” I exclaimed. ” No magic, it is a glow-in-the-dark watch,” he responded. I was fascinated and learned years later that it was a radium watch. The dials had been painted with a salt containing radium.
Today we shall look closely at the discovery and use of one of the radioactive elements, radium (mention others in nuggets) and the terrible results of exposure due to ignorance and careless/negligent planning.
Radium was discovered by Pierre and Marie Curie in 1897 along with Polonium.(Ref.1) Pierre and Marie Curie were unaware of the dangers in the late 19th century/ early 20th century about nuclear reactions.
Most chemical reactions occur through transference/sharing of electrons, those very tiny particles that circle far away from the nucleus of an atom of any element. The nucleus is not touched in such reactions; however by the end of the 19th century, scientists were entering the realm of nuclear reactions. The nucleus is where the protons and neutrons are situated. The energy released when the nucleus is attacked, is several times that of a chemical reaction. Such attacks can be man-made as in nuclear reactors, and the explosion of atomic bombs, but radioactive elements that naturally decay can also cause nuclear reactions.
In fact Henri Becquerel was the first to observe mysterious radiation in uranium compounds and Maria and Pierre Curie did measurements on the amount of radiation emitted.(Ref.1) It is important to note that elements like technitium,Tc, prometheium, Pm as well as elements starting with polonium Po, all the way to the end of the Periodic Table exhibit radioactivity. In other words all the elements from atomic number 84 to atomic number 105 are radioactive, besides technitium and prometheium. Some of these elements are not too stable having very short half-lives.(Ref.2,3) Half life for an element is the time needed for half the mass of the element to decay.
The radioactive decay of elements leads to three kinds of ionizing radiation: alpha and beta particles as well as gamma radiation. Alpha particles consist of a pair of protons and neutrons, viz., it is a Helium ion. This is the least dangerous as far as radiation effects go, since they do not penetrate very deeply into clothing or skin. However, once ingested or inhaled through water or food sources, they could become carcinogenic and ultimately lead to lung cancer and other cancers. Beta particles are electrons that move very quickly; being 8000 times smaller than an alpha particle, this allows them to penetrate clothing and skin very easily. External exposure leads to burns and tissue damage and ingested/inhaled through water/food contamination could lead to serious health problems. Gamma rays are the most dangerous, these are fast-moving photons with no mass , passing easily through all body tissues and bone marrow causing extensive damage to the body and death based on amount/duration of exposure.(Ref.4)
While Marie and Pierre Curie may have been ignorant of the dangers of radium’s radioactivity, years later, many women were dangerously exposed to radium in U.S.factories where they were making radium watches and clocks. Referred to as the “radium girls” in Waterbury,Connecticut, Orange,New Jersey and in Ottawa, Illinois, young girls worked in factories and painted radium mixed as a paint with zinc sulfide, on dials of watches and clocks.(Ref.5) The managers, wanted them to lick the brushes so they were pointed to do the fine painting on the dials. Some of these girls even painted their buttons and finger nails to glow in the dark unaware of the terrible consequences. Initially because of ingesting alpha particles from the radioactive radium, they had terrible pains near the teeth and jaw, but eventually developed swelling and total destruction of the jaw and finally death in some cases. In Orange, new Jersey, 4 dial painters died and 8 were very ill. Dial painters there filed a suit in March of 1925 and following that workers no longer used their mouths to lick and point the brushes, they started wearing rubber gloves and use fume hoods after 1927. No more cases of cancers in dial painters were officially blamed on radiation. But the damage had been done.(Ref.5,6,7)
Years later, the suffering of the Radium girls led to safety measures for World War II atomic bomb workers.(Ref.5) Aah! But at what cost??
Activities for Middle School Teachers:
Teachers need to discuss how loosely and incorrectly certain words are used in daily life. The most common errors are made when the word ‘chemical’or ‘radiation’ is used, for example. All chemicals, radiation are considered harmful whereas water is also a chemical and electromagnetic radiation encompasses visible light. Let students research these words in science and understand the variation in meaning depending on context. Also, let students find other words in science that are mis-understood or partially explained by the non-scientific community.
Teachers should collaborate with Language Arts teachers and see if the word ‘synecdoche’ could be used to describe the incorrect usage of certain scientific words. (This word is a part of speech akin to a metaphor or simile; it means when a word is used to describe part of what it actually means)
Nuggets of Information:
Marie Curie’s notebooks and even her cookbook are so radioactively charged that they can only be viewed through lead screens today.(Ref.8)
Henri Becquerel received a burn carrying radium-rich barium chloride in his waist-pocket. Pierre Curie suggested that radium could be used for cancer therapy and in the 20’s it was used to treat some forms of skin cancer. In fact radium was touted as a cure for hypertension, diabetic pain, arthritis, gout and even for tuberculosis of the lung. Today, however radium is not used for any of this, but some research is underway to study its use to relieve intractable pain.(Ref.9)
Because of prolonged exposure to uranium, polonium and especially radium, Marie Curie succumbed to anemia related to radiation in bone marrow.(Ref.4)
The Geiger Counter was invented in 1928 and is used to measure radioactivity levels in many elements.(Ref.9)
It is important to note that all forms of radiation are not harmful to humans; e.g., electromagnetic radiation includes visible light. Also many man-made products like televisions,smart phones, microwave ovens emit radiation that are not dangerous and the danger varies with strength and length of exposure.(Ref.4)
There were 30 women in Connecticut, 35 women in Illinois and 41 women in New Jersey who died because of being dial painters (Radium Girls) in the 1920’s.(Ref.5)
Alexander Litvinenko, a former KGB officer died 3 weeks after ingesting a cup of tea containing Polonium 210.(Ref.8)
6.Clark, Claudia, Radium Girls,(University of North Carolina Press, 1997)
7.Mullner, Ross, Deadly Glow,( American Public Health Association, 1999)

Science Makes Sense-Week35:Organic Chemistry,Benzenoid aromatic compounds

May 2, 2016

Every year my mother would clean her silk saris by washing them in mild soap, getting them ironed and stack them in the cupboard with a few moth balls. So every time I would open the cupboard to wear her saris I would smell the odor of moth balls and hope it did not cling to me! Moth balls originally contained naphthalene which is a benzenoid compound and we shall look at a few of these today.
Benzenoid compounds contain the benzene ring and last time we had a chance to look at the simplest of these, benzene. The structure of benzene was discovered almost simultaneously by Loschmidt and Kekule around the mid-19th century,(both German scientists) as a six-membered cyclic hydrocarbon containing 6 carbon and 6 hydrogen atoms with alternating double bonds. But it was Kekule who modified the structure to one where the oscillation of the double bonds gave two equivalent structures in rapid equilibrium. Then in 1931, Linus Pauling suggested that benzene had a single structure that was a resonance hybrid of the two Kekule structures.(Ref.1)
Benzene is a colorless volatile liquid with a characteristic strong odor and is the starting point for the manufacture of many aromatic compounds including aniline, phenols.(Ref.1)
Modern bonding models (valence bonding and molecular orbital theory) explain the stability of the benzene due to the delocalization of the six electrons. This delocalization refers to the attraction of an electron by all six carbon atoms instead of one or two, making benzene very stable. Unlike other unsaturated hydrocarbons, the hydrogenation and oxidation of benzene is a slow process. Most reactions of benzene are electrophilic aromatic substitution where the ring is intact and replacement of hydrogen occurs. Such reactions are important in forming derivatives of benzene.(Ref.1)
Benzene is present/manufactured in oil refineries, rubber and shoe manufacturing as well as in gas stations and firefighting.(Ref.2). Benzene has been documented as a cancer-causing agent and the results of exposure are mentioned in Nuggets.
The next aromatic compound we will study is toluene, also known as methyl benzene where one of the hydrogen atoms is replaced by a methyl(CH3)group. The odor is similar to benzene and it is usually a stable compound unless subjected to high temperatures. It is one of the by-products of gasoline production, but most of the benzene is manufactured starting with toluene. Toluene is used in the manufacture of adhesives, rubber, laboratory paints, pesticides and pharmaceuticals.(Ref.3)
The third set of aromatic compounds are called phenols. When a hydroxyl group, -OH group is attached to a carbon atom of a benzenoid ring, the compound is called a phenol. Phenols are similar to alcohols; however the hydrogen bond is stronger so they are more soluble in water than alcohols and have a higher boiling point. They are usually colorless liquids or white solids and are toxic and caustic. Household products that contain phenols include disinfectants and mouthwash. In industry, phenol is the starting point for plastics, explosives,photography, dyes and aspirin.(Ref.4)
Finally we will look at the chemical composition of moth balls, another benzenoid compound. Today we use dichloro-benzene , but years ago naphthalene was used in the manufacture of moth balls. 2 fused rings of benzene comprise naphthalene with the formula C10H8. Naphthalene is a white, solid crystal and has a strong odor of coal tar. It can undergo electrophilic aromatic substitution. It can be hydrogenated partially to form 1,2,3,4 tetra hydro-naphthalene or completely to form decalin, C10H18. Both are used as low volatile solvents. Naphthalene is used as a fumigant/ pesticide mainly as well as in the production of dyes.(Ref.5)
We have looked at some of the benzenoid compounds; we use them in our everyday lives. Look at Nuggets to realize that some of these compounds are carcinogenic, some are explosives and some are also medicines. However, all are essential in our lives today.
Activities for Middle School Teachers:
Benzene has 3 different positions on the 6 carbon atoms: Immediately adjacent to the first carbon atom is called the ortho position, next to it is the meta position and directly opposite to it is the para position. Create the basic structure of benzene using kits available and then substitute different methyl groups in the different positions. Name them. Then change the hydrogen atom in the first position and insert an amine or hydroxyl group and repeat the process. Find out if such benzenoid compounds exist and what their names and uses are.
Also create structure of aspirin and salicylic acid. What is the latter used for?
Build structures for other pain relievers like ibuprofin and tylenol; find out their chemical/generic names as well.
Nuggets of Information:
Most of the benzene was originally obtained from coal tar, but from 1950, it has been derived from petroleum-based processes. More than half the benzene is converted to polystyrene, a common plastic. The steps to the conversion as as follows: benzene to ethyl benzene to styrene and then the polymer polystyrene.(Ref.1)
Benzene is one of the twenty most widely used chemicals in the United States. It is used mainly to manufacture plastics, lubricants, rubbers, dyes, detergents, drugs, and pesticides. You could breathe or ingest this aromatic compound easily in such environments.(Ref.2)
Benzene is present in cigarette smoke; in the presence of smokers we inhale benzene vapor. In fact, cigarette smoking causes half the exposure to benzene in the U.S.(Ref.2)
Benzene is a known carcinogen and workers who are constantly exposed to it are at a higher risk in developing leukemia and related cancers.(Ref.2)
Toluene derived its name from a tree in Colombia which has an aromatic extract called tolu balsam.(Ref.3)
TNT or tri-nitro-toluene is a known explosive and is made from nitric acid and toluene.(Ref.3)
Toluene is also used as an octane booster in gasoline. In biochemistry experiments toluene is used to rupture red blood cells for hemoglobin extraction.(Ref.3)
Phenols were the first surgical antiseptic used in 1865. Surgical amputations fell from 45% to 15% after using phenols. However, they were toxic as well.
A less toxic phenol like resorcinol, that contains two hydroxyl groups is often found in cough drops.(Ref.4)
Picric acid, which is trinitro phenol is used as a yellow dye as well as an explosive like TNT.(Ref.6)
Trace amounts of naphthalene are found in magnolias and certain kinds of deer.(Ref.5)
Naphthalene is considered to be a carcinogen; excessive inhalation or ingestion could cause hemolytic anemia.(Ref.7) Hemolytic anemia is caused by the destruction of red blood cells in the body.(Ref.8)
Aspirin, which is also known as methyl salicylate or 2 acetoxy-benzoic acid is an analgesic and is a non-steroidal anti-inflammatory agent. It is used usually for minor headaches and pains. Aspirin exhibits anti-coagulant properties(Ref.9) and therefore small doses are recommended every day to prevent heart attacks for some patients. It is an aromatic benzenoid compound.
Aniline, which is benzene with a hydrogen atom replaced by an amine _NH2 group is essential in the manufacture of dyes. It is responsible for the indigo color in blue jeans. Aniline is also used to make polymers like polyurethane, fungicides and herbicides. It is also used to make additives in rubber.(Ref.10)