CATALYSIS ON FUEL CHEMISTRY BASIC INFORMATION AND TUTORIALS

CATALYSIS AND ITS APPLICATION IN FUEL CHEMISTRY
What is Catalysis?

The topic of catalysis recurs throughout fuel chemistry. A catalyst increases the rate of a chemical reaction without itself being permanently altered by the reaction, or appearing among the products. The key word is rate. Catalysts affect reaction kinetics.

A catalyst affects reaction rate by providing a different mechanism for the reaction, usually one that has a markedly lower activation energy than that of the non-catalyzed reaction. Catalysts do not change reaction thermodynamics; they do not alter the position of equilibrium [A], but they can help reach equilibrium much more quickly. And, they cannot cause a thermodynamically unfavorable reaction to occur.

Catalysts can be classified as homogeneous, in the same phase as the reactants and products, and heterogeneous, in a separate phase. Homogeneous catalysts mix intimately with the reactants. This good mixing often leads to enormous rate enhancements, in some cases by more than eight orders of magnitude.

But, because they are in the same phase as the reactants and products, industrial use would require a separation operation for catalyst recovery downstream of the reaction, unless one were willing to throw away the catalyst (possibly allowing it to contaminate the products) as it passes through the reactor. For many catalytic processes, the catalyst costs much more than the reactants do, so loss of the catalyst would result in a significant economic penalty.

Usually, heterogeneous catalysts have no major separation problems, thanks to their being in a separate phase from reactants and products. However, because of their being in a separate phase, mass-transfer limitations can hold up access of the reactants to the catalyst, or hold up departure of products. Heterogeneous catalysis can also be affected by various problems at the catalyst surface.

Large-scale industrial processing almost always favors use of heterogeneous catalysts, to avoid possibly difficult downstream separation issues. Nevertheless, steady progress is being made in finding ways to overcome separation problems with homogeneous catalysts, including, as examples, membrane separation, selective crystallization, and use of supercritical solvents.

While, by definition, a catalyst remains unchanged at the end of a reaction, it can, and often does, change during a reaction. Mechanisms of many catalytic reactions often involve many steps, which collectively comprise the catalytic cycle. The catalyst might undergo change during one or more of the elementary reaction steps of the mechanism, but at the end, when its action is complete, the catalyst must emerge in its original form, ready for another catalytic cycle.

Most homogeneous catalytic reactions occur in the liquid phase. Some reactions can be catalyzed in the gas phase by homogeneous catalysts (which, because they are homogeneous, must be gases themselves). Probably the most important example of homogeneous catalysis in the gas phase is the chlorine-catalyzed decomposition of ozone, the reaction responsible for the so-called ozone hole in the atmosphere [B].

Various parameters can be used to describe quantitatively the quality or “goodness” of a catalyst. Turnover number, and the related turnover frequency, compare the efficiency of different catalysts. Turnover number indicates the number of molecules of reactant that one molecule of catalyst can convert into product.

The term “turnover” comes from the notion that the catalytic conversion is “turning over” reactant molecules into product molecules. Turnover frequency is the turnover number expressed per unit time. Selectivity expresses the fraction of the desired product, usually in weight percent or mole percent, among all products of the reaction. Ideally, selectivity should be as close to 1, or 100%, as possible. Catalyst activity can be broadly defined in terms of rate of consumption of the reactant(s) or rate of formation of products.

THE IMMUNE SYSTEM CHEMISTRY BASIC INFORMATION AND TUTORIALS

WHAT IS THE CHEMISTRY OF IMMUNE SYSTEM?
Immune System Chemistry Basics

The immune system has two main functions; to recognize invading pathogens and then to trigger pathways that will destroy them. The humoral immune system relies on B lymphocytes to produce soluble antibodies that will bind the foreign antigens.

The cellular immune system uses killer T lymphocytes that recognize and destroy invading cells directly.

The primary immune response occurs on initial contact with a foreign antigen and results in production of immunoglobulin M (IgM) and then immunoglobulin G (IgG). If the same antigen is encountered again, immunological memory leads to a secondary immune response that produces a much more rapid and larger increase in specific IgG production.

A large number of antibody-producing cells exist in an animal even before it encounters a foreign antigen, each cell producing only one specific antibody and displaying this on its cell surface. An antigen binds to cells that display antibodies with appropriate binding sites and causes proliferation of those cells to form clones of cells secreting the same antibody in high concentration.
Cells that produce antibody that reacts with normal body components are killed early in fetal life so that the adult animal normally is unable tomake antibodies against self, a condition called self tolerance.

Antibodies bound to an invading microorganism activate the complement system via the classical pathway. This consists of a cascade of proteolytic reactions leading to the formation of membrane attack complexes on the plasma membrane of the microorganism that cause its lysis.

Polysaccharides on the surface of infecting microorganisms can also activate complement directly in the absence of antibody via the alternative pathway.

RESPIRATORY FIBROGEN BASIC INFORMATION AND TUTORIALS

BASIC INFORMATION ON RESPIRATORY FIBROGEN

What are Respiratory fibrogens?

The hazard of particulate matter is influenced by the toxicity and size and morphology of the particle. Figure below gives typical particle size ranges for particles from various sources.

The critical size of dust (and aerosol) particles is 0.5 to 7 μm, since these can become deposited in the respiratory bronchioles and alveoli.

If dust particles of specific chemicals, e.g. silica or the various grades of asbestos, are not cleared from the lungs then, over a period, scar tissue (collagen) may build up; this reduces the elasticity of the lungs and impairs breathing.

The characteristic disease is classified as pneumoconiosis. Common examples are silicosis, asbestosis, coal pneumoconiosis and talc pneumoconiosis.

An appreciation of the composition and morphology of the dust is important in the assessment of hazard.

Thus, among silica-containing compounds, crystalline silicates and amorphous silicas (silicon dioxide) are generally not considered fibrogenic, whereas free crystalline silica and certain fibrous silicates such as asbestos and talcs can cause disabling lung diseases.

RATES OF CHEMICAL REACTION BASIC INFORMATION AND TUTORIALS

BASIC INFORMATION ON RATES OF CHEMICAL REACTION

What is the rate of chemical reaction?

Rates of chemical reaction
Whereas thermodynamics describes the energy requirements of a reaction, the speed at which it progresses is termed kinetics. It is important to be able to control the rate of chemical reactions for commercial and safety reasons.

If a reaction takes too long to progress the rate at which a product is manufactured would not be viable. Alternatively, if reactions progress too fast and ‘runaway’ out of control there could be dangers such as explosions.

The rate at which reactions take place can be affected by the concentration of reactants, pressure, temperature, wavelength and intensity of light, size of particles of solid reactants, or the presence of catalysts (i.e. substances which alter the speed of reactions without being consumed during the reaction) or impurities.

Catalysts tend to be specific to a particular reaction or family of reactions. Thus nickel is used to facilitate hydrogenation reactions (e.g. add hydrogen to C==C double bonds) whereas platinum is used to catalyse certain oxidation reactions. Sometimes care is needed with the purity of reactants since impurities can act as unwanted catalysts; alternatively, catalysts can be inactivated by ‘poisoning’.

The effect of temperature on different types of reaction is shown in figure below:

For reactions which progress slowly at room temperature it may be necessary to heat the mixture or add a catalyst for the reaction to occur at an economically-viable rate. For very fast reactions the mixture may need to be cooled or solvent added to dilute the reactants and hence reduce the speed of reaction to manageable proportions.

In general the speed of reaction

• doubles for every 10°C rise in temperature;
• is proportional to the concentration of reactants in solution;
• increases with decreased particle size for reactions involving a solid;
• increases with pressure for gas phase reactions.

LIST OF ATOMIC RADIUS AND ATOMIC WEIGHTS OF ELEMENTS BASIC INFORMATION

Here is a list of atomic numbers and atomic weights.

The radius of an atom can be estimated by taking half the distance between the nucleus of two of the same atoms. For example, the distance between the nuclei of is 2.66 Å, half that distance would be the radius of atomic iodine or 1.33 Å. Using this method the atomic radius of nearly all the elements can be estimated.

Note that going across the periodic table, the atomic radius decreases. This is due to the fact that the principal energy level (principal quantum number) remains the same, but the number of electrons increase.

The increase in the number of electrons causes an increase in the electrostatic attraction which causes the radius to decrease. However, going down the periodic table the principal energy level increases and hence the atomic radius increases.

Below is a lists the atomic radii of some of the elements.

Below is a list of its atomic weights:

GLENN SEABORG AND SEABORGIUM BASIC INFORMATION AND TUTORIALS

Prior to 1940 the periodic table ended at uranium, element number 92. Since that time, no scientist has had a greater effect on the periodic table than Glenn Seaborg.

In 1940 Seaborg, Edwin McMillan, and coworkers at the University of California, Berkeley, succeeded in isolating plutonium (Pu) as a product of the reaction between uranium and neutrons.

Between 1944 and 1958, Seaborg and his coworkers also identified various products of nuclear reactions as being the elements having atomic numbers 95 through 102. All these elements are radioactive and are not found in nature; they can be synthesized only via nuclear reactions.

For their efforts in identifying the elements beyond uranium (the transuranium elements), McMillan and Seaborg shared the 1951 Nobel Prize in Chemistry.

From 1961 to 1971, Seaborg served as the chairman of the US Atomic Energy Commission (now the Department of Energy). In this position he had an important role in establishing international treaties to limit the testing of nuclear weapons.

Upon his return to Berkeley, he was part of the team that in 1974 first identified element number 106. In 1994, to honor Seaborg’s many contributions to the discovery of new elements, the American Chemical Society proposed that element number 106 be named seaborgium (Sg).

After several years of controversy about whether an element should be named after a living person, the IUPAC officially adopted the name in 1997. Seaborg became the first person to have an element named after him while he was alive.

ATOMIC THEORY OF MATTER - BASIC INFORMATION AND TUTORIALS

Philosophers from the earliest times speculated about the nature of the fundamental “stuff” from which the world is made. Democritus (460–370 BC) and other early Greek philosophers described the material world as made up of tiny indivisible particles they called atomos, meaning “indivisible or uncuttable.”

Later, however, Plato and Aristotle formulated the notion that there can be no ultimately indivisible particles, and the “atomic” view of matter faded for many centuries during which Aristotelean philosophy dominated Western culture.

The notion of atoms reemerged in Europe during the seventeenth century. As chemists learned to measure the amounts of elements that reacted with one another to form new substances, the ground was laid for an atomic theory that linked the idea of elements with the idea of atoms.

That theory came from the work of John Dalton during the period from 1803 to 1807. Dalton’s atomic theory was based on the four postulates:

1. Each element is composed of extremely small particles called atoms.

2. All atoms of a given element are identical, but the atoms of one element are different from the atoms of all other elements.

3. Atoms of one element cannot be changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.

4. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

Dalton’s theory explains several laws of chemical combination that were known during his time, including the law of constant composition, based on postulate 4:

In a given compound, the relative numbers and kinds of atoms are constant. It also explains the law of conservation of mass, based on postulate 3:

The total mass of materials present after a chemical reaction is the same as the total mass present before the reaction.

A good theory explains known facts and predicts new ones. Dalton used his theory to deduce the law of multiple proportions:

If two elements A and B combine to form more than one compound, the masses of B that can combine with a given mass of A are in the ratio of small whole numbers.

We can illustrate this law by considering water and hydrogen peroxide, both of which consist of the elements hydrogen and oxygen. In forming water, 8.0 g of oxygen combine with 1.0 g of hydrogen. In forming hydrogen peroxide, 16.0 g of oxygen combine with 1.0 g of hydrogen.

Thus, the ratio of the mass of oxygen per gram of hydrogen in the two compounds is 2:1. Using Dalton’s atomic theory, we conclude that hydrogen peroxide contains twice as many atoms of oxygen per hydrogen atom as does water.

John Dalton (1766–1844), the son of a poor English weaver, began teaching at age 12. He spent most of his years in Manchester, where he taught both grammar school and college. His lifelong interest in meteorology led him to study gases, then chemistry, and eventually atomic theory. Despite his humble beginnings, Dalton gained a strong scientific reputation during his lifetime.

JOB OR WORKS OF CHEMIST - WHAT ARE THE POSSIBLE JOBS FOR CHEMIST?

So What Does a Chemist Do All Day?

You can group the activities of chemists into these major categories:
~ Chemists analyze substances. They determine what is in a substance, how much of something is in a substance, or both. They analyze solids, liquids, and gases. They may try to find the active compound in a substance found in nature, or they may analyze water to see how much lead is present.

~ Chemists create, or synthesize, new substances. They may try to make the synthetic version of a substance found in nature, or they may create an entirely new and unique compound. They may try to find a way to synthesize insulin. They may create a new plastic, pill, or paint. Or they may try to find a new, more efficient process to use for the production of an established product.

~ Chemists create models and test the predictive power of theories. This area of chemistry is referred to as theoretical chemistry. Chemists who work in this branch of chemistry use computers to model chemical systems. Theirs is the world of mathematics and computers. Some of these chemists don't even own a lab coat.

~ Chemists measure the physical properties of substances. They may take new compounds and measure the melting points and boiling points. They may measure the strength of a new polymer strand or determine the octane rating of a new gasoline.

And Where Do Chemists Actually Work?

You may be thinking that all chemists can be found deep in a musty lab, working for some large chemical company, but chemists hold a variety of jobs in a variety of places:

~ Quality control chemist: These chemists analyze raw materials, intermediate products, and final products for purity to make sure that they . fall within specifications. They may also offer technical support for the customer or analyze returned products. Many of these chemists often solve problems when they occur within the manufacturing process.

~Industrial research chemist: Chemists in this profession perform a large number of physical and chemical tests on materials. They may develop new products, and they may work on improving existing products. They may work with particular customers to formulate products that meet specific needs. They may also supply technical support to customers.

~Sales representative: Chemists may work as sales representatives for companies that sell chemicals or pharmaceuticals. They may call on their customers and let them know of new products being developed. They may also help their customers solve problems.

~Forensic chemist: These chemists may analyze samples taken from crime scenes or analyze samples for the presence of drugs. They may also be called to testify in court as expert witnesses.

~Environmental chemist: These chemists may work for water purification plants, the Environmental Protection Agency, the Department of Energy, or similar agencies. This type of work appeals to people who like chemistry but also like to get out in nature. They often go out to sites to collect their own samples.

~Preservationist of art and historical works: Chemists may work to restore paintings or statues, or they may work to detect forgeries. With air and water pollution destroying works of art daily, these chemists work to preserve our heritage.

~Chemical educator: Chemists working as educators may teach physical science and chemistry in public schools. They may also teach at the college or university level. University chemistry teachers often conduct research and work with graduate students. Chemists may even become chemical education specialists for organizations such as the American Chemical Society.

These are just a few of the professions chemists may find themselves in. I didn't even get into law, medicine, technical writing, governmental relations, and consulting. Chemists are involved in almost every aspect of society. Some chemists even write books.

If you aren't interested in becoming a chemist, why should you be interested in chemistry? (The quick answer is probably "to pass a course.,,) Chemistry is an integral part of our everyday world, and knowing something about chemistry will help you interact more effectively with our chemical environment.

LPG CYLINDERS ROAD TRANSPORT SAFETY PROCEDURES BASICS AND TUTORIALS

Procedures for safe transport of LPG cylinders by road.

Transport
• Carry cylinders on open vehicles. Keep cylinders upright and adequately secured, e.g. with a rope.
• Keep a fire extinguisher, e.g. 1 kg dry power, in the cab to deal with any small fire, e.g. an engine fire.
• Do not leave cylinders on vehicles unsupervised.
• Ensure that the driver has received adequate training and instructions about the hazards of LPG, emergency procedures, driver duties, etc.
• Ensure that relevant information is readily available on the vehicle, e.g. on a clipboard in the cab. This written information, e.g. as a TREMCARD, should contain details of the nature of the load and the action to take in an emergency.

Duties of vehicle operator
• Check whether the Road Traffic (Carriage of Dangerous Packages, etc.) Regulations 1986 apply. Exceptions apply to cylinders <5 litres; cylinders which are part of equipment carried on the vehicles, e.g. burning gear, bitumen boilers; cylinders associated with vehicle operation, e.g. cooking, water heating.
• Ensure the vehicle is suitable, normally an open vehicle. Use of a closed vehicle should be restricted to a small number of cylinders with a load compartment having adequate ventilation.
• Ensure the driver has adequate information in writing, e.g. a TREMCARD.
• Ensure the driver is provided with adequate instruction and training and keeps necessary records.
• Ensure loading, stowage, unloading are performed safely. All cylinders should be packed, strapped, supported in frames, or loaded to avoid damage resulting from relative movement. Cylinders should be stowed with valves uppermost.
• Ensure all precautions are taken to prevent fire or explosion.
• Ensure suitable fire extinguishers are provided.
• Ensure the vehicle displays two orange plates if 500 kg of LPG is carried.
• Report any fire, uncontrolled release or escape of the LPG, to the appropriate authority.

Duties of the driver
• Ensure the relevant written information from the operator is always available during carriage. Destroy, remove or lockaway information about previous loads.
• Ensure loading, stowage and unloading are performed safely.
• Ensure all precautions against fire or explosion are taken during carriage.
• Display orange plates (when required) and keep them clean and free from obstruction.
• If >3 tonnes of LPG is carried, when the vehicle is not being driven, ensure parking is in a safe place or that it is supervised (by the driver or a competent person aged >18).
• On request provide appropriate information to persons authorized to inspect the vehicle and load.
• Report any fire, uncontrolled release or escape of LPG, to the operator.

EMERGENCY PROCEDURES FOR DRIVERS IN TRANSPORTING RADIOACTIVE SUBSTANCE

Arrange for the police and emergency services to be alerted

Arrange for assistance to be given to any person injured or in immediate danger

If considered safe to do so – having regard to the nature of the emergency, the substance and the emergency equipment available – follow a selection of the following procedures in an appropriate order:

Stop the engine

Turn off any battery isolating switch

If there is no danger of ignition, operate the emergency flashing device

Move the vehicle to a location where any leakage would cause less harm

Wear appropriate protective clothing

Keep onlookers away

Place a red triangle warning device at the rear of the vehicle and near any spillage

Prevent smoking and direct other vehicles away from any fire risk area

Upon the police/fire brigade taking charge:

Show the written information, e.g. Tremcard, to them

Tell them of action taken and anything helpful about the load, etc.

At the end of the emergency, inform the operator.

The written information given to the driver should include:

The name of the substance

Its inherent dangers and appropriate safety measures

Action and treatment following contact/exposure

Action in the event of fire and fire-fighting equipment to be used

Action following spillage on the road

How and when to use any special safety equipment

HOW WAS THE EARTH FORMED? - BASIC INFORMATION ON THE FORMATION OF PLANET EARTH

The solar system formed about 4.6 billion years ago. The Earth and other terrestrial planets are believed to have formed by gathering together the so-called planetesimals.

Planetesimals are formed by the coalescence of fine- or coarse-grained mineral matters, metals, and gases of various kinds. As planetesimals stuck together mostly by gravity and the body thus formed grew larger, it became a precursor of terrestrial planet.

Some of these bodies were smashed by other bodies, and their fragments became meteorites. Hence, studies of meteorites would provide a lot of insight into the formation and the earlier state of the Earth.

The planet Earth was thus formed. Heat was created as the coalescence (of planetesimals) proceeded due to gravity, and heat also came from radioactivity of several radioactive elements such as aluminum-26. So the newly formed body was heated and the core was melted.

As the material becomes liquid (as a result of melting), the materials contained in the liquid separate out according to their densities. The more dense material would sink closer to the bottom (core).

Thus, the present layer structure of the Earth formed. The innermost core is a dense solid of about 1,200 km radius, whose density is about 12.6 g per cubic centimeter (12.6 ×106 kg/m3).

It is made of mostly iron metal and a small amount of nickel. By the way, the density of iron metal is only 7.8×106 kg/m3 under the ordinary pressure. The next layer is the outer core (up to 3,500 km from the center of the Earth), which is liquid and has a density of 9.5–12×106 kg/m3. The chemical composition seems to be about the same as that of the inner core.

There is an abrupt change in density in the next layer, mantle. The width of mantle is about 2,900 km (3,500–6,380 km from the center). Its density ranges from 4 to 5.5 ×106 kg/m3. The mantle is made of mostly magnesium–iron silicates (silicon oxides). The outermost layer is the thin crust of about 35–45 km on the land portion, and about 6 km under the ocean portion.

IRON (FE) CHEMICAL INFORMATION - THE CHEMISTRY OF IRON

What Is Iron? All you need to know about the element Iron (Fe)

Iron, a familiar metal, tends to rust, as everybody has seen. What happens chemically when iron rusts? Iron atoms in the metallic iron carries no electric charge Fe(0), in which 26 electrons (negatively charged) are orbiting around a nucleus that contains 26 protons (with positive charge) and 30 neutrons (with no electric charge).

This applies to an isotope 26Fe56, the most abundant isotope of element iron. But iron atom can lose its electrons. This process (loss of electrons) is called “oxidation.” Iron becomes either Fe(II) by losing two electrons or Fe(III) by losing three electrons (under normal conditions), though it can take Fe(I) (under special conditions).

Fe(0) is said to have been oxidized to Fe(II) or Fe(III). [Fe(II) means an iron atom that carries two positive charges; this is so because there are now only 24 electrons (negative charges), but there are still 26 positive charges at the nucleus.]

For this to happen you have to have a chemical entity that removes the electrons from the iron atom. Such an entity is called an oxidant or oxidizing agent. The iron atom is said to be a reductant or reducing agent in this process, for a chemical reaction in which a chemical entity (oxidant) gains electron(s) is called “reduction.”

Hence, oxidation and reduction reactions occur simultaneously and are like “head and tail” of a coin. Iron (Fe) reacts with oxygen in the air and is oxidized first to Fe(II) and then Fe(III) ending up with iron oxide Fe2O3. [Fe(II) can also be expressed as Fe2+ or FeII, and such a state is called an “oxidation state”; in this case, the oxidation state of iron atom is +2 or II. Likewise, Fe(III)=FeIII=Fe3+.

We will usually use Roman numerals to express the oxidation states in this book]. Here oxygen (O2) in the air is the oxidizing agent. In the process, oxygen O2 which is in “zero” oxidation state gains four electron and is reduced to two of O−II (−2 oxidation state); therefore, the chemical reaction is + → III ( −II ) 2 2 3 4Fe(0) 3O 2Fe O . In this chemical reaction, 12 electrons are exchanged between four iron atoms and three oxygen molecules.

When this is not purely oxide and contains hydroxide Fe(OH)O or Fe2(OH)2O2, it shows that rust color, brown. Pure oxide Fe2O3 forms an ore called “hematite,” which is red. The red bed is found in many geological locations.

These descriptions suggest that iron, when forming chemical compounds, takes the form of Fe(II) or Fe(III). And it can go back and forth between Fe(II) and Fe(III) readily. Fe(II) gives off an electron to become Fe(III), and Fe(III) becomes Fe(II) when it accepts an electron. This kind of process is also called “electron transfer” reaction.

Hence, iron (in the form of Fe(II) and Fe(III)) can readily undergo an “electron transfer” reaction or alternatively an “oxidation–reduction” reaction, because the process of Fe(II)s becoming Fe(III) is an oxidation and the reverse (Fe(III) → Fe(II)) is a reduction reaction.

Some of you might have experienced, as this author has, to have your toilet bowl and others stained brown by your well water. The water underground can contain (depending on the location and other conditions) iron compounds; the iron is in the form of Fe(II), which is dissolved in water and almost colorless. It remains as Fe(II) in the underground, because no oxidant such as oxygen in the air is available.

However, once pumped out above ground and being exposed to the air, the iron soon turns into Fe(III) (through oxidation by oxygen). Fe(III) in water (neutral water, that is) is not stable, and soon reacts with water itself and forms iron hydroxide Fe(OH)3, which is brown and precipitates.

This is the brown stain. And the fact of the easy formation of iron stain suggests an easy affinity or reaction of Fe(II) with oxygen O2. This is indeed the basis of the usefulness of iron in the biological systems and our health.

DNA REPLICATION - HOW IS DNA REPLICATED? BASIC INFORMATION AND TUTORIALS

Really. Just how dna is replicated?

This is quite clear at least in principle by now. It is based on the specific interaction between A and T, and between G and C. That is, take, for example, the double helix in figure below.

Let us label the left strand as “l” strand and the other “r” strand. (This is the complementary strand of “l”). Suppose that you separate the two strands and the “l” strand is isolated. Then you provide a pool of components A, C, G, and T and a means to bind nucleotides (enzyme called DNA polymerase) for the “l” strand.

This enzyme binds nucleotides one by one sequentially. The top bead A on the “l” strand binds a bead T (laterally through hydrogen bond), and next another bead on “l” binds laterally a bead T. Beads T and T are then connected through the phosphate group by the enzyme.

Next the bead G on “l” binds a bead C, and the bead C then is connected to the previous T on the right hand by the enzyme. This is repeated; then you see that an “l” strand will reproduce the complementary “r” strand. The reverse will also be true; i.e., an “r” strand will reproduce the corresponding “l” strand.

Thus, a double strand will have been replicated. How this is accomplished, i.e., mechanics of these chemical reactions are currently very intensely studied, is beyond the level of this book.

Hence, this topic will not be pursued further here. But, the very basic reason why we are like our parents or in other words why a gene molecule (DNA) is (almost) faithfully replicated and transmitted to a progeny can be understood as in the previous paragraph.

This replication mechanism of DNA, however, applies to only cell division. The issue of inheritance in sexual organisms like us is a little more complicated, because we get half of the gene from mother and the other half from father.

But again we are not able to elaborate on this issue here. The issue is more of biology (so-called genetics) than chemistry. The chemical principles are about the same.

We said, “DNA is (almost) faithfully replicated” in the paragraph above. The qualification “almost” implies that replication may not always be exact. In other words, a cell may make mistakes in replicating a DNA. It happens not very often, but frequently enough. If this happens, a wrong DNA may form, which would give
wrong information.

Mistakes can be caused by some factors (some cancer causing factors, for example) or without any particularly cause. The distinction between the right combination A–T/G–C and wrong combinations such as A–C/G–T is not quite definite.

Chemically speaking, the difference in interaction energy between the right and the wrong combination is not very great. Hence, there is some chance that the DNA-making mechanism may simply connect wrong nucleotides occasionally. This may be disastrous to the organism.

Therefore, many DNA-making mechanisms (DNA polymerases) contain in it three functions. One is polymerizing nucleotides (making DNA chain), of course.

The other two are monitoring and repairing mechanisms. It monitors what nucleotides are connected and can identify a wrong one. When it has recognized a wrong one, the repairing mechanism snips off the wrong one.

And then the polymerase portion reconnects another; this time a right one, hopefully. There are many other mechanisms known in organisms that repair “damaged” DNAs. All these are chemical reactions, but too complex to be talked about here. It is also to be noted that these occasional changes in DNA are the ultimate cause of change of species, i.e., evolution.

MERCURY AND MERCURY POISONING - THE CONTROVERSIAL ELEMENT (THE APPLICATIONS AND DANGERS OF MERCURY)

Virtually all metals exist as solids at room temperature. Mercury is the only metallic element that is a liquid under normal conditions. If cooled to 39°C, it does freeze to a solid. Liquid mercury is shiny and metalliclooking.

You have probably heard a fair amount about the toxicity of mercury. As a liquid, it is not especially toxic when swallowed since most of it passes through the body unchanged.

However, mercury vapor is highly toxic, as are all compounds of mercury that dissolve in water to form solutions. Once they enter the body, these forms of mercury can attack the brain and produce mental and physiological disturbances.

An incident in Texarkana, on the Texas–Arkansas border, illustrated the hazards of handling mercury. Two teenagers stole 40 pounds of liquid mercury from a site where it had been used to make neon lights.

They poured it over themselves and on floors in their homes, gave it out to friends, and even dipped cigarettes into the liquid and smoked them. Within days they began to exhibit the signs of mercury poisoning: coughing up blood, vomiting, breathing difficulties, and seizures.

The end result was that eight contaminated homes were evacuated, a family dog was killed by the vapors, and more than 170 people in the town and surrounding areas received medical treatment for mercury exposure.

Mercury poisoning was much more common in the 19th century when workers who used mercury to cure felt hats developed twitches, spoke incoherently, and drooled as a result of long-term exposure to mercury vapors.

These workers provided Lewis Carroll with a model for the Mad Hatter in Alice in Wonderland. These days, most of the mercury that enters the environment comes from the incineration of waste and sewage sludge, and the burning of coal.

Recently, scrapping cars without removing the elemental mercury used in light switches and other components was identified as a significant source of the element to the environment.

MERCURY DANGERS IN DENTAL CARE?
Until quite recently, an alloy that most people had an intimate acquaintance with was the material used to fill cavities in decayed teeth. You may be surprised to learn that mercury was one of the metals used to fill teeth.

Although mercury is a liquid at room and body temperatures, it forms many alloys, called amalgams, that are solid at normal temperatures. Those having melting points in the 60°C range are useful for fillings, since they can be placed in the decay cavity as a warm liquid metal without causing the patient pain.

The liquid assumes the cavity shape as it cools and solidifies in place. Dental amalgam combines mercury with silver, which imparts resistance to tarnishing and mechanical strength, and about half as much tin, which readily amalgamates with mercury.

When first placed in a tooth, and whenever the filling is involved in the chewing of food, a tiny amount of the mercury is vaporized. Some scientists believe that mercury exposure from this source causes long-term health problems in some individuals, but an expert panel of the U.S. National Institute of Health concluded that dental amalgams do not pose a health risk.

A recent study of adults found that no measure of exposure to mercury—whether the level of the element in the urine or the number of dental fillings—correlated with any measure of mental functioning or fine motor control.

THE SCIENTIFIC MODEL OF GAS - BASIC TUTORIALS

Perhaps you have had the unpleasant experience of walking down the street and being accosted by the noxious smell of rotten eggs emanating from a nearby sewer. The odor, which is produced by the gaseous compound hydrogen sulfide, will reach your nose even if there is no wind.

This experience confirms the existence of gases in air, and the theory that the particles in a gas are constantly in motion. If they were not, odors would not carry unless there was a wind current present. As the Roman poet Lucretius said 2000 years ago in his epic poem The Nature of Things:

We can perceive the various scents of things

Yet never see them coming to our nostrils

The scientific model for gases is that of independent, tiny particles traveling rapidly in straight-line motion through empty space, as a rocket ship travels through outer space. Owing to the rapid motion of its constituent particles, a gas quickly expands to fill completely whatever space is accessible to it.

As a given gas particle travels through space, it occasionally collides with other gas particles or with the walls of its container if it is in one. These collisions result in a change in direction for the particles—much as a billiard ball changes direction when it hits another ball or hits the side of the pool table.

One of the many pieces of evidence that led to the scientific model for gases is that gases are much easier to compress to a smaller volume than are liquids or solids. Compressing a gas corresponds only to reducing the amount of empty space that lies between the independent particles.

A piece of evidence that led to the notion that the particles in a gas are in constant motion is the fact that a gas exerts a force on the walls of whatever container it occupies. Technically, the pressure exerted by a gas is the amount of force that it exerts on a specified area of surface, say one square centimeter (see Figure a).

For example, the helium gas atoms in a helium-filled balloon are in constant motion. As a consequence of their movements, they often collide with the inside skin of the balloon (see Figure b).

The pressure exerted on the balloon walls by this constant bombardment is sufficient to keep the balloon “blown up,” even though the stretched elastic of the balloon’s material is trying to contract and thereby collapse the interior. Indeed, the balloon collapses only when some of the helium leaks into the air outside the balloon.

ORDINARY CHEMISTRY AND NUCLEAR CHEMISTRY - BASIC COMPARISON AND TUTORIALS

An atom consists of a nucleus that is made of positively charged protons and neutral neutrons, and electrons surrounding it, as we outlined above. Two entirely different types of chemistry stem from this structure.

One is concerned with the nucleus and the other with how electrons behave. The former is “nuclear chemistry,” with “radiochemistry” as its important sub-discipline. The latter is the ordinary “chemistry.”

The basic reason for this division is that the nuclear forces binding protons and neutrons in the nucleus are enormously stronger than the electrostatic force binding the electrons to the nucleus. When one applies a force to a substance and induces a change, a certain amount of energy may be expended or gained.

Hence, an energy change always accompanies a change in substance. “Energy” is often used as a measure of a change in science, particularly in chemistry.

In terms of energy, then, a nuclear reaction (change in general) is greater by several orders of magnitude (typically a million times) than a typical chemical reaction, as the nuclear reaction involves changes in protons/neutrons in the nucleus while chemical reactions involve changes in electrons.

Therefore, ordinary chemical reactions would not be able to cause a change in nucleus (i.e., nuclear reaction). As a result, it is quite safe to deal with nuclear chemistry as separate from “ordinary” chemistry.

As a corollary, all isotopes that belong to an element, though they have different atomic masses, can be assumed to behave (approximately) the same chemically. However, isotopes behave very differently in terms of nuclear reactions.

It is now obvious that principles governing nuclear reactions are quite different from those operating in the ordinary chemical reactions.

SURFACE LAYERS CHARACTERIZATION METHODS BASIC AND TUTORIALS

Numerous surface analytical techniques that can be used for the characterization of surface layers are commercially available (Buckley, 1981; Bhushan, 1996).

The metallurgical properties (grain structure) of the deformed layer can be determined by sectioning the surface and examining the cross section by a high magnification optical microscope or a scanning electron microscope (SEM).

Microcrystalline structure and dislocation density can be studied by preparing thin samples (a few hundred nm thick) of the cross section and examining them with a transmission electron microscope (TEM). The crystalline structure of a surface layer can also be studied by X-ray, high-energy or low-energy electron diffraction techniques.

An elemental analysis of a surface layer can be performed by an X-ray energy dispersive analyzer (X-REDA) available with most SEMs, an Auger electron spectroscope (AES), an electron probe microanalyzer (EPMA), an ion scattering spectrometer (ISS), a Rutherford backscattering spectrometer (RBS), or by X-ray fluorescence (XRF). The chemical analysis can be performed using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS).

The thickness of the layers can be measured by depth-profiling a surface, while simultaneously conducting surface analysis. The thickness and severity of deformed layer can be measured by measuring residual stresses in the surface.

The chemical analysis of adsorbed organic layers can be conducted by using surface analytical tools, such as mass spectrometry, Fourier transform infrared spectroscopy (FTIR), Raman scattering, nuclear magnetic resonance (NMR) and XPS. The most commonly used techniques for the measurement of organic layer (including lubricant) thickness are depth profiling using XPS and ellipsometry.

ISOTOPES OF HYDROGEN AND OXYGEN BASIC INFORMATION AND TUTORIALS

The heaviest water must fall first. Aristotle

In ordinary natural water the hydrogen and oxygen each consist of three different isotopic forms with different masses; this fact is of some geochemical significance.

The isotopes present in water are:
1H, 2Hor D, 3Hor T, 16O, 17O, 18O:

The first isotope of hydrogen has a nucleus consisting of only a single proton, and accordingly the mass number is 1. The second isotope has both one proton and one neutron in the nucleus, and the mass number is 2; this isotope has a special name: “deuterium,” hence the common use of the letter “D” to represent the isotope.

The third isotope has one proton and two neutrons, a mass number of 3, and also has a special name: “tritium.” Tritium is radioactive.

The nuclei of oxygen have 8 protons, and 8, 9, or 10 neutrons. These isotopes are present in all possible combinations, so that (not including molecules with tritium) all natural water contains nine kinds of water molecules.

The ratios of the different isotopes, one to another, can be measured with remarkably high precision using an isotope ratio mass spectrometer.

The different isotopic forms of water each have different vapor pressures and freezing points; these physical differences are important because they make it possible to use the isotopes as tracers of geochemical processes.

The differences in vapor pressure lead to a fractionation of the isotopes whenever water evaporates or condenses. The heavier isotopes are, in every case, concentrated into the liquid phase. This leads to differing isotopic compositions in water from different sources.

When water freezes, there is also a fractionation such that the heavier isotopes are concentrated into the solid phase, although the effect is less than in the
gas–liquid exchange processes.

CYANIDES - DANGER OF CYANIDES BASIC INFORMATION AND TUTORIALS

What are the dangers of cyanide?

As a group, the cyanides are among the most toxic and fast-acting poisons. (This is due to the cyanide ion which interferes with cellular oxidation.)

Hydrogen cyanide (prussic acid) is a liquid with a boiling point of 26°C. Its vapour is flammable and extremely toxic. This material is a basic building block for the manufacture of a range of chemical products such as sodium, iron or potassium cyanide, methyl methacrylate, adiponitrile, triazines, chelates.

Toxic effects of hydrogen cyanide 
Concentration in air Effect (ppm)
2–5 Odour detectable by trained individual
10 (UK MEL 10 mg/m3 STEL (SK))
18–36 Slight symptoms after several hours
45–54 Tolerated for 3–60 min without immediate or late effects
100 Toxic amount of vapours can be absorbed through skin
110–135 Fatal after 30–60 min, or dangerous to life
135 Fatal after 30 min
181 Fatal after 10 min
270 Immediately fatal

Although organocyanides (alkyl cyanides, nitriles or carbonitriles), in which the cyanide group is covalently bonded, tend as a class to be less toxic than hydrogen cyanide, many are toxic in their own right by inhalation, ingestion or skin absorption. Some generate hydrogen cyanide under certain conditions, e.g. on thermal degradation.

Depending upon scale of operation, precautions for cyanides include:
• techniques to contain substances and avoid dust formation (solid cyanides), aerosol formation (aqueous solutions), and leakages (gas);
• gloves, face and hand protection;
• high standards of personal hygiene;
• ventilation and respiratory protection (dust or gaseous forms);
• environmental monitoring for routine processes;
• health surveillance.

CARBON MONOXIDE DANGER AND EFFECTS BASIC INFORMATION AND TUTORIALS

What are the dangers of carbon monoxide?

Carbon monoxide
Carbon monoxide is a colourless, odourless gas and – without chemical analysis – its presence is undetectable. It is produced by steam reforming or incomplete combustion of carbonaceous fuels;

Carbon monoxide is extremely toxic by inhalation since it reduces the oxygen-carrying capacity of the blood. In sufficient concentration it will result in unconsciousness and death.

The STEL is 200 ppm but extended periods of exposure around this, particularly without interruption, raise concern for adverse health effects and should be avoided. If a potential carbon monoxide hazard is identified, or confirmed by atmospheric monitoring.

Typical carbon monoxide concentrations in gases

Gas Typical carbon monoxide concentration (%)
Blast furnace gas 20–25
Coal and coke oven gas 7–16
Natural gas, LPG (unburnt) nil
Petrol or LPG engine exhaust gas 1–10
Diesel engine exhaust gas 0.1–0.5

Typical reactions of persons to carbon monoxide in air

Carbon monoxide (ppm) Effect
30 Recommended exposure limit (8 hr time-weighted average concentration)
200 Headache after about 7 hr if resting or after 2 hr exertion
400 Headache with discomfort with possibility of collapse after 2 hr at rest or 45 min exertion
1200 Palpitation after 30 min at rest or 10 min exertion
2000 Unconscious after 30 min at rest or 10 min exertion