CHEMISTRY:
SOAPS AND DETERGENTS
SOAPS AND DETERGENTS
About soaps
· Soaps are anionic surfactants used for washing and cleaning. Surfactants are wetting agents that lower the surface tension of a liquid
· Soaps consist of sodium or potassium salts of fatty acids.
· They are obtained by reacting common oils or fats with a strong alkaline solution
· The earliest recorded evidence for use of soap is from Babylon c. 2800 BC
Mode of action
· Soap molecules have both a hydrophilic end and a hydrophobic end
· The hydrophilic end dissolves in water, while the hydrophobic end dissolves dirt and oil molecules
· As a result, although water and oil don’t mix, soaps allow oil to dissolve in water, allowing them to be rinsed away
· Thus, soaps allow water to remove normally insoluble matter by emulsification
Detergents
· Detergents are surfactants other than soap
· Detergents are commonly used as industrial soaps, due to their heavy duty grease removal capabilities
· Soaps differs from detergents in that in the case of former, excess of fat is used to consume the alkali and the glycerine is not removed, leaving a naturally moisturising soap
· In general detergents are substances that have cleaning properties. By definition, even water is a detergent
CHEMISTRY: ENVIRONMENTAL CHEMISTRY
· Environmental chemistry is the study of chemical and biochemical phenomena that occur in natural places
· Environmental chemistry is used to detect and identify the nature and source of pollutants, including
Ø Heavy metal contamination of land by industry. These can transported to water bodies and taken up ingested by living organisms
Ø Nutrients leaching from agricultural land into water sources
Ø Urban pollutants runoff. Typical pollutants include petrol and other fuel, metals, nutrients and sediments
· Common environmental phenomena arising out of contamination include acid rain, soil salination and ocean acidification
WATER QUALITY PARAMETERS
· Dissolved Oxygen (Oxygen Saturation)
Ø It is a relative measure of the amount of oxygen dissolved in water.
Ø Supersaturation (excess of oxygen) can be harmful to organisms and also cause decompression sickness
Ø It is expressed in mg/l
· Chemical Oxygen Demand (COD)
Ø COD is used to indirectly measure the amount of organic compounds in water
Ø It is expressed in mg/l, which indicates the amount of oxygen consumed per litre of water
· Biochemical Oxygen Demand (BOD)
Ø BOD measures the rate of uptake of oxygen by microorganisms in water
Ø BOD is measured at a temperature of 20 C and over a period of 5 days in the dark
Ø BOD is widely used to determine the threshold at which treated wastewater can be re-introduced into the environment
Ø Pristine rivers have a BOD of below 1 mg/l. Municipal sewage treated effectively by a three-stage process would have BOD of 20 mg/l or less
· Total Dissolved Solids (TDS)
Ø TDS is a measure of combined content of all inorganic and organic substances contained in a liquid
Ø TDS is generally not considered a primary pollutant, but is used to indicate the aesthetic characteristics of drinking water
Ø High TDS levels generally indicate hard water
Ø Drinking water is expected to have a TDS of 100 mg/l or less
Ø TDS is different from TSS (Total Suspended Solids). The former are those solids that are small enough to pass through a filter of size 2 um, while the latter are those solids that cannot pass through
ENVIRONMENTAL POLLUTION PHENOMENA
Acid rain
· Acid rain is form of rain that is unusually acidic i.e. has low pH
· Acid rain is mostly caused by emission of sulphur, nitrogen and carbon which react with water molecules in the atmosphere to produce acids
· The biggest human activity causes of acid rain include coal-based power plants, factories and automobile emissions
· It can also be caused by natural phenomena such as
Ø lightning strikes (which splits nitrogen compounds)
Ø volcanic eruptions (which release large quantities of sulphur dioxide)
· Natural (unpolluted) rain is slightly acidic with pH of 5.2 due to the reaction of carbon dioxide with water to produce carbonic acid
· Acid rain has many adverse effects including
Ø Damage to aquatic animals
Ø Damage to soil chemistry by killing off essential microbes
Ø Loss of forests and vegetation
Ø Human illnesses such as cancer, asthma and other diseases
Ø Damage to buildings and historical monuments (esp. those made of limestone and marble)
Ocean acidification
· Ocean acidification is the continuing phenomenon of decreasing pH in the world’s oceans
· Between 1751 and 1994, ocean pH is estimated to have decreased from 8.179 to 8.104 (decrease of 0.075). Ocean pH is expected to decrease by a further 0.3-0.5 by 2100
· This acidification is mainly the result of uptake of carbon dioxide from the atmosphere. The world’s oceans naturally absorb carbon dioxide from the atmosphere, indirectly mitigating climate change
· Ocean acidification adversely affects marine organisms especially calcifying organisms like corals, crustaceans and molluscs, and also affects other organisms by entering the food chain
Soli salination
· Salt affected soils are caused by excess accumulation of salts at the soil surface
· Salt can be transported to the soil surface by capillary action from salt-laden water tables, or by human activity
· Increasing soil salinity adversely affects soil quality and vegetation
· Human activities that increase soil salinity include
Ø Land clearing
Ø Aquaculture activities (shrimp farms etc)
Ø Irrigation (over a period time causes deposition of salts)
· The adverse effects of salination include
Ø loss of soil fertility
Ø damage to infrastructure (such as roads etc)
Ø damage to plant growth and yield
Ø deterioration of underground water quality
Ø soil erosion
COMMON ENVIRONMENTAL TOXINS
1. Chlorofluorocarbons
1. They are organic compounds that contain carbon, chlorine and fluorine
2. Examples of CFCs include Freon, Teflon
3. CFCs have been widely used as refrigerants, propellants (in aerosols) and solvents
4. The use of CFCs has been banned under the Montreal Protocol due to their adverse effect on the ozone layer
2. Endocrine disruptors
1. Endocrine disruptors are substances that affect the function of natural hormones in the body
2. Food is the main source of exposure to endocrine disruptors
3. There are five main types of endocrine disruptors:
1. DDT
2. Polychlorinated biphenyls
3. Bisphenol A
4. Polybrominated diphenyl ethers
5. Pthalates
3. DDT
1. Dichlorodiphenyltrichloroethane (DDT) is one of the most well-known synthetic pesticides
2. DDT is one of the most effective and simple to deploy pesticides, especially to fight mosquitoes that cause malaria and typhus
3. DDT has significant adverse effect on aquatic life, insects and humans (esp. diabetes and reproductive disorders)
4. It is a significant reproductive toxicant for certain bird species, and is a major reason for the decline of the bald eagle, brown pelican peregrine falcon and osprey. This is the main reason DDT use has been banned
5. The use of DDT for agricultural use has been banned under the Stockholm Convention, however it can still be used for disease vector control (mosquito eradication)
4. Polychlorinated biphenyls (PCBs)
1. PCBs are a class of industrial compounds
2. They are used mainly as industrial coolants and lubricants
3. Exposure to PCBs increases the risk of skin cancer, brain cancer and liver cancer. Additionally it also increases childhood obesity and the risk of developing diabetes
4. The use of PCBs was banned in 1977
5. Bisphenol A (BPA)
1. BPA is an organic compound with two functional phenol groups
2. BPA is used as a building block of several important plastics and plastic additives
3. It is found commonly in water bottles, plastic food containers and the lining of infant formula cans
4. The use of BPA has been linked to diabetes, mammary and prostrate cancers, reproductive problems, obesity and neurological disorders
5. BPA use has not been banned
6. Polybrominated diphenyl ethers (PBDE)
1. PBDEs are a class of compounds used as flame retardants
2. They are used commonly in televisions, computers, electronics, carpets, bedding, clothing car components etc
3. PBDEs have the potential to affect thyroid balance, and contribute to a variety of neurological and developmental disordersincluding learning disabilities and low intelligence
4. Many of the most common PBDEs were banned by the European Union in 2006
7. Phthalates
1. Phthalates are esters of phthalic acid
2. They are mainly used as plasticisers to soften polyvinyl chloride (PVC)
3. Phthalates are found in soft toys, flooring, medical equipment, cosmetics and air fresheners
4. Phthalates have been shown to have adverse effects on the male reproductive system
5. The EU and the US have begun phasing out widespread use of phthalates
8. Dioxins
1. Polychlorinated dibenzodioxins (PCDDs) are a group of polyhalogenatated compounds
2. The main sources of Dioxins include
1. By-products in the manufacture of organochlorides
2. in the incineration of chlorine containing substances (like PVC)
3. bleaching of paper
4. natural sources like volcanoes and forest fires
3. Dioxins accumulate and build up in the food chain (bioaccumulation)
4. Health effects of dioxins include
1. Severe form of acne called chloracne
2. Abnormalities in teeth enamel of children
3. Nervous system pathology
4. Thyroid disorders
5. Diabetes
6. Damage to immune system
5. Exposure to dioxins has been shown to affect the ratio of male to female births, such that more females are born than males
CHEMISTRY: PROPELLANTS
Ø A propellant is a material that is used to propel an object
Ø The object is usually expelled by the pressure created by a gas
Ø This pressure may be created by a compressed gas or by a gas produced by a chemical reaction
Ø Propellants may be solids, liquids, gases or plasmas
Ø Common chemical propellants consist of a fuel and an oxidiser
Types of propellants
Ø Aerosol sprays
· Aerosol spray is a dispensing system that creates an aerosol (fine) mist of liquid particles
· In aerosol sprays, the propellant is simply a pressurised gas in equilibrium with its liquid form
· As some gas escapes to expel the payload, more liquid evaporates thereby maintaining an even pressure
· The aerosol spray can was invented by Erik Rotheim (Norway) in 1927
· Aerosol sprays are typically used to dispense insecticides, deodorants and paints
Ø Propellants used for propulsion
· Rockets typically use bipropellants, which contain a combination of a fuel and an oxidiser. Tripropellants, which are not used commonly, use liquid hydrogen as a third component to provide additional efficiency
· Propellants are usually made from low explosives, which deflagrate (burn) rather than detonate (explode)
· The controlled burning of the propellants produces thrust by gas pressure which is then used to accelerate a rocket, projectile or other vehicles
· Propellants are commonly used in rockets, firearms and artillery
Solid propellants
Ø Solid propellants are used for rockets, firearms and artillery
Ø Examples of solid propellants include gunpowder (sulphur + charcoal + potassium nitrate), nitrocellulose and cordite
Ø Single based propellants: They have nitrocellulose as its chief ingredient. Stabilizers and other chemicals may be added for chemical stability
Ø Double based propellants: they contain nitrocellulose with nitroglycerin or other liquid nitrate explosives added. Nitroglycerin reduces smoke and increases energy output. Used in small arms, cannons, mortars and rockets
Ø Triple based propellants: consist of nitrocellulose, nitroquanidine, and nitroglycerin or other nitrate explosives. Used in cannons
Ø Composite propellants: consist of a fuel such as metallic aluminium, a binder such as synthetic rubber and an oxidiser such as ammonium perchlorate. Used in large rocket motors such as spacecraft
Ø Solid propellants have been used since the 11th century to power rockets based on gunpowder
Ø Solid fuel rockets offer ease of handling, reliability and long storage periods
Ø Solid fuel rockets are used for missiles due to their long storage periods and reliability of launch on short notice
Ø Currently, solid fuel rockets are not used for space explorations, but are commonly used as booster rockets to launch spacecraft
Liquid propellants
Ø Liquid propellants are usually used in combinations of fuel and oxidiser
Ø Common liquid propellant combinations include
· Liquid oxygen and liquid hydrogen
· Liquid oxygen and kerosene
· Nitrogen tetraoxide and kerosene
Ø Liquid fuel rockets are desirable because they offer higher energy output, they can be throttled and shut down and can be reused
Ø Liquid fuel rockets are used to power space shuttles
Ø A variant of liquid fuel engine is cryogenic fuel engine – these are engines that use gases which are super-cooled into their liquid forms
Propellants used in the PSLV
Ø The Polar Satellite Launch Vehicle (PSLV) has a four stage propulsion system, using solid and liquid propellants alternately
Ø First stage: solid – Hydroxyl terminated polybutadiene (HTPB)
Ø Second stage: liquid – unsymmetrical di-methyl hydrazine (UDMH) as fuel and nitrogen tetraoxide as oxidiser
Ø Third stage: solid – HTPB
Ø Fourth stage: solid – mono methyl hydrazine as fuel and mixed oxides of nitrogen as oxidiser
Propellants used in the GSLV
Ø The Geosynchronous Satellite Launch Vehicle (GSLV) is a three stage launch vehicle using solid, liquid and cryogenic propellants
Ø First stage – solid – HTPB
Ø Second stage – liquid – UDMH as fuel and nitrogen tetraoxide as oxidiser
Ø Third stage – cryogenic – liquid hydrogen and liquid oxygen
CHEMISTRY: EXPLOSIVES
Ø An explosive is a substance that contains a great deal of stored energy that can produce an explosion, usually accompanied by the production of light, heat and pressure
Ø The energy stored in an explosive material may be
· Chemical energy such as nitroglycerine
· Pressurised compressed gas such as a gas cylinder or aerosol can
· Nuclear energy such as Uranium and plutonium
CHEMICAL REACTIONS IN EXPLOSIVES
1. Deflagration
1. Deflagration is a term that describes subsonic combustion that propagates through thermal conductivity
2. Deflagration is easier to control and so is used when the goal is to move an object with the force of expanding gas
3. Examples of deflagration include gas stove, internal combustion engine, gunpowder, pyrotechnics etc
2. Detonation
1. Detonation is a combustion process in which a supersonic shock wave through the body of a material
2. In detonation, a supersonic shock wave originating at the point of ignition compresses the surrounding material, thus increasing its temperature to the point of ignition
3. Because detonations generate high pressures, they are much more destructive than deflagrations
4. Detonations are difficult to control and are used primarily for demolition and in warfare.
5. Examples of detonation includes high explosives, oxygen-methane mixture
CLASSIFICATION OF EXPLOSIVES
1. High explosives
ü Materials that explode faster than the speed of sound are called high explosives
ü This type of explosion is known as detonation
ü Used in mining, demolition and military applications
1. Low explosives
1. Materials that explode slower than the speed of sound are called low explosives.
2. This type of explosion is known as deflagration
3. Used as propellants, gun powder, pyrotechnics (such as flares and fireworks)
2. Primary explosives
1. A primary explosive is an explosive that is extremely sensitive to stimuli. These stimuli include impact, friction, heat, static electricity and electromagnetic radiation
2. For primary explosives, a relatively small amount of energy is required for initiation of explosion
3. In general, primary explosives are considered to be those explosives that are more sensitive than PETN
4. Used in detonators to trigger larger charges of more stable secondary explosives
5. E.g.: Mercury fulminate, Nitrogen trichloride, acetone peroxide, ammonium permanganate
3. Secondary explosives
1. Secondary explosives are less sensitive than primary explosives and require more energy to be initiated
2. They are safer to handle and store
3. In general, secondary explosives are considered to be those explosives that are less sensitive than PETN
4. Secondary explosives are usually used in large quantities and are initiated by small amounts of primary explosives
5. E.g.: TNT, RDX
SOME COMMON EXPLOSIVES
1. Trinitrotoluene (TNT)
1. TNT is a useful explosive material with convenient handling properties. TNT is sometimes also used as a reagent in chemical synthesis
2. TNT was first prepared by Joseph Wilbrand (GermanY) in 1863
3. The explosive yield of TNT is considered to be the standard measure of strength of bombs and other explosives
4. Sulphitation is a process used in the manufacture of TNT, specifically to stabilize the explosive
5. TNT is one of the most commonly used explosives for industrial and military applications
6. It is insensitive to shock and friction, reducing the occurrence of accidental detonation. TNT melts without exploding (allowing it to be combined with other explosives), does not absorb or dissolve in water (allowing use in wet environments) and is stable compared to other explosive
7. TNT contains energy of 4.6 Mega Joules per kilogram (MJ/kg). By comparison gun powder contains 3 MJ/kg, dynamite contains 7.5 MJ/kg and gasoline contains 47.2 MJ/kg
8. TNT is used as a reference for other explosives. Nuclear weapons have energy content measured in kilotonnes (kT) or megatonnes (MT) of TNT equivalent.
9. TNT is usually used in mixture with other substances. E.g.: Amatol (TNT + ammonium nitrate)
2. RDX
1. RDX, chemically cyclotrimethylnetrinitramine, is also known as cyclonite and T4
2. RDX is usually used in mixture with other explosives and plasticizers
3. RDX is stable in storage and is considered one of the most powerful of military explosives
4. RDX was discovered in 1898 by Goerg Friedrich Henning (Germany)
3. Pentaerythritol tetranitrate (PETN)
1. PETN is one of the most powerful high explosives known
2. It is more difficult to detonate than primary explosives, but less stable than secondary explosives
3. It is more sensitive than other high explosives, and is rarely used alone
4. Usually used in small calibre ammunition, detonators of land mines
5. PETN is an effective underwater explosive
6. PETN is a major ingredient of Semtex (plastic explosive)
7. PETN was first synthesised by Bernhard Tollens (Germany) in 1891
4. Dynamite
1. Dynamite is based on nitroglycerine
2. It was invented by Alfred Nobel (Sweden) in 1867
3. Used mainly for mining, quarrying, construction
4. Dynamite was the first safely manageable explosive stronger than black powder
5. Plastic explosive
1. Plastic explosives are explosives that are soft and can be moulded by hand
2. Common plastic explosives include Semtex (Czech Republic) and C-4 (USA)
3. Used mainly for demolition, also used by terrorists
4. The first plastic explosive was Gelignite, invented by Alfred Nobel (Sweden) in 1875
5. C-4 (composition 4) is made of RDX while Semtex is made from RDX and PETN
6. Semtex became notoriously popular with terrorists because it is difficult to detect. Semtex was invented by Stanislav Berbera (Czech R.) in the 1950s
CHEMISTY: CERAMICS
Ø A ceramic is an inorganic, non-metallic solid prepared by the action of heating and subsequent cooling
Ø The earliest ceramic materials were pottery made from clay
Ø Ceramics are resistant to chemical erosion and high temperatures (up to 1600C)
PROPERTIES OF CERAMICS
Ø Mechanical properties
· Ceramic materials are usually formed by ionic or covalent bonds
· These materials tend to not be elastic and fracture easily
· Ceramics are also porous
· In general ceramics have poor toughness and have low tensile strength
Ø Electrical properties
· Some ceramics are semiconductors
· Semiconducting ceramics are made using zinc oxide
· Under extremely low temperatures, some ceramics exhibit superconductivity
· Most ceramics exhibit piezoelectricity i.e. the conversion of mechanical stress to electrical signals. This effect is commonly used in quartz watches
Ø Optical properties
· Ceramics (esp. those based on aluminium oxide) can be made translucent
· This has immediate applications in sodium-vapour lamps and dental restorations
· Ceramics can be made transparent with applications in laser technology
TYPES OF CERAMICS
1. Structural ceramics such as bricks, pipes, floor, roof tiles etc
2. Refractory ceramics such as kiln lining, steel and glass making crucibles
3. Whitewares such as tableware, wall tiles, pottery, sanitary products
4. Technical ceramics such as jet engine turbine blades, ballistic protection etc
MANUFACTURE OF CERAMICS
1. Milling
1. Process by which materials are reduced in size
2. Involves breaking of cemented material or pulverization
3. Techniques used include ball mill, roll crusher, jaw crusher, wet attrition mills
2. Batching
1. Is the process of weighing the oxides according to recipes and preparing them for further processing
3. Mixing
1. Involves mixing the various components in the appropriate proportions
2. Uses ribbon mixers, Mueller mixers and pug mills
4. Forming
1. This is the process of the making the mixed materials into desired shapes such as toilet bowls, spark plugs etc
2. Forming techniques include extrusion, pressing and slip casting
5. Drying
1. Controlled heat is applied to dry the materials and obtain rigid shape
6. Firing
1. Dried parts are processed through a controlled heating process and oxides are chemically changed to cause sintering and bonding
BIO-CERAMICS
o Bacteria, plants and animals exhibit a tendency to form crystalline materials composed of silicon
o These bioceramics show exceptional physical properties such as strength, fracture resistance etc
o Bio-ceramics are usually made of proteins such as keratin, elastin, chitin and collagen
o The mother-of-pearl portion of marine shells exhibit the strongest mechanical strength and fracture toughness of any non-metallic substance known
APPLICATIONS OF CERAMICS
| Application | Ceramic components | Notes |
| Armoured vests | Alumina, boron carbide | Protects against high-calibre rifle fire |
| Dental implants, synthetic bone | Artificial hydroxyapatite (natural mineral of bone) | |
| Ball bearings | Silicon nitride | Harder, more resistant to heat than metal bearings |
| Earthenware | Kaolin, boll, flint | Opaque, Used to make cups, saucers etc |
| Chinaware | Leached granite (to remove quartz and mica) | Translucent, Resists scratching |
| Porcelain | Kaolin, feldspar, quartz | White, semi-opaque, Highly resistant to scratching Stronger than glass |
| Stoneware | Kaolin, feldspar, quartz | Similar to porcelain but from poor grade raw materials, Hard, infusible |
| Space shuttles | Extremely pure Silica | Used on the outer surface of shuttles to withstand heating during atmospheric re-entry Space shuttle Colombia burnt up on re-entry due to damage to ceramic tiles |
CHEMISTRY: POLYMERS
Ø A polymer is a large molecule consisting of repeating structural units
Ø The repeating units are usually connected by covalent chemical bonds
Ø Polymers can be of two types
· Natural polymers: shellac, amber, rubber, proteins etc
· Synthetic polymers: nylon, polyethylene, neoprene, synthetic rubber etc
Ø Synthetic polymers are commonly referred to as plastics
Ø The first plastic based on a synthetic polymer to be created was Bakelite, by Leo Baekeland(Belgium/USA) in 1906
Ø Vulcanization of rubber was invented by Charles Goodyear (USA) in 1839. Vulcanization is the process of making rubber more durable by addition of sulphur
Ø The first plastic to be created was Parkesine (aka celluloid) invented by Alexander Parkes (England) in 1855
Synthesis of polymers
Ø The synthesis of polymers – both natural and synthetic – involves the step called polymerization
Ø Polymerization is the process of combining many small molecules (monomers) into a covalently bonded chain (polymer)
Ø Synthetic polymers are created using of two techniques
· Step growth polymerization: chains of monomers are combined directly
· Chain growth polymerization: monomers are added to the chain one at a time
Ø Natural polymers are usually created by enzyme-mediated processes, such as the synthesis of proteins from amino acids using DNA and RNA
Categories of polymers
Ø Organic polymers are polymers that are based on the element carbon. Eg: polyethylene, cellulose etc
Ø Inorganic polymers are polymers that are not based on carbon. Eg: silicone, which uses silicon and oxygen
Ø Copolymer is one that is derived from two or more monomeric units. Eg: ABS plastic
Ø Fluoropolymers are polymers based on fluorocarbons. They have high resistance to solvents, acids and bases. Eg: teflon
TYPES OF BIOPOLYMERS
DNA as a biopolymer
1. Structural proteins
1. Structural proteins are proteins that provide structural support to tissues
2. They are usually used to construct connective tissues, tendons, bone matrix, muscle fibre
3. Examples include collagen, keratin, elastin
2. Functional proteins
1. Proteins that perform a chemical function in organisms
2. Usually used for initiate or sustain chemical reactions
3. Examples include hormones, enzymes
3. Structural polysaccharides
1. They are carbohydrates that provide structural support to cells and tissues
2. Examples include cellulose, chitin
4. Storage polysaccharides
1. Carbohydrates that are used for storing energy
2. Eg: starch, glycogen
5. Nucleic acids
1. Nucleic acids are macromolecules composed of chains of nucleotides
2. Nucleic acids are universal in living beings, as they are found in all plant and animal cells
3. Eg: DNA, RNA
TYPES OF SYNTHETIC POLYMERS
1. Thermoplastics
1. Thermoplastics are plastics that turn into liquids upon heating
2. Also known as thermosoftening plastic
3. Thermoplastics can be remelted and remoulded
4. Eg: polyethylene, Teflon, nylon
5. Recyclable bottles (such as Coke/Pepsi) are made from thermoplastics
2. Thermosetting plastics
1. Thermosettings plastics are plastics that do not turn into liquid upon heating
2. Thermosetting plastics, once cured, cannot be remoulded
3. They are stronger, more suitable for high-temperature applications, but cannot be easily recycled
4. Eg: vulcanized rubber, bakelite, Kevlar
3. Elastomers
1. Elastomers are polymers that are elastic
2. Elastomers are relatively soft and deformable
3. Eg: natural rubber, synthetic polyisoprene
IMPORTANT NATURAL POLYMERS AND THEIR APPLICATIONS
| Polymer | Application | Notes |
| Collagen | Connective tissue Gelatine (food) | Most abundant protein in mammals |
| Keratin | Hair, nails, claw etc | |
| Enzymes | Catalysis | |
| Hormones | Cell signalling | |
| Cellulose | Cell wall of plants, Cardboard, paper | Most common organic compound on Earth |
| Chitin | Cell wall of fungi, insects | |
| Starch | Energy storage in plants | Most important carbohydrate in human diet |
| Glycogen | Energy storage in animals | |
| DNA | Genetic information | |
| RNA | Protein synthesis |
IMPORTANT SYNTHETIC POLYMERS AND THEIR APPLICATIONS
| Polymer | Developed by | Constituent elements | Application | Notes |
| Parkesine | Alexander Parkes (Britain, 1855) | Cellulose | Plastic moulding | First man-made polymer |
| Bakelite | Leo Baekeland (USA, 1906) | Phenol and formaldehyde | Radios, telephones, clocks | First polymer made completely synthetically |
| Polyvinylchloride (PVC) | Henri Regnault (France, 1835) | Vinyl groups and chlorine | Construction material | Third most widely used plastic |
| Styrofoam | Ray McIntre (USA, 1941) | Phenyl group | Thermal insulation | Brand name for polystyrene |
| Nylon | Wallace Carothers (USA, 1935) | Amides | Fabric, toothbrush, rope etc | Family of polyamides First commercially successful synthetic polymer |
| Synthetic rubber | Fritz Hoffman (Germany, 1909) | Isoprene | Tyres, textile printing, rocket fuel | |
| Vulcanized rubber | Charles Goodyear (USA, 1839) | Rubber, sulphur | Tyres | Vulcanized rubber is much stronger than natural rubber |
| Polypropylene | Karl Rehn and Guilio Natta (Italy, 1954) | Propene | Textiles, stationary, automotive components | Second most widely used synthetic polymer |
| Polyethylene | Hans von Pechmann (Germany, 1898) | Ethylene | Packaging (shopping bags) | Most widely used synthetic polymer |
| Teflon | Roy Plunkett (USA, 1938) | Ethylene | Cookware, construction, lubricant | Brand name for polytetrafluoroehtylene (PTFE) Very low friction, non-reactive |
DEGRADATION OF POLYMERS
Ozone cracking in natural rubber tubing
Ø Degradation of polymers can be desirable as well undesirable: desirable when looking for biological degradation, undesirable when faced with loss of strength, colour etc
Ø Polymer degradation usually occurs due to hydrolysis of covalent bonds connecting the polymer chain
Ø Polymer degradation can happen because of heat, light, chemicals and galvanic action
Ø Ozone cracking is the cracking effect of ozone on rubber products such as tyres, seals, fuel lines etc. Usually prevented by adding antiozonants to the rubber before vulcanization
Ø Chlorine can cause degradation of plastic as well, especially plumbing
Ø Resin Identification Code is the system of labelling plastic bottles on the basis of their constituent polymers. This Code helps in the sorting and recycling of plastic bottles
Ø Degradation of plastics can take hundreds to thousands of years
Biodegradable plastics
Ø Biodegradable plastics are plastics than can break down upon exposure to sunlight (especially UV), water, bacteria etc
Ø Biopol is a biodegradable polymer synthesized by genetically engineered bacteria
Ø Ecoflex is a fully biodegradable synthetic polymer for food packaging
Bioplastics
Ø They are organic plastics derived from renewable biomass sources such as vegetable oil, corn, starch etc
Oxy-biodegradable plastics
Ø Plastics to which a small amount of metals salts have been added
Ø As long as the plastic has access to oxygen the metal salts speed up process of degradation
Ø Degradation process is shortened from hundreds of years to months
CHEMISTRY: FERTILIZERS AND PESTICIDES
About fertilizers
Ø Fertilizers are soil amendments applied to promote plant growth
Ø Can be applied to soil or directly to leaves
Ø Main nutrients in a fertilizer are nitrogen, phosphorous and potassium
Synthetic fertilizers
Ø Synthetic fertilizers are manufactured using the Haber-Bosch process to produce ammonia, which is then used to manufacture other nitrogen fertilizers
Ø Urea is the most commonly used fertilizer. It has the highest nitrogen content
Ø Synthetic fertilizers do not replace trace minerals in the soil (eg Zinc, copper, magnesium etc)
Ø Production of synthetic fertilizers is highly energy intensive. The production of synthetic ammonia currently accounts for 5% of global natural gas consumption
Ø Excess and unregulated use of synthetic fertilizers can cause Fertilizer Burn, in which plant tissues die due to excess nitrogenous salts
Biofertilizers
Ø Include naturally occurring minerals such as manure, worm castings, compost, etc.
Ø Primary sources of biofertilizers are
· Bacteria: Rhibozium, Azopirillum
· Fungi: Mycorrhiza
· Fern: Azolla
Ø Cover crops can also be used to enrich soil between plantings of the main crop. Cover crops work through the principle of nitrogen fixation: i.e. convert atmospheric nitrogen into a plant-accessible form
Ø Minerals such as limestone, rock phosphate and sulphate of potash can also be used
Ø Biofertilizers release their nutrients much slowly compared to synthetic fertilizers and thereby prevent Fertilizer Burn
Ø In addition to improving crop yields, biofertilizers also improve the health and long-term productivity of soil
Environmental effects of fertilizer use
Ø Oxygen depletion: Nitrogen compounds in fertilizer run-off are primarily responsible for serious oxygen depletion in oceans and lakes. This lack of dissolved oxygen causes serious damage to aquatic life in lakes and along coastal areas. Also leads to discolouration of water (green, yellow, red, brown)
Ø Soil acidification: Nitrogen containing synthetic fertilizers cause soil acidification
Ø Heavy metal accumulation: Synthetic fertilizers, especially those based on phosphates, can contain significant amounts of cadmium, uranium, zinc, lead and radioactive polonium, all of which can be stored in plant tissues, and later enter the food chain in the form of produce
Ø Greenhouse gases: Due to the large scale use of fertilizers, nitrous oxide has now become the third most important greenhouse gas (after carbon dioxide and methane).
PESTICIDES
Ø A pesticide is a substance that is used to kill pests
Ø Pests can include insects, molluscs, birds, weeds etc
Ø In addition to preventing crop losses due to pests, pesticides can kill disease-spreading mosquitoes, allergy inducing bees or wasps, and also to control algae levels in lakes
Ø Due to its negative effects on birds, DDT has been banned as a pesticide for agricultural use under the 2001 Stockholm Convention. However, it is still used in developing countries for malaria prevention and other vector control
Commonly used pesticides
| Pesticide | Used to control | Example |
| Algaecide | Algae | Copper sulphate, barley straw |
| Avicide | Birds | Strychnine, DRC1339, parathion (in diesel oil) |
| Bactericides | Bacteria | Chlorine, iodine, oxygen, alchohol, phenol |
| Fungicide | Fungi, oomycete (water molds) | Sulphur, neem oil, tea tree oil, rosemary oil, milk |
| Herbicide | Weeds | Dichlorophenoxyacetic acid (2,4D), atrazine, glyphosate |
| Insecticide | Insects | Organochlorine, organophosphates, carbamates, pyrethroids |
| Miticide | Mites | Methoprene, permethrin, dicofol |
| Molluscicides | Molluscs (slugs and snails) | Metal salts (iron phosphate, aluminium sulphate), metaldehyde |
| Nematicide | Nematodes (worms) | Nematophagus fungi, neem cake |
| Rodenticide | Rodents | Anticoagulants, metal phosphides, hypercalcemia |
Environmental effects of pesticides
Ø Over 98% of insecticides and 95% of herbicides reach a destination other than their target species
Ø Pesticides contaminate land and water when they run-off from fields, when discarded, sprayed etc
Ø Air pollution: pesticide drift occurs when pesticides suspended in the air get carried away to other areas. Pesticides also react with other chemicals to produce ozone, accounting for about 6% of total ozone production
Ø Water pollution: run-off and eroding soil lead to pesticide pollution of water. This affects water solubility, and also the pesticides enter the food chain through water. Some pesticides are toxic to fish, kill off zooplankton (the main food source for fish). Harmful to amphibians such as tadpoles and frogs
Ø Soil contamination: nitrogen fixation is affected by pesticides in soil. Pesticides also kill bees and are responsible for pollinator decline, leading to decreased crop yields. Widespread use of pesticides eliminates animals’ food sources causing them to change food habits or starve. Pesticide poisoning also travels up the food chain
Pest resistance and rebound
Ø Pests may evolve to become resistant to pesticides
Ø Managed through pesticide rotation
Ø Mixture of pesticides may also be used
Ø Certain pests sometimes themselves act as pesticides in the sense that they control other pests. In this case pesticides that target one pest species may lead to a secondary pest outbreak due to the other species
Ø Also, sometimes use of pesticides may affect natural enemies of the pest more than the pest itself. In this case, the pesticide may lead to temporary decrease in pest populations, but in the long-term the pest population may increase due to the absence of its natural enemies (especially for mosquitoes). This is called pest rebound.
CHEMISTRY: RADIOACTIVITY
Ø It is the process by which an unstable atomic nucleus spontaneously decays (loses energy) by emitting ionizing particles and radiation
Ø This decay results in the atom of one type (parent nuclide) transforming into an atom of a different type (daughter nuclide)
Ø Eg: Carbon-14 emits radiation and transforms into nitrogen-14
Ø The SI unit of radioactivity is Becquerel (Bq). Another commonly used unit is the Curie (Ci)
Ø Radioactivity of a material is quantified by its half life. This is the time taken for a given amount of a radioactive material to decay to half its initial value
Ø Radiation can be measured using scintillation counters and Geiger counters
History of radioactivity research
Ø Radioactivity was first discovered by French scientist Henri Becquerel in 1896
Ø Research in radioactivity of uranium led Marie Curie to isolate a new element Polonium and to separate Radium from Barium
Ø The dangers of radioactivity was discovered by Nikola Tesla in 1896, when he intentionally subjected his fingers to X-rays
Ø Henri Joseph Muller was awarded the Nobel Prize in Physiology or Medicine in 1946 for his discovery (in 1927) of the harmful genetic effects of radiation
Transmutation of elements
Ø Isotopes: they are atoms of an element with the same atomic number but different mass number (eg uranium-238 and uranium-235)
Ø Isobars: elements with same mass number but different atomic number. Usually occurs when a radioactive nucleus loses a beta particle (eg. Thorium-234 and palladium-234)
Ø Isotones: radioactive nuclei that contain the same number of neutrons (eg. Radium-226 and Actium-227)
Ø Isomers: are different excitation states of nuclei. The higher-energy (unstable) element undergoes isomeric transition to form the less energetic variant without change in atomic or mass number
Types of radioactive decay
Alpha rays can be stopped by a sheet of paper, beta rays by aluminium shielding, while gamma rays can only be reduced by a thick layer of lead
Ø Radioactive radiation can be split into three types of beams
Ø Alpha rays: they are helium particles that carry a positive charge. They have low energy and can be stopped by a sheet of paper
Ø Beta rays: they are streams of electrons and carry negative charge. They have higher energy than alpha rays
Ø Gamma rays: they are high energy rays (like X-rays) that carry no electrical charge
Radioactivity and the Big Bang theory
Ø According to the Big Bang theory stable isotopes of the lightest elements (H, He, Li, Be, B) were formed immediately after the Big Bang
Ø Radioactive (unstable) isotopes of these light elements have long since decayed, and isotopes of elements heavier than boron were not produce at all in the Big Bang
Ø Thus, the radioactive materials currently in the universe were formed later and are relatively young compared to the age of the universe
Ø These radioactive nuclei were formed in nucleosynthesis in stars and during interactions between stable isotopes and energetic particles
Ø For instance, carbon-14 is constantly produced in the earth’s upper atmosphere due to interactions between cosmic rays and nitrogen
Applications of radioactivity
Ø Radioisotopic labeling: used to track the passage of a chemical through the human body. Some common radio isotopes used for labeling are
· Tritium: used to label proteins, nucleic acids
· Sodium-22 and Sodium-36: ion transporters
· Sulphur-35: proteins and nucleic acids
· Phosporous-32 and Phosphorous-33: nucleotides (like DNA)
· Iodine-125: thyroxine
· Carbon-14 is not used for radioactive labeling due to its long half life (5730 years)
Ø Random number generators: based on the premise that radioactive decay is truly random
Ø Radiometric dating: used to date materials based on a comparison between observed abundance of radioactive isotopes and its decay products, using known decay rates. The most common methods of radiometric dating are
· Carbon dating: when organic matter grows, it traps carbon-14. The age of the organic matter can be estimated by measuring the amount carbon-14 remaining in the body. Used for dating material up to 60,000 years old
· Potassium-argon dating: used in geochronology and archeology, especially for dating volcanic material. Used for samples older than a few thousand years
· Uranium-lead: one of the oldest and most refined radiometric dating techniques. Used in geochronology to estimate material from 1 million to 4.5 billion years old. A variant, the lead-lead dating scheme was used by American scientist Clair Cameron Patterson to estimate the age of the earth (4.55 billion years) in 1953
Radioactive therapy
Ø Used for palliative and therapeutic treatment
Ø Common applications include treatment of thyroid eye disease, heterotopic ossification, trigeminal neuralgia
Ø In low doses, it is used for cancer treatment. However, in large doses, it can cause cancer
Ø Total body irradiation is used to prepare the body to receive a bone marrow transplant
Radiation poisoning
Ø It is a form of damage to organ tissue due to excessive exposure to ionizing radiation
Ø Caused by exposure to large doses of radiation in short periods of time, or by exposure to small doses over long periods
Ø Increases the probability of contracting other diseases like cancers, tumours and genetic damage
Ø Common symptoms are nausea and vomiting
Ø Common occurrances of radiation poisoning include nuclear warfare, nuclear reactor accidents, spaceflight (exposure to cosmic rays), ingestion and inhalation of radioactive compounds (such as strontium in cow’s milk)
· In Nov 2006, Russian dissident died due to suspected deliberate ingestion of Polonium-210
CHEMISTRY: ELECTROLYTES
Electrolytes in the human body
Ø Electrolytes are required in the body to maintain balance between intracellular and extracellular liquids. In particular, it is important to maintain the osmotic gradient between inside and outside.
Ø Electrolyte balance is maintained by oral and intravenous intake
Ø Kidneys flush out excess electrolytes
Ø Dehydration and overhydration are caused by electrolyte imbalance
Ø Hormones that maintain electrolyte balance are antidiuretic hormone, aldosterone and parathyroid hormone
Ø The most common electrolyte in the body is salt (sodium chloride)
Functions of electrolytes in the body
Ø Maintain blood pH
Ø Muscle and neuron activation
Ø Hydration of the body
Other common applications of electrolytes
Ø Sports drinks
Ø Batteries
Ø Fuel cells
Ø Electroplating
Ø Capacitors
Sports Drinks
Ø Sports drinks replenish the body’s water and electrolyte levels after dehydration caused by exercise, vomiting, diarrhea etc.
Ø They are made of electrolytes containing sodium and potassium salts
Ø Examples of sports drinks: Glucon-D, Gatorade etc
Ø Simplest electrolyte drink that can be made at home is water + sugar + salt
Batteries
| Battery | Electrode | Electrolyte | Other notes |
| Alkaline | Zinc, Manganese oxide | Potassium Hydroxide | |
| Daniell cell | Copper, Zinc | Copper sulphate, zinc sulphate | |
| Leclanche cell | Zinc, carbon | Ammonium chloride | Precursor of modern dry cell |
| Voltaic pile | Copper, zinc | Brine | First electric battery, invented in 1880 |
| Zinc carbon | Zinc, carbon, manganese dioxide | Zinc chloride, ammonium chloride | Most common battery |
| Zinc chloride | Same as above | Zinc chloride | Improvement on zinc carbon battery |
| Lead-acid | Lead, lead dioxide | Sulphuric acid | Oldest rechargeable battery Used in vehicles as they provide high surge currents |
| Lithium-ion | Graphite, Lithium Cobalt oxide | Non-aqueous lithium salts | Rechargable Slow self-discharge, high energy to weight ratio |
| Nickel Cadmium | Nickel oxide hydroxide, cadmium | Rechargable Last longer, more stable than lithium ion | |
| Fuel cell | Hydrogen (fuel), oxygen (oxidant) | Polymer membrane Aqueous alkaline solution | Consumes reactant from an external source High energy efficiency and high reliability No moving parts Used in space shuttles, submarines |
Common electrolytes and their uses
| Electrolyte | Uses | Other notes |
| Sodium chloride | Primary component of extracellular fluid Food preservative | |
| Sodium hydroxide (caustic soda) | Manufacture of paper, soaps, detergents, drain cleaners Purification of drinking water | |
| Silver nitrate | Photographic films Water disinfection (esp. on space shuttles) | |
| Hydrochloric acid | Manufacture of PVC, household cleaners Food additives (like gelatin) Leather processing | Found naturally in gastric acid |
| Sulphuric acid | Lead-acid batteries Ore processing Fertilizer manufacture | Soluble in water at all concentrations One of the largest products of chemical industry |
| Nitric acid | Determining metal traces in solutions Wood finishing | Colourless when pure, yellows with age Highly corrosive |
| Acetic acid | Manufacture of soft drink bottles Photographic films Synthetic fibres and fabrics | Dilute acetic acid is called vinegar |
| Ammonium hydroxide (aqueous ammonia) | Cleaning agent | |
| Calcium hydroxide (slaked lime or pickling lime) | Sewage treatment Whitewash, plaster, mortar Hair relaxers | Natural mineral form is called portlandite (rare mineral occurring in volcanic rocks) |