general science-chemistry-1

CHEMISTRY: 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
  

  Overview
  
  
• 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
  • Heavy metal contamination of land by industry. These can transported to water bodies and taken up ingested by living organisms
  • Nutrients leaching from agricultural land into water sources
    
  • 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)
  
  • It is a relative measure of the amount of oxygen dissolved in water.
    
  • Supersaturation (excess of oxygen) can be harmful to organisms and also cause decompression sickness
    
  • It is expressed in mg/l
    
• Chemical Oxygen Demand (COD)
  
  • COD is used to indirectly measure the amount of organic compounds in water
    
  • It is expressed in mg/l, which indicates the amount of oxygen consumed per litre of water
    
• Biochemical Oxygen Demand (BOD)
  
  • BOD measures the rate of uptake of oxygen by microorganisms in water
    
  • BOD is measured at a temperature of 20 C and over a period of 5 days in the dark
    
  • BOD is widely used to determine the threshold at which treated wastewater can be re-introduced into the environment
    
  • 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)
  
  • TDS is a measure of combined content of all inorganic and organic substances contained in a liquid
    
  • TDS is generally not considered a primary pollutant, but is used to indicate the aesthetic characteristics of drinking water
  • High TDS levels generally indicate hard water
    
  • Drinking water is expected to have a TDS of 100 mg/l or less
    
  • 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
  • lightning strikes (which splits nitrogen compounds)
  • 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
  
  • Damage to aquatic animals
  • Damage to soil chemistry by killing off essential microbes
  • Loss of forests and vegetation
  • Human illnesses such as cancer, asthma and other diseases
  • 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
  • Land clearing
    
  • Aquaculture activities (shrimp farms etc)
  • Irrigation (over a period time causes deposition of salts)
• The adverse effects of salination include
  • loss of soil fertility
    
  • damage to infrastructure (such as roads etc)
    
  • damage to plant growth and yield
    
  • deterioration of underground water quality
    
  • 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 disorders including 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: MEDICINAL CHEMISTRY
      

   6. Medicinal chemistry involves the design, synthesis and development of pharmaceutical drugs
   7. Compounds used as medicines are overwhelmingly organic compounds including small molecules and biopolymers. However, some inorganic compounds and metals have been found to have medicinal properties as well
   Classes of drugs
   
   

   Class of drug	Application	Example	Notes
   Antipyretics	Reduce body temperature	Aspirin, paracetamol (acetaminophen)	Antipyretics cause the hypothalamus to override an increase in temperature Taking antipyretics in empty stomach can cause ulcer
   Analgesics	Pain relief	Paracetamol Non steroidal anti inflammatory drugs (NSAIDS) Morphine	Some antipyretics act as analgesics as well Some narcotics (heroin, morphine, marijuana) can also act as analgesics
   Tranquilizers	Induce sedation	Barbiturates, antihistamines	Sedatives cause sleep, poor judgement, slow reflexes Excessive use can cause unconsciousness and even death
   Antiseptics	Reduce possibility of infection	Boric acid, hydrogen peroxide, iodine	Antiseptics are applied externally to living tissues Antiseptics also reduce body odour caused due to bacterial decomposition They are used in breath freshners and deodorants
   Antibiotics	Kill bacteria	Penicillin, gramicidin, amoxicillin, streptomycin	An antibiotic is defined as a substance produced by a microorganism that kills other microorganisms Antibiotics are considered life-saving drugs
   Diuretics	Increases rate of urination	Amiloride, triamterene
   Vasodilators	Widen blood vessels	Histamine, nitric oxide	Decrease blood pressure Increase blood flow
   Vasoconstrictors	Narrow blood vessels Staunch blood loss due to haemorrhage	Antihistamines, cocaine, LSD, caffeine	Increase blood pressure Decrease blood flow Make skin look paler because less blood reaches the skin
   Anaesthetics	Cause loss of sensation	Cocaine, nitrous oxide, halothane	General anaesthetics cause a loss of consciousness Local anaesthetics cause loss of sensation in a specific part of the body
   Antifungals	Fungal diseases like ringworm, athlete’s foot, meningitis	Ketoconazole, benzoic acid, neem seed oil, tea tree oil	Since both fungi and human cells are eukaryotes, the possibility of side effects is higher than in anti-bacterial drugs (like antibiotics)
   Antivirals (Antiretrovirals)	Inhibit growth of virus	Zedovudine, lamivudine	Unlike antibiotics, antiviral drugs do not destroy target microbes but only inhibit their growth Designing antiviral drugs is difficult because virus use host’s cells to replicate Some virus, like influenza and HIV, mutate rapidly which means they can be treated with antivirals only and not be prevented by vaccines Antiretrovirals are a subclass of antivirals that treat retroviruses such as HIV

   Some important common drugs
   
   

   Drug	Classification	Application	Notes
   Penicillin	Antibiotic	Syphilis, staphylococcal infections (food poisoning)	Narrow spectrum antibiotic (treats only a narrow range of diseases)
   Zedovudine	Antiviral	HIV
   Lamivudine	Antiviral	Hepatitis B
   Streptomycin	Antibiotic	Tuberculosis
   Erythromycin	Antibiotic	Respiratory tract infections
   Ciprofloxacin	Antibiotic	Urinary tract infections, common pneumonia, myoplasmal infections	Broad spectrum antibiotic
   Amoxicillin	Antibiotic	Wide range of infections	Broad spectrum
   Tetracycline	Antibiotic	Cholera
   Chloroquine	Antibiotic	Malaria
   Aspirin	Analgesic, Antipyretic	Fever, pain	One of the most widely used medications in the world
   Paracetamol (Acetaminophen)	Analgesic, antipyretic	Fever, pain