Antacids
The chemical substances which neutralize the excess acid in stomach and raise the pH to an appropriate level in stomach are used as antacids.
The most commonly used antacids are weak bases such as sodium bicarbonate [NaHCO3], magnesium hydroxide [Mg(OH)2] and aluminium hydroxide [Al(OH)3].
Generally liquid antacids are more effective than tablets because they have more surface area available for interaction and neutralisation acid. Milk is a weak antacid.
Ranitidine (zantac), omeprazole and lansoprazole are other examples of antacids.
Antihistamines
Antihistamines are Anti- allergic drugs and used for the treatment of allergic diseases like nasal congestion associated with common cold and allergic response to pollen.
Eg: brompheniramine (Dimetapp) and terfenadine (Seldane), act as antihistamines
Antipyretics
These are the chemical substance which reduce body temperature during high fever.
Paracetamol, aspirin, phenacetin (4-hydroxy acetanilide), analgin and novalgin, etc., are common antipyretics. Out of these, paracetamol (4-acetamidophenol) is most common.
Tranquilizers
Chemical substances used for the treatment of stress, anxiety, irritability and mild or even severe mental diseases, are known as tranquilizers. These affect the central nervous system and induce sleep for the patients as well as eliminate the symptoms of emotional distress. They are the common constituents of sleeping pills.
They are of two types:
1) Sedative or hypnotics: Reduce nervous tension and promote relaxation
2) Mood elevators or Antidepressants: A drug used for treatment of highly depressed patient.
Analgesics (pain killers)
Medicines used for getting relief from pain are called analgesics. These are of two types
1) Narcotics: Drugs which produce sleep and unconsciousness are called narcotics. These are habit forming drugs. Eg. Morphine, codeine, heroin.
2) Non-narcotics: These are non-habit forming chemicals which reduce mild to moderate pain such as headache, toothache, muscle and joint pain, etc. These are also termed as non-addictive. These drugs do not produce sleep unconsciousness.
Aspirin (2-acetoxybenzoic acid) is most commonly used analgesic with antipyretic properties. Now these days because its anti-blood clotting action, aspirin is widely used to prevent heart-attacks.
Naproxen, ibuprofen, paracetamol, dichlorofenac are other widely used analgesics.
Antimicrobials
An antimicrobial tends to kill or prevent the development of microbes and inhibit the pathogenic action of microbes such as bacteria, fungi and virus selectively.
Different types of antimicrobial drugs are as follows :
(a) Antibiotics
(b) Antiseptics and
(c) disinfectants
Antibiotics
The chemical substances produced from some microorganism and are used to inhibits the growth of other harmful microorganism. Antibiotic therapy has been likened to “setting one thief against another‟.
Antibiotics are of two types :
1. Bactericidal antibiotics have cidal (killing) effect on microbes. Eg. penicillin, ofloxacin, amino glycosides, etc.
2. Bacteriostatic antibiotics have a static (inhibitory) effect on microbes. Eg. erythromycin, tetracycline, chloramphenicol, etc
If effective against a single organism or disease, they are referred to as limited spectrum antibiotics or narrow spectrum antibiotics. Penicillin was the first antibiotic discovered (by Alexander Fleming) in 1929. It is a narrow spectrum antibiotic. Ampicillin and amoxicillin are other examples.
Broad-spectrum antibiotics are those which are effective against different types of harmful microorganisms. e.g., Tetracycline, etc.
General examples of antibiotics are penicillin, streptomycin, chloromycetin, tetracyclins, etc.
Antiseptics
These are the chemicals which either kill or prevent the growth microorganisms. Antiseptics are applied to the living tissues such wounds, cuts, ulcers and skin diseases in the form of antiseptic creams like furacin and soframycin. e.g., Some important examples of antiseptics are
(i) Dettol is a mixture of chloroxylenol and terpineol.
(ii) Bithional is added to soaps to impart antiseptic properties to reduce the odours produced by bacterial organic matter on the skin.
(iii) Tincture of iodine is a 2-3% solution of iodine in alcohol, which is a powerful antiseptic for wounds.
(iv) Iodoform (CHI3) is also used as an antiseptic for wounds.
(v) Boric acid in dilute aqueous solution is weak acid and used for cleaning eyes.
Disinfectants
These are the chemical substances which kill microorganisms not safe to be applied to the living tissues. They are generally kill the microorganisms present on inanimate objects such as drainage systems, instruments, etc.
Some common examples of disinfectants are as follows :
(i) 1% phenol solution is disinfectant while in lower concentration 0.2% solution of phenol is antiseptic.
(ii) 0.2-0.4 ppm aqueous solution of chlorine is used for sterilisation of water to make it fit for drinking purpose.
(iii) SO2 at very low concentrations behaves like disinfectant.
Chemicals in Food
Sucrose (table sugar) and fructose are the most widely used natural sweeteners. But they add to our calorie intake and promote tooth decay. To avoid these problems many people take artificial sweeteners. In this Section we will discuss only sweeteners and food preservatives.
Artificial Sweetening Agents
Organic substances which have been synthesized in lab are known to be many times sweeter than cane sugar. Such compounds are known as artificial sweetening agents or artificial sweeteners
Aspartame
It is also known as “Nutra sweet”.
It decomposes at baking or cooking temperatures and hence, can used only in cold food and soft drinks.
Aspartame has the same amount of calories as sugar (4 cal per gram).
Aspartame should not be used by people suffering from the genetic disease.
Aspartame is the most successful and widely used artificial sweetener. It is roughly 100 times as sweet as cane sugar. Use of aspartame is limited to cold foods and soft drinks because it is unstable at cooking temperature.
Saccharin
It is the most popular artificial sweetener. It is 550 times as sweet as cane Sugar, since it is insoluble in water, so it is sold in the market as its soluble or calcium salt.
It is non-biodegradable so excreted from the body in urine (unchanged). Its use is of great value for diabetic persons and people who need to control intake of calories. It appears to be entirely inert and harmless when taken.
Alitame
It is quite similar to aspartame but more stable than aspartame. It is 2000 times as sweet as sucrose. The main problem for such sweetener is the control of sweetness of the substance to which it is added because it is high potency sweetener.
Sucralose
It is a trichloro derivative of sucrose. It’s appearance and taste are like sugar. It is stable at cooking temperature. It is almost 600 times as sweet as sucrose. However, it neither provides calories nor causes tooth decay.
Food Preservatives
These are the chemical substances added to food to prevent their spoilage due to microbial growth (bacteria, yeasts and moulds) and to retain their nutritive value for longer periods.
The most commonly used preservatives include table salt, sugar, vegetable oil, vinegar, citric acid, spices and sodium benzonate (C6H5COONa), Salts of sorbic acid and propanoic acid are also used as food preservatives
Sodium benzoate is metabolised in human body.It is used in soft drinks and acidic foods.
Antioxidants in Food
These are important and necessary food additives. These help in food preservation by retarding the action of oxygen on food. These are more reactive towards oxygen than the food material which they are protecting. The two most familiar antioxidants are
Butylated hydroxy toluene (BHT)
Butylated hydroxy anisole (BHA).
The addition of BHA to butter increases its shelf life from months to years. Sometimes BHT and BHA along with citric acid are added to produce more effect. Sulphur dioxide and sulphite are useful antioxidants for wine and beer, sugar syrups and cut, peeled or dried fruits and vegetables.
Cleansing Agents
In this Section, we will learn about cleansing agents. Two types of cleansing agents are used:
1) soaps
2) synthetic detergents.
These improve cleansing properties of water. These help in removal of fats which bind other materials to the fabric or skin.
Soaps
Soaps used for cleaning purpose are sodium or potassium salts of long chain fatty acids, e.g., stearic, oleic and palmitic acids. Soaps containing sodium salts are formed by heating fat (i.e., glyceryl ester of fatty acid) with aqueous sodium hydroxide solution. This reaction is known as SAPONIFICATION.
Only sodium and potassium soaps are soluble in water and are used for cleaning purposes. Generally potassium soaps are soft to the skin than sodium soaps. These can be prepared by using potassium hydroxide solution in place of sodium hydroxide.
Why do soaps not work in hard water?
The cleansing action of soap is based on Micelles action mechanism. Hard water contains calcium and magnesium ions. These ions form insoluble calcium and magnesium soaps respectively when sodium or potassium soaps are dissolved in hard water. These insoluble soaps separate as SCUM in water and are useless as cleansing agent. In fact these are hindrance to good washing, because the precipitate adheres onto the fibre of the cloth as gummy mass.
Hair washed with hard water looks dull because of this sticky precipitate.
Dye does not absorb evenly on cloth washed with soap using hard water, because of this gummy mass.
Synthetic Detergents
Synthetic detergents are cleansing agents which have all the properties of soaps, but which actually do not contain any soap. These can be used both in soft and hard water as they give foam even in hard water. Some of the detergents give foam even in ice cold water.
Synthetic detergents are mainly classified into three categories:
(i) Anionic detergents
(ii) Cationic detergents and
(iii) Non-ionic detergents
Anionic detergents
Anionic detergents are sodium salts of sulphonated long chain alcohols or hydrocarbons.
Alkyl hydrogen sulphates formed by treating long chain alcohols with concentrated sulphuric acid are neutralised with alkali to form anionic detergents.
Similarly alkyl benzene sulphonates are obtained by neutralising alkyl benzene sulphonic acids with alkali.
In anionic detergents, the anionic part of the molecule is involved in the cleansing action.
Sodium salts of alkyl benzene sulphonates are an important class of anionic detergents. They are mostly used for household work. Anionic detergents are also used in toothpastes.
Cationic detergents
Cationic detergents are quaternary ammonium salts of amines with acetates, chlorides or bromides as anions.
Cationic part possess a long hydrocarbon chain and a positive charge on nitrogen atom. Hence, these are called cationic detergents.
Cetyl trimethylammonium bromide is a popular cationic detergent and is used in hair conditioners.
Cationic detergents have germicidal properties and are expensive, therefore, these are of limited use.
Non-ionic detergents
Non-ionic detergents do not contain any ion in their constitution. One such detergent is formed when stearic acid reacts with polyethyleneglycol.
Liquid dishwashing detergents are non-ionic type.
Disadvantages of using detergents
Main problem that appears in the use of detergents is that if their hydrocarbon chain is highly branched, then bacteria cannot degrade this easily.
Slow degradation of detergents leads to their accumulation. Effluents containing such detergents reach the rivers, ponds, etc and water gets polluted (i.e Non biodegradable)
These days the branching of the hydrocarbon chain is controlled and kept to the minimum. Unbranched chains can be biodegraded more easily and hence pollution is prevented.