Drugs, Dyes & Food Chemistry – NDA Chemistry Notes

When you take a tablet for a headache, wear a coloured shirt, or eat food preserved in a packet. Chemistry is at work. Drugs, dyes, and food chemistry are all parts of applied chemistry that directly affect daily life.

This chapter is fact-heavy and rewards students who memorise specific names, uses, and connections.

1. Drugs

A drug is a chemical substance that affects the functioning of the body. Drugs are used as medicines to prevent, diagnose, or treat diseases. Drugs are classified by their action on the body.

Analgesics (Pain Killers)

Analgesics relieve pain without causing loss of consciousness.

Aspirin (acetylsalicylic acid) is one of the most common analgesics. It also reduces fever (antipyretic) and reduces inflammation. Paracetamol (acetaminophen) is another common analgesic and antipyretic. Morphine and codeine are narcotic analgesics, powerful pain relievers derived from opium. They can cause addiction.

Antipyretics (Fever Reducers)

Antipyretics reduce fever. Aspirin, paracetamol, and ibuprofen are common antipyretics.

Antibiotics

Antibiotics kill or stop the growth of bacteria. They do not work against viruses.

Penicillin was the first antibiotic. It was discovered by Alexander Fleming in 1928 by accident. Streptomycin is an antibiotic used to treat tuberculosis (TB). Sulphonamides were the first class of synthetic antibiotics. They were used before penicillin became available.

Antiseptics

Antiseptics are substances applied to living tissue (skin, wounds) to kill or stop the growth of harmful microorganisms. They prevent infection.

Iodine solution (tincture of iodine) is a commonly used antiseptic for fresh wounds. Iodine is used in the preparation of antiseptic solution. Dettol contains chloroxylenol, a common antiseptic. Potassium permanganate (KMnO₄) solution is used as an antiseptic for washing wounds and for water purification. Hydrogen peroxide (H₂O₂) in 3% solution is used as an antiseptic to clean wounds. [Chapter 12, Chapter 14 cross-reference]

Disinfectants

Disinfectants kill microorganisms on non-living surfaces (floors, toilets, water). They are too strong to be used on living tissue.

Chlorine is used as a disinfectant for drinking water. Phenol is one of the oldest disinfectants. Bleaching powder is used to disinfect water and swimming pools. [Chapter 7 cross-reference]

Feature	Antiseptic	Disinfectant
Used on	Living tissue (skin, wounds)	Non-living surfaces (floors, water)
Concentration	Lower, milder	Higher, stronger
Examples	Iodine solution, Dettol, H₂O₂	Chlorine, phenol, bleaching powder

Antacids

Antacids neutralise excess acid in the stomach. They relieve acidity and indigestion.

Milk of magnesia (magnesium hydroxide, Mg(OH)₂) is a commonly used antacid. Sodium bicarbonate (NaHCO₃, baking soda) also acts as an antacid. [Chapter 7 cross-reference] Aluminium hydroxide (Al(OH)₃) is used in some antacid tablets.

Alum

Alum (potassium aluminium sulphate, KAl(SO₄)₂·12H₂O) is used as a water purifier. [NDA 2009-I] It is also used as an astringent (to stop minor bleeding from shaving cuts) and in water treatment.

Alum is NOT an analgesic and NOT a fertiliser.

2. Metals in Living Systems

Some metal ions are essential for life. Examiners directly test which metal is present in key biological molecules.

Iron (Fe) in Haemoglobin: Haemoglobin is the red protein in blood that carries oxygen. The metal present in haemoglobin is iron (Fe). This is why iron deficiency causes anaemia: without enough iron, the body cannot make enough haemoglobin to carry oxygen.

Magnesium (Mg) in Chlorophyll: Chlorophyll is the green pigment in plants that traps sunlight for photosynthesis. The metal present in chlorophyll is magnesium (Mg). This is why magnesium deficiency causes yellowing of leaves (chlorosis) in plants.

Magnesium (Mg) and Photosynthesis: Magnesium traps the energy of sunlight in photosynthesis.

Calcium (Ca) and Muscle Contraction: Calcium ions control muscle contraction.

Barium (Ba) in Medicine: Barium sulphate (BaSO₄) is used as a contrast agent in X-ray examination of the alimentary canal (stomach and intestines). Barium sulphate is insoluble and does not get absorbed into the blood. It makes the digestive tract visible on X-ray.

Strontium (Sr) and Flame Colour: Strontium gives red colour to flames. This is used in red fireworks.

The most frequently tested pair: Metal in haemoglobin = Iron (Fe). Metal in chlorophyll = Magnesium (Mg). Metal in haemoglobin and chlorophyll respectively = Fe and Mg.

3. Dyes

Dyes are coloured substances used to colour fabrics, food, paper, and other materials. A dye must be able to attach itself to the material permanently.

Natural Dyes

These are obtained from plants and animals.

Indigo is a natural blue dye obtained from the indigo plant (Indigofera tinctoria). It was used for centuries to dye cloth blue. Jeans owe their blue colour to indigo dye. Curcumin is the natural yellow dye present in turmeric. [NDA 2009-I] Alizarin is a red dye originally obtained from the roots of the madder plant.

Synthetic Dyes

Most modern dyes are synthetic. They are made from coal tar derivatives (aromatic compounds from coal tar).

The first synthetic dye was mauveine (mauve), discovered accidentally by William Henry Perkin in 1856 while trying to make quinine (a medicine for malaria). Azo dyes are the largest class of synthetic dyes. They contain the azo group (-N=N-). They are used to colour textiles, leather, and food. Methyl orange and phenolphthalein are synthetic dyes used as acid-base indicators in laboratories. [Chapter 7 cross-reference]

Mordants

A mordant is a substance that helps a dye bond permanently to fabric. Without a mordant, many dyes would wash out quickly.

Magnesium sulphate is used as a mordant in the dyeing and tanning industry. Alum is also used as a mordant in some dyeing processes.

4. Sindoor (Kumkum) and Lead

Sindoor or kumkum is a red powder used in Hindu religious practices. The traditional metal compound in sindoor is based on lead. [NDA 2009-I]

The red compound in sindoor is red lead (lead tetroxide, Pb₃O₄) or vermilion (mercuric sulphide, HgS). Both lead and mercury compounds are toxic. Modern sindoor products often use artificial colours to avoid health risks.

5. Food Chemistry

Food chemistry is the study of the chemical processes and interactions of all biological and non-biological components of food.

Major Food Components: Food contains three main types of nutrients. Carbohydrates provide energy, made of carbon, hydrogen, and oxygen (sugar, starch, rice, wheat). Proteins build and repair body tissue, made of amino acids (dal, meat, eggs, milk). Fats provide energy (more than double that of carbohydrates per gram) and help absorb fat-soluble vitamins (oil, butter, ghee).

Vitamins and Deficiency Diseases: Vitamins are organic compounds needed in small quantities for normal body function.

Vitamin	Chemical Name	Deficiency Disease	Source
Vitamin A	Retinol	Night blindness, xerophthalmia	Carrots, liver, eggs
Vitamin B₁	Thiamine	Beriberi	Whole grains, legumes
Vitamin B₂	Riboflavin	Ariboflavinosis (cracks around mouth)	Milk, eggs, green vegetables
Vitamin B₃	Niacin	Pellagra	Meat, fish, whole grains
Vitamin B₁₂	Cobalamin	Pernicious anaemia	Meat, eggs, dairy
Vitamin C	Ascorbic acid	Scurvy	Citrus fruits, amla, guava
Vitamin D	Calciferol	Rickets (in children), Osteomalacia (in adults)	Sunlight, fish oil, egg yolk
Vitamin E	Tocopherol	Sterility, muscle weakness	Nuts, seeds, vegetable oils
Vitamin K	Phylloquinone	Blood clotting disorders	Green leafy vegetables

Fat-soluble vitamins: A, D, E, K (remember “ADEK”). Water-soluble vitamins: B group and C. Fat-soluble vitamins are stored in the body. Excess can be toxic. Water-soluble vitamins are not stored and must be consumed regularly.

Key deficiency diseases to remember: Night blindness = Vitamin A deficiency. Scurvy = Vitamin C deficiency (bleeding gums, weak joints). Rickets = Vitamin D deficiency (soft bones in children). Beriberi = Vitamin B₁ (Thiamine) deficiency (nerve damage). Pellagra = Vitamin B₃ (Niacin) deficiency (the “3 Ds”: Dermatitis, Diarrhoea, Dementia).

Food Preservatives: Food preservatives prevent food from spoiling due to microbial growth or oxidation. Common preservatives: Salt (NaCl), sugar, vinegar (acetic acid), sodium benzoate, potassium sorbate, citric acid. Salt and sugar preserve food by drawing out water from microorganisms (osmosis), preventing their growth. Sodium benzoate (C₆H₅COONa) is widely used as an artificial food preservative.

Artificial Sweeteners: Artificial sweeteners give a sweet taste without the calories of sugar. They are used in “diet” foods and drinks. Saccharin was the first artificial sweetener, about 300 times sweeter than sugar. Aspartame is another common artificial sweetener used in diet drinks.

Food Colours: Food colours are added to food to make it visually appealing. Natural food colours: turmeric (yellow), saffron (yellow-orange), beetroot (red). Artificial food colours are synthetic dyes. Some have been found to be harmful and are banned.

Rancidity: Rancidity is the spoiling of fats and oils due to oxidation. It produces an unpleasant smell and taste. [Chapter 6 cross-reference] Antioxidants (vitamin C, vitamin E, BHA, BHT) are added to foods to prevent rancidity.