Chemistry in Everyday Life

Both soaps and detergents clean by trapping oily dirt, but they differ sharply in chemistry and in how they behave in hard water.

• Detergents are the sodium salts of long-chain benzene sulphonic acids (or alkyl sulphates) — i.e. synthetic, soap-free cleaners.
• A soap/detergent molecule has two ends — a water-loving (hydrophilic) head and an oil-loving (hydrophobic) tail.

• The hydrophobic tail dissolves in oily dirt while the hydrophilic head stays in water, lifting grease off the surface.
• Many such molecules surround a droplet of oil, forming a tiny ball called a micelle, which carries the dirt away in water.
• The dirt is emulsified (broken into fine droplets) and rinsed off, leaving the surface clean.

This is a classic SSC question — the difference comes from how each reacts with the calcium and magnesium in hard water.

• Soap reacts with these ions to form an insoluble, sticky precipitate called scum, instead of a lather.
• Because soap is wasted in forming scum, soap does not lather well and cleans poorly in hard water.

• The calcium and magnesium salts of detergents are soluble in water, so no scum forms.
• Therefore detergents lather and clean effectively even in hard water — their key advantage over soap.
• Detergents are also used in shampoos and products for cleaning where hard water is a problem.

Plants need a steady supply of three major nutrients, and fertilisers are graded by how much of these they supply — remembered by the letters NPK.

• P = Phosphorus — promotes root growth, flowering and fruiting.
• K = Potassium (Kalium) — improves overall plant strength, disease resistance and quality of produce.
• NPK stands for Nitrogen, Phosphorus and Potassium — the three primary (macro) nutrients.

• Urea is a nitrogenous fertiliser and has the highest nitrogen content (~46%) of common solid fertilisers.
• Diammonium phosphate (DAP) supplies both nitrogen and phosphorus.

To keep food safe, tasty and long-lasting, several chemicals are added — each with a specific job.

• Sodium benzoate (C₆H₅COONa) is a common preservative used in jams, squashes and soft drinks.
• Common salt, sugar, vinegar and oil are traditional (household) preservatives.
• Sodium metabisulphite and potassium metabisulphite are used to preserve coloured foods.

• Antioxidants are added to fats and oils to prevent them from turning rancid (oxidising).
• BHA (butylated hydroxyanisole) and BHT are common antioxidants; Vitamin C and Vitamin E act as natural antioxidants.

• MSG (Monosodium glutamate), also called Ajinomoto, is a flavour enhancer used in soups, noodles and Chinese food.

A small kitchen chemical with a big role — it makes cakes and bread rise and is also a mild antacid.

• On heating, baking soda releases carbon dioxide (CO₂) gas, which makes bread and cakes soft and spongy.
• Baking powder = baking soda + a mild edible acid (e.g. tartaric acid); the acid neutralises the bitter taste of the residue.
• Baking soda is mildly alkaline (basic) and is also used as an antacid to relieve acidity.

The most familiar of all kitchen chemicals, plus the sugar-free substitutes used by diabetics and dieters.

• It is the raw material for making NaOH, Na₂CO₃ (washing soda), baking soda and bleaching powder.
• Iodised salt (salt + small amount of potassium iodide/iodate) prevents goitre and iodine-deficiency disorders.

• Artificial sweeteners give sweetness without calories — useful for diabetics and weight control.
• Saccharin is about 550 times sweeter than sugar and was the first artificial sweetener.
• Aspartame is used in cold foods and soft drinks; it becomes unstable (decomposes) when heated, so it is unsuitable for cooking.
• Sucralose and Alitame are heat-stable and can be used in cooking.

Medicines are grouped by what they do in the body; SSC loves to test "which type does what".

The most frequently asked medicine facts, with examples.

• Milk of magnesia (Mg(OH)₂), aluminium hydroxide and baking soda (NaHCO₃) act as antacids — they are mild bases.

• An antibiotic kills or stops the growth of harmful bacteria; it does NOT work against viruses.
• Penicillin, the first antibiotic, was discovered by Alexander Fleming from the mould *Penicillium*.
• Other examples: streptomycin, tetracycline, chloramphenicol, ampicillin.

• Analgesics are painkillers — e.g. aspirin, paracetamol, ibuprofen, morphine.
• Aspirin and paracetamol are both analgesic and antipyretic (relieve pain and reduce fever).

A guaranteed exam trap — both kill germs, but the difference is *where* they are applied.

• A disinfectant is applied on non-living surfaces — floors, drains, instruments — and is too strong for skin.
• The same chemical can be an antiseptic at low concentration and a disinfectant at high concentration (e.g. phenol/carbolic acid).

The chemistry of the materials that make our homes — cement, glass, gypsum and plaster of Paris.

• Setting of cement is exothermic and involves hydration; that is why concrete is sprinkled with water (curing).
• Concrete = cement + sand + gravel + water; RCC is reinforced cement concrete (with steel rods).

• Glass is an amorphous solid (a supercooled liquid), made by fusing sand (SiO₂), soda and limestone.
• Adding lead oxide gives flint/crystal glass; boron oxide gives heat-resistant Pyrex glass.

• Gypsum is calcium sulphate dihydrate, CaSO₄·2H₂O.
• Heating gypsum to about 100°C gives Plaster of Paris (POP), CaSO₄·½H₂O (calcium sulphate hemihydrate).
• POP sets into a hard mass on mixing with water — used for plaster casts (broken bones), statues and decorations.

A single useful compound that whitens, disinfects and supplies chlorine.

• It is made by passing chlorine gas over dry slaked lime, Ca(OH)₂.
• It releases chlorine, which gives its bleaching and disinfecting (germ-killing) action.
• Uses: bleaching cotton/paper, disinfecting drinking water, and as an oxidising agent.

The everyday chemistry of personal care and household cleaning.

• Toothpaste is mildly basic and contains an abrasive plus fluoride to strengthen teeth.
• Nail polish remover contains acetone; perfumes use esters for fragrance.

• Washing soda is sodium carbonate, Na₂CO₃·10H₂O, used to soften hard water and clean.
• Bleach (for laundry) contains sodium hypochlorite, NaOCl.
• Glass cleaners contain ammonia; many scouring powders are abrasive plus mild alkali.

The acids and bases hiding in plain sight in the kitchen and bathroom.

• Lemon and citrus fruits contain citric acid; curd/sour milk contains lactic acid.
• Tomato contains oxalic acid; tamarind contains tartaric acid; an ant/bee sting injects formic acid.

• Baking soda (NaHCO₃) and milk of magnesia (Mg(OH)₂) are mild bases.
• Lime water is calcium hydroxide, Ca(OH)₂; soap is basic in nature.
• An acid sting (formic acid) is neutralised by rubbing a mild base like baking soda.