Common Organic Compounds in Daily Life – NDA Chemistry Notes

You use organic compounds every single day. The alcohol in hand sanitiser, the vinegar in pickles, the acetone in nail polish remover, the soap you use to wash your hands. All of these are organic compounds.

This chapter covers the most commonly tested organic compounds. These include alcohols, organic acids, aldehydes and ketones, esters, soaps, and detergents.

The chapter is almost entirely fact-based and daily-life-connected. Every concept here links directly to something you see around you.

1. Alcohols

Think of hand sanitiser or spirit used to clean wounds. Both contain alcohol. The scientific name for the alcohol in these products is ethanol.

Alcohols are organic compounds that contain a hydroxyl group (-OH) attached to a carbon atom.

Methanol (CH₃OH)

Methanol is also called wood spirit or wood alcohol.  It was originally made by destructive distillation of wood.

Methanol is highly poisonous. Even a small amount can cause blindness. Drinking methanol causes death.

Methanol is used as a solvent, as a fuel, and in making formaldehyde. It is NOT safe to drink.

Ethanol (C₂H₅OH)

Ethanol is the alcohol found in alcoholic drinks (beer, wine, whisky). It is also used as a fuel, a solvent, and in medicines.

Ethanol is made by fermentation. Yeast acts on sugar (glucose) to produce ethanol and carbon dioxide.

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (yeast, 30-40°C)

Fermentation of sugar cane juice, fruits, and grains all produce ethanol. Fermentation is a chemical change.

Name	Approximate Ethanol %	Use
Rectified spirit	~95.6% ethanol in water	Industrial solvent
Absolute alcohol	~99.9% pure ethanol	Lab reagent
Denatured spirit (Methylated spirit)	Ethanol + methanol + other additives	Fuel, cleaning, made undrinkable deliberately

Denatured spirit has methanol and other toxic substances added to ethanol to make it unfit for drinking. This prevents misuse and avoids alcohol taxes.

Breathalyser Test: The breathalyser is used by police to test if a driver has drunk alcohol. The driver blows into a bag containing sodium dichromate solution in acidic medium. Ethanol is oxidised and the colour changes from orange to green.

Glycerol (C₃H₈O₃)

Glycerol is also called glycerin. It is a thick, sweet, colourless liquid. It contains three hydroxyl (-OH) groups.

Glycerol is produced as a by-product during soap manufacture. It is used in medicines, cosmetics, and food as a moisturiser and sweetener.

2. Organic Acids

You have tasted organic acids. Lemon is sour because of citric acid. Vinegar is sour because of acetic acid. Sour milk is sour because of lactic acid.

Acetic Acid (CH₃COOH): Acetic acid is also called ethanoic acid. [NDA 2009-I] Vinegar is a dilute solution of acetic acid (5-8% acetic acid in water). [NDA 2009-I, NDA 2011-II] Vinegar is produced from ethanol by oxidation. [NDA 2010-I Q149] Acetic acid has a sharp, sour smell. It is a weak acid. Concentrated acetic acid (glacial acetic acid) freezes at 17°C, just below room temperature. This is why pure acetic acid is called glacial acetic acid.

Formic Acid (HCOOH): Formic acid is also called methanoic acid. It is found in ant stings and bee stings. [NDA 2011-I] The pain and irritation of an ant bite is caused by formic acid injected under the skin.

Citric Acid: Found in lemon, orange, and other citrus fruits. Responsible for their sour taste.

Lactic Acid: Found in sour milk and curd. Produced when bacteria ferment lactose in milk.

Tartaric Acid: Found in tamarind and grapes.

Acid	Source	NDA Relevance
Acetic acid	Vinegar	Most tested acid in this chapter
Formic acid	Ant/bee stings	Frequently tested
Citric acid	Citrus fruits	Source identification questions
Lactic acid	Sour milk, curd	Source identification questions
Tartaric acid	Tamarind	Source identification

3. Aldehydes and Ketones

Formaldehyde (HCHO): Formaldehyde is the simplest aldehyde. Its 40% aqueous solution is called formalin. Formalin is used to preserve biological specimens (dead animals, tissues). Formaldehyde is toxic. Exposure causes irritation of the eyes, nose, and throat.

Acetaldehyde (CH₃CHO): Acetaldehyde is produced when ethanol is oxidised mildly. It has a fruity smell.

Acetone (CH₃COCH₃): Acetone is the simplest ketone. It is a colourless, volatile liquid with a sweet smell. Acetone is used as nail polish remover. Acetone is used as a solvent in labs and industry. Acetone and alcohol can be separated by fractional distillation because they have different boiling points. [NDA 2011-I]

4. Esters and Flavours

Esters are organic compounds formed when an acid reacts with an alcohol. This reaction is called esterification.

Acid + Alcohol → Ester + Water (in the presence of concentrated H₂SO₄ as catalyst)

Esters have characteristic fruity smells. They are responsible for the natural flavours and fragrances of fruits.

Benzaldehyde gives apple its characteristic flavour.

Ester	Smell/Flavour
Ethyl acetate	Pear
Amyl acetate (isoamyl acetate)	Banana
Methyl salicylate	Wintergreen
Benzaldehyde	Apple/almond

Esters are used in perfumes, artificial fruit flavours, and food additives.

5. Chloroform and Carbon Tetrachloride

Chloroform (CHCl₃): Chloroform is a sweet-smelling, dense, colourless liquid. It was used as an anaesthetic in the past. Patients were made unconscious by inhaling chloroform before surgery. It is no longer used for this purpose because it is toxic.

Carbon Tetrachloride (CCl₄): Carbon tetrachloride is a colourless, non-flammable liquid. It was used as a dry cleaning solvent and in fire extinguishers. It is now known to be toxic and carcinogenic, so its use is restricted.

6. Soap

Soap is what happens when fat meets a strong alkali. Soap is the sodium or potassium salt of long chain fatty acids. [NDA 2011-II]

Sodium salts of fatty acids make hard soap. Hard soap is used for washing clothes and bathing. Potassium salts of fatty acids make soft soap. Soft soap is used in shaving creams and liquid soaps.

Saponification

The reaction of fat or oil with a strong alkali (NaOH or KOH) to produce soap and glycerol is called saponification. [NDA 2011-II]

Fat/Oil + NaOH → Soap (sodium fatty acid salt) + Glycerol

Saponification is an example of a chemical change.

Structure of a Soap Molecule

A soap molecule has two very different ends.

One end is hydrophilic. This means it loves water. It is the ionic end of the molecule. It points outward into water.

The other end is hydrophobic. This means it hates water. It is the long hydrocarbon (non-polar) chain end. It points inward toward grease and oil.

How Soap Removes Dirt (Micelle Formation)

Grease and oily dirt do not dissolve in water on their own. Soap makes them come off.

When soap is added to water containing a greasy surface, the soap molecules arrange themselves around the grease. The hydrophobic tails of soap molecules point inward into the grease. The hydrophilic heads point outward into the water. This creates a spherical cluster called a micelle. The grease is trapped inside the micelle. The micelle is washed away with water.

Soap removes dirt by forming micelles that trap the dirt in their core and keep it suspended in water so it can be rinsed away. [NDA 2010-II]

Soap in Acidic Conditions

Soap does not work in acidic conditions. In acids, the soap molecules react to form free fatty acids, which are insoluble. No micelles form. No lather forms.

Soap in Hard Water

Hard water contains Ca²⁺ and Mg²⁺ ions. These ions react with soap to form insoluble calcium and magnesium fatty acid salts (the grey scum seen on bathtubs). The soap is wasted forming this scum instead of forming micelles. So, no lather forms.

Turmeric and Soap

Turmeric (haldi) contains curcumin. Curcumin is yellow in acidic and neutral conditions. It turns reddish-brown in alkaline (basic) conditions.

Soap is alkaline. When soap is rubbed on a turmeric stain, the turmeric turns reddish-brown. When the cloth is rinsed with water (which is neutral), the stain turns yellow again. [NDA 2013-II, NDA 2020 I & II]

The colour sequence is: yellow (original stain) → reddish-brown (after soap, alkaline) → yellow (after washing with water, neutral). [NDA 2020 I & II]

7. Detergents

Detergents are synthetic cleaning agents. They are derived from petroleum products, not from natural fats.

Detergents also have a hydrophilic head and a hydrophobic tail, just like soap. They also clean by forming micelles. But detergents work in hard water and in acidic conditions. They do not form insoluble salts with Ca²⁺ and Mg²⁺ ions.

Property	Soap	Detergent
Made from	Natural fats and oils	Petroleum products
Works in hard water	No (forms scum)	Yes
Works in acidic conditions	No	Yes
Biodegradable	Yes	Older ones were not, newer ones are
Examples	Bathing soap, laundry soap	Surf, Ariel, Vim

Biodegradability of Detergents: Older detergents had branched hydrocarbon chains. Bacteria could not break them down. They polluted rivers and water bodies with foam. Modern detergents use straight hydrocarbon chains. Bacteria can break these down. So modern detergents are biodegradable.

8. Emulsion

An emulsion is a mixture of two liquids that do not normally mix. One liquid is dispersed as tiny droplets inside the other.

An emulsion is a colloidal solution of two liquids. [NDA 2016-II]

Examples:

• Milk is an emulsion. Fat droplets are dispersed in water.
• Butter is an emulsion. Water droplets are dispersed in fat.
• Mayonnaise is an emulsion.
• Cold cream is an emulsion.

9. Hydrogenation of Oils (Vanaspati)

Liquid vegetable oils can be converted into solid fats by a process called hydrogenation.

In hydrogenation, hydrogen gas is passed through the oil at high temperature and pressure in the presence of a nickel catalyst.

The double bonds (C=C) in the unsaturated fatty acids of the oil react with hydrogen to become single bonds (C-C). The oil becomes a saturated fat and solidifies.

Vanaspati ghee (dalda) is made by hydrogenating vegetable oils. This makes the oil solid at room temperature, similar to butter.

NDA 2026-I tested a statement about nickel being used as a catalyst in converting vegetable oil into fat.

10. DDT

DDT (Dichlorodiphenyltrichloroethane) is a chlorinated organic compound. It was widely used as a pesticide to kill insects, especially mosquitoes.

DDT was very effective but has serious problems. It does not break down easily in the environment (not biodegradable). It accumulates in the food chain (bioaccumulation). It causes harm to birds and mammals.

DDT is now banned in most countries.