General Science Module

Chemistry in Everyday Life

Applied chemistry underpins household substances, pharmaceutical agents, food preservation, and industrial manufacturing. Common household chemicals include sodium chloride (table salt), sodium bicarbonate (baking soda), sodium carbonate decahydrate (washing soda), and calcium hypochlorite (bleaching powder). The pH scale, formulated by Danish chemist S.P.L. Sørensen in 1909, measures hydrogen ion activity from 0 to 14, where human blood is maintained within a narrow alkaline buffer of 7.35 to 7.45. Synthetic detergents differ from soaps because their sulfonate groups do not form insoluble precipitates in hard water containing magnesium and calcium ions. Common food preservatives such as sodium benzoate prevent microbial spoilage by lowering intracellular pH.

Practice Topic MCQs All Category Topics

Key Concepts & Examination Highlights

S.P.L. Sørensen introduced the pH scale in 1909 to quantify the acidity or basicity of aqueous chemical solutions.
Baking soda is chemically known as sodium hydrogen carbonate ( $NaHCO_3$ ), whereas washing soda is sodium carbonate decahydrate ( $Na_2CO_3\cdot 10H_2O$ ).
Soaps are sodium or potassium salts of fatty acids, while detergents are alkylbenzenesulfonate salts that remain soluble in hard water.
Bleaching powder is chemically calcium hypochlorite ( $CaOCl_2$ ), synthesized by the action of chlorine gas on dry slaked lime ( $Ca(OH)_2$ ).
Plaster of Paris is calcium sulfate hemihydrate ( $CaSO_4 \cdot \frac{1}{2}H_2O$ ), produced by heating gypsum ( $CaSO_4 \cdot 2H_2O$ ) to approximately 373 Kelvin (100°C).
Rusting of iron is an electrochemical redox process requiring both oxygen and moisture, forming hydrated ferric oxide ( $Fe_2O_3 \cdot xH_2O$ ).
Galvanization prevents iron corrosion by applying a thin protective coating of zinc, which acts as a sacrificial anode.
Aspartame and saccharin are synthetic artificial sweeteners; saccharin is approximately 550 times sweeter than sucrose and is excreted unmetabolized by the human kidneys.
Common antacids like milk of magnesia (magnesium hydroxide, $Mg(OH)_2$ ) and aluminum hydroxide neutralize excess hydrochloric acid in gastric juice.
Sodium benzoate and potassium metabisulfite are widely used chemical food preservatives that inhibit bacterial and fungal growth in acidic foods.
Ethanol ( $C_2H_5OH$ ) is produced commercially by the fermentation of sugars using yeast enzymes invertase and zymase.
Soap molecules form spherical aggregates called micelles in water, where hydrophobic hydrocarbon tails orient inward toward oily dirt and hydrophilic ionic heads face outward toward water.
Water hardness is classified into temporary hardness, caused by dissolved calcium and magnesium bicarbonates removable by boiling, and permanent hardness, caused by chlorides and sulfates removable by sodium carbonate or zeolite ion-exchange.
Washing soda ( $Na_2CO_3\cdot 10H_2O$ ) is manufactured industrially via the Solvay process, utilizing brine, limestone, and ammonia.
Hydrochloric acid ( $HCl$ ) present in gastric juice maintains a stomach pH between 1.5 and 3.5, which activates the digestive enzyme pepsin from pepsinogen.
Tooth enamel consists primarily of hydroxyapatite ( $Ca_5(PO_4)_3(OH)$ ), a crystalline calcium phosphate that begins to demineralize when oral pH drops below 5.5.
Tear gas commonly contains active chemical agents such as 2-chlorobenzalmalononitrile (CS gas) or phenacyl chloride (CN gas), which stimulate corneal sensory nerves.
Liquefied Petroleum Gas (LPG) consists primarily of propane and butane, with ethyl mercaptan ( $C_2H_5SH$ ) added as a pungent odorant to detect leaks.
Compressed Natural Gas (CNG) consists predominantly of methane ( $CH_4$ , 85-95%) and burns with cleaner emissions compared to petrol and diesel.
Dry chemical fire extinguishers typically contain monoammonium phosphate ( $NH_4H_2PO_4$ ) or sodium bicarbonate, which decompose upon heating to release carbon dioxide and smother flames.
Formalin is a 37-40% aqueous solution of formaldehyde ( $HCHO$ ), widely used for preserving biological specimens and anatomical tissues.
Aspirin, chemically known as acetylsalicylic acid ( $C_9H_8O_4$ ), is synthesized by esterifying salicylic acid with acetic anhydride and acts as an analgesic, antipyretic, and antiplatelet agent.
Paracetamol (acetaminophen, $C_8H_9NO_2$ ) is a widely used over-the-counter antipyretic and analgesic that inhibits central prostaglandin synthesis.
Hydrogen peroxide ( $H_2O_2$ ) acts as an oxidizing and reducing agent, used at 3% concentration as a topical antiseptic and disinfectant.
The ozone layer in the stratosphere protects the Earth from harmful ultraviolet radiation (UV-B and UV-C), and its depletion by chlorofluorocarbons (CFCs) was regulated globally by the 1987 Montreal Protocol.
Aqua regia is a highly corrosive, fuming mixture of concentrated nitric acid ( $HNO_3$ ) and concentrated hydrochloric acid ( $HCl$ ) in a 1:3 volumetric ratio, capable of dissolving noble metals like gold and platinum.
Quicklime is calcium oxide ( $CaO$ ), which reacts vigorously with water in an exothermic reaction to produce slaked lime (calcium hydroxide, $Ca(OH)_2$ ).
Lime water turns milky when carbon dioxide is bubbled through it due to the precipitation of insoluble calcium carbonate ( $CaCO_3$ ), but clears upon excess $CO_2$ due to soluble calcium bicarbonate formation.
Carbon monoxide ( $CO$ ) is a toxic, colorless gas that binds to blood hemoglobin with an affinity roughly 200 times higher than oxygen, forming carboxyhemoglobin and causing tissue hypoxia.
Vinegar is an aqueous solution containing 5% to 8% acetic acid (ethanoic acid, $CH_3COOH$ ) produced by the bacterial fermentation of ethanol by Acetobacter.
The Haber-Bosch process synthesizes ammonia ( $NH_3$ ) from atmospheric nitrogen and hydrogen gas under high pressure (150–200 atm) and temperature (400–500°C) using an iron catalyst with molybdenum promoter.
The Contact process is the primary industrial method for manufacturing concentrated sulfuric acid ( $H_2SO_4$ ), using vanadium pentoxide ( $V_2O_5$ ) as a catalyst.
Dry ice is solid carbon dioxide ( $CO_2$ ) that sublimes directly into gas at $-78.5^\circ\ ext{C}$ (194.65 K) under standard atmospheric pressure without passing through a liquid phase.
Hard water containing dissolved calcium and magnesium ions reacts with soap to form an insoluble grayish-white precipitate called scum (calcium stearate).
Zeolites (hydrated sodium aluminosilicates) and ion-exchange resin columns are used in water softeners to replace dissolved $Ca^{2+}$ and $Mg^{2+}$ ions with $Na^+$ ions.
Vulcanization of natural rubber involves heating crude rubber with sulfur at 373–415 K to create cross-linked disulfide bridges that enhance elasticity, mechanical strength, and thermal stability.
Bakelite (polyoxybenzylmethylenglycolanhydride) is a thermosetting phenol-formaldehyde polymer, widely used in electrical switches and cookware handles due to its high electrical and thermal resistance.
Teflon (polytetrafluoroethylene, PTFE) is a synthetic fluoropolymer used in non-stick cookware coatings due to its extreme chemical inertness, high melting point, and low coefficient of friction.
Nylon 6,6 is a synthetic polyamide fiber synthesized by the condensation polymerization of hexamethylenediamine and adipic acid.
Potassium permanganate ( $KMnO_4$ ) is a powerful oxidizing agent used in water treatment to remove iron, manganese, and hydrogen sulfide, and as an antiseptic disinfectant.
Iodized table salt contains minute quantities of potassium iodate ( $KIO_3$ ) or potassium iodide ( $KI$ ) added to prevent iodine deficiency disorders and endemic goiter.
Blue vitriol is copper(II) sulfate pentahydrate ( $CuSO_4 \cdot 5H_2O$ ), which turns into anhydrous white copper sulfate upon heating as water of crystallization is driven off.
Green vitriol is ferrous sulfate heptahydrate ( $FeSO_4 \cdot 7H_2O$ ), used historically in manufacturing iron gall ink and as a nutritional iron supplement.
Laughing gas is nitrous oxide ( $N_2O$ ), used in dentistry and surgery for its mild anesthetic and analgesic properties.
Epsom salt is magnesium sulfate heptahydrate ( $MgSO_4 \cdot 7H_2O$ ), used in bath soaks and as an osmotic laxative.
Acid rain is caused primarily by atmospheric sulfur dioxide ( $SO_2$ ) and nitrogen oxides ( $NO_x$ ) reacting with water vapor to form sulfuric and nitric acids, lowering precipitation pH below 5.6.
Barium sulfate ( $BaSO_4$ ) is an insoluble radiopaque contrast agent administered orally as a 'barium meal' for radiographic X-ray imaging of the gastrointestinal tract.
Boric acid ( $H_3BO_3$ ) is a mild antiseptic and antifungal agent used in eye washes and dusting powders.
Hydrogenation of polyunsaturated vegetable oils into solid vegetable ghee (vanaspati) is an industrial catalytic reduction process using finely divided nickel catalyst at 473 K.
Rancidity in fat-containing foods is caused by aerial oxidation of unsaturated fatty acids, prevented commercially by packing snacks under inert nitrogen gas and adding antioxidants like BHA and BHT.

Curriculum & Reference Sources: NCERT Chemistry Class XI/XII, Royal Society of Chemistry, IUPAC Educational Resources

Sample Solved Questions & Concept Explanations

8 Verified Concept Questions

Q1.EASY

What is the chemical formula of common table salt?

Q2.EASY

What is the pH value of pure, neutral water at 25°C?

Q3.EASY

Which gas is most abundant in Earth's atmosphere by volume?

Q4.EASY

What is the chemical name of baking soda?

Q5.EASY

What is the primary gas found in natural gas and biogas (gobar gas)?

Q6.MEDIUM

Which law in chemistry states that at constant temperature, the volume of a given mass of gas is inversely proportional to its pressure (P ∝ 1/V)?

Q7.MEDIUM

What is the chemical name of the acid present in vinegar?

Q8.MEDIUM

The sour taste of curd and yogurt is caused by the presence of which organic acid?