Chemistry — Static GK for Competitive Exams
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Why Chemistry GK Matters for SSC GD and RPF Constable
Static chemistry questions turn up in almost every SSC GD, RPF Constable and RRB exam paper, usually as one-line factual questions rather than numerical problems. Examiners like this topic because it has a fixed, unambiguous answer key — the symbol of an element, the gas released in a reaction, the pH of milk, the full form of an acronym like LPG. A constable candidate does not need to master reaction mechanisms; what pays off is a firm grip on the periodic table basics, common elements and compounds, and the chemistry hidden in everyday life — cooking gas, soap, rust, vinegar, the air we breathe. This chapter collects exactly that kind of high-yield, exam-tested material.
Matter and Its States
Matter is anything that has mass and occupies space. Chemistry examiners frequently test the states of matter and the terms used to describe changes between them.
- Solid — definite shape and volume; particles tightly packed with strong intermolecular forces.
- Liquid — definite volume but takes the shape of its container; particles close but able to move past each other.
- Gas — no definite shape or volume; particles far apart and move freely.
- Plasma — an ionised gas, often called the fourth state of matter; found in lightning, neon signs and stars.
Key change-of-state terms: melting (solid to liquid), freezing (liquid to solid), evaporation (liquid to gas at surface, below boiling point), boiling (liquid to gas throughout the liquid, at boiling point), condensation (gas to liquid), sublimation (solid directly to gas, e.g. camphor, naphthalene, dry ice/solid carbon dioxide, iodine), and deposition (gas directly to solid).
Atomic Structure Basics
An atom consists of three fundamental particles:
| Particle | Charge | Location | Relative Mass |
|---|---|---|---|
| Proton | Positive (+1) | Nucleus | 1 |
| Neutron | Neutral (0) | Nucleus | 1 |
| Electron | Negative (-1) | Orbits around nucleus (shells) | Negligible (1/1836 of proton) |
The atomic number equals the number of protons in an atom (and, in a neutral atom, the number of electrons too). The mass number equals the sum of protons and neutrons. Atoms of the same element with different numbers of neutrons are called isotopes — for example, hydrogen has three isotopes: protium, deuterium and tritium. Atoms with the same mass number but different atomic numbers are called isobars.
J.J. Thomson discovered the electron in 1897. Ernest Rutherford discovered the nucleus through his gold foil experiment in 1911. James Chadwick discovered the neutron in 1932. Niels Bohr proposed the model of electrons moving in fixed orbits (shells) around the nucleus.
The Periodic Table — Structure and Key Points
The modern periodic table, based on the periodic law that properties of elements are a periodic function of their atomic number, was refined into its current form building on the earlier work of Dmitri Mendeleev, who arranged elements by atomic mass in 1869. The modern table has 18 groups (vertical columns) and 7 periods (horizontal rows).
- Groups 1 and 2 — alkali metals (lithium, sodium, potassium, rubidium, caesium, francium) and alkaline earth metals (beryllium, magnesium, calcium, strontium, barium, radium).
- Group 17 — halogens (fluorine, chlorine, bromine, iodine, astatine).
- Group 18 — noble/inert gases (helium, neon, argon, krypton, xenon, radon) — these have complete outer electron shells and are largely unreactive.
- Groups 3 to 12 — transition metals (iron, copper, zinc, nickel, gold, silver, and others).
- Period 6 and 7 side rows — lanthanides (atomic numbers 57-71) and actinides (atomic numbers 89-103), placed separately at the bottom of the table.
Elements are broadly classified into metals, non-metals and metalloids (semi-metals such as silicon, germanium, arsenic, antimony and boron, which show properties of both metals and non-metals).
Common Elements Every Candidate Should Know
| Element | Symbol | Atomic Number | One Key Fact |
|---|---|---|---|
| Hydrogen | H | 1 | Lightest and most abundant element in the universe |
| Helium | He | 2 | Used in balloons and airships; does not burn |
| Carbon | C | 6 | Basis of all organic compounds; forms diamond and graphite |
| Nitrogen | N | 7 | Makes up about 78% of the atmosphere by volume |
| Oxygen | O | 8 | Makes up about 21% of the atmosphere; essential for respiration |
| Sodium | Na | 11 | Soft, reactive metal; stored under kerosene |
| Aluminium | Al | 13 | Most abundant metal in the Earth's crust |
| Silicon | Si | 14 | Second most abundant element in the Earth's crust; used in electronics |
| Chlorine | Cl | 17 | Greenish-yellow gas; used for water purification |
| Calcium | Ca | 20 | Essential for bones and teeth; found in limestone, chalk, marble |
| Iron | Fe | 26 | Most widely used metal; symbol from Latin "ferrum" |
| Copper | Cu | 29 | Good conductor of electricity; symbol from Latin "cuprum" |
| Zinc | Zn | 30 | Used for galvanising iron to prevent rusting |
| Silver | Ag | 47 | Best conductor of heat and electricity among metals; symbol from "argentum" |
| Iodine | I | 53 | Essential for the thyroid gland; sublimes on heating |
| Gold | Au | 79 | Most malleable and ductile metal; symbol from "aurum" |
| Mercury | Hg | 80 | Only metal that is liquid at room temperature; symbol from "hydrargyrum" |
| Lead | Pb | 82 | Heavy, soft metal; symbol from Latin "plumbum" |
| Uranium | U | 92 | Radioactive element used as nuclear fuel |
Everyday Chemical Compounds and Their Common Names
SSC and RRB papers love asking for the common name or chemical formula of substances used in daily life. This table is one of the highest-yield sections in the whole chapter.
| Common Name | Chemical Name | Formula |
|---|---|---|
| Table salt | Sodium chloride | NaCl |
| Baking soda | Sodium bicarbonate | NaHCO3 |
| Washing soda | Sodium carbonate | Na2CO3 |
| Caustic soda | Sodium hydroxide | NaOH |
| Caustic potash | Potassium hydroxide | KOH |
| Quick lime | Calcium oxide | CaO |
| Slaked lime | Calcium hydroxide | Ca(OH)2 |
| Limestone/marble/chalk | Calcium carbonate | CaCO3 |
| Plaster of Paris | Calcium sulphate hemihydrate | CaSO4.1/2H2O |
| Gypsum | Calcium sulphate dihydrate | CaSO4.2H2O |
| Vinegar | Dilute acetic acid | CH3COOH (dilute) |
| Alcohol (spirit) | Ethanol | C2H5OH |
| Laughing gas | Nitrous oxide | N2O |
| Marsh gas | Methane | CH4 |
| Dry ice | Solid carbon dioxide | CO2 |
| Blue vitriol | Copper sulphate | CuSO4.5H2O |
| Green vitriol | Ferrous sulphate | FeSO4.7H2O |
| Epsom salt | Magnesium sulphate | MgSO4.7H2O |
| Alum (phitkari) | Potassium aluminium sulphate | KAl(SO4)2.12H2O |
| Heavy water | Deuterium oxide | D2O |
| Rock salt | Sodium chloride (mined form) | NaCl |
Acids, Bases and pH
An acid turns blue litmus red and has a pH less than 7; a base turns red litmus blue and has a pH greater than 7. A neutral substance, like pure water, has a pH of exactly 7. The pH scale runs from 0 to 14.
| Substance | Approximate pH | Nature |
|---|---|---|
| Gastric (stomach) juice | 1.5-2 | Strongly acidic (hydrochloric acid) |
| Lemon juice | 2-3 | Acidic (citric acid) |
| Vinegar | ~3 | Acidic (acetic acid) |
| Tomato juice | ~4 | Acidic |
| Black coffee | ~5 | Mildly acidic |
| Milk | ~6.5 | Mildly acidic |
| Pure water | 7 | Neutral |
| Human blood | 7.35-7.45 | Mildly alkaline |
| Sea water | ~8 | Mildly alkaline |
| Baking soda solution | ~9 | Alkaline |
| Soap solution | 9-10 | Alkaline |
| Household ammonia | ~11-12 | Strongly alkaline |
| Caustic soda solution | 13-14 | Strongly alkaline |
Common acids found naturally: citric acid in citrus fruits (lemon, orange), tartaric acid in tamarind and grapes, lactic acid in curd/sour milk, oxalic acid in tomato and spinach, malic acid in apples, formic acid in ant and bee stings, acetic acid in vinegar, and ascorbic acid, which is vitamin C. Common laboratory/industrial acids include hydrochloric acid (HCl), sulphuric acid (H2SO4, called the "king of chemicals"), nitric acid (HNO3) and phosphoric acid (H3PO4).
Common Gases
| Gas | Property/Use |
|---|---|
| Oxygen (O2) | Supports combustion and respiration; about 21% of air |
| Nitrogen (N2) | Inert, about 78% of air; used to preserve packaged food |
| Carbon dioxide (CO2) | Used in fire extinguishers and fizzy drinks; turns lime water milky |
| Carbon monoxide (CO) | Colourless, odourless, highly poisonous; produced by incomplete combustion |
| Hydrogen (H2) | Lightest gas; highly flammable; burns with a pop sound |
| Helium (He) | Inert, non-flammable; used in weather balloons and airships |
| Ammonia (NH3) | Pungent smell; used in fertilisers and as a refrigerant |
| Chlorine (Cl2) | Greenish-yellow, toxic; used to disinfect drinking water |
| Sulphur dioxide (SO2) | Pungent gas released by burning coal/fuel; causes acid rain |
| Ozone (O3) | Found in the stratosphere; absorbs harmful UV radiation |
| Neon (Ne) | Used in advertising/neon signs; glows reddish-orange |
| LPG | Liquefied Petroleum Gas — mainly butane and propane; domestic cooking fuel |
| CNG | Compressed Natural Gas — mainly methane; used as vehicle fuel |
Chemistry in Daily Life
Several everyday phenomena and products are chemistry-based facts frequently tested:
- Rusting of iron is an oxidation reaction in which iron reacts with oxygen and moisture to form hydrated iron oxide (Fe2O3.xH2O). Galvanising (coating with zinc) and painting prevent rusting.
- Soap is a sodium or potassium salt of long-chain fatty acids, made by saponification (reaction of fats/oils with sodium hydroxide). Detergents are synthetic cleaning agents that work even in hard water, unlike soap.
- Hard water contains dissolved calcium and magnesium salts and does not lather easily with soap; boiling or adding washing soda can soften it.
- LPG cylinders contain a mixture of butane and propane; a foul-smelling compound called ethyl mercaptan is added deliberately so leaks can be detected by smell.
- Photosynthesis uses carbon dioxide and water in the presence of sunlight and chlorophyll to produce glucose and oxygen.
- Milk turning sour happens because lactic acid bacteria convert lactose into lactic acid.
- Tears while cutting onions are caused by a volatile sulphur compound (syn-propanethial-S-oxide) released when onion cells are broken.
- Baking powder contains baking soda plus a mild edible acid (like tartaric acid); it releases carbon dioxide on heating/mixing, which makes dough rise.
- Fire extinguishers commonly use carbon dioxide, which is heavier than air and cuts off the oxygen supply to a fire.
- Toothpaste is generally mildly basic/alkaline, which helps neutralise the acids formed in the mouth by bacteria.
- Antacids such as milk of magnesia (magnesium hydroxide) neutralise excess stomach acid.
Metals, Alloys and Their Uses
An alloy is a homogeneous mixture of two or more metals (or a metal and a non-metal) made to improve properties like strength, hardness or resistance to corrosion.
| Alloy | Main Components | Common Use |
|---|---|---|
| Steel | Iron + carbon | Construction, tools, machinery |
| Stainless steel | Iron + chromium + nickel + carbon | Cutlery, utensils, surgical instruments |
| Brass | Copper + zinc | Utensils, musical instruments, fittings |
| Bronze | Copper + tin | Statues, medals, bearings |
| Duralumin | Aluminium + copper + magnesium + manganese | Aircraft bodies, light and strong |
| Solder | Tin + lead | Joining electrical wires (low melting point) |
| Amalgam | Mercury + another metal | Dental fillings |
| Invar | Iron + nickel | Precision instruments, low thermal expansion |
| German silver | Copper + zinc + nickel (no actual silver) | Utensils, ornaments |
Allotropes of Carbon
Carbon exists in several forms with very different physical properties despite being made of the same element:
- Diamond — hardest known natural substance; each carbon atom is bonded to four others in a rigid tetrahedral lattice; used in cutting tools and jewellery.
- Graphite — soft, slippery, good conductor of electricity; used in pencils and as a lubricant; carbon atoms arranged in flat, layered hexagonal sheets.
- Fullerenes — cage-like molecules of carbon, such as C60 (buckminsterfullerene), discovered in 1985.
- Graphene — a single layer of graphite, one atom thick; extremely strong and an excellent conductor.
- Charcoal, coke and carbon black — amorphous forms of carbon.
Radioactivity and Nuclear Chemistry Basics
Henri Becquerel discovered radioactivity in 1896 while studying uranium salts. Marie Curie and Pierre Curie extended this research and discovered the elements polonium and radium; Marie Curie won Nobel Prizes in both Physics (1903) and Chemistry (1911). Radioactive decay involves the emission of alpha particles (helium nuclei), beta particles (electrons) or gamma rays (high-energy electromagnetic radiation) from an unstable nucleus. Uranium-235 and Plutonium-239 are used as nuclear fuel in reactors; Carbon-14 dating is used to estimate the age of archaeological/organic remains.
Types of Chemical Reactions
Exam papers occasionally test the basic classification of chemical reactions along with an example of each:
- Combination reaction — two or more substances combine to form a single product. Example: burning of hydrogen with oxygen to form water.
- Decomposition reaction — a single compound breaks down into two or more simpler substances, often on heating. Example: heating of calcium carbonate to give calcium oxide and carbon dioxide.
- Displacement reaction — a more reactive element displaces a less reactive one from its compound. Example: iron displacing copper from copper sulphate solution.
- Double displacement reaction — ions are exchanged between two compounds, often producing a precipitate. Example: silver nitrate reacting with sodium chloride to give silver chloride precipitate.
- Oxidation — gain of oxygen or loss of electrons; reduction — loss of oxygen or gain of electrons. Both occur together in what is called a redox reaction.
- Neutralisation reaction — an acid reacts with a base to form a salt and water. Example: hydrochloric acid reacting with sodium hydroxide to give sodium chloride and water.
- Exothermic reaction — releases heat (e.g. combustion). Endothermic reaction — absorbs heat (e.g. photosynthesis).
Organic Chemistry — The Basics
Organic chemistry is the study of carbon compounds. Carbon's unique ability to form long chains and rings with itself (catenation) and to bond with hydrogen, oxygen, nitrogen and other elements gives rise to millions of organic compounds.
- Hydrocarbons are compounds made only of carbon and hydrogen. Saturated hydrocarbons (alkanes, e.g. methane CH4, ethane C2H6) have only single bonds; unsaturated hydrocarbons (alkenes, e.g. ethylene C2H4, and alkynes, e.g. acetylene C2H2) contain double or triple bonds.
- Petroleum (crude oil) is refined by fractional distillation into products such as LPG, petrol, kerosene, diesel, lubricating oil, paraffin wax and bitumen, arranged by increasing boiling point/molecular size.
- Ethanol (drinking alcohol) is produced by fermentation of sugars using yeast; methanol is a more toxic, industrial alcohol.
- Polymers are large molecules made of repeating units called monomers. Natural polymers include cellulose, starch, natural rubber and proteins; synthetic polymers include polythene, PVC, nylon, polyester and Teflon.
- Soaps are sodium salts of fatty acids (organic), while most modern detergents are synthetic organic compounds derived from petroleum.
Separation Techniques Used in Chemistry
| Technique | Principle/Use |
|---|---|
| Filtration | Separates insoluble solids from liquids, e.g. sand from water |
| Evaporation | Separates a dissolved solid from a solution by removing the liquid, e.g. obtaining salt from seawater |
| Distillation | Separates liquids with different boiling points, e.g. separating alcohol from water |
| Fractional distillation | Separates a mixture of miscible liquids with close boiling points, e.g. refining crude petroleum |
| Sublimation | Separates a sublimable solid (like camphor or naphthalene) from a non-sublimable one |
| Chromatography | Separates components of a mixture based on differing rates of movement through a medium, e.g. separating dyes in ink |
| Centrifugation | Separates suspended particles from a liquid using high-speed spinning, e.g. separating cream from milk |
| Magnetic separation | Separates magnetic materials (like iron filings) from a non-magnetic mixture |
Important Scientists and Discoveries in Chemistry
| Scientist | Contribution |
|---|---|
| Antoine Lavoisier | Known as the "Father of Modern Chemistry"; established the law of conservation of mass |
| Dmitri Mendeleev | Devised the first widely accepted periodic table (1869), arranged by atomic mass |
| John Dalton | Proposed the atomic theory of matter |
| Amedeo Avogadro | Proposed Avogadro's law relating volume of gas to number of molecules |
| Alfred Nobel | Invented dynamite; endowed the Nobel Prizes |
| Fritz Haber | Developed the Haber process for industrial synthesis of ammonia |
| Linus Pauling | Pioneered the theory of chemical bonding; won Nobel Prizes in Chemistry and Peace |
Key Facts at a Glance
- The modern periodic table has 18 groups and 7 periods, arranged by increasing atomic number.
- Atomic number = number of protons; mass number = protons + neutrons.
- Water's chemical formula is H2O; it has a pH of 7 (neutral).
- The most abundant gas in the atmosphere is nitrogen (~78%); the most abundant element in the Earth's crust is oxygen, followed by silicon.
- Mercury is the only metal liquid at room temperature; bromine is the only non-metal liquid at room temperature.
- Diamond and graphite are both pure forms of carbon but have opposite properties (hardest vs softest).
- Sodium bicarbonate (NaHCO3) is baking soda; sodium carbonate (Na2CO3) is washing soda.
- LPG is mainly butane and propane; CNG and biogas are mainly methane.
- Rusting is an oxidation reaction requiring both oxygen and moisture.
- Marie Curie is the only person to win Nobel Prizes in two different sciences (Physics and Chemistry).
- Alloys like brass (copper + zinc) and bronze (copper + tin) both contain copper as a base metal.
- Vitamin C is chemically known as ascorbic acid.
Practice MCQs
- Which scientist discovered the electron?
- (a) Ernest Rutherford
- (b) J.J. Thomson
- (c) James Chadwick
- (d) Niels Bohr
- What is the chemical formula of baking soda?
- (a) Na2CO3
- (b) NaOH
- (c) NaHCO3
- (d) CaCO3
- Which gas is released when zinc reacts with dilute hydrochloric acid?
- (a) Oxygen
- (b) Carbon dioxide
- (c) Hydrogen
- (d) Nitrogen
- The most abundant metal in the Earth's crust is:
- (a) Iron
- (b) Copper
- (c) Aluminium
- (d) Calcium
- Which of these is an allotrope of carbon known for being an excellent conductor of electricity?
- (a) Diamond
- (b) Graphite
- (c) Charcoal
- (d) Coke
- The pH value of pure water is:
- (a) 0
- (b) 5
- (c) 7
- (d) 14
- Which metal is used for galvanising iron to prevent rusting?
- (a) Copper
- (b) Zinc
- (c) Tin
- (d) Lead
- Brass is an alloy of which two metals?
- (a) Copper and tin
- (b) Copper and zinc
- (c) Iron and carbon
- (d) Tin and lead
- Marie Curie won Nobel Prizes in which two fields?
- (a) Physics and Medicine
- (b) Chemistry and Medicine
- (c) Physics and Chemistry
- (d) Physics and Peace
- Which gas is commonly called "laughing gas"?
- (a) Nitrous oxide
- (b) Nitrogen dioxide
- (c) Nitric oxide
- (d) Ammonia
- Which of the following is used in fire extinguishers because it is heavier than air?
- (a) Oxygen
- (b) Hydrogen
- (c) Carbon dioxide
- (d) Nitrogen
- The chemical name for common salt is:
- (a) Sodium bicarbonate
- (b) Sodium chloride
- (c) Sodium carbonate
- (d) Sodium hydroxide