Science & Tech· Prelims · GS-III
Chemistry facts for prelims: periodic table, everyday chemicals, fuels and alloys
Periodic table extremes, everyday chemicals with their common names, fuels, alloys, ores and polymers: the chemistry facts prelims tests, with tables, practice questions and model answers.
Chemistry is the study of matter: what substances are made of, how they change, and the compounds hidden in everyday life. For prelims, chemistry questions cluster around a small set of recurring facts: the extremes of the periodic table, the common names of everyday chemicals, and the composition of fuels, alloys and ores. This article collects those facts with the exact details prelims has tested.
The periodic table: extremes and firsts
The modern periodic table arranges 118 known elements by atomic number. The lightest element is hydrogen, with atomic number 1, and it is also the most abundant element in the universe. The most abundant element in the Earth's crust is oxygen, followed by silicon.
Extreme | Element |
|---|---|
Lightest element | Hydrogen |
Densest naturally occurring element | Osmium |
Most abundant element in the universe | Hydrogen |
Most abundant element in the Earth's crust | Oxygen |
Most abundant metal in the Earth's crust | Aluminium |
Most abundant gas in air | Nitrogen, about 78 per cent |
Most reactive stable metal | Caesium |
Most reactive non-metal | Fluorine |
Liquid metal at room temperature | Mercury |
Liquid non-metal at room temperature | Bromine |
Best conductor of electricity | Silver |
Asked in SSC CGL 2026
Everyday chemicals: common names and formulas
Prelims tests the common name against the chemical name. Baking soda is sodium bicarbonate, washing soda is sodium carbonate, and bleaching powder is calcium oxychloride. Mixing up baking soda and washing soda is the classic trap.
Common name | Chemical name | Formula |
|---|---|---|
Baking soda | Sodium bicarbonate | NaHCO3 |
Washing soda | Sodium carbonate | Na2CO3 |
Bleaching powder | Calcium oxychloride | Ca(OCl)Cl |
Common salt | Sodium chloride | NaCl |
Caustic soda | Sodium hydroxide | NaOH |
Blue vitriol | Copper sulphate | CuSO4.5H2O |
Dry ice | Solid carbon dioxide | CO2 |
Laughing gas | Nitrous oxide | N2O |
Vinegar | Acetic acid | CH3COOH |
Aqua regia | Hydrochloric acid and nitric acid, 3:1 | 3 HCl : 1 HNO3 |
Aqua regia, a 3:1 mixture of concentrated hydrochloric acid and concentrated nitric acid, is one of the few liquids that can dissolve gold and platinum.
Malic acid gives apples and strawberries their tart taste. Citric acid is the sour acid of lemons and oranges, tartaric acid occurs in tamarind and grapes, and lactic acid builds up in muscles during heavy exercise and sours milk.
Asked in RRB NTPC
Fuels, alloys, ores and polymers
An alloy is a mixture of metals, or of a metal with another element, made to improve strength, hardness or resistance to corrosion.
Alloy | Composition |
|---|---|
Brass | Copper and zinc |
Bronze | Copper and tin |
Steel | Iron and carbon |
Stainless steel | Iron, chromium and nickel |
Solder | Lead and tin |
German silver | Copper, zinc and nickel |
Bell metal | Copper and tin, with more tin than bronze |
Ore | Metal obtained |
|---|---|
Bauxite | Aluminium |
Haematite | Iron |
Galena | Lead |
Cinnabar | Mercury |
Baryte | Barium |
Malachite | Copper |
Fuels store chemical energy. LPG is mainly butane and propane, CNG is mainly methane, and biogas is methane with carbon dioxide. Coal is fossilised plant matter, and its best variety is anthracite.
Polymers are long chains of repeating units. Teflon (PTFE) is used for non-stick coatings, Bakelite (phenol-formaldehyde resin) for electrical switches, PVC for pipes, and nylon for fibres.
Asked in SSC CGL 2026
Acids, bases and the pH scale
The pH scale runs from 0 to 14. A pH below 7 is acidic, 7 is neutral and above 7 is basic. Human blood is slightly basic at about pH 7.4, and gastric juice is strongly acidic at about pH 1.5 to 2.
A chemical change makes a new substance, while a physical change only changes form or state. Rusting of iron, burning of paper and curdling of milk are chemical changes; melting of ice, boiling of water and dissolving sugar are physical changes.
Soap is made by treating fats with an alkali, a process called saponification. Detergents are synthetic cleaning agents that work in hard water, where ordinary soap forms scum with calcium and magnesium salts.
Prelims practice
Bleaching powder is chemically:
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Answer: (A) Bleaching powder is calcium oxychloride, Ca(OCl)Cl; sodium bicarbonate is baking soda.
Malic acid is found in:
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Answer: (A) Malic acid gives apples and strawberries their tart taste; vinegar contains acetic acid and tamarind contains tartaric acid.
The densest naturally occurring element is:
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Answer: (A) Osmium is the densest naturally occurring element; iridium is the second densest.
Aqua regia is a mixture of concentrated hydrochloric acid and nitric acid in the ratio:
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Answer: (A) Aqua regia is three parts concentrated hydrochloric acid to one part concentrated nitric acid.
Brass is an alloy of:
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Answer: (A) Brass is copper and zinc; copper and tin make bronze, and lead and tin make solder.
Answer key
- (a): Bleaching powder is calcium oxychloride, Ca(OCl)Cl; sodium bicarbonate is baking soda.
- (a): Malic acid gives apples and strawberries their tart taste; vinegar contains acetic acid and tamarind contains tartaric acid.
- (a): Osmium is the densest naturally occurring element; iridium is the second densest.
- (a): Aqua regia is three parts concentrated hydrochloric acid to one part concentrated nitric acid.
- (a): Brass is copper and zinc; copper and tin make bronze, and lead and tin make solder.
Mains Practice question
150 words: Chemistry in everyday life is invisible until it goes wrong. Discuss how knowledge of common chemicals improves public health and safety.
- Bleaching powder and chlorine disinfect drinking water and prevent disease.
- Knowing which chemical is which prevents dangerous mixing at home and in labs.
- Food adulteration can be detected by simple chemical tests for common additives.
- Understanding pH explains digestion, antacids and the safety of stored food.
- Safe storage and labelling of acids and alkalis prevents household accidents.
250 words: India's energy transition depends on fuels, materials and storage. Examine the role of chemistry in clean energy.
- Hydrogen as a fuel needs catalysts and storage materials that chemistry provides.
- Batteries for electric vehicles depend on lithium, cobalt and new cathode chemistry.
- Biofuels are made by chemical conversion of biomass into ethanol and biodiesel.
- Solar cells need high-purity silicon and new materials such as perovskites.
- Carbon capture turns waste carbon dioxide into useful chemicals and fuels.
Frequently asked questions
Why is water called the universal solvent?
Water is a polar molecule with slightly positive and slightly negative ends, so it surrounds and separates ions and polar molecules, dissolving more substances than any other liquid.
What is the difference between baking soda and washing soda?
Baking soda is sodium bicarbonate, used in cooking and as a mild antacid, while washing soda is sodium carbonate, which is more alkaline and used for cleaning.
Which acid is present in vinegar?
Acetic acid. Vinegar is a dilute solution of acetic acid in water, usually about 5 per cent.
What is dry ice?
Dry ice is solid carbon dioxide. It sublimes directly from solid to gas without becoming liquid, which is why it is used to keep things cold.