What is the pH value of a neutral solution such as pure water at 25°C?

Pure water is neutral with a pH of 7 at 25°C. Values below 7 indicate acids (which turn blue litmus red), and values above 7 indicate bases (which turn red litmus blue). pH 0 is strongly acidic, pH 14 is strongly basic, and pH 1 is also acidic — none of these describe a neutral solution.

Which pair correctly matches the common name to its chemical name?

Baking soda — sodium hydrogen carbonate. Baking soda is sodium hydrogen carbonate (sodium bicarbonate, NaHCO₃). Washing soda is sodium carbonate decahydrate, quicklime is calcium oxide and slaked lime is calcium hydroxide — the last two are routinely swapped in distractors, so fix in memory that adding water (slaking) to quicklime gives slaked lime.

A farmer reports that soap does not lather in the village well water and the kettle has a thick white deposit. What is the most likely cause?

The water is hard, containing dissolved calcium and magnesium salts. Poor lathering together with scale formation is the classic signature of hard water, which contains dissolved calcium and magnesium salts that react with soap to form scum and deposit carbonates as scale. Acidity would not produce scale, high BOD indicates organic pollution, and excess fluoride causes fluorosis in teeth and bones without affecting lathering.

Urea is the most widely used nitrogen fertiliser in India. Approximately what percentage of nitrogen does it contain?

46%. Urea contains about 46% nitrogen, the highest nitrogen content among common solid fertilisers, which is why it dominates Indian consumption. DAP supplies about 18% nitrogen along with phosphorus, and muriate of potash supplies potassium rather than nitrogen.

General Science — Chemistry & Everyday Mater | Free Guide 2026

Key Takeaways

Pure water is neutral at pH 7; acids lie below 7 and turn blue litmus red, while bases lie above 7 and turn red litmus blue.
Common-name chemistry is high-yield: baking soda is sodium bicarbonate (NaHCO3), washing soda is sodium carbonate decahydrate, bleaching powder is calcium hypochlorite and quicklime is calcium oxide.
The three primary fertiliser nutrients are nitrogen, phosphorus and potassium (NPK); urea is the most widely used nitrogen fertiliser at about 46% nitrogen.
Diamond is the hardest natural form of carbon and graphite is a good conductor, even though both are pure carbon — a difference of structure, not composition.
Hard water contains dissolved calcium and magnesium salts, which is why it wastes soap and forms scale in kettles and boilers.

Chemistry — Key Concepts

Matter and Its States

State	Property
Solid	Definite shape and volume; particles tightly packed
Liquid	Definite volume, takes container shape; particles loosely packed
Gas	No definite shape or volume; particles far apart

State changes: melting (solid→liquid), evaporation (liquid→gas), condensation (gas→liquid), freezing (liquid→solid), sublimation (solid→gas directly).

Atoms and Molecules

Atom — smallest particle of an element that retains its properties
Molecule — two or more atoms chemically bonded
Atomic number (Z) = number of protons
Mass number (A) = protons + neutrons
Isotopes — same atomic number, different mass number (e.g., ¹H, ²H, ³H)

Acids, Bases, Salts and pH

Substance	pH Range	Litmus Effect
Acid	< 7	Turns blue litmus red
Neutral	= 7	No change
Base	> 7	Turns red litmus blue

Strong acids: HCl, H₂SO₄, HNO₃
Strong bases: NaOH, KOH
Common salts: NaCl (common salt), CaCO₃ (limestone), NaHCO₃ (baking soda)

Chemical Reactions

Type	Example
Combination	A + B → AB
Decomposition	AB → A + B
Displacement	A + BC → AC + B
Double displacement	AB + CD → AD + CB
Oxidation-reduction (redox)	transfer of electrons; oxidation = loss, reduction = gain

Periodic Table Basics

Groups = vertical columns (1–18); elements in a group have similar outer electron configuration
Periods = horizontal rows (1–7); atomic number increases left to right
Alkali metals (Group 1): Li, Na, K — highly reactive
Halogens (Group 17): F, Cl, Br, I — reactive non-metals
Noble gases (Group 18): He, Ne, Ar — inert

Carbon Compounds

Allotropes of carbon — diamond (hardest natural), graphite (conductor), fullerene, graphene
Hydrocarbons — alkanes (single bond), alkenes (double bond), alkynes (triple bond)
Functional groups — alcohol (-OH), aldehyde (-CHO), carboxylic acid (-COOH)
Ethanol (C₂H₅OH) — used in alcoholic drinks and as fuel
Ethanoic acid (CH₃COOH) — vinegar (5–8% solution)

Metals and Non-Metals

Property	Metals	Non-metals
Appearance	Lustrous	Mostly dull
Conductivity	Good conductors of heat and electricity	Poor conductors (graphite is the exception)
Malleable / ductile	Yes	No — brittle when solid
Oxides	Basic	Acidic
At room temperature	Solid, except mercury (liquid)	Solid, liquid (bromine) or gas

Reactivity series (most to least reactive): K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Ag, Au. A more reactive metal displaces a less reactive one from its salt solution — iron nails placed in copper sulphate solution turn brown and the blue solution fades.
Rusting of iron needs both oxygen and moisture; it is prevented by painting, oiling, galvanising (zinc coating) or alloying into stainless steel.
Alloys to remember: brass (copper + zinc), bronze (copper + tin), steel (iron + carbon), stainless steel (iron + chromium + nickel), solder (lead + tin).
Noble metals — gold, silver, platinum — resist corrosion, which is why they occur in native form.

Everyday Chemicals — Common Name to Formula

Common name	Chemical name	Formula	Everyday use
Common salt	Sodium chloride	NaCl	Food; raw material for chlor-alkali industry
Baking soda	Sodium hydrogen carbonate	NaHCO₃	Baking, antacid, fire extinguishers
Washing soda	Sodium carbonate decahydrate	Na₂CO₃·10H₂O	Cleaning, softening hard water
Bleaching powder	Calcium oxychloride / hypochlorite	CaOCl₂	Disinfecting drinking water
Quicklime	Calcium oxide	CaO	Whitewashing, cement, soil treatment
Slaked lime	Calcium hydroxide	Ca(OH)₂	Whitewash, neutralising acidic soil
Gypsum	Calcium sulphate dihydrate	CaSO₄·2H₂O	Cement, plaster of Paris, soil conditioner
Blue vitriol	Copper sulphate	CuSO₄·5H₂O	Fungicide (Bordeaux mixture)
Marsh gas	Methane	CH₄	Biogas, gobar gas plants

Water Quality — Directly Relevant to Village Work

Hard water contains dissolved calcium and magnesium salts. It wastes soap by forming scum and deposits scale in kettles and boilers. Soft water lathers easily.
Temporary hardness (bicarbonates) is removed by boiling; permanent hardness (sulphates and chlorides) needs washing soda or an ion-exchange resin.
Drinking water is disinfected by chlorination (bleaching powder) or boiling. Excess fluoride in groundwater causes fluorosis — a real problem in parts of north Karnataka — and excess arsenic or nitrate contamination also arises from groundwater.
Water pollution indicators: high BOD (biochemical oxygen demand) means heavy organic load; eutrophication is nutrient enrichment causing algal blooms, as seen in Bengaluru's lakes.

Fertilisers, Soil Chemistry and Crops

Plants need three primary nutrients — nitrogen (N) for leaf growth, phosphorus (P) for roots and flowering, potassium (K) for overall vigour and disease resistance.
Urea — CO(NH₂)₂, about 46% nitrogen — is the most widely used nitrogen fertiliser in India. DAP supplies nitrogen and phosphorus; MOP (muriate of potash) supplies potassium.
Acidic soil is corrected by adding lime; alkaline or saline soil is treated with gypsum. A VAO recording soil type and irrigation source on the RTC is, in effect, recording the inputs a soil-health question would ask about.
Biofertilisers — Rhizobium in legume root nodules, Azotobacter, blue-green algae — fix atmospheric nitrogen biologically. Compost and green manure improve organic carbon.

Exam Angle for Chemistry

Chemistry questions in this paper are overwhelmingly definitional or common-name based. Three habits cover most of them: memorise the pH and litmus rules in one line each; keep a running common name to formula to use table like the one above; and learn the reactivity series as a spoken sentence so displacement questions become instant. Balancing equations and stoichiometry are effectively never asked at this level, so do not spend time there.

Karnataka Village Administrative Officer (VAO) Exam

3.2 General Science — Chemistry & Everyday Materials