Carbon and Its Compounds — Important Questions & Answers

Compound 'X' is Ethanol (\(CH_3CH_2OH\)) — the alcohol found in wine.
Compound 'Y' is Ethanoic Acid (\(CH_3COOH\)) — it turns blue litmus red because it is acidic.

LPG (saturated hydrocarbons) + air holes → ample oxygen → complete combustion → carbon fully oxidised → clean, soot-free blue flame.

Wax vapour around the wick cannot mix quickly enough with air → incomplete combustion. Unburnt carbon particles become red-hot and glow yellow, escaping as black soot.

Carbon (atomic number 6): configuration (2, 4) → needs 4 more electrons to complete its octet.

Carbon shares its 4 valence electrons with other atoms to form stable covalent bonds. This is the basis of the vast organic world.

Brisk effervescence (vigorous bubbling) is seen due to rapid evolution of a colourless, odourless gas (hydrogen).

The gas burns with a 'pop' sound when a burning matchstick is brought near, confirming the gas is H₂. Sodium gradually dissolves.

Structural isomers are compounds sharing the same molecular formula but with different structural arrangements of the carbon skeleton.

Isomerism requires branching. 1, 2, or 3 carbon atoms can only be arranged in a single straight chain — branching is geometrically impossible with so few carbons. Isomers appear only from Butane (C₄H₁₀) onwards.

Vegetable oils contain unsaturated fatty acids (C=C double bonds). H₂ gas is added in the presence of a Nickel (Ni) catalyst at high temperature, converting double bonds to single bonds → solid saturated fat (vanaspati).

\(C_3H_6\) (Propene) and \(C_5H_{10}\) (Pentene) belong to the Alkene series.
(\(C_4H_{10}\) is Butane — an alkane, different series.)

Both fit the alkene general formula \(C_nH_{2n}\): hydrogen atoms = exactly 2× carbon atoms.

Both contain a C=C double bond (unsaturation), giving them identical chemical properties and reaction types (e.g., addition reactions).

Each carbon shares 3 pairs of electrons with the other carbon → triple bond. Each carbon also shares 1 pair with a hydrogen atom → single bond.

Each H has 2 electrons around it (duet); each C has 8 electrons (octet).

• 2 single covalent bonds (C–H bonds)
• 1 triple covalent bond (C≡C bond)
• Total shared pairs = 5

Saponification — the reaction of an ester with a strong base (NaOH) to produce a soap salt and an alcohol.

Hard water contains dissolved Ca²⁺ and Mg²⁺ ions. Soap molecules react with these ions instantly to form a sticky, insoluble white precipitate called scum — which wastes soap and stains clothes.

Detergents are made from ammonium or sulphonate salts. Their charged ends do not react with Ca²⁺ or Mg²⁺ ions, so they remain soluble and produce a rich lather.

2-Methylbutan-1-ol — longest chain = 4C (butanol); –OH at C1; –CH₃ branch at C2.

Pent-2-yne — 5-carbon chain (pent); triple bond starting at C2 from the end nearest to it.

Methanal — 1 carbon with aldehyde (–CHO) functional group.

1. Industrial solvent — dissolves organic substances; used in paints, varnishes, and lacquers.
2. Medical/antiseptic use — main ingredient in hand sanitisers, cough syrups, and medical rubs.

Food preservation (vinegar) — a 5–8% aqueous solution of ethanoic acid is vinegar, used to preserve pickles and sauces.

Reactants: Ethanoic Acid + Ethanol. Process: Esterification. Catalyst: concentrated \(H_2SO_4\).

Carbon has a very small atomic size, so its nucleus holds shared electron pairs tightly → C–C bond is very strong and stable → long chains and rings form easily.

Silicon atoms are much larger → shared electrons are farther from the nucleus → Si–Si bonds are weak and break after only a few atoms.

Lower carbon-to-hydrogen ratio → enough oxygen available to completely oxidise all carbon → complete combustion → clean blue flame.

Higher carbon percentage → air does not supply enough oxygen → incomplete combustion → unburnt carbon particles glow yellow, escape as black soot (smoke).

Contains a C=C double bond. One bond can open up to accept extra atoms → addition is possible.

Contains only single bonds — all valencies are fully satisfied → no room to add atoms → addition reaction not possible.

Substitution Reaction — in the presence of sunlight, a highly reactive Cl atom replaces (substitutes) one H atom in methane.