NDA Chemistry · Formula sheet
Carbon and Its Compounds formulas
2 formulas, 12 reference tables and 13 common traps for NDA Chemistry Carbon and Its Compounds, grouped by subtopic.
Tetra-valency, Catenation and Isomerism
Learn this subtopic in the notesStructural isomerism and counting isomers
Structural isomer counts (alkanes)
Common traps
Carbon forms a triple bond, not a 'four' bond
A statement that 'carbon forms compounds with quadruple bonds between carbon atoms' is false. The maximum is a triple bond (as in ethyne, HC≡CH).
Covalent means poor conductor
'Most carbon compounds are good conductors of electricity' is NOT correct — covalent compounds have no free charges. (Graphite is the famous exception, because of its delocalised electrons.)
Pentane has 3 isomers, not 5
Students confuse the number of carbons with the number of isomers. C5H12 has 3 isomers (the carbon count is 5, the isomer count is 3). Hexane (6 carbons) is the one with 5 isomers.
Allotropes of Carbon
Learn this subtopic in the notesCrystalline allotropes — structure, hybridisation and properties
| Allotrope | Structure / hybridisation | Key property | Use / identity |
|---|---|---|---|
| Diamond | 3-D tetrahedral network, sp³ | Hardest natural substance; electrical insulator | Cutting/abrasives; isomorphous with silicon Diamond does NOT conduct electricity — all four electrons are locked in covalent bonds. |
| Graphite | Flat hexagonal sheets, sp² | Soft, slippery; good conductor; most stable form | Pencil lead, lubricant, electrodes |
| Fullerene (C₆₀) | Closed cage (football), sp² | Purest form of carbon | Nanotechnology, lubricants |
| Graphene | Single one-atom-thick sheet, sp² | Thinnest and strongest material | Electronics, composites |
Diamond = hardest + insulator; Graphite = soft + conductor + most stable; Fullerene = purest; Graphene = thinnest & strongest.
Property traps and impure forms of carbon
| Common false claim | The truth |
|---|---|
| Diamond conducts electricity | Insulator — no free electrons |
| Graphite is the second-hardest substance | Soft and slippery (a lubricant) |
| Graphite layers held by covalent single bonds | Held by weak van der Waals forces |
| Diamond and graphite differ chemically | Same element → same chemistry; only physical properties differ Allotropes are the SAME element, so they always share chemical properties — only physical properties change. |
| Fly ash is an allotrope of carbon | A combustion residue, not an allotrope |
Common traps
Graphite is sp², diamond is sp³
A statement that 'the hybridisation of each carbon in graphite is sp³' is NOT true — graphite is sp² (three bonds per carbon, in sheets). Diamond is the sp³ one.
Only fullerene is cage-like
Of diamond, graphite and fullerene, only fullerene has a cage (football) structure. Diamond is a network and graphite is layered sheets.
Allotropes share chemistry, not physics
Because allotropes are the same element, their chemical properties match — both diamond and graphite burn to give CO₂. The statement that they differ in both physical and chemical properties is the wrong one.
Hydrocarbons and Organic Classification
Learn this subtopic in the notesHomologous series and general formulas
General formulas of hydrocarbon series
Organic vs inorganic — and Wöhler's synthesis
| Compound | Organic or inorganic | Note |
|---|---|---|
| Marsh gas (methane, CH₄) | Organic | Simplest alkane |
| Urea | Organic | First lab-synthesised organic compound (Wöhler, 1828) Wöhler made urea FROM ammonium cyanate — the product is organic, the starting salt is inorganic. |
| Cane sugar (sucrose) | Organic | A carbohydrate |
| Ammonium cyanate (NH₄OCN) | Inorganic | An ionic salt — Wöhler's precursor |
Common traps
CₙH₂ₙ is shared by alkenes and cycloalkanes
An open-chain CₙH₂ₙ is an alkene, but a ring (cycloalkane) has the same formula. For the bank's classification question on an open-chain formula like C₄H₈, the intended answer is alkene.
The starting salt is inorganic, the product is organic
Ammonium cyanate (NH₄OCN) is the inorganic answer to 'which is NOT organic', even though Wöhler turned it into urea (organic). Don't let the urea connection fool you into calling the salt organic.
Functional Groups and Common Organic Compounds
Learn this subtopic in the notesFunctional groups and their families
| Family | Functional group | Example | Giveaway property |
|---|---|---|---|
| Alcohol | -OH | Ethanol | Neutral to litmus Ethanol does NOT turn litmus red — alcohols are neutral, unlike acids. |
| Carboxylic acid | -COOH | Acetic acid; formic (methanoic) acid | Sour; turns blue litmus red |
| Ester | -COO- | Ethyl acetate | Sweet, fruity smell |
| Aldehyde / Ketone | -CHO / C=O | Formaldehyde / Acetone | Reactive carbonyl group |
Carbon monoxide and other named facts
| Fact | Detail |
|---|---|
| CO is poisonous because… | It binds haemoglobin (carboxyhaemoglobin), blocking O₂ transport CO is dangerous because of its affinity for haemoglobin — not because it is acidic. CO is a neutral oxide. |
| Litmus is derived from… | Lichens |
| Element forming the most compounds | Carbon |
Common compounds — formula and use
| Common name | Formula | Key fact / use |
|---|---|---|
| Baking soda | NaHCO₃ | Decomposes on heating → CO₂ makes cakes rise It is the released CO₂ — not water vapour — that raises the dough. |
| Gypsum | CaSO₄·2H₂O | Two waters of crystallization; used to make plaster of Paris |
Common traps
Alcohol is neutral, acid turns litmus red
Ethanol (an alcohol) is neutral to litmus. Only the -COOH acids (acetic, formic) turn blue litmus red. Options that say ethanol turns litmus red are wrong.
Common Carbon Compounds and Pigments
Learn this subtopic in the notesCommon names, formulas and uses
| Common name | Chemical name / formula | Use or identity |
|---|---|---|
| Washing soda | Na₂CO₃·10H₂O | Cleaning, water softening |
| Baking soda | NaHCO₃ | Baking, antacid |
| Dry ice | Solid CO₂ | Refrigerant — sublimes, no liquid Dry ice is solid carbon dioxide, NOT frozen water. |
| Chalk / Marble | CaCO₃ | Building, blackboard chalk |
| Vinegar | Acetic (ethanoic) acid | Food preservative, flavouring |
| Silica gel | SiO₂ (hydrated) | Desiccant — absorbs moisture |
Water of crystallization
| Salt | Formula | Water molecules |
|---|---|---|
| Blue vitriol (copper sulphate) | CuSO₄·5H₂O | 5 |
| Washing soda | Na₂CO₃·10H₂O | 10 |
| Gypsum | CaSO₄·2H₂O | 2 |
| Plaster of Paris | (CaSO₄)₂·H₂O | 1 (shared by two CaSO₄ units) Plaster of Paris has ONE water of crystallization per TWO formula units of CaSO₄ — i.e. CaSO₄·½H₂O. |
Pigments and carbon black
| Substance | Pigment? | Note |
|---|---|---|
| Zinc oxide | Yes (white) | Common white pigment |
| White lead | Yes (white) | Traditional white pigment |
| Chalk (CaCO₃) | Yes (white) | Cheap white pigment/filler |
| Silica | No | A filler/abrasive, not a pigment Of zinc oxide, chalk, white lead and silica, the odd one out (NOT a pigment) is silica. |
| Carbon black | Yes (black) | Made by incomplete combustion of hydrocarbons |
Common traps
Dry ice is CO₂, not ice
'Dry ice' is solid carbon dioxide, not frozen water. It sublimes (solid → gas) with no liquid stage, which is why it is 'dry'.
Plaster of Paris = half a water per CaSO₄
Plaster of Paris is written (CaSO₄)₂·H₂O — one water molecule shared by two units of CaSO₄. It is not two waters; gypsum (CaSO₄·2H₂O) is the one with two.
Soaps, Detergents and Hydrogenation of Oils
Learn this subtopic in the notesSoaps, saponification and micelles
| Feature | Detail |
|---|---|
| What a soap is | Na or K salt of a long-chain fatty acid |
| Two ends of the molecule | Hydrophobic tail + hydrophilic (ionic) head |
| Micelle orientation | Tails inward onto oil; ionic heads outward into water The ionic heads face the WATER, not the oil — the common trap reverses this. |
| NaOH vs KOH in saponification | NaOH → hard soap; KOH → soft (liquid) soap |
Detergents vs soaps
| Soap | Synthetic detergent | |
|---|---|---|
| Head group | Carboxylate (-COO⁻Na⁺) | Sulphonate or quaternary ammonium |
| Source | Natural fats/oils | Petrochemicals (synthetic) |
| Works in hard water? | No — forms scum | Yes Sodium stearate is a SOAP, not a detergent — the carboxylate head gives it away. |
Hydrogenation of oils
| Starting material | Reagent / catalyst | Product |
|---|---|---|
| Unsaturated vegetable oil (liquid) | H₂ gas, nickel catalyst | Saturated fat (solid) — margarine / vanaspati The reagent is HYDROGEN gas (with a Ni catalyst) — that is what 'hydrogenation' means. |
Common traps
Micelle: ionic heads face the water
In a micelle the ionic heads point outward into the water and the oily tails point inward onto the grease. A statement that the ionic end points toward the oil droplet is the one that is NOT correct.
The carboxylate is the soap
In a 'which is NOT a synthetic detergent' list, the molecule ending in -COO⁻Na⁺ (a carboxylate, e.g. sodium stearate) is the soap. Sulphonates (-OSO₃⁻) and quaternary ammonium salts are the detergents.