Common compounds
The 54 compounds NDA Chemistry actually tests
Single page, every compound grouped by theme. Each entry shows the common name, the formula in plain-text + unicode, the primary use, and a link to the playbook where it most appears. Bookmark and active-recall the morning of the exam.
- compounds indexed
- 54
- themed clusters
- 6
- page to revise from
- 1
- years of PYQs behind it
- 10
How to use this page
- First read: cover-to-cover. Mark compounds you DON’T already know cold — the ones you couldn’t derive from the formula or the name alone. Most candidates know ~30 of the 54.
- Active recall: cover the right two columns (formula + use), read just the compound NAME, write the formula + one use from memory. Repeat for any you miss.
- Drill the playbook: click the ‘Playbook’ link on any row to jump to the chapter’s deep-dive + drill the bank questions where that compound appears.
- Trap-aware: the amber ‘Note’ on a row flags the most-common distractor for that compound (oxalic NOT citric in tomatoes; graphite NOT diamond conducts electricity; Cr is essential in stainless steel).
Common acids — sources and uses
Acids you'll meet by name. NDA tests source-recall (oxalic in tomatoes, citric in lemons) almost every paper. Drill this cluster against the /playbooks/acids-bases-and-salts deep-dive.
| Name | Formula | Use / context | |
|---|---|---|---|
Citric acid | C₆H₈O₇ | Citrus fruits (lemons, oranges) — sour taste | Playbook |
Oxalic acid Note:Recurring NDA question: 'acid in tomatoes' = oxalic, not citric. | (COOH)₂ · 2H₂O | Tomatoes, spinach, rhubarb — rust remover | Playbook |
Lactic acid | CH₃CH(OH)COOH | Sour milk + curd; fatigued muscle build-up | Playbook |
Acetic acid (vinegar) | CH₃COOH | Vinegar (5–8% solution) — food preservation, cooking | Playbook |
Formic acid | HCOOH | Ant + bee sting venom — leather processing | Playbook |
Malic acid | C₄H₆O₅ | Apples, grapes (less ripe) — tart flavour | Playbook |
Tartaric acid | C₄H₆O₆ | Grapes, tamarind — baking powder ingredient | Playbook |
Hydrochloric acid Note:First mineral acid discovered historically — recurring HARD-trap question. | HCl | Gastric juice (digestion) — industrial cleaning | Playbook |
Sulphuric acid | H₂SO₄ | Car batteries, fertilisers (superphosphate), oil refining | Playbook |
Nitric acid | HNO₃ | Fertilisers (ammonium nitrate), explosives (TNT) | Playbook |
Common salts and bases
The salts and bases NDA names directly. Watch the 'soda' suffix — multiple distinct compounds wear it.
| Name | Formula | Use / context | |
|---|---|---|---|
Common salt | NaCl | Edible salt — saline; soap manufacture; freezing-mixture lowerant | Playbook |
Washing soda Note:10 H₂O of crystallisation — recurring 'water of crystallisation' q. | Na₂CO₃ · 10H₂O | Glass + soap manufacture; water softening (laundry) | Playbook |
Baking soda | NaHCO₃ | Baking (CO₂ leavening); antacid (neutralises stomach HCl); fire extinguisher | Playbook |
Bleaching powder | Ca(OCl)Cl | Disinfectant (water treatment); bleaching cotton/paper | Playbook |
Caustic soda | NaOH | Soap + paper + textile manufacture; drain cleaner | Playbook |
Slaked lime | Ca(OH)₂ | Whitewashing; mortar; CO₂ detection (lime water turns milky) | Playbook |
Quick lime | CaO | Cement; steel manufacture; flux in metallurgy | Playbook |
Plaster of Paris Note:Half a water of crystallisation per CaSO₄ unit (2:1 ratio). | CaSO₄ · ½H₂O | Casts (medical); decorative; dental moulds | Playbook |
Gypsum | CaSO₄ · 2H₂O | Source of Plaster of Paris (heated to drive off 1.5 H₂O) | Playbook |
Epsom salt | MgSO₄ · 7H₂O | Laxative; bath salts; muscle-soreness soak | Playbook |
Blue vitriol Note:Loses 5 H₂O on heating → anhydrous white CuSO₄ (dehydration colour-change trap). | CuSO₄ · 5H₂O | Algicide; electroplating; fungicide | Playbook |
Green vitriol | FeSO₄ · 7H₂O | Ink + pigment manufacture; water treatment | Playbook |
Common gases — uses + tests
Gases NDA names. The 'test-for-gas' subtopic (lime water for CO₂, glowing-splint for O₂) recurs every 2–3 papers.
| Name | Formula | Use / context | |
|---|---|---|---|
Oxygen Note:Test: relights a glowing wooden splint. | O₂ | Respiration; combustion; medical use; deep-sea diver mix (with He) | Playbook |
Nitrogen | N₂ | 78% of air; inert atmosphere for chips/food packaging; liquid N₂ for cryogenics | Playbook |
Carbon dioxide Note:Test: turns lime water Ca(OH)₂ milky (CaCO₃ precipitate). | CO₂ | Soft drinks; fire extinguisher (heavier than air, smothers); photosynthesis input | Playbook |
Carbon monoxide Note:Neutral oxide — does NOT react with acid or base. Don't confuse with CO₂. | CO | Reducing agent in metal extraction; toxic combustion product (poor ventilation) | Playbook |
Hydrogen Note:Lightest gas; burns with pale-blue flame; produces only H₂O on combustion. | H₂ | Rocket fuel; ammonia synthesis (Haber); margarine manufacture (hydrogenation) | Playbook |
Ammonia Note:Brønsted base; Lewis base (lone pair); pungent smell. | NH₃ | Fertilisers (urea, ammonium nitrate); cleaning agent; refrigerant | Playbook |
Chlorine | Cl₂ | Water disinfection; PVC manufacture; bleaching | Playbook |
Sulphur dioxide Note:Acidic oxide — pollutant causing acid rain. | SO₂ | H₂SO₄ manufacture (contact process); food preservative; bleaching wool/silk | Playbook |
Nitrogen dioxide Note:Acidic oxide; reddish-brown gas. | NO₂ | HNO₃ manufacture; pollutant in vehicle exhaust | Playbook |
Helium | He | Balloons; deep-sea diver mix (with O₂, replaces N₂ to avoid nitrogen narcosis); MRI cooling | Playbook |
Fuels, hydrocarbons + organic everyday
Burnable fuels + common organic compounds. The 'industrial fuel gas' (water gas / producer gas / coal gas) category recurs.
| Name | Formula | Use / context | |
|---|---|---|---|
Methane (natural gas) | CH₄ | Domestic + power-plant fuel; chief component of natural gas; biogas | Playbook |
Ethanol (ethyl alcohol) | C₂H₅OH | Alcoholic drinks; antiseptic; solvent; biofuel additive | Playbook |
Methanol (wood alcohol) Note:TOXIC if consumed — blindness + death. | CH₃OH | Industrial solvent; antifreeze; biodiesel feedstock | Playbook |
LPG (cooking gas) | C₃H₈ + C₄H₁₀ | Domestic cooking; vehicles (autogas); industrial heating | Playbook |
Water gas Note:Made by steam over hot coke: C + H₂O → CO + H₂. | CO + H₂ | Industrial fuel; syngas for synthesis (methanol, NH₃) | Playbook |
Producer gas | CO + N₂ | Industrial fuel (lower CV than water gas — N₂ is inert) | Playbook |
Biogas | CH₄ + CO₂ | Rural cooking + lighting fuel; from anaerobic digestion of organic waste | Playbook |
Urea | CO(NH₂)₂ | Nitrogen fertiliser (46% N — highest of any solid fertiliser); plastics | Playbook |
Glucose | C₆H₁₂O₆ | Blood sugar; cellular respiration substrate; food sweetener (corn syrup) | Playbook |
Formaldehyde | HCHO | Biological specimen preservative; phenolic resin (Bakelite) feedstock; disinfectant | Playbook |
Allotropes + key elements
Allotropes (different forms of the same element) and a handful of named elements. NDA repeatedly tests diamond-vs-graphite property contrasts.
| Name | Formula | Use / context | |
|---|---|---|---|
Diamond Note:Hardest natural substance. ELECTRICAL INSULATOR (sp³, no free e⁻). | C (sp³ tetrahedral) | Cutting tool; abrasive; jewellery; semiconductor (doped) | Playbook |
Graphite Note:Thermodynamically MORE stable than diamond. Conducts electricity. | C (sp² layered) | Pencil lead; lubricant; electrode (sp² conducts e⁻) | Playbook |
Fullerene (Buckyball) | C₆₀ | Drug delivery research; superconductor (alkali-doped); nanotech | Playbook |
Graphene | C (single sp² layer) | Flexible electronics; strongest known material; high-conductivity composites | Playbook |
Ozone Note:Allotrope of oxygen; pale-blue gas; pungent smell. | O₃ | Stratospheric UV shield; water + air disinfectant (bleaching agent) | Playbook |
Alloys — composition recall
Alloys NDA tests by composition. Memorise the four big ones; the rest are variations.
| Name | Formula | Use / context | |
|---|---|---|---|
Brass | Cu + Zn (60–70% Cu) | Hardware; musical instruments; decorative items | Playbook |
Bronze | Cu + Sn (~88% Cu + 12% Sn) | Statues, coins, bells, sculpture | Playbook |
Stainless steel Note:REQUIRES Cr (≥10.5%) for stain-resistance. Trap: 'Cr is not essential' is wrong. | Fe + Cr (10–18%) + Ni (8–10%) | Cutlery; surgical instruments; kitchenware; building | Playbook |
Solder | Pb + Sn (60% Pb + 40% Sn) | Joining electrical wires + electronic components (low melting point) | Playbook |
Duralumin | Al + Cu (4%) + Mg + Mn | Aircraft body; lightweight high-strength structures | Playbook |
Steel | Fe + C (<2% C) | Construction; tools; machinery; vehicles — most-used alloy | Playbook |
German silver | Cu + Zn + Ni (no actual silver) | Decorative items; resistance wire — name is a misnomer | Playbook |
Why plain-text formulas (not LaTeX)
Chemical formulas are short enough to read in plain text + unicode (Na₂CO₃·10H₂O, CaSO₄·½H₂O, Ca(OCl)Cl). Plain text means the page loads instantly, copies cleanly into your notes, and screen readers handle every symbol. The complex chemistry notation (skeletal formulas, stereochemistry) appears only in the worked-example PYQs on the playbook detail pages.