Science Important Chemical Formulas
Important Chemical Formulas – RRB Quick Revision
🔍 Universal Constants & Elements (Must-Know)
| Symbol | Element/Compound | Common Name | Memory Trick |
|---|---|---|---|
| H₂O | Water | जल | “H-to-O” sounds like H₂O |
| NaCl | Sodium Chloride | Common Salt | “Na” + “Cl” = नमक |
| CO₂ | Carbon Dioxide | खरगोश गैस | “C-O-two” → cold-drink bubbles |
| O₂ | Oxygen | जीवन गैस | We breathe O-two, not O-one |
| N₂ | Nitrogen | वायु का 78 % | N-two fills the sky |
⚗️ Acids, Bases & Salts (ALWAYS Asked)
| Formula | Name | Use / Source | Quick Note |
|---|---|---|---|
| HCl | Hydrochloric acid | Toilet cleaner | Strong acid |
| H₂SO₄ | Sulphuric acid | Battery acid | Oil of Vitriol |
| HNO₃ | Nitric acid | Fertilizers | Aqua fortis |
| NaOH | Caustic soda | Drain cleaner | Strong base |
| Ca(OH)₂ | Slaked lime | Whitewash | Base |
| NaHCO₃ | Baking soda | Cooking | Mild base |
| CaCO₃ | Limestone | Chalk, marble | Salt |
Mnemonic: “Happy Henry Likes Beer But Could Not Obtain Food”
HCl, H₂SO₄, HNO₃ → Strong Acids (remember 3-H’s)
🔥 Common Gases & Their Formulas
| Gas | Formula | Test / Property | RRB Favourite |
|---|---|---|---|
| Ammonia | NH₃ | Pungent smell, basic | Refrigerant |
| Methane | CH₄ | Main component of Gobar-gas | CH₄ = 1C + 4H |
| Hydrogen | H₂ | Pop sound with lighted splint | Lightest gas |
| Chlorine | Cl₂ | Yellow-green, poison | Water purification |
| Sulphur dioxide | SO₂ | Rotten egg smell | Acid rain |
🧪 Metals & Ores (1-marker Sure-Shot)
| Ore | Formula | Metal Extracted | State Famous For |
|---|---|---|---|
| Haematite | Fe₂O₃ | Iron (Fe) | Odisha |
| Bauxite | Al₂O₃·2H₂O | Aluminium (Al) | Odisha |
| Copper pyrites | CuFeS₂ | Copper (Cu) | Rajasthan |
| Galena | PbS | Lead (Pb) | Rajasthan |
| Cinnabar | HgS | Mercury (Hg) | Rajasthan |
Memory: “Hero Bought Cute Gifts” → Haematite, Bauxite, Copper-pyrites, Galena
⚡ Fertilizers & Industrial Chemicals
| Formula | Fertilizer | % Nutrient | Exam Note |
|---|---|---|---|
| NH₄NO₃ | Ammonium nitrate | 34 % N | High-nitrogen |
| (NH₄)₂SO₄ | Ammonium sulphate | 21 % N | By-product |
| Ca(H₂PO₄)₂ | Super-phosphate | 16 % P₂O₅ | Phosphatic |
| KCl | Muriate of potash | 60 % K₂O | Potassic |
🌈 pH Values to Memorize
| Substance | pH | Nature |
|---|---|---|
| Gastric juice | 1.5 | Strong acid |
| Lemon juice | 2.4 | Acid |
| Pure water | 7 | Neutral |
| Blood | 7.4 | Slightly basic |
| Baking soda | 8.3 | Basic |
| Soap solution | 9–10 | Basic |
🔢 Important Numbers
- 78 % N₂ in air
- 21 % O₂ in air
- 0.04 % CO₂ in air
- 22.4 L = Molar volume of gas at STP
- 6.022×10²³ = Avogadro’s number (atoms/mole)
10 Likely RRB Exam Questions (Click to Expand)
-
Chemical formula of Baking soda is?
Ans. NaHCO₃ -
Which gas is released when limestone is heated?
Ans. CO₂ (CaCO₃ → CaO + CO₂) -
Haematite is an ore of which metal?
Ans. Iron (Fe) -
pH of blood is approximately?
Ans. 7.4 -
The gas that gives rotten egg smell is?
Ans. H₂S (not SO₂) -
Strongest acid among the following: HCl, H₂SO₄, HNO₃, CH₃COOH?
Ans. H₂SO₄ -
Chemical name of Caustic soda is?
Ans. Sodium hydroxide (NaOH) -
Lightest gas?
Ans. H₂ -
Percentage of nitrogen in Ammonium nitrate (NH₄NO₃)?
Ans. 34 % -
Avogadro’s number is?
Ans. 6.022 × 10²³
Last-day mantra: Revise tables twice → solve 10 Qs → sleep tight!
BETA
