Chemistry (Class 10) — RRB NTPC Study Notes

Overview

Chemistry at the Class 10 level forms a substantial part of the General Awareness section in RRB NTPC. Questions are typically straightforward, testing your recall of basic chemical concepts, reactions, everyday applications, and the periodic table. Expect 3–5 questions from chemistry in each exam paper, often focusing on practical applications — acids-bases in daily life, corrosion, fuels, metals and non-metals, and the periodic classification.

Mastering this topic requires memorizing key reactions, understanding the properties of elements and compounds, and recognizing chemistry in your surroundings (soaps, medicines, food preservation). The questions rarely involve numerical calculations; instead, they test conceptual clarity and real-world linkage. Since this is a moderate-scoring area with predictable question types, a focused revision of NCERT Class 10 Chemistry chapters will yield good returns.

Your goal is to know the *why* behind everyday chemical phenomena and to recall standard reactions, properties, and applications without hesitation.

Key Concepts

• **Chemical reactions and equations**: A chemical reaction involves the transformation of reactants into products. Balancing equations ensures the law of conservation of mass. Types include combination, decomposition, displacement, double displacement, and redox reactions.

• **Acids, bases, and salts**: Acids produce H⁺ ions in water, bases produce OH⁻ ions. pH scale (0–14) measures acidity/basicity; pH < 7 is acidic, pH = 7 is neutral, pH > 7 is basic. Salts are products of neutralization reactions.

• **Metals and non-metals**: Metals are lustrous, malleable, ductile, good conductors; non-metals are brittle, poor conductors. Reactivity series determines displacement reactions. Corrosion (rusting of iron) and metal extraction (reduction of ores) are key applications.

• **Carbon and its compounds**: Carbon forms covalent bonds and shows catenation (chaining). Organic compounds include hydrocarbons (alkanes, alkenes, alkynes), functional groups (alcohol, aldehyde, ketone, carboxylic acid), and polymers.

• **Periodic classification**: Elements arranged by atomic number. Groups (vertical columns) share similar properties; periods (horizontal rows) show gradation. Metals on left, non-metals on right, metalloids in between.

• **Redox reactions**: Oxidation is loss of electrons or gain of oxygen; reduction is gain of electrons or loss of oxygen. They occur simultaneously.

• **Everyday chemistry**: Soaps and detergents clean by micelle formation. Baking soda, washing soda, bleaching powder, and plaster of Paris have household and industrial uses.

• **Environmental chemistry**: Ozone layer protects from UV rays; CFCs cause ozone depletion. Air and water pollution from chemical pollutants (SO₂, NO₂, CO, industrial waste) affect health and ecosystems.

Key Facts

1. **Indictor colors**: Litmus paper turns red in acid, blue in base. Phenolphthalein is colorless in acid, pink in base. Methyl orange is red in acid, yellow in base.

2. **Common acids**: HCl (hydrochloric acid in stomach), H₂SO₄ (sulfuric acid in car batteries), HNO₃ (nitric acid), CH₃COOH (acetic acid in vinegar), H₂CO₃ (carbonic acid in soft drinks).

3. **Common bases**: NaOH (sodium hydroxide or caustic soda), Ca(OH)₂ (slaked lime), Mg(OH)₂ (milk of magnesia).

4. **Reactivity series of metals** (decreasing order): K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au > Pt. More reactive metals displace less reactive ones from compounds.

5. **Allotropes of carbon**: Diamond (hardest natural substance, each carbon bonded to 4 others), graphite (slippery, conducts electricity, used in pencils), fullerenes (C₆₀, football-shaped molecules).

6. **Functional groups**: –OH (alcohol), –CHO (aldehyde), –CO– (ketone), –COOH (carboxylic acid), –O– (ether).

7. **Baking soda (NaHCO₃)**: Used in baking (releases CO₂), antacid, fire extinguishers. Washing soda (Na₂CO₃·10H₂O): Used in glass, soap, paper industries; water softening.

8. **Plaster of Paris (CaSO₄·½H₂O)**: Sets hard when mixed with water; used in casts, moulds, statues.

9. **Ozone formula**: O₃. Ozone layer in stratosphere absorbs harmful UV radiation. CFCs (chlorofluorocarbons) deplete ozone.

10. **Corrosion**: Rusting of iron (Fe + O₂ + H₂O → rust, Fe₂O₃·xH₂O). Prevented by painting, galvanizing (zinc coating), alloying.

Worked Examples

**Example 1: Balancing a chemical equation** *Question*: Balance the equation: Fe + H₂O → Fe₃O₄ + H₂ *Solution*: Step 1: Count atoms on both sides. Step 2: To balance Fe, put 3 before Fe on left: 3Fe + H₂O → Fe₃O₄ + H₂ Step 3: To balance O, put 4 before H₂O: 3Fe + 4H₂O → Fe₃O₄ + H₂ Step 4: H on left = 8, so put 4 before H₂: 3Fe + 4H₂O → Fe₃O₄ + 4H₂ *Balanced equation*: **3Fe + 4H₂O → Fe₃O₄ + 4H₂**

**Example 2: pH and daily life** *Question*: Why does tooth decay start when mouth pH falls below 5.5? *Solution*: Tooth enamel is made of calcium phosphate, the hardest substance in the body. It does not dissolve in water but is corroded when pH in the mouth is below 5.5 (acidic). Bacteria in the mouth produce acids by degrading sugar and food particles. Using toothpaste (basic) neutralizes the acid and prevents decay. *Answer*: **Acidic pH corrodes enamel; toothpaste neutralizes acid.**

**Example 3: Reactivity series application** *Question*: Can iron displace copper from copper sulfate solution? *Solution*: Check reactivity series: Fe is above Cu. A more reactive metal displaces a less reactive metal from its compound. Reaction: Fe + CuSO₄ → FeSO₄ + Cu *Answer*: **Yes, iron will displace copper.**

Common Mistakes

• **Forgetting to balance equations**: Students write correct reactants and products but leave equations unbalanced. *Fix*: Always count atoms on both sides and adjust coefficients systematically.

• **Confusing oxidation and reduction**: Thinking oxidation is gain of oxygen only, forgetting electron transfer. *Fix*: Remember LEO (Loss of Electrons = Oxidation), GER (Gain of Electrons = Reduction).

• **Mixing up acids and bases in daily life**: Calling lemon juice a base because it tastes sour. *Fix*: Sour taste = acidic (citric acid in lemon). Bitter taste and slippery feel = basic (soap).

• **Not distinguishing allotropes**: Saying diamond and graphite are different elements. *Fix*: They are allotropes — same element (carbon), different structures and properties.

• **Ignoring the reactivity series order**: Assuming any metal can displace any other. *Fix*: Only a more reactive metal displaces a less reactive one. Memorize the series: K Na Ca Mg Al Zn Fe... Cu Ag Au.

Quick Reference

• **Acids + Bases → Salt + Water** (neutralization). • **pH < 7 = acidic, pH = 7 = neutral, pH > 7 = basic**. • **Metals lose electrons (form cations); non-metals gain electrons (form anions)**. • **Reactivity series**: K most reactive, Au least reactive. • **Carbon shows catenation and forms millions of compounds**. • **Baking soda = NaHCO₃; Washing soda = Na₂CO₃·10H₂O; Bleaching powder = Ca(OCl)₂**. • **Ozone (O₃) protects from UV; CFCs deplete ozone layer**. • **Rusting requires both oxygen and water; prevention = painting/galvanizing/alloying**.