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CC09 — Chemical Reactions & Everyday Chemistry

📖 CC09  ·  CDS General Science — Chemistry ★ High Priority

Chemistry is everywhere — from the soap you use to the matches you strike. CDS consistently tests the composition of everyday substances and the types of chemical reactions, making this one of the most scoring chapters with focused preparation.

📌 CDS Focus: Types of reactions (combination, decomposition, displacement, double displacement, redox); soap making (saponification: fat + NaOH → soap + glycerol); micelle formation (how soap works); bleaching powder composition; composition of gunpowder and safety matches; fertiliser types. These are direct factual questions.

1. Types of Chemical Reactions

Fig. 1 — Six Types of Chemical Reactions with Equations and Examples
SIX TYPES OF CHEMICAL REACTIONS Type Definition Example 1. Combination A + B → AB Two or more substances combine to form one product. 2H₂ + O₂ → 2H₂O CaO + H₂O → Ca(OH)₂ 2. Decomposition AB → A + B One substance breaks down into two or more products. 2H₂O → 2H₂ + O₂ 2KClO₃ → 2KCl + 3O₂ 3. Displacement A + BC → AC + B More reactive element displaces a less reactive one from its salt. Zn + H₂SO₄ → ZnSO₄ + H₂ Fe + CuSO₄ → FeSO₄ + Cu 4. Double Disp. AB + CD → AD + CB Ions exchange between two compounds; precipitate forms. AgNO₃ + NaCl → AgCl↓ + NaNO₃ 5. Oxidation (loss of electrons) Gain of oxygen OR loss of hydrogen/electrons. 2Mg + O₂ → 2MgO Na → Na⁺ + e⁻ 6. Reduction (gain of electrons) Loss of oxygen OR gain of hydrogen/electrons. CuO + H₂ → Cu + H₂O Cl₂ + 2e⁻ → 2Cl⁻
💡 OILRIG — Oxidation Is Loss; Reduction Is Gain (of electrons).
In redox reactions both oxidation and reduction happen simultaneously. The substance that gets oxidised is the reducing agent; the substance that gets reduced is the oxidising agent. CDS often asks: "In the reaction Fe + CuSO₄ → FeSO₄ + Cu, which is the reducing agent?" — Iron (Fe) is oxidised, so Fe is the reducing agent.

2. Everyday Chemistry — Industrial Substances

SubstanceComposition / ProcessUses SoapMade by saponification: fat/oil + NaOH (caustic soda) → sodium salt of fatty acid (soap) + glycerol. Works by forming micelles around dirt/grease in water.Cleaning; emulsification of oils DetergentsSodium alkyl benzene sulphonate (synthetic). Work in hard water (unlike soap which forms scum).Washing powder, dishwashing liquid GlassSoda glass: SiO₂ + Na₂CO₃ + CaCO₃. Borosilicate glass (Pyrex): SiO₂ + B₂O₃ (heat-resistant)Windows, bottles, lenses, lab glassware Cement (Portland)CaO + SiO₂ + Al₂O₃ + Fe₂O₃. Setting: hydration reactions produce calcium silicate hydrate crystals.Construction (concrete = cement + sand + gravel) Safety MatchesHead: KClO₃ + Sb₂S₃ + glass powder. Side strip: red phosphorus + powdered glass. Friction causes ignition.Lighting fires safely GunpowderKNO₃ (75%) + Charcoal (15%) + S (10%). Black powder; deflagrates rapidly.Propellants, fireworks, mining FertilisersUrea CO(NH₂)₂ — N fertiliser. Superphosphate Ca(H₂PO₄)₂ — P fertiliser. Muriate of potash KCl — K fertiliser.Agriculture — N, P, K are essential plant nutrients

📝 CDS PYQs — Reactions & Everyday Chemistry

Q1. The process of making soap from fats and alkali is called: CDS PYQ
(a) Hydrogenation(b) Saponification(c) Esterification(d) Oxidation
✔ Answer: (b) Saponification
Saponification is the reaction of a fat/oil (triglyceride) with a strong alkali (NaOH for hard soap; KOH for soft soap). Products: sodium/potassium salt of fatty acid (= soap) + glycerol. Soap works by forming micelles — the non-polar tail dissolves in grease and the polar head faces the water, allowing dirt to be washed away.
Q2. In the reaction Zn + CuSO₄ → ZnSO₄ + Cu, what type of reaction is this? CDS PYQ
(a) Combination(b) Decomposition(c) Displacement(d) Double displacement
✔ Answer: (c) Displacement
Zinc is more reactive than copper in the reactivity series. So Zn displaces Cu from CuSO₄ solution, depositing copper metal on the zinc. This is a displacement reaction (also a redox: Zn is oxidised to Zn²⁺; Cu²⁺ is reduced to Cu). The blue CuSO₄ solution becomes colourless as Cu²⁺ is removed.
Q3. The main active ingredient in bleaching powder is: CDS PYQ
(a) CaCO₃(b) Ca(OCl)Cl(c) CaSO₄(d) CaO
✔ Answer: (b) Ca(OCl)Cl
Bleaching powder is calcium hypochlorite-chloride, formula Ca(OCl)Cl. It is made by passing Cl₂ over slaked lime Ca(OH)₂. The hypochlorite ion (OCl⁻) releases active oxygen which oxidises coloured compounds, bleaching them. Used for bleaching cotton/paper and disinfecting water supplies.
Q4. The main nitrogen source fertiliser used in agriculture is: CDS PYQ
(a) Superphosphate(b) Muriate of potash(c) Urea(d) Ammonium sulphate
✔ Answer: (c) Urea [also accept (d) ammonium sulphate]
Urea CO(NH₂)₂ is the most widely used nitrogen fertiliser globally (46% N content — highest among solid fertilisers). Superphosphate provides phosphorus (P); muriate of potash (KCl) provides potassium (K). The three main plant nutrients are N, P, K — the NPK fertilisers. CDS asks which compound provides which nutrient.

🧠 Quick Memory Chart — CC09

⚛ Reaction Types
  • Combination: A+B→AB
  • Decomposition: AB→A+B
  • Displacement: A+BC→AC+B
  • Double disp: ions exchange
  • Redox: OIL RIG (electrons)
🔥 Everyday Chemistry
  • Soap: saponification (fat+NaOH)
  • Micelles: non-polar in grease
  • Glass: SiO₂+Na₂CO₃+CaCO₃
  • Safety matches: KClO₃+Sb₂S₃
  • Gunpowder: KNO₃+C+S
🌿 Fertilisers
  • N: Urea CO(NH₂)₂ (46% N)
  • N also: Ammonium sulphate
  • P: Superphosphate
  • K: Muriate of potash (KCl)
  • NPK = essential plant nutrients

📝 Practice Exercise

E1. AgNO₃ + NaCl → AgCl + NaNO₃ is an example of:
(a) Combination(b) Displacement(c) Double displacement(d) Decomposition
E2. Soft soap (used in shaving cream) is made using:
(a) NaOH (caustic soda)(b) KOH (caustic potash)(c) Ca(OH)₂ (lime)(d) NH₄OH (ammonia)
E3. In CuO + H₂ → Cu + H₂O, hydrogen is acting as:
(a) Oxidising agent(b) Reducing agent(c) Catalyst(d) Inhibitor
Answers: E1 → (c) Double displacement [ions Ag⁺ and Na⁺ exchange partners; AgCl precipitates]  |  E2 → (b) KOH [potassium soap is softer and more soluble; NaOH gives hard soap bars]  |  E3 → (b) Reducing agent [H₂ reduces CuO by removing oxygen; H₂ itself is oxidised to H₂O]
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