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ChemistryMediumClass 11

Important Compounds — NaOH, Na₂CO₃, CaCO₃, CaO, Gypsum

s-block Elements

5

JEE Qs

8%

Hard

75

min

Focus on understanding the reaction mechanisms and conditions for the synthesis and interconversion of these compounds, rather than just rote memorization of equations.

🧮 Key Formulas

2NaCl(aq) + 2H2O(l) --(electrolysis)--> 2NaOH(aq) + Cl2(g) + H2(g) (Castner-Kellner process)
NH3(g) + H2O(l) + CO2(g) --> NH4HCO3(aq)
NH4HCO3(aq) + NaCl(aq) --> NaHCO3(s) + NH4Cl(aq) (Solvay process, precipitation)
2NaHCO3(s) --(heat)--> Na2CO3(s) + H2O(g) + CO2(g) (Calcination of bicarbonate)
2NH4Cl(aq) + Ca(OH)2(aq) --> CaCl2(aq) + 2NH3(g) + 2H2O(l) (Ammonia recovery in Solvay process)
CaCO3(s) --(heat, >1200K)--> CaO(s) + CO2(g) (Lime kiln reaction)
CaO(s) + H2O(l) --> Ca(OH)2(aq) (Slaking of lime)
Ca(OH)2(aq) + CO2(g) --> CaCO3(s) + H2O(l)
CaSO4.2H2O(s) --(heat, 373K)--> CaSO4.1/2H2O(s) + 3/2H2O(g) (Gypsum to Plaster of Paris)
CaSO4.1/2H2O(s) + 3/2H2O(l) --> CaSO4.2H2O(s) (Setting of Plaster of Paris)

✅ Key Points for JEE

  • 1Understand the detailed steps and underlying chemistry of the Solvay process for Na2CO3 synthesis, including the recycling of ammonia and why K2CO3 cannot be made by this method (due to KHCO3 solubility).
  • 2Master the Castner-Kellner process for NaOH production, specifically identifying anode, cathode reactions, the role of mercury, and the products generated (NaOH, Cl2, H2).
  • 3Learn the thermal decomposition reactions and relative stabilities of carbonates and bicarbonates of Group 1 and Group 2 elements (e.g., CaCO3 decomposes readily, Na2CO3 is stable, NaHCO3 decomposes to Na2CO3).
  • 4Know the interconversion reactions between CaCO3, CaO, and Ca(OH)2 (limestone cycle), and their industrial significance (e.g., quicklime, slaked lime).
  • 5Distinguish between gypsum (CaSO4.2H2O), Plaster of Paris (CaSO4.1/2H2O), and dead burnt plaster (anhydrous CaSO4) based on their hydration states and heating conditions, along with their uses.

⚠️ Common Mistakes

  • ✕Confusing the intermediate products and their roles in the Solvay process, especially the precipitation of NaHCO3 and the recovery of ammonia.
  • ✕Incorrectly stating the products or reaction conditions for the thermal decomposition of various carbonates or bicarbonates.
  • ✕Mistaking the chemical formulas and properties of gypsum, Plaster of Paris, and anhydrous calcium sulfate, leading to errors in questions involving their interconversion or uses.

📝 Practice Questions

See all

Q49. List - I List - II Reaction Type of redox reaction (A) Li (I) 589.2 Match List - I with List - II. Choose the correct answer from the options (B) Na (II) 455.5 (C) Rb (III) 670.8 (D) Cs (IV) 780.0 given below : (1) (A)-(II), (B)-(IV), (C)-(III), (D)-(I) (2) (A)-(I), (B)-(IV), (C)-(III), (D)-(II) (3) (A)-(IV), (B)-(II), (C)-(I), (D)-(III) (4) (A)-(III), (B)-(I), (C)-(IV), (D)-(II)

2024·MCQMedium

Q40.Ion having highest hydration enthalpy among the given alkaline earth metal ions is: (1) Be2+ (2) Sr2+ (3) Ba2+ (4) Ca2+

2023·MCQEasy

Q32.Match List I with List II (A) Slaked lime (I) NaOH (B) Dead burnt plaster (II) Ca ( OH ) 2 (C) Caustic soda (III) Na2CO3 · 10H2O (D) Washing soda (IV) CaSO4 Choose the correct answer form the options given below: (1) (A) - I, (B) - IV, (C) - II, (D) - III (2) (A) - III, (B) - IV, (C) - II, (D) - I (3) (A) - II, (B) - IV, (C) - I, (D) - III (4) (A) - III, (B) - II, (C) -IV, (D) -I

2023·MCQEasy

Q33.Choose the correct statement(s): A. Beryllium oxide is purely acidic in nature. B. Beryllium carbonate is kept in the atmosphere of CO2. C. Beryllium sulphate is readily soluble in water. D. Beryllium shows anomalous behavior. Choose the correct answer from the options given below: JEE Main 2023 (01 Feb Shift 1) JEE Main Previous Year Paper (1) A, B and C only (2) B,C and D only (3) A and B only (4) A only

2023·MCQMedium

Q40.The correct order of bond enthalpy ( kJ mol–1 ) is: (1) Si −Si > C −C > Sn −Sn > Ge −Ge (2) Si −Si > C −C > Ge −Ge > Sn −Sn (3) C −C > Si −Si > Sn −Sn > Ge −Ge (4) C −C > Si −Si > Ge −Ge > Sn −Sn

2023·Assertion ReasoningMedium

Q37. O −O bond length in H2O2 is X than the O −O bond length in F2O2 . The O −H bond length in H2O2 is Y ¯¯ than that of the O −F bond in F2O2 . Choose the correct option for X and Y from the given below. ¯¯ (1) X - shorter, Y− shorter (2) X -shorter, Y -longer (3) X -longer, Y -longer (4) X-longer, Y - shorter

2023·Assertion ReasoningMedium

NCERT Chapters

  • Class 11 Chemistry Ch 10: The s-Block Elements