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NDA 2 2025 GAT, question 96

Topic: Chemistry

Q96

The reaction that occurs on passing carbon dioxide gas through lime water is

  1. (a) CaCO3+H2O+CO2→Ca(HCO3)2CaCO_{3}+H_{2}O+CO_{2}\to Ca(HCO_{3})_{2}
  2. (b) Ca(OH)2+CO2→CaCO3+H2OCa(OH)_{2}+CO_{2}\to CaCO_{3}+H_{2}OCorrect answer
  3. (c) CaO+CO2→CaCO3CaO+CO_{2}\to CaCO_{3}
  4. (d) CaCl2+H2O+CO2→CaCO3+2HClCaCl_{2}+H_{2}O+CO_{2}\to CaCO_{3}+2HCl

Solution.

Answer: (b) Ca(OH)2+CO2→CaCO3+H2OCa(OH)_{2}+CO_{2}\to CaCO_{3}+H_{2}O

  1. Initially, CO₂ reacts with lime water, Ca(OH)₂, to form insoluble calcium carbonate and water: Ca(OH)₂+CO₂→CaCO₃+H₂O.
  2. The white precipitate makes lime water milky.
  3. Option (a) describes the later reaction of excess CO₂ with already formed carbonate.