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Q54 (NDA-II/2021) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Basic chemical principles

What is the colour of the precipitate obtained by passing C02 gas through lime water ?

Result
Your answer: —  Â·  Correct: C
Explanation

When carbon dioxide (CO2) gas is passed through lime water, which is a solution of calcium hydroxide (Ca(OH)2), a chemical reaction occurs that produces calcium carbonate (CaCO3) and water [1][2]. Calcium carbonate is an insoluble substance that forms a white precipitate [2]. This precipitate remains suspended in the liquid, causing the initially clear lime water to turn milky or cloudy [1][4]. This 'milky' appearance is the standard qualitative test for the presence of carbon dioxide [1][3]. If CO2 continues to be bubbled through the solution in excess, the white precipitate of calcium carbonate reacts further to form calcium hydrogencarbonate (Ca(HCO3)2), which is soluble in water, causing the milkiness to disappear [5]. Therefore, the initial precipitate obtained is white in colour [2].

Sources

  1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > Fig. 5.2: Blowing air in (a) tap water; (b) lime water > p. 61
  2. [2] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Activity 2.5 > p. 20
  3. [4] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.4 > p. 87
  4. [3] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > 2.1.6 Reaction of a Non-metallic Oxide with Base > p. 22
  5. [5] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Activity 2.5 > p. 21
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