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Which of the following is formed when carbon dioxide reacts with calcium hydroxide?
Carbon monoxide
Methane
Calcium oxide
Calcium carbonate
Calcium carbonate
When carbon dioxide (CO2тАЛ) is passed through lime water (an aqueous solution of calcium hydroxide, Ca(OH)2тАЛ), it reacts to form a white precipitate of calcium carbonate (CaCO3тАЛ), which turns the solution milky.
When carbon dioxide (CO2тАЛ) is passed through lime water (an aqueous solution of calcium hydroxide, Ca(OH)2тАЛ), it reacts to form a white precipitate of calcium carbonate (CaCO3тАЛ), which turns the solution milky.
This is the classic breath test in school laboratories: when you exhale air through a straw into lime water, the carbon dioxide from your breath turns the clear liquid milky white.
Lime + Carbon Dioxide = Milky White Calcium Carbonate (CaCO3тАЛ).
Ca(OH)2тАЛ+CO2тАЛтЖТCaCO3тАЛтЖУ+H2тАЛO тАФ Standard lime water test for carbon dioxide
CaCO3тАЛ+H2тАЛO+CO2тАЛтЖТCa(HCO3тАЛ)2тАЛ тАФ Reaction with excess carbon dioxide
The chemical reaction involved is: Ca(OH)2тАЛ(aq)+CO2тАЛ(g)тЖТCaCO3тАЛ(s)тЖУ+H2тАЛO(l). The formation of insoluble calcium carbonate is responsible for the milky appearance. If excess carbon dioxide is passed through the solution, the milkiness disappears due to the formation of soluble calcium hydrogen carbonate (Ca(HCO3тАЛ)2тАЛ).
Calcium hydroxide is commonly known as slaked lime or lime water.
Carbon dioxide gas turns lime water milky due to the precipitation of insoluble calcium carbonate.
Passing excess CO2тАЛ dissolves the precipitate back into soluble calcium bicarbonate.
This reaction is a standard laboratory test to identify carbon dioxide gas.
Provides a simple, reliable visual confirmation for the presence of carbon dioxide gas in analytical chemistry.
Other acidic gases like sulfur dioxide (SO2тАЛ) can also turn lime water milky, making the test non-exclusive if interfering gases are present.
Detection of carbon dioxide in respiration experiments.
Verification of gases evolved during the thermal decomposition of metal carbonates.
Option A (Carbon monoxide) does not react with calcium hydroxide.
Option B (Methane) is an alkane and does not react with lime water under normal conditions.
Option C (Calcium oxide) is quicklime, which dissolves in water to form calcium hydroxide.
D is correct тАФ Calcium carbonate is formed when carbon dioxide reacts with calcium hydroxide.
Always remember that excess CO2тАЛ dissolves milky CaCO3тАЛ back into soluble Ca(HCO3тАЛ)2тАЛ, a frequently asked conceptual trap in competitive chemistry exams.
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