You test for carbon dioxide gas using limewater (a solution of calcium hydroxide); the limewater will turn milky or cloudy white in the presence of carbon dioxide.
The standard method for testing for carbon dioxide involves bubbling the gas through limewater. Here's a more detailed explanation:
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Prepare Limewater: Limewater is a solution of calcium hydroxide (Ca(OH)₂). It is typically clear and colorless. You can prepare it by dissolving calcium hydroxide in water and filtering off any undissolved solid.
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Collect the Gas Sample: You need a way to collect the gas you suspect contains carbon dioxide. This could involve using a gas syringe, a test tube inverted over a reaction that produces the gas, or other appropriate methods.
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Bubble the Gas Through Limewater: The key step is to bubble the collected gas through the limewater. This is usually done using a delivery tube connected to the gas source and inserted into the limewater.
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Observe the Result: If carbon dioxide is present, the limewater will turn milky or cloudy white. This is due to the formation of insoluble calcium carbonate (CaCO₃), also known as chalk, according to the following reaction:
Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃ (s) + H₂O (l)
Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
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Confirm the Result: It's important to note that if too much carbon dioxide is bubbled through the limewater, the milky solution can eventually become clear again. This is because the calcium carbonate reacts with excess carbon dioxide to form soluble calcium hydrogen carbonate (calcium bicarbonate). Therefore, the initial milky appearance is crucial.
In summary, the limewater test provides a simple and reliable way to identify the presence of carbon dioxide gas. The visual change from clear limewater to a milky white solution is a clear indication of carbon dioxide.
