You can continue to collect the gas for as long as the reaction occurs. For classroom demonstrations, you only need a small amount of hydrochloric acid, which is diluted to 1 M; a 2 M concentration works best, but should be used with extra care because it’s a strong acid. The equation is: CaCO3(s) + 2HCl(aq) ==> CaCl2(aq) + H2O(l) + CO2(g). Be very careful when working with hydrochloric acid – wear gloves, a lab coat, and protective goggles, and do not let the acid touch your skin! It’s best to only perform this reaction if you have access to a lab environment. [2] X Research source
Limewater is also called “white wash” or “milk of lime. " If you see these terms, you’ll know they mean limewater. [5] X Research source
Put 1 teaspoon (4. 9 mL) of calcium hydroxide into a clean 1 gallon (3. 8 L) or smaller glass jar. Limewater is a saturated solution, which means there will be some extra chemical that doesn’t dissolve. A teaspoon will result in a fully saturated solution, whether you use a gallon jar or a smaller container. Fill the jar with distilled water. It’s best to use distilled water for this experiment, as it will give you a purer solution. Put a lid on the jar. Shake the solution vigorously for 1-2 minutes, then let it stand for 24 hours. Pour the clearer solution off the top of the jar through a clean coffee filter or filter paper. Be very careful not to stir up the sediment. If necessary, repeat this filtering step until you obtain a clear limewater solution. Store in a clean jar or bottle.
If you don’t want to boil anything, you can use a gas syringe to discharge the CO2 gas directly into the half-filled limewater test tube. Stopper the test tube, then shake vigorously for 1-2 minutes. If there is carbon dioxide in the sample, then the solution should grow cloudy. [6] X Research source
If you bubble the CO2 through the limewater for an extended period of time, your water will eventually turn clear. That’s because of a chemical reaction! Here’s why: CO2 + H2O ==> H2CO3 (carbon dioxide + water = carbonic acid) H2CO3 + CaCO3 ==> Ca(HCO3)2 (carbonic acid + calcium carbonate = calcium hydrogen carbonate) Calcium hydrogen carbonate is soluble in water, making your solution clear!
Bear in mind that any oxygen-free gas will also extinguish a flame in this manner. Thus, this is an unreliable test for carbon dioxide, and it may lead you to misidentify the gas. [9] X Research source
