Carbon dioxide (CO2) is colorless and odorless so you cannot detect it by direct observation. You must collect an air sample (or a CO. sample2), then performs one of several simple tests to identify the presence of the gas. You can blow the gas as bubbles through the lime water, or hold something lit to see if the fire is extinguished by the presence of CO2.
Step
Method 1 of 3: Preparing the Sample
Step 1. Collect CO. samples2.
To start the test, you will need a sealed test tube containing the collected gas. Carbon dioxide can be put in a gas cylinder, boiling tube, or other airtight container. The process of collecting carbon dioxide gas is usually carried out on water in a beaker. CO. gas2 denser than air. So you can collect them using their downward-flowing properties or with a gas syringe.
Step 2. Mix calcium carbonate with hydrochloric acid (HCl)
The simplest way to collect carbon dioxide is to react calcium carbonate (or limestone chips) with hydrochloric acid. First, pour 20 ml of HCl into a conical flask. Add a spoonful of calcium carbonate (or limestone chips) to the HCl. Once the chemical reaction begins to occur, cover the conical flask with the stopper and the delivery tube, collecting the gas through the delivery tube into an inverted test tube (and immersed in a bowl of water). If the water in the test tube is used up, then the gas has collected.
- You can continue to collect the gas as long as the reaction occurs.
- For a classroom demonstration, you will only need a small amount of hydrochloric acid, diluted to 1 M. A concentration of 2 M is best, but should only be used with extreme caution. The reaction equation is: CaCO3(s) + 2HCl(aq) ==> CaCl2(aq) + H2O(l) + CO2(g).
- You have to be very careful when working with hydrochloric acid – wear gloves, a lab coat and protective goggles. Don't let the acid get on your skin! The best environment to perform this reaction is if you have access to a laboratory.
Step 3. Close the test tube with the stopper
Place the tube on the rack to keep it secure until the test is performed. A tube stopper is a small cork or cap that allows you to pass the contents of a test tube through a tube to another container via a delivery tube. Important for sealing CO. gas2 in the container. If left open, the gas will mix with the air and the effectiveness of the test will be significantly reduced.
Method 2 of 3: Bubbling Through Lime Water
Step 1. Bubble the gas through the lime water
The most effective way to test CO2 is by bubbling the gas through "lime water", a diluted solution of calcium hydroxide (dead lime). When you blow carbon dioxide into the solution, it forms a solid precipitate of calcium carbonate – lime or limestone. Calcium carbonate is insoluble in water. Thus, if there is CO2 in the sample, the lime water will turn milky, cloudy white.
Step 2. Make a lime water solution
The process is simple, dilute calcium hydroxide with water. Calcium hydroxide (Ca(OH)2) is a white, colorless powder that can be purchased at most chemical suppliers. Pure lime water, after mixing, is clear and colorless, slightly earthy odor and bitter taste, characteristic of alkaline calcium hydroxide. Follow these steps to make your own lime water:
- Place 1 teaspoon of calcium hydroxide in a one-gallon (or smaller) clear glass jar. Lime water is a saturated solution, meaning there are some extra chemicals that are insoluble. A teaspoon will give you a fully saturated solution, whether you're using a gallon or a smaller container.
- Fill the gallon with distilled or tap water. Distilled water will always produce a purer solution, but the minerals in the tap water should not hinder the test.
- Put the lid on the jar. Shake the solution vigorously for 1-2 minutes, then leave for 24 hours.
- Pour the clearer solution at the top of the jar through coffee or clean filter paper. Be very careful not to disturb the sediment. If needed, repeat the filtering step until you get a clear lime water solution. Store in a clean jar or bottle.
Step 3. Blow the gas through the lime water
Half fill a test tube with lime water – then bring it to a boil. Use the delivery tube to deliver the CO. sample2 in a test tube directly into boiling lime water. You can use a flexible pipe or (metal) hose as a delivery tube, if nothing else is better. Allow the trapped gas to "bubble" through the liquid, and wait for the reaction to take place.
If you don't want to boil anything, use a gas syringe to release the CO. gas2 directly into a test tube half filled with lime water. Plug the test tube, then shake vigorously for 1-2 minutes. If the sample contains carbon dioxide, the solution will become cloudy.
Step 4. Notice if the water is cloudy
If there is CO2, lime water will turn cloudy white with particulate calcium carbonate. If the lime water boils, and the gas is piped directly into the lime water, the reaction will take place immediately. If nothing happens after a minute or so, it can be assumed that your sample does not contain carbon dioxide.
Step 5. Know the chemical reaction
Understand what is really going on to indicate the presence of CO2. The reaction equation for this test is: Ca(OH)2 (aq) + CO2 (g) -> CaCO3 (s) + H2O(l). In non-chemical terms: lime water + gas (which contains CO2) reacts with solid lime (particles) and water.
Method 3 of 3: Test with a Lit Bar
Step 1. Try using a sample to turn off the fire
Carbon dioxide in high concentrations will extinguish the fire. You only need to hold a small lit rod into a test tube that is thought to contain CO2. If there is CO. gas2, the flame will soon be extinguished. Combustion (the occurrence of a flame) is a reaction between oxygen and other substances, in the form of rapid oxidation of organic compounds and reduction of oxygen. The fire goes out because oxygen is replaced by CO2, which is a non-combustible gas.
Remember that gases that do not contain oxygen will also extinguish the flame. Therefore, this is an unreliable carbon dioxide test as it could lead you to incorrectly identify the gas
Step 2. Collect carbon dioxide gas in an inverted test tube
Make sure the sample is properly stored and corked before you try it to test for CO2. Make sure that the test tube does not contain flammable or explosive gases. In this case, exposure to fire can be dangerous, or at least very frightening.
Step 3. Put a small flame into the test tube
Use a splint or small long stick. In an emergency, matches can be used – but the further your hand is from the mouth of the test tube, the safer the experiment will be. If the flame goes out quickly, there may be a concentration of CO2 high in the test tube.
Step 4. Alternatively, try using a gas syringe to extinguish the candle
Fill the syringe with carbon dioxide. Next, use a drop of melted wax to attach the short wax to the surface of the coin. Then, place the candle and the coin in a cup with a wide mouth – and light the candle. Complete the syringe with a small hose, and press the syringe to displace the CO2 to the bottom of the cup. If you remove the entire syringe in a second or two, the flame will go out.
