The chirp experiment is a typical science lab technique used to test for the presence of hydrogen, which is colorless and odorless. When hydrogen gas is trapped in a container, you can place a lit match nearby and it will make a characteristic "screeching" sound as it reacts with the flame. If you ever need to check for hydrogen gas, this is a simple (and fun) method you can use.
Steps
Part 1 of 3: Create Hydrogen Gas
Step 1. Gather the necessary supplies
To create hydrogen gas, you will need hydrochloric acid, magnesium strips, a test tube, a match, lab gloves, and eye protection. By placing a metal in hydrochloric acid, it will react to form hydrogen gas and a chlorinated metal compound.
- You will only need 20 ml of dilute hydrochloric acid (about two molars).
- Magnesium strips can be purchased online.
- Safety is important, so wear gloves and eye protection throughout the experiment.
- Adult supervision is necessary for this experiment.
Step 2. Create the correct environment
Ideally, this experiment should be done in a chemistry lab. Safety equipment such as fire extinguishers, an eye wash station, and a safety shower should be easily accessible. The room should also be open and well ventilated.
Don't do this experiment alone in your bedroom. Make sure there is an adult around to supervise
Step 3. Add hydrochloric acid to the test tube
Once you put on your gloves and eye protection, pour about 0.7 fl oz (20 ml) of hydrochloric acid into a test tube. You don't need exactly 0.7 fluid ounces (20 ml), but pour enough until there is almost 0.8 inches (2 cm) at the bottom of the tube.
- If you want to dilute the acid, always add it directly to the water. If you do it the other way around, the acid could explode and cause injury.
- Be aware that hydrochloric acid is corrosive and releases acid fumes.
Step 4. Place a magnesium strip in the test tube
Place the strip in the tube with the hydrochloric acid. The solution will begin to bubble as soon as the metal comes into contact with the liquid. These bubbles are hydrogen gas.
You can add more than one strip to speed up the hydrogen formation
Step 5. Cover the tube securely with plastic
Place plastic wrap on top of the test tube immediately after incorporating the metal. Attach a rubber band to secure the plastic in place and cover the tube as tightly as possible so that hydrogen gas does not escape into the air. Since gas is less dense than liquid, it will rise to the top of the test tube as it is created.
- You can also cover the tube with another test tube or just put your thumb up.
- Allow the reaction to last at least one minute to create the amount of gas in the tube.
Part 2 of 3: Perform the Squeak Test
Step 1. Light a match
You don't need to use a match for this step, but you will need something that lights up. You can use a lighter if you prefer. Regardless of the fire source you use, turn it on and have it ready to place near the tube as soon as you remove the coating.
Adult supervision is essential when working with open flames
Step 2. Remove the cap from the tube
Remove the rubber band that secures the plastic in place and lift the plastic off the top of the tube. Proceed immediately to the next step after removing the cap from the tube so that not much gas escapes.
As soon as you remove the cap, the hydrogen will begin to escape into the surrounding air
Step 3. Place the match near the top of the tube
Bring the lit match to the tube immediately after removing the cap. Once the flame comes in contact with the gas, it may go out, but you will hear the characteristic "screech" at the same time.
- Be careful during this process. Remember that you will be working with flammable gases and open flames.
- Allow an adult to supervise you as you do this.
- If you don't hear the screech, there is probably not enough gas in the tube. Cover it back up and allow the reaction to continue longer. Make sure the reaction bubbles.
Step 4. Dispose of everything properly
Remove the metal from the test tube with tweezers. Dilute the hydrochloric acid in about 1 US gallon (4 liters) of water. Then, pour the diluted solution down the drain while running water. Rinse the metal in the sink and dispose of it in the trash.
- You can also save the metal and reuse it to repeat the experiment if you wish.
- Make sure you know the regulations in your region regarding the disposal of hydrochloric acid, as they can vary.
Part 3 of 3: Using the experiment
Step 1. Create learning goals
The main goal of teaching this type of experiment is to talk about chemical reactions. This specific experiment is an example of the reaction of metals with acids to create gases. Students will be able to see with their own eyes how the metal reacts and how quickly the gas is produced by the reaction.
A secondary goal may be to discuss laboratory safety and working with flammable gases
Step 2. Talk about the reaction that occurred
Talk about how acids react with metal. When talking about chemical reactions, talk about reactants and how they combine to form various products. Talk about the states in which the products and reactants exist. Magnesium is a solid that reacts with aqueous hydrochloric acid to form hydrogen gas and aqueous magnesium chloride.
- The chemical equation for this experiment is: Mg (s) + 2 HCl (aq) MgCl2 (aq) + H2(g).
- This reaction is also known as a simple replacement reaction, which means that magnesium replaces the hydrogen bond with chloride to form magnesium chloride.
Step 3. Talk about the applications of the experiment
This type of experiment is a good way to check for the presence of small amounts of hydrogen gas. Remember that hydrogen is flammable, so if you suspect that there has been a lot of hydrogen gas, you don't want to do this experiment.
In a controlled laboratory setting where you know the experiment will produce hydrogen, you can use this test to confirm it
Step 4. Expand the experiment with other metals
Provide students with other types of metals, such as iron, aluminum, copper, and zinc. Do the same procedure and check for the presence of hydrogen gas. You will notice that not all types react with hydrochloric acid to form hydrogen gas.
- Do the same experiment, but heat the acid a little. You will notice that more metals react to form hydrogen gas when the acid is warm.
- Discuss the results with the students.
Warnings
- Be careful not to let the acid get on your skin or clothing.
- If you are a child or adolescent, be sure to do this experiment with an adult present.
- Uses forever eye protection as hydrochloric acid releases acid fumes.