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We've all been there; you have a bunch of unknown gases trapped in test tubes, and you need to figure out what you're dealing with. Okay, maybe we haven't all been there, but there are some nifty ways you can identify gases by using burning splits, limewater, or litmus paper. Most of the gases we'll focus on are colorless and odorless, so it's not possible to identify them by appearance.
In order to perform the tests, you'll need the following supplies:
The first gas we will focus on is hydrogen, which is a non-toxic, colorless, odorless gas that's the most abundant element in the universe. Before we test for hydrogen, remember to wear your goggles for all of these tests. They'll protect you if the test tube breaks.
Here are the steps you need to take in order to test for hydrogen gas:
So, why the popping sound? When exposed to the flame, the hydrogen gas in the test tube reacts with the oxygen gas in the air. This reaction releases energy and that results in the popping sound.
We are going to use the splint again to test for oxygen, which is a non-toxic, colorless, odorless gas that you need to breathe in order to survive.
The directions for testing oxygen are a little different than for hydrogen, so pay attention:
Oxygen is responsible for combustion (burning of the splint), but normal atmospheric oxygen levels (around 21%) aren't enough to reignite the glowing splint. The test tube contains a higher percentage of oxygen, so when the glowing splint is placed inside, it's able to reignite.
The third gas we are going to test is carbon dioxide, which is colorless, odorless and you're breathing it out right now. It's also the stuff that makes your soda fizzy. There are a couple of easy ways to identify carbon dioxide gas.
Let's go over the first:
While the first method is simple, if the gas in the test tube is oxygen, the ignited splint could cause the test tube to explode, so there's another method that uses limewater.
Limewater can be made by mixing water with calcium hydroxide (about 1 teaspoon calcium hydroxide for every gallon of water). Let the solution sit for 24 hours and then pour the solution through a coffee filter.
In order to perform the test do the following:
Another option is to use a straw to blow directly into the limewater (you are exhaling carbon dioxide). This is a simple way to demonstrate the test.
What happened in each of these tests? In the first test, the flame goes out in the presence of carbon dioxide because, unlike oxygen, carbon dioxide is not flammable.
In the second and third tests, the limewater will change to a milky color, and chunks of carbonate will form because carbon dioxide reacts with the calcium hydroxide to make calcium carbonate. The calcium carbonate makes the water milky and creates the solid chunks you can see.
Unlike our first three gases, chlorine gas has a distinctive smell and is a green-yellowish color, so you can probably identify it without doing a test. That being said, there's an additional test you can complete. Chlorine gas is toxic, so take care not to breathe it in.
This occurs because the chlorine reacts with the water on the litmus paper, making hydrochloric acid. The acid changes the litmus paper to red (and red indicates an acid).
Now you're armed with the knowledge to identify all of the mystery gases in your possession. In case you're feeling overwhelmed with the directions, take a look at the table that summarizes each test.
| Gas Name | Gas Description | Test |
|---|---|---|
| Hydrogen | Colorless, odorless gas | Place a burning splint near the opening of a test tube. If a popping noise occurs, it's probably hydrogen. |
| Oxygen | Colorless, odorless gas that you breathe | Place a glowing splint in the test tube, and if it reignites, it could be oxygen. |
| Carbon dioxide | Colorless, odorless gas that you breathe out | Place a burning splint into a test tube, and if it goes out, it could be carbon dioxide. Or, place carbon dioxide gas in limewater, and if it turns milky and gets chunks, it is carbon dioxide. |
| Chlorine | Strong smelling, yellow-green gas that is toxic | Place moist litmus paper in the test tube, and if it turns red, it could be chlorine gas. |
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In this activity, students are going to be applying marketing skills to the idea of testing for common gases. Here, students will be asked to create a full page advertisement that might run in a magazine or online that advertises the available services for a gas testing company. Students should use graphic design and include the four tests, why someone might need these tests, an image of what happens during the test and sample prices. Students should ideally complete this digitally, but it can also be done as a poster project if computers are not available. This project will help students stretch their creative thinking and practice applying the different tests they learned.
Testing for different gases is a great hands on science experiment! In this extension, you are going to be creating an advertisement that markets these services to people who might need them. Put yourself in the shoes of a gas testing company wanting to market your skills. Your ad should explain what tests are offered with images, what the prices might be, and should be colorful, attractive and easy to read. To really improve your marketable skills, this poster should be completed online in a digital drawing program, such as Google Drawings or Adobe Illustrator. Check out the list below for the requirements for your advertisement.
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GCSE Chemistry: Practice & Study Guide21 chapters | 182 lessons | 18 flashcard sets
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