Gas Tests. Distinguishing Chemical Property acts as the fuel for combustion, allowing things to burn more vigorously in its presence

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1 Gas Tests Date: As we have learned, air is made up of a mixture of many gases, including nitrogen, oxygen, carbon dioxide and hydrogen. Most of these gases are colourless, odourless, and, making them difficult to distinguish from one another. So how can we tell them apart? Different gases exhibit different chemical properties, such as reactivity with other chemical substances. These chemical properties are like fingerprints and allow for a gas' identity to be discovered. Oxygen (O 2 ) Physical Properties Colourless, Odourless, Transparent Density: 1.429g/L (gas) exists in all three states Distinguishing Chemical Property acts as the fuel for combustion, allowing things to burn more vigorously in its presence Hydrogen (H 2 ) Physical Properties Colourless, Odourless, Transparent Density: 0.089g/L (gas) Distinguishing Chemical Property when ignited in air, hydrogen combines with oxygen atoms to form gaseous H 2 O (water vapour), if given a sufficient amount of hydrogen, its combustion can result in an explosion Carbon dioxide (CO 2 ) Physical Properties Colourless, Odourless at low concentrations, Transparent Density: 1.977g/L (gas) Distinguishing Chemical Property does not burn or support combustion making it a good fire extinguisher in limewater, CO 2 reacts to produce a white solid called calcium carbonate 1

2 Testing for Gases laboratory exercise The purpose of the exercise is to learn how to test for the presence of oxygen, hydrogen, and carbon dioxide Materials Two test tubes candle calcium nodule 40 ml beakers wood splint 2 mol/l Acetic acid small piece of chalk hydrogen peroxide (30%) pyrolucite stone SAFETY: BE VERY CAREFUL HANDLING THE ACID AND HYDROGEN PEROXIDE. IF IT GETS ON YOUR SKIN RINSE IMMEDIATELY. WEAR GOGGLES AND AN APRON AT ALL TIMES Methods Test 1 1) Carefully obtain 20 ml of hydrogen peroxide into the beaker. 2) Fill a test tube full with water and quickly invert into the hydrogen peroxide trying not to get too much air in the test tube. 3) Place a pyrolucite stone into the solution and place the mouth of the test tube just above the stone to collect the gas. 4) When the test tube is about 3/4 full with the gas (after about 10 minutes), prepare a glowing splint. Light the splint then blow it out to get a glowing splint. 5) Remove the test tube from the water and quickly insert the glowing splint into the test tube. 6) Record your observations in the data table. 7) Rinse out the beaker and return the stone. Test 2 1) Carefully obtain 30 ml of acetic acid into the beaker. 2) Fill a test tube full with water and quickly invert into the acid trying not to get too much air in the test tube. 3) Place a small piece of chalk into the solution and place the mouth of the test tube jus above the chalk to collect the gas. 4) When the test tube is about 3/4 full with the gas, prepare a burning splint. 5) Remove the test tube from the water and quickly insert the burnong splint into the test tube. 6) Record your observations in the data table. 7) Rinse out the beaker and return any remaining the chalk. 2

3 Test 3 1) Obtain 40 ml of water into the beaker. 2) Fill a test tube full with water and quickly invert into the water trying not to get too much air in the test tube. 3) Place a calcium nodule into the water and place the mouth of the test tube just above the nodule to collect the gas. 4) When the test tube is about 3/4 full with the gas (after about 10 minutes), prepare a burning splint. 5) Remove the test tube from the water and quickly insert the burning splint into the test tube. 6) Record your observations in the data table. 7) Make sure that all the calcium has reacted and then rinse out the beaker. Table 1. Test # Qualitative observations (splint test) Discussion 1. Which test do you believe tested for the presence of oxygen? Explain why based on your observations of the splint. 3

4 Discussion (continued) 2. Which test do you believe tested for the presence of carbon dioxide? Explain why based on your observations of the splint. 3. Which test do you believe tested for the presence of hydrogen? Explain why based on your observations of the splint. Summary of Gas Tests Gas Test Result if gas is present. 4

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