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To prepare ethylene in the laboratory, we first need to dehydrate ethanol (alcohol). In this step, ethanol will be heated with an excess of concentrated sulfuric acid (H2SO4), which acts as a dehydrating agent. The presence of sulfuric acid will remove water (H2O) from the ethanol molecules, resulting in the formation of ethylene. The chemical reaction is as follows: C2H5OH (Ethanol) + H2SO4 (Sulfuric acid) -> C2H4 (Ethylene) + H2O (Water) So, to begin the preparation, we need to heat ethanol mixed with concentrated sulfuric acid.

After heating the mixture of ethanol and sulfuric acid, ethylene gas will be produced. This gas can be collected by one of the methods: downward displacement of air or water. The choice of method depends on the specific experiment setup, but in most instances, water displacement is used for the following reasons: 1. Ethylene is lighter than air (making downward displacement of air time-consuming). 2. Ethylene is slightly soluble in water (making the loss of ethylene in the water minimal). 3. Water displacement provides a visual indication of the amount of gas collected. To collect ethylene using the water displacement method, have the gas produced pass through a gas delivery tube and into a gas collection container (e.g., an inverted burette, cylinder, or jar) filled with water. As ethylene fills up the container, the water level will decrease, allowing you to measure the amount of ethylene collected.

The ethylene gas collected may contain impurities such as traces of ethanol, sulfur dioxide, and water vapor. To purify the gas, it needs to be passed through a drying agent such as calcium chloride (CaCl2). This will remove any water vapor present in the gas. After passing through the drying agent, the purified ethylene gas can be collected in another container.

To verify that the gas produced is indeed ethylene, you can perform the following tests: 1. Bromine water test: Ethylene decolorizes a solution of bromine in carbon tetrachloride (Br2/CCl4) due to the addition reaction between the double bonds in ethylene and bromine molecules. Add a few drops of the gas to the bromine water, and it should turn from brownish-orange to colorless. 2. Flammability test: Ethylene is a highly flammable gas. Hold a burning splint at the mouth of the container where ethylene is collected. It should ignite instantly and burn with a pale blue flame, indicating the presence of ethylene. These tests will help confirm that the gas produced in the laboratory is ethylene.