Video Demo: Flame Tests

Every chemical has its unique characteristic properties. These properties can include hardness, density, melting point, boiling point, color, taste, texture etc. No matter what sample you have of a pure substance they will display its characteristic properties. This is how a an unknown chemical can be identified. The properties of the unknown chemical can be compared to the properties of known chemicals. In this activity there are 3 unknown chemicals (X, Y, and Z) that are to be identified based on 5 properties: color, boiling point, melting point, density, and color when burned. This is a simple and quick lab activity. The handout has the density, boiling point, and melting point filled in already. The students must observe the color and the color when burned–a flame test. Slide 1 shows the materials needed for the activity (the 3 chemicals are copper sulfate, strontium chloride, and lithium chloride). Slide 2 shows the Bunsen burner flame with the typical blue color. Slide 3 shows the inoculating loop collecting some of chemical Y. When the different chemicals are put in the flame, they burn at different colors (Slide 4 shows copper sulfate’s green flame, and slide 5 shows lithium chloride’s red flame).

Tips: Make sure students are careful to not contaminate the tubes and to thoroughly clean loop before testing each chemical.

Safety: Make sure students wear goggles, and know how to properly use a Bunsen burner safely.

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This is a variation on the flame test lab. Instead of using a Bunsen burner, a denatured alcohol flame is used (the best results is achieved by using methanol). Put a spoonful of strontium chloride into a Pyrex petri dish (this glass can take the heat, any other non Pyrex glass will break). Put about 2-3 spoonfuls of denatured alcohol into the dish. Swirl around to mix. Carefully light the alcohol on fire. You will probably need to swirl it so that the strontium chloride will burn and produce the red flame (lower left image). Try this with other salts and compounds that are safe to burn and will give color (like copper sulfate–lower right image).

Precautions: ONLY TEACHER DEMO! Be sure to use only Pyrex petri dish. The dish will get very hot! Don’t let water hit it right away. Be sure to blow flame out.