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Overview:
In this lesson, students will be able to explain that if they mix baking soda with two different substances in separate containers and observe different signs of chemical reactions, it must be because the two substances are different. The substances must be made from different molecules, which react differently with baking soda. Students conduct a reaction with citric acid and baking soda in a universal indicator solution. The resulting chemical reaction produces a gas, causes a color change with an indicator, and results in a decrease in temperature. Students then carry out a second reaction with calcium chloride and baking soda in the universal indicator solution. In this example, students observe the production of both a gas and a solid, a color change with the indicator, and a slight increase in temperature. Students reason that since baking soda was reacted with two different substances, it makes sense that the reactions they observed were different. Finally, students conclude that different substances have characteristic chemical reactions and that these reactions can be used to identify a substance.