Classifying Chemical and Physical Changes in the Kitchen

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Goal

Students will view chemical and physical changes in cooking and preparing food.

45 Minutes

Inside

S5P1. Obtain, evaluate, and communicate information to explain the differences between a physical change and a chemical change.
- a. Plan and carry out investigations by manipulating, separating and mixing dry and liquid materials and communicate collected data to demonstrate examples of physical change.
- b. Construct an argument based on observations that the physical changes in the state of water are due to temperature differences, which cause small particles that cannot be seen to move differently.
- c. Plan and carry out an investigation to determine if a chemical change occurred based on observable evidence (color, gas, temperature change, odor, new substance produced)

Review with students that in addition to color change, other evidence of a chemical reaction can be production of a gas, change in temperature without heat being added or taken away, new odor, burning, or formation of a precipitate when two liquids are combined. Components that are changed in size or shape then combined are examples of physical change (as when water boils, condenses or freezes).
Demo multiple recipes for students that include either a chemical or physical change for students to classify. Easy recipe options include:
– Mixing a raw salad, where size and shape of ingredients change but not substance
– Making a smoothie or salsa, where raw foods are changed in form but not substance
– Making popsicles, where foods change phase but not substance
– Making sun tea, where sugar dissolves but does not change substance
– Making pancakes, that result in bubbles rising in the batter as it cooks
– Observing apples (or other food) that changes color due to oxidation
– Sauteing a vegetable, in which it is browned or burned by a flame