- PK – GRADE 3 students
At this stage, students should understand the difference between the three phases of matter as well as the cause and effect relationship between two chemical compounds that undergo a reaction. When one substance is added to another, there is an observable change. These changes could include bubbles, indicating the release of gas, a rise/drop in temperature that can be felt, as well as a shift in color. They should also understand that these compounds are made up of small particles known as atoms that cannot be seen but interact in different ways to make these changes possible. Different reaction take place at different rates which determine an observable change takes place slowly or rapidly.
- Grade 4 – Grade 6
At this level, students should understand that different compounds are composed of molecules, which are collections of atoms with distinctive structures. These differences in structure lead to attractive or repulsive interactions and can form new structures that manifest in products with different states of matter and color characteristics. They measure the change of the system in terms of an observable difference over time. They should understand that energy can be transferred in various ways between these particles and on a larger scale, between visible objects. Students should realize that although changes are taking place, no form of matter is being produced out of nothing, and that the total amount of material (by mass) inside the bag remains the same throughout the reaction. They can be given information on what the chemical reactants can be used for in the real world, with sodium bicarbonate (NaHCO3), also known as baking soda, being used to clean and deodorize. Calcium chloride can be used to flavor salty foods and prevent mold from forming by absorbing surrounding water.
- Middle School
At this level, students should be able to decipher the meaning of chemical equations and which molecules correspond to products and reactants. The individual atoms break their bonds and switch to form bonds with the opposite ion, commonly referred to as “switching dance partners”. This process promotes the release of energy, and energy may take a variety of forms including the motion of atoms and thermal energy that we perceive as heat. This energy drives the reaction forward, allowing the production of new compounds, and can be tracked as it cycles through the closed system. The concept of equilibrium is introduced as a balance of two mechanisms and can be seen as stability in a reaction. They should be able to ask observational questions about the experiment, such as when a gas is produced, as well as its possible identity. The role of the indicator should be clearly defined as way to see whether the solution has turned acidic or not and the role of energy in this exothermic reaction in heating up the bag of reactants can be established.
- College Level/Scientific Description
Students have the ability to construct explanations of how things change and understand the actual mechanism of change in the reaction. Calcium chloride (CaCl2) and sodium bicarbonate (NaHCO3) are combined in solution with water and phenolphthalein indicator. The calcium and carbonate ions disassociate from their original bonds and combine to form calcium carbonate, a powdery solid found in limestone and shells. The positively charged hydrogen ions pair with negatively charged chloride ions to produce hydrochloric acid and lower the overall pH of the solution, making it acidic and activating the indicator. As a result, the solution turns a vivid pink color. Sodium and the remaining chloride ions form NaCl (Table Salt) leaving carbon dioxide (CO2) gas as a byproduct, producing the bubbles seen during the reaction. As an exothermic reaction, the bonding of atoms releases energy in the form of heat, raising the temperature of the solution.