Question

chemical changes
directions: follow the instructions to go through the simulation. respond to the questions and
prompts in the orange boxes.
vocabulary: acid, base, catalyst, chemical change, coefficient, conservation of matter, decomposition,
dissolve, double replacement, endothermic, exothermic, indicator, ion, physical change, product, reactant,
single replacement, subscript, synthesis
prior knowledge questions (do these before using the gizmo.)

1. a student mixes baking soda and vinegar in a glass. the results are shown at

left. do you think any new substances are being created in this mixture? if so,
how do you know?

1. suppose this was done on top of a balance. do you think the mass would

change as the reaction proceeded?

1. what do you think would happen to the mass if the reaction took place inside a sealed plastic bag?

Explanation:

1. When baking soda (sodium bicarbonate, \(NaHCO_3\)) reacts with vinegar (acetic acid, \(CH_3COOH\)), a chemical reaction occurs. The reaction produces carbon dioxide (\(CO_2\)) gas, water (\(H_2O\)), and sodium acetate (\(CH_3COONa\)). The formation of gas (bubbles are visible) is an indication of a new substance being created.
2. According to the law of conservation of matter, matter is neither created nor destroyed in a chemical reaction. However, if the reaction is done in an open system (like on a balance without a cover), the carbon dioxide gas produced can escape into the air. So, the mass measured on the balance would decrease as the reaction proceeds because some of the matter (in the form of \(CO_2\) gas) is leaving the system.
3. If the reaction takes place inside a sealed plastic bag (a closed system), no matter (including the \(CO_2\) gas) can escape. According to the law of conservation of matter, the total mass of the reactants (baking soda and vinegar) is equal to the total mass of the products (sodium acetate, water, and \(CO_2\)). So, the mass would remain the same.

Answer:

1. Yes, new substances are being created. We know this because there are bubbles (indicating the formation of a gas, which is a new substance).
2. The mass would decrease. This is because the \(CO_2\) gas produced can escape into the air in an open - system (on top of a balance without a cover).
3. The mass would remain the same. In a sealed plastic bag (a closed system), according to the law of conservation of matter, the total mass of reactants equals the total mass of products.