Question

student exploration: chemical changes
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?
2. what do you think would happen to the mass if the reaction took place inside a sealed plastic bag?

gizmo warm - up
a chemical change, (or chemical reaction) occurs when one or more substances, called reactants, are transformed into different substances, or products. in the chemical changes gizmo, you will look for evidence of chemical changes by looking at changes you can see, touch, or smell.
to begin, check that reactant 1 is sodium and reactant 2 is water. sodium is a metal so soft you can cut it with a knife.

1. click play (▶). what do you observe?

1. do you think a chemical reaction has taken place? explain

Answer:

Prior Knowledge Questions

1. Answer & Explanation:

• Brief Explanations: When baking soda (sodium bicarbonate) and vinegar (acetic acid) are mixed, a chemical reaction occurs. The signs of a new substance being created include the production of gas bubbles (carbon dioxide), a change in temperature (usually endothermic, feeling cooler), and a change in the appearance (fizzing, foaming). So yes, new substances are formed. We know this because of the visible gas production, the change in the mixture's appearance, and the chemical nature of the reaction (acid - base reaction between the bicarbonate and the acetic acid).
• Answer: Yes, new substances are being created. We know this because there is fizzing (gas production), a change in the mixture's appearance, and it is an acid - base chemical reaction (baking soda is a base, vinegar is an acid) that produces carbon dioxide, water, and sodium acetate.

1. Answer & Explanation:

• Brief Explanations: The reaction between baking soda and vinegar produces carbon dioxide gas. If the reaction is done on a balance (open system), the carbon dioxide gas will escape into the air. According to the law of conservation of mass, the total mass of reactants should equal the total mass of products. But since the gas escapes, the mass measured by the balance (which is measuring the mass of the remaining substances in the glass) will decrease as the reaction proceeds.
• Answer: Yes, the mass would decrease. Because the carbon dioxide gas produced escapes into the air, so the mass of the substances remaining in the glass (measured by the balance) will be less than the initial mass of the reactants.

1. Answer & Explanation:

• Brief Explanations: If the reaction takes place inside a sealed plastic bag, it is a closed system. The law of conservation of mass states that in a closed system, the total mass of reactants is equal to the total mass of products. The carbon dioxide gas produced will be trapped inside the sealed bag. So the mass of the system (the bag and its contents) will remain the same because no matter (in the form of the gas) can escape.
• Answer: The mass would remain the same. Because the reaction is in a sealed (closed) system, and according to the law of conservation of mass, the total mass of reactants equals the total mass of products, and no matter can escape the sealed bag.

Gizmo Warm - up

1. Answer & Explanation:

• Brief Explanations: When sodium (Reactant 1) is added to water (Reactant 2), a vigorous chemical reaction occurs. You will observe that the sodium metal moves rapidly on the surface of the water, there is fizzing (gas production), the solution may become hot (exothermic reaction), and the sodium metal will be consumed (dissolve or react completely).
• Answer: The sodium metal moves rapidly on the surface of the water, there is fizzing (gas production), the solution gets hot, and the sodium metal is consumed (reacts).

1. Answer & Explanation:

• Brief Explanations: A chemical reaction has taken place. Evidence for this includes the production of gas (fizzing), a change in temperature (the solution gets hot, indicating an exothermic reaction), and the disappearance of the sodium metal (a reactant is consumed). Also, the reaction between sodium and water produces sodium hydroxide and hydrogen gas (\(2Na + 2H_2O=2NaOH + H_2\uparrow\)), which are new substances.
• Answer: Yes, a chemical reaction has taken place. Because there is gas production (fizzing), a change in temperature (exothermic, solution gets hot), and the sodium metal (reactant) is consumed to form new substances (sodium hydroxide and hydrogen gas).