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?
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2 suppose this was done on top of a balance. do you think the mass would change as the reaction proceeded? ____________
3 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? _____________________________________
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2 do you think a chemical reaction has taken place? explain _____________________________________

Question

Accepted Answer

Since the problem is about "Student Exploration: Chemical Changes" and involves questions about chemical reactions and observations, the subfield under Natural Science is Chemistry. Here are the answers to the questions:

### Prior Knowledge Questions
1. **Brief Explanations**: When baking soda and vinegar mix, a chemical reaction occurs (acid - base reaction between sodium bicarbonate and acetic acid). New substances (like carbon dioxide gas, water, and sodium acetate) are created. We know this because we can observe bubbles (gas production), which is a sign of a chemical change (formation of a new substance).
   **Answer**: Yes, new substances are being created. We know this because bubbles (gas) are produced, indicating a chemical reaction where reactants are transformed into new products.
2. **Brief Explanations**: In an open system (like on a balance without a cover), if a gas is produced (as in the baking soda - vinegar reaction), the gas can escape. According to the law of conservation of mass, mass should be conserved in a chemical reaction, but if gas escapes, the mass measured by the balance will decrease as the reaction proceeds.
   **Answer**: Yes, the mass would decrease (if gas is produced and escapes). Because the gas produced can leave the system, so the mass of the remaining substances on the balance will be less than the initial total mass of reactants.
3. **Brief Explanations**: In a sealed plastic bag, the system is closed (no matter can enter or leave). According to the law of conservation of mass, the total mass of substances before and after the reaction remains the same. So the mass of the system (plastic bag with reactants and products) should stay constant.
   **Answer**: The mass would remain the same. Because the sealed plastic bag is a closed system, and according to the law of conservation of mass, mass is conserved in a chemical reaction (no matter can enter or exit the system).

### Gizmo Warm - up Questions
1. **Brief Explanations**: When sodium (Reactant 1) reacts with water (Reactant 2), a chemical reaction occurs. Sodium is a highly reactive metal. When it is added to water, we observe that sodium moves rapidly on the surface of the water, there is fizzing (gas production, hydrogen gas), the solution may become hot (exothermic reaction), and the sodium may dissolve or react completely, and the solution may change color (due to the formation of sodium hydroxide, which is basic).
   **Answer**: Sodium moves rapidly on the water's surface, fizzing (gas production) occurs, the reaction is exothermic (the solution gets hot), and the sodium reacts (may dissolve or be used up), and the solution may show signs of the formation of a new substance (like a change related to the formation of sodium hydroxide).
2. **Brief Explanations**: A chemical reaction has taken place. We can tell this because new substances are formed (sodium hydroxide and hydrogen gas), and we observe signs of a chemical change: gas production (fizzing), energy change (exothermic - the solution gets hot), and the reactant (sodium) is consumed. These are all indicators of a chemical reaction (transformation of reactants into different products).
   **Answer**: Yes, a chemical reaction has taken place. We know this because there are signs of chemical change: gas production (fizzing), energy change (exothermic), and the reactant (sodium) is consumed, indicating the formation of new substances (sodium hydroxide and hydrogen gas).

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