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Chemical Changes Investigation

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Chemical Changes Investigation

A science team is investigating whether mixing two substances creates new substances. Read the lab notes, analyze the evidence, and use what you know about atoms and mass. In this model investigation, all measurements are provided; do not mix substances.

Lab notes: Baking soda and vinegar

A team placed baking soda and vinegar in a sealed bag and measured the total mass. Before mixing, the sealed bag and its contents had a mass of 52.4 g. After mixing, the bag was puffy with gas, and its total mass was 52.4 g. The mixture felt cooler. The gas was carbon dioxide, a substance with different properties from either starting material. The seal stayed closed, so matter could not enter or leave.

Part A — Read the evidence

Use the lab notes to answer Questions 1–5.

1.Which observation is the clearest evidence that a chemical change occurred?

The bag became puffy as gas formed.
The bag was sealed.
The mass was measured in grams.
The mixture was placed in a bag.

2.Select two observations from the notes that support the idea that a chemical reaction occurred.

3.The bag’s mass was 52.4 g before and 52.4 g after mixing. What does this result show about the total mass in this sealed system?

4.A second team repeats the reaction in an open cup. They measure less mass afterward. Give one reasonable explanation for the difference from the sealed-bag result.

5.Complete the statement: During a chemical reaction, atoms are ; they are not created or destroyed.

6.Complete the statement: In a closed system, the total amount of matter, measured as , is conserved.

Part B — Test the claim

Use evidence and scientific reasoning. Chemical change means that one or more new substances form; a physical change changes form or state without making a new substance.

7.Carlos says, “Sugar disappearing in water proves it changed chemically.” Do you agree? Explain what happens to the sugar and how the mixture could be checked.

8.Classify each change as mainly physical or chemical: (a) an ice cube melting, (b) iron forming reddish rust, (c) paper being torn. Give one clue for your choice in (b).

9.Which statement best explains why atoms do not vanish when a reaction produces gas?

The atoms are rearranged into gas molecules that can move into the surrounding space.
The atoms are used up to make energy.
The atoms change into empty space.
The atoms disappear when they cannot be seen.

Part C — Plan a fair investigation

Imagine you want to test whether changing the amount of baking soda affects how much gas the reaction makes. A fair test changes one factor and keeps other conditions the same.

10.Name the factor you would change, one factor you would keep the same, and one measurement you could record to compare gas production.

11.A student starts with 10.0 g of baking soda and 15.0 g of vinegar in a closed container. Predict the total mass of all products after the reaction and explain your reasoning.