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Elements and Changes Web Quest

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Elements and Changes Web Quest

A science fair team has found several mystery samples and recorded changes in the kitchen. Use the evidence on this page to solve each task. You do not need a website or other resources. Remember: an element contains one type of atom; a compound contains atoms of different elements chemically joined. A physical change alters form or state without making a new substance. A chemical change makes one or more new substances.

Identify the substances

Use the clues below. The number of atoms in a molecule does not decide whether it is an element or compound; the kinds of atoms do.

1.The oxygen model is made from two oxygen atoms joined together. Is oxygen gas an element or a compound? Explain your choice.

2.Sort these substances into elements and compounds: gold (Au), water (H₂O), copper (Cu), carbon dioxide (CO₂), helium (He), table salt (NaCl). Write at least two examples in each group.

3.Which statement best explains why water is a compound?

It is a liquid at room temperature.
It contains hydrogen and oxygen atoms chemically joined in a fixed combination.
It can be found in rivers and clouds.
It contains only one kind of atom.

4.A sample of shiny copper wire is bent into a loop. Has a new substance formed? State whether this is a physical or chemical change and give a reason.

Follow the evidence

The science fair team recorded observations from four investigations. Use the evidence, not just whether a change looks dramatic, to decide what happened.

Investigation

Observation

Ice left on a plate

Solid ice becomes liquid water.

Paper cut into strips

The pieces are smaller, but remain paper.

Steel nail left outside

A reddish-brown coating forms over time.

Baking soda mixed with vinegar

Bubbles form and the mixture fizzes.

5.Classify each investigation in the notes as a physical change or chemical change. For each one, give the key clue from the observation.

6.Which observation is the strongest evidence that a chemical change occurred when vinegar and baking soda were mixed?

The ingredients were poured into the same container.
Bubbles formed as a gas was produced.
The container was moved to the bench.
The mixture took up space.

7.A student says, “Dissolving sugar in water must be a chemical change because the sugar disappears.” Do you agree? Explain what happens to the sugar and how you could recover it.

Explain and apply

Scientists use observations and clear explanations to support their conclusions. Check each claim against the evidence.

8.Choose one reliable sign of a chemical change: formation of a new solid, gas production, lasting colour change, or heat/light produced without heating. Explain why the sign can be evidence that a new substance formed.

9.Cooking an egg involves several changes. Name one physical change and one chemical change that could happen while preparing breakfast, and explain how they differ.

10.Mystery conclusion: A silvery metal reacts with a green gas. The product is a green solid with properties different from either starting substance. Is the product an element or a compound? Is the process a physical or chemical change? Justify both decisions.