1. What is the primary difference between a new substance being formed, like rust, and a mixture being created?
- A. A new substance involves a chemical bond, while a mixture is a physical blend.
- B. A mixture always results in a substance that has a higher density than its original parts.
- C. A new substance can always be easily separated back into its original components, unlike a mixture.
- D. Creating a mixture requires a significant input of energy, like heat or electricity.
2. Which of the following is an example of a single, pure substance, not a mixture?
- A. Air
- B. Soil
- C. Saltwater
- D. Water
3. A chef makes a salad dressing by shaking oil, vinegar, and herbs together. After a few minutes, the oil and vinegar separate into layers. What does this separation demonstrate about the salad dressing?
- A. That a new, permanent substance was created when the ingredients were shaken.
- B. That the dressing is a mixture whose components can be physically separated.
- C. That the oil and vinegar are chemically bonded together into a single liquid.
- D. That the herbs have dissolved to form a new chemical compound with the oil.
4. Which statement best describes the components of a mixture?
- A. They chemically react to form a new substance with different properties.
- B. They are physically blended together but each keeps its own original properties.
- C. They can only be separated from each other using chemical reactions.
- D. They must all be in the same state of matter (solid, liquid, or gas).
5. Which of the following is the best example of a mixture?
- A. A piece of pure iron
- B. A single grain of salt
- C. A bowl of salad with lettuce and tomatoes
- D. A glass of pure water
6. Which of the following statements best defines a pure substance?
- A. It is a material that is found in nature and has not been processed in a lab.
- B. It is a substance composed of only one type of atom or one type of molecule.
- C. It is any liquid that is clear and has no visible particles floating within it.
- D. It is a substance that can be easily separated into its components by physical means.
7. If you have a container filled with pure gaseous oxygen (O₂), what does this imply about the particles inside?
- A. The container holds a random mix of individual oxygen and hydrogen atoms.
- B. The particles consist of various different types of oxygen-containing molecules.
- C. The container is filled exclusively with identical O₂ molecules.
- D. The particles are a combination of O₂ molecules and other atmospheric gases.
8. A scientist is analyzing an unknown liquid. Which observation would most strongly suggest that the liquid is a pure substance?
- A. The liquid is colorless.
- B. The liquid has a constant, sharp boiling point.
- C. The liquid can dissolve sugar.
- D. The liquid's volume decreases when heated.
9. Why is a sample of ocean water NOT considered a pure substance?
- A. Because it contains multiple substances, such as water, salts, and minerals.
- B. Because it is a liquid and only solids can be truly pure substances.
- C. Because its chemical composition is represented by the formula H₂O.
- D. Because it covers a majority of the Earth's surface area.
10. A large, solid block of pure aluminum (Al) is cut in half. How do the properties of the first half compare to the properties of the second half?
- A. One half will be denser than the other.
- B. The properties, such as melting point and density, will be identical.
- C. The smaller half will have a lower melting point.
- D. The chemical composition will be different between the two halves.