1. The chemical formula for the reddish powder known as rust is Fe₂O₃. What does this formula indicate about the composition of the substance?
- A. It is a simple mixture of two iron atoms and three oxygen atoms that can be easily separated.
- B. For every two iron atoms, there are three oxygen atoms that are chemically bonded together.
- C. The substance is mostly made of iron, with a small amount of oxygen impurity.
- D. It contains five atoms in total, with more iron than oxygen.
2. Iron oxide is described as having a repeating "extended structure." What does this term imply about how the iron and oxygen atoms are arranged?
- A. The atoms are arranged in small, separate groups of five that float around independently.
- B. The iron and oxygen atoms are linked in a large, continuous, and repeating crystal-like network.
- C. The atoms are randomly mixed together without any specific order or pattern.
- D. The substance is a gas where individual atoms move freely and are far apart from each other.
3. A student observes a shiny, metallic iron nail and a pile of reddish, powdery rust. Although both contain iron atoms, why are their properties so different?
- A. The rust is simply iron that has been crushed into a fine powder.
- B. The iron atoms in rust have chemically bonded with oxygen, forming a new substance with new properties.
- C. The rust is older than the nail, and its properties have changed over time.
- D. There is no real difference; the color change is just on the surface.
4. What is the primary scientific purpose of using a model to represent the atomic composition of iron oxide?
- A. To provide a tool for physically building the substance in a classroom.
- B. To create an exact, full-scale replica of the atoms.
- C. To make the substance look more interesting than it is.
- D. To visualize a structure that is too small to be seen with the naked eye.
5. A sample is analyzed and found to contain only iron and oxygen atoms. Which piece of information would confirm that the sample is the compound iron oxide and not just a mixture?
- A. The sample is reddish in color.
- B. The atoms are chemically bonded together in a fixed ratio.
- C. The sample was found on a piece of metal.
- D. The sample contains more oxygen atoms than iron atoms.
6. What is the fundamental reason that rust, which is brittle and reddish-brown, has different properties from iron, which is strong and silvery?
- A. Rust forms because the iron atoms have physically decayed and broken apart over time.
- B. The properties are different because rust contains iron atoms bonded to oxygen atoms.
- C. The difference in properties is only due to a change in physical state from a solid to a powder.
- D. Rust is simply iron that has been exposed to cold temperatures for a long period.
7. A scientist combines highly reactive sodium metal (Na) and toxic chlorine gas (Cl₂) to produce sodium chloride (NaCl), or table salt. Why is table salt safe to eat while its components are dangerous?
- A. The dangerous properties are diluted when the two substances are mixed together in a large volume.
- B. A new substance (sodium chloride) is formed, and its properties are completely different from its component atoms.
- C. The change in physical state from metal/gas to a crystalline solid is the sole reason for the change in properties.
- D. The toxicity is only present when sodium and chlorine are in their pure forms and disappears upon any mixing.
8. At an atomic level, what is the key characteristic of a pure element like iron?
- A. It is always found in a solid state.
- B. It is composed of only one type of atom.
- C. It can be easily broken down into simpler substances.
- D. It is a mixture of several different types of atoms.
9. What is the primary consequence of changing the type or number of atoms within a substance's fundamental repeating structure?
- A. The substance's mass decreases, but its other properties remain the same.
- B. A completely new substance with a new set of properties is created.
- C. The original atoms are destroyed and converted into energy.
- D. The substance only changes its physical state, for example from a solid to a liquid.
10. The chemical change from pure iron (Fe) to rust (an iron oxide) is most similar to the change between which of the following pairs?
- A. An ice cube and liquid water
- B. Hydrogen gas (H₂) and water (H₂O)
- C. A large iron bar and small iron filings
- D. A diamond and a piece of graphite