1. Of the following, the only change that is an example of a chemical change is —
A. water evaporating from a puddle
B. an iron nail rusting and turning an orange color
C. a piece of paper being cut into smaller pieces
D. a stick being broken in half
2. All of the following involve chemical changes except —
A. an ice cube disappearing after being placed in a glass of water
B. frying an egg
C. a piece of silver jewelry tarnishing
D. a green coating forming on a copper statue
hint: both correct choices involve only water
1. To determine which change is an example of a chemical change, we need to understand the difference between a physical change and a chemical change.
A physical change is a change in the physical properties of a substance, but the substance itself remains the same. Examples of physical changes include changes in size, shape, state of matter, or phase transitions.
A chemical change, on the other hand, is a change in the chemical composition of a substance. In a chemical change, the starting substance(s) are transformed into a different substance(s) with different properties.
Now let's analyze the given options:
A. Water evaporating from a puddle: This is a physical change. The liquid water is changing into water vapor, but the substance itself is still water.
B. An iron nail rusting and turning an orange color: This is a chemical change. The iron nail is reacting with oxygen in the presence of moisture to form iron oxide (rust), resulting in a change in both appearance and chemical composition.
C. A piece of paper being cut into smaller pieces: This is a physical change. The paper is being physically divided into smaller pieces, but the substance itself remains paper.
D. A stick being broken in half: This is also a physical change. The stick is being physically broken into two pieces, but the substance itself is still wood.
Therefore, the only change that is an example of a chemical change is option B: an iron nail rusting and turning an orange color.
2. Similarly, to determine which change does not involve a chemical change, we can apply the same concepts.
A. An ice cube disappearing after being placed in a glass of water: This is a physical change. The ice cube is melting and becoming water, but the substance remains H2O.
B. Frying an egg: This is a chemical change. The heat causes the proteins in the egg to denature and undergo a chemical reaction, resulting in the formation of a solid cooked egg.
C. A piece of silver jewelry tarnishing: This is a chemical change. The silver is reacting with sulfur compounds in the air or on the skin, forming a dark coating known as tarnish.
D. A green coating forming on a copper statue: This is a chemical change. The copper is reacting with oxygen and moisture in the air to form copper oxide, which appears green.
Therefore, the change that does not involve a chemical change is option A: an ice cube disappearing after being placed in a glass of water.