Which of the following laboratory activities involves a chemical change?

• A. Burning a strip of magnesium ribbon in air
• B. Dissolving table salt (NaCl) in water
• C. Crushing a piece of chalk into powder
• D. Heating copper wire until it glows red and then cools

Answer: (A)

Verified step by step guidance

1. Understand the difference between physical and chemical changes: A physical change affects the form of a substance but not its chemical composition, while a chemical change results in the formation of one or more new substances with different properties.
2. Analyze each option to determine if a chemical change occurs:
3. 1. Burning a strip of magnesium ribbon in air: This involves magnesium reacting with oxygen to form magnesium oxide, a new substance, indicating a chemical change.
4. 2. Dissolving table salt (NaCl) in water: This is a physical change because the salt dissociates into ions but no new substance is formed.
5. 3. Crushing a piece of chalk into powder: This is a physical change since the chalk's chemical composition remains the same, only its physical form changes.
6. 4. Heating copper wire until it glows red and then cools: This is a physical change because the copper changes temperature and color due to heat but does not form a new substance.