Which of the following reactions performed in the experiment involved a chemical change?

• A. Burning magnesium ribbon in air
• B. Crushing a piece of chalk
• C. Heating copper to melt it
• D. Dissolving sugar in water

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the difference between physical and chemical changes. A chemical change results in the formation of new substances with different properties, while a physical change affects only the form or state of a substance without changing its identity.
2. Step 2: Analyze each reaction given: Crushing a piece of chalk changes its shape but not its chemical composition, so it is a physical change.
3. Step 3: Heating copper to melt it changes copper from solid to liquid, which is a change of state and thus a physical change.
4. Step 4: Dissolving sugar in water disperses sugar molecules in water but does not change the chemical identity of sugar, so this is a physical change.
5. Step 5: Burning magnesium ribbon in air causes magnesium to react with oxygen, forming magnesium oxide, a new substance. This is a chemical change because new chemical bonds are formed and the properties of the product differ from the reactants.