Question

If a piece of hard white blackboard chalk is heated strongly in a flame, the mass of the piece of chalk will decrease, and eventually the chalk will crumble into a fine white dust. Does this change suggest that the chalk is composed of an element or a compound?

Short answer

The heated chalk undergoes a chemical change, as its mass decreases and it crumbles into a fine white dust. Elements generally do not undergo chemical changes when heated. Therefore, the chalk is a compound and not an element.

Step-by-step solution

Define Elements and Compounds.

An element is a pure substance consisting of only one type of atom. A compound is a pure substance formed when two or more different elements are chemically bonded together in a fixed proportion.

Observe the Changes in Chalk During Heating.

When the chalk is heated strongly, the mass of the piece of chalk decreases, and eventually, the chalk crumbles into a fine white dust. This is a chemical change because the initial properties of the chalk have been altered. The color, mass, and physical state of the chalk have all undergone a change due to the reaction that has taken place.

Analyze the Changes to Determine if Chalk is an Element or Compound.

Elements do not generally undergo chemical changes when subjected to heat; instead, they may undergo physical changes such as melting or boiling. In this case, the changes observed in the chalk are indicative of a chemical reaction, which suggests that the chalk is not an element.

Conclusion.

Since the chalk undergoes a chemical change and is not an element, it must be a compound. The observed change in the heated chalk's mass (decreasing) and physical state (crumbling into a fine white dust) indicates that it is composed of a compound that decomposes when subjected to high temperatures. Therefore, the chalk is a compound and not an element.