Question

1. a student notices that sugar, when heated over a flame, turns black. what is the best indication that a new substance is being formed?

a. the sugar melted within the test tube
b. the temperature of the test tube increased.
c. the color of the sugar changed to black
d. the mass of the sugar decreased

Explanation:

• Melting (Option A) is a physical change as the substance remains sugar in a different state.
• Temperature increase (Option B) is a physical property change and not evidence of a new substance.
• Color change (Option C) is a strong indication of a chemical reaction forming a new substance (like carbon when sugar is charred).
• Mass decrease (Option D) could be due to evaporation (a physical change) and not necessarily a new substance formation.

Answer:

C. The color of the sugar changed to black