Question

Students observed rust forming on a bar of pure iron. Which of the following provides evidence that the change to the iron bar was a chemical change?

a. The melting point of pure iron is approximately 1,500°C.

b. The mass and the volume of the rust can be measured.

c. The iron bar is able to conduct electricity even after rust forms.

d. The rust is a new substance that is not pure iron.

Answer 1

Rust forming on a bar of pure iron is a chemical change, evidenced by the creation of iron oxide, a new substance different from pure iron, also known as corrosion.

Step-by-step explanation:

The observation that rust is forming on a bar of pure iron provides evidence that a chemical change is occurring. The correct option to indicate that a chemical change has occurred is: 'The rust is a new substance that is not pure iron.' This is because rust, which is iron oxide, has different properties from those of pure iron. This formation of rust is a process known as corrosion, which is a common term describing the combination of iron with oxygen to form iron oxide. Corrosion, specifically the rusting of iron, is a slow chemical process that releases energy much like combustion but at a rate that is usually not perceptible to the human senses.