Question

which of the following processes is a chemical change?
liquid nitrogen dumped onto the floor vaporizes at room temperature.
when a few drops of red food coloring are added to a beaker of hot water, the water immediately turns red
the light on a candle burns until a bell jar is placed over it for a period of time.
dry ice sublimes when left on the demo table in lecture.

Explanation:

• Option a: Liquid nitrogen vaporizing is a physical change (phase change from liquid to gas).
• Option b: Adding food coloring to water is a physical mixing (no new substance formed).
• Option c: When a bell - jar is placed over a burning candle, the wax burns. Burning is a chemical reaction (wax reacts with oxygen to form new substances like carbon dioxide and water).
• Option d: Dry ice subliming is a physical change (phase change from solid to gas).

Answer:

C. When a few drops of red food coloring are added to a beaker of hot water, the water immediately turns red