Posted by Emily Grossman on .
I need help classifying these as physical or chemical changes!
1. sodium metal exposed to air turns dark gray.
2. steam in a test tube condenses to moisture.
3. baking soda in vinegar releases bubbles.
4. water dissolves in vinegar to give a solution.
5. tap water and soap form an insoluble deposit.
6. solid "dry ice" slowly disappears completely.
The question you must answer is, does the change form a new chemical compound or is it the same material after the change as before the change? For example,
1. The sodium is oxidized to Na2O because it reacts with oxygen in the air. Something new has been formed; therefore, this is a chemical change.
2. Steam condenses. It was H2O as steam, it is H2O as liquid, same material, physical change.
3. Baking soda reacts with vinegar to form carbon dioxide (CO2) and those are the bubbles. Baking soda (NaHCO3) has been changed to CO2, H2O, and Na2CO3.
I'll leave the others for you.
Most often chemical changes are associated with a color change(not always but often), a solid forms, a gas forms. (Note that 1 was a color change, 2 was none of these, 3 was a gas formed.)