Physical Change Evidence: How to Confirm Only Physical Change Occurred

What experimental evidence would best help a student confirm that a new compound had not been made and that only a physical change occurred?

After mixing white crystals with distilled water in a beaker, no crystals were visible and the solution became clear. After several days, all of the water evaporated and white crystals were found in the beaker.

Answer:

To confirm that only a physical change occurred and no new compound was formed, the student can observe that the visible characteristics of the substance did not change, measure that the mass of the substance remained constant, and verify that there were no color changes in the solution.

When conducting experiments involving the mixing of substances and observing changes in physical properties, it is important to differentiate between physical changes and chemical changes. In the scenario provided, where white crystals were mixed with distilled water, the subsequent observation of clear solution followed by the reformation of white crystals can be indicative of a physical change rather than a chemical one.

One piece of evidence that can support the conclusion of a physical change is the visual appearance of the substance before and after the process. If the initial and final substances exhibit identical appearances, it suggests that only physical transformations have taken place. This phenomenon is akin to scenarios where substances change state, such as solid wax melting into liquid wax, or steam condensing into liquid water.

Another method to confirm the occurrence of a physical change is to measure the mass of the substance before and after the process. The conservation of mass principle dictates that in physical changes, the mass should remain constant. By verifying that the total mass before the change is equal to the total mass after the change, the student can strengthen the argument for a physical change.

Additionally, monitoring the color changes in the solution can provide further evidence. If there are no color changes observed throughout the process, similar to when copper is immersed in a silver nitrate solution, it supports the notion that no new chemical substances were formed.

In conclusion, by considering the visual characteristics, mass measurements, and color changes in the solution, the student can confidently confirm that only a physical change occurred and that no new compound was created during the experiment.