Physical Changes and Crystals: An Exciting Experiment
What evidence can help confirm that only a physical change occurred in the experiment?
A student mixes 20.0g of white KCl crystals with distilled water in a beaker. After the mixture was stirred, no crystals are visible and the solution is clear. After several days, all of the water evaporates and white crystals are found in the beaker. Which of the following pieces of experimental evidence would best help the student to confirm that a new compound had not been made and that only a physical change occurred?
Answer:
After the water has evaporated, the white crystals in the beaker have a mass of 20.0g.
The pieces of experimental evidence that would best help the student to confirm that a new compound had not been made and that only a physical change occurred is the 20.0g of white KCl crystals. This evidence indicates that the mass of the crystals remains the same throughout the experiment, suggesting that no new compound was formed.
Physical changes are defined as a modification to a sample of material when some of the substance's attributes change but the composition of the sample remains the same. Examples of physical changes include changes in state (such as melting or freezing), changes in shape or size, and changes in density.
Crystals are solid substances with a highly organized microscopic structure. They form when molecules group together in a specific pattern during solidification. The presence of white crystals in the beaker after the water evaporates indicates a physical change rather than a chemical change.
In conclusion, the 20.0g of white KCl crystals in the experiment serve as the best evidence to confirm that no new compound was formed and that only a physical change occurred. This reinforces the importance of understanding the distinction between physical and chemical changes in scientific experiments.