Final answer:
To check if a gel has solidified, observe the transition from a liquid to a semi-solid state upon cooling, and feel for its viscosity and resistance to motion. Color is less indicative of solidification in gels, though it can show chemical changes in other contexts.
Step-by-step explanation:
To determine if a gel has solidified, you should observe its physical characteristics. A solidified gel, like gelatin desserts, transforms from a liquid to a viscous semi-solid state upon cooling, indicating that it has set. This process occurs because the gelatin molecules form a three-dimensional network that traps water, changing the mixture's phase from liquid to solid-like. While color might not directly indicate solidification, it can signal chemical changes if a color change occurs during the process. Understanding the common phases of matter—solids, liquids, and gases—is essential for this. Solids maintain a fixed volume and shape due to the organized arrangement of their atoms. Conversely, liquids and gases flow freely and fill their containers because their atoms are less tightly bound. When a gel sets, its atoms are structured in a way that is typical of solid substances, even if it is technically a colloid, with properties between those of a solid and a liquid. Note that in the context of chemical reactions, a color change might indicate the formation of a new substance, but for gels, the color is usually due to dyes and doesn't inherently demonstrate solidification. To test for solidification, you might gently touch it to feel its resistance or tip the container slightly to see if the gel maintains its shape.