Question

1. what are three common clues that a chemical change has occurred?
2. how is a chemical change different from a physical change?

using science skills
use the table to answer each question. write the answers on a separate sheet of paper.
physical properties of four materials used to make sculptures

	malleability	hardness	melting point
unbaked clay	can be molded	soft	very high melting point
baked clay	brittle after being baked at a high temperature	hard	very high melting point
metal (a mixture of copper, zinc, and lead)	can be hammered without shattering	hard	high melting point

figure 2 - 2

1. comparing and contrasting use figure 2 - 2 to compare the physical properties of clay before and after it is baked at a high temperature.
2. using tables and graphs which of the materials in figure 2 - 2 are malleable?
3. comparing and contrasting based on the information in figure 2 - 2, compare the properties of a sculpture made from metal and a sculpture made from baked clay.
4. inferring an object made from a material listed in figure 2 - 2 changes shape when you leave it in a sunny window. which material is the object made from? how do you know?
5. inferring which of the materials described in figure 2 - 2 would be least likely to be recycled? explain your choice.

Explanation:

1. Three common clues of a chemical change are production of gas, formation of a precipitate, and change in color.
2. A chemical change results in the formation of new substances with different chemical properties, while a physical change only alters physical properties like shape, size or state without forming new substances.
3. Unbaked clay is moldable and soft, while baked clay is brittle and hard. Unbaked clay has a very high melting - point and so does baked clay.
4. Wax is soft enough to be carved and molded and metal can be hammered without shattering, so wax and metal are malleable.
5. Metal is malleable (can be hammered without shattering) and hard, while baked clay is hard but brittle. Both have high melting - points.
6. The object is likely made of wax. Wax has a low melting - point, so it can change shape when exposed to the heat from the sun in a sunny window.
7. Baked clay would be least likely to be recycled. Once baked, it becomes brittle and its structure is permanently changed, making it difficult to re - form into new objects compared to wax (which can be remelted easily) and metal (which can be melted and remolded).

Answer:

1. Production of gas, formation of a precipitate, change in color.
2. A chemical change forms new substances with different chemical properties; a physical change only alters physical properties.
3. Unbaked clay: moldable, soft; Baked clay: brittle, hard. Both have high melting - points.
4. Wax, Metal.
5. Metal is malleable and hard; Baked clay is hard but brittle. Both have high melting - points.
6. Wax. It has a low melting - point and can be affected by sun heat.
7. Baked clay. Its structure is permanently changed and it's brittle, hard to re - form.