2.3. Changes in Matter http://www.ck12.org
FIGURE 2.13
A yellow precipitate of solid lead(II) io-
dide forms immediately when solutions of
lead(II) nitrate and potassium iodide are
mixed.of a gas releases energy. The only way to be certain that a chemical reaction has occurred is to test the composition
of the substances after the change has taken place to see if they are different from the starting substances.
Lesson Summary
- Matter can undergo chemical and physical changes.
- Mixtures can be separated through physical changes, including techniques such as chromatography, distilla-
tion, evaporation, and filtration. Physical changes do not alter the nature of the substance, they simply alter
the form. - Pure substances, such as compounds, can be separated through chemical changes. Chemical changes change
the chemical composition of a substance and can only occur through a chemical reaction. - Four clues to a possible chemical reaction include a color change, the production of a gas, the formation of a
precipitate, and an observable transfer of energy.
Lesson Review Questions
- Can elements be broken down further into other pure substances?
- For each of the following mixtures, describe how you might separate out the components using one of the
techniques discussed in this chapter.
a. separating dyes in inks
b. separating sand from water
c. separating ethanol from water
d. separating water from ink
e. separating salt from water - A candle is a mixture of substances that, when burned, breaks down primarily into carbon dioxide and water.
How might you test for the presence of water that is produced when a candle is burned?