s8pe-205st-ca
12/7/05
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MAZER
Page 161
Standards-Based Assessment
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Analyzing Changes
8.5.c, 8.5.d
Read the following paragraphs and answer the questions below.
Many changes occur during food processing and cooking. Some changes are physical changes. Others are chemical changes. A physical change is a change in a substance that does not change the substance. Grinding coffee beans, for example, is a
physical change. All that happens is the beans are broken apart. They are still coffee
beans. After a chemical change, however, the identity of a substance is different. For
example, roasting coffee beans involves many chemical changes. During roasting,
starches and sugars in the coffee change into oils. You can detect these chemical
changes in the strong odors, colors, and flavors of the roasted beans. Odors, changing colors, and a rise in temperature are often indications of chemical changes.
As another example of the physical and chemical changes that take place during
food preparation, consider making tortillas. Tortillas have been made in Mexico
since pre-Columbian times. Following is an example:
1. The harvested corn kernels are dried in sunlight.
2. The kernels are soaked and simmered in a lime water solution until the outer
skins are softened. The lime water solution contains calcium hydroxide.
3. The softened kernels are then ground and formed into a dough called masa.
4. The masa is then pressed into a round shape and baked on a hot pan known as
a comal until it turns golden brown.
1. Drying the corn kernels in sunlight is an example of a
a. physical change
c. mixture of substances
b. chemical change
d. separation of substances
2. In which of the following steps of the tortillamaking process does a chemical change occur?
a. harvesting of the corn
b. soaking in the lime water
c. grinding of the corn kernels
d. pressing of the masa
Extended Response
Answer the two following questions in detail. Include
some of the terms from the list in the box at right.
Underline each term that you use in your answer.
5. Physical changes do not change a substance, but
can all physical changes be undone? Explain your
answer.
3. Cooking often involves reactions that create new
substance from the substances in the ingredients.
This process is an example of a
a. chemical change
b. physical change
c. mixture of substances
d. separation of substances
4. The kernels are traditionally ground using a stone
tool known as a metate y mano. This grinding
process is an example of a
a. chemical change
c. mixture of substances
b. physical change
d. separation of substances
element
physical change
molecule
compound
chemical change
mixture
atom
6. The air we breathe is a mixture of several elements. Oxygen and hydrogen are two of them.
Water also contains oxygen and hydrogen. How
can both these elements appear so different?
Chapter 5: Properties of Matter 161
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