Meet Christina Elson - Chapter 1 Structure of Living Things... 1 Chapter 2 Plant Structures and

Christina Elson is a scientist at the American Museum of Natural History.

She studies how salt was used by the ancient Aztec culture.

From the 12th to 16th centuries, the Aztecs lived in the area that is now Mexico. This area was very rich in salt, which is a natural mineral resource that is mined from the ground. Christina studies a region in Mexico where salt was obtained from deposits around a dried lake bed. The Aztecs turned these deposits into different kinds of salt. First, they collected the salty soils by scraping and digging them out of the ground. Then they filtered water through the soils to dissolve out the salts into big pots. The final step required boiling the salt solution so the water evaporated away.

The salt remained behind in the form of crystals.

Aztecs used salt for much more than a cooking spice. In one Aztec town, Christina found thousands of ceramic fragments, pieces of clay pots that were used to transport salt for sale or trade. She also found that salt was used to dye cloth. Colorfully dyed cotton cloth was a valuable product because it was greatly desired by the Aztec nobles. Aztec women learned to spin cloth at an early age. The cloth was dyed with pigment in a hot watery dye-bath. When salt was added to the dye-bath, it

helped the pigment “stick” to the cloth. The salt combined with the color pigment to make a compound that could not be dissolved in water.

Salt was important to many other ancient cultures, and continues to be important today. Salt can be used to preserve food so it can be stored for a long time without refrigeration; to prepare and preserve animal skins for clothing; and to make soap. Salt’s value stems from its usefulness, durability, and portability.

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Reading and Writing in Science Salts

Reading

Draw Conclusions

•

Use information in the text and background knowledge.

•

Support your conclusions with information found in the text.

Write About It

Draw Conclusions

1.

How did the Aztecs change a mineral resource into a finished product?

2.

What would happen to the colors in Aztec cloth when washed if salt was not part of the dye-bath?

They collected the salty soils and ﬁ ltered water through them to dissolve the salts into the water. The water was collected in pots and then boiled so the water evaporated away. The salt crystals were left behind.

The colors would not stick to the cloth as well and would fade. If salt was not combined with the color pigment to make a compound, it could dissolve in water.

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Writing

Clean Up

Read the Writing in Science feature in your textbook.

Write About It

Explanatory Writing Do research online to find other products that come from the reaction of an acid and a base. Choose one of those products and write out instructions to make it. Explain clearly what the finished product will look like and do.

Planning and Organizing

Alicia planned to write instructions for how to model an erupting volcano. Organize the steps she wrote from 1 to 4, with 4 being the last step.

A.

Gather all your ingredients and equipment.

B.

Finally, pour the vinegar mixture into the bottle of sodium carbonate.

C.

Then prepare your base. Use the funnel to pour sodium carbonate into a small plastic bottle. Fill the bottle to the halfway point.

D.

Pour the vinegar into a measuring cup. Add a few drops of the red food coloring to the vinegar and stir.

Write the purpose of your instructions, then write five steps in sequence.

I plan to write instructions to make

1.

Chapter 8 • Changes in Matter Use with Lesson 3

Reading and Writing in Science Salts

Writing

Now write the first draft of your instructions on a separate sheet of paper.

Begin with a paragraph that explains the purpose of the instructions and tells what the finished product will look like. Then write the list of materials needed. Arrange the steps in sequence. End with a paragraph that explains the chemical reaction.

Revising and Proofreading

Here are some sentences that Alicia wrote for her instructions. Each sentence contains a grammatical error. Find the error and correct it.

Write the corrected sentence on the lines.

1.

Pour the vinegar into the sodium carbonate and watch the liquid raise.

2.

A real volcano erupt when the pressure builds up.

3.

This demonstration will shown what an erupting volcano looks like.

4.

A chemical reaction occurs when a base was combined with an acid.

5.

Sit the bottle in the middle of the pile of gravel.

Now revise and proofread your instructions. Ask yourself:

This demonstration will show what an erupting volcano looks like.

A chemical reaction occurs when a base is combined with an acid.

Set the bottle in the middle of the pile of gravel.

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CHAP TE R LE VE L

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base.

c.

indicator.

d.

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Reading and Writing in Science

In document Chapter 1 Structure of Living Things... 1 Chapter 2 Plant Structures and Functions Chapter 3 Human Body Systems... 41 (Page 193-200)