Review and apply Investigation 3. Let s review Page 158

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1 Review and apply Investigation 3 Let s review Page In this investigation you conducted different tests to identify unknown liquids. Describe one of the tests you conducted with the known liquids and the unknown. Be sure to explain what you did to control the variables so that the test was fair. Students may describe either the absorption test or combining-with-water test. Absorption test: My group placed the known liquids and the unknown on different paper surfaces: brown paper towel, wax paper, newsprint, and construction paper. We were careful to place a single drop of each liquid on brown paper towel at the same time. We tired to hold the droppers at the same height. Then we looked for any differences in the way the liquids absorbed or didn t absorb into the paper. We did the same thing with each of the paper surfaces. Combining-with-water test: All of the liquids were colored yellow and large drops of them were placed on a laminated chart opposite large drops of blue water. The circles on this chart helped us to use the same amount of each liquid. Then we used clean toothpicks to drag the drop of blue water over to each drop of yellow liquid. We were careful not to mix the drops together with the toothpick so that the drops could combine on their own. 2. How did you identify the unknown? Absorption test: (Water as the unknown.) The unknown, water, and salt water all beaded up on wax paper, while rubbing alcohol and detergent spread out. So the unknown must have been either water or salt water. The saltwater seemed to stay beaded up longer on construction paper than the water and unknown did. So the unknown had to be water. Combining-with-water test: We compared what happened as each of the 4 unknown liquids combined with water to our observations of the 4 known liquids combining with water. The yellow water seemed to combine very slowly with the blue water. Saltwater combined very quickly with blue water. Rubbing alcohol shook as it combined. And detergent combined at a medium speed turning green throughout.

2 Science in action! Pages Students will develop two tests that can be used to tell water and mineral oil apart. They will likely have to work on several tests before coming up with two that show distinct enough differences between the two similar-looking liquids. Students should record some of their plans on the activity sheet, and then try their plans. Once they have found 2 tests, they should use drawings and explanations to describe each test and should explain the observations that distinguish the two liquids.

3 Think about it Pages Look at the picture of water dripping off a leaf. Why does the water droplet hold together? a. Water is a molecule. b. Water is an atom and atoms are round. c. Water molecules are attracted to each other and cling together. d. Water molecules have two atoms of hydrogen and one atom of oxygen. 2. According to the details in the reading, what does capillary action do for a plant? a. Capillary action helps turn the plant towards sunshine. b. Capillary action helps make leaves green. c. Capillary action helps move water and nutrients into the stems, leaves, and roots. d. Capillary action helps bring the plant carbon dioxide. 3. Surface tension is a term used to describe a. the number of water molecules on the surface of water. b. a water strider or other insect that can stand on the surface of water. c. the strength and flexibility of the top layer of water. d. the evaporation of water from the surface. 4. What happens to water molecules when they freeze? a. Molecules get closer together and the water shrinks when it becomes ice. b. Molecules move further apart, and the water expands when it becomes ice. c. Molecules slow down but water neither shrinks nor expands when it becomes ice. d. Molecules spread out but then get closer together at the end. 5. Which sentence is the best summary of the entire passage about water? a. Water is found everywhere. b. Water has many unique characteristics which help it cling to itself, be a good dissolver, and keep organisms alive. c. Water is a great dissolver. d. Water helps keep things alive in the winter. 6. Which detail in the story supports the idea that water is essential to living things? a. The kangaroo rat makes its own metabolic water and seals off its home to keep from losing water. b. Creosote bushes release a nasty chemical to keep other plants from sprouting around them. c. Plants use the characteristics of water to help them move nutrients to their stems and roots. d. All of the above.

4 7. Water molecules tend to cling together. What is it about water molecules that makes them do this? Water molecules have a slight positive charge at one end (near the hydrogen atoms) and a slight negative charge at the other end (near the oxygen atom). The positive area on one water molecule is attracted to the negative area of another water molecule. This causes water molecules to be attracted to each other and cling together. 8. How is frozen water (ice) different from most other liquids when they freeze? Instead of moving closer together like most liquids, the molecules of water move further apart when they freeze. The water molecules in ice take up more space than they do when they are liquid water. Since ice takes up more space than the same amount of liquid water, it is less dense than water and floats. 9. What are two ways that water is important in keeping people alive and healthy? Students should mention any two of the following: Water helps dissolve food in the digestive tract. Water transports nutrients through the blood to the cells of the body. Water regulates the concentration of substances in the cells. Water is involved in many chemical reactions in our bodies. Water helps keep the body s temperature within a normal range. 10. Describe one strategy an animal uses and one strategy a plant uses to survive where there is very little water. Students should mention one item from each category: Animals: The specialized kidneys of a kangaroo rat help it conserve more water than any other mammal. The kangaroo rat seals the entrance to its burrow during the hot days keeping cooler moister air inside. The kangaroo rat doesn t sweat. The kangaroo rat s fur is covered in oil which prevents moisture loss. Plants: Creosote bushes release a chemical that keeps other plants from sprouting around them. Some plants use chemicals on their seed coats that only wash away when there is enough water for the plant to grow. Cacti are able to quickly absorb water because they have lots of roots near the surface. Cacti store water in waxy thick stems. Cacti have prickly spines that don t lose as much water as leaves do.

5 What s going on here? 1. Why does water bead up on wax paper? Water molecules are much more attracted to each other than they are to wax paper. Since the water molecules at the surface of a drop are pulled down and in by the water molecules beneath them, water tends to bead up on wax paper. 2. Why doesn t detergent solution bead up on wax paper the way that water does? Detergent molecules have parts that are attracted to water and parts that are not attracted to water. The parts that are not attracted to water interfere with the water molecules at the surface of the drop, keeping the solution from beading up. 3. What are some of the factors that affect the rate a liquid evaporates from a surface? The molecules of a liquid are attracted to each other. When a liquid is absorbed into a paper, the molecules of the liquid are also attracted to the molecules in the paper. When they evaporate, the molecules of a liquid gain enough energy to break away from the molecules they are attracted to and move into the air.