Salty-Sweet Density Treat Teacher Instructions

Transcription

1 Salty-Sweet Density Treat Teacher Instructions Lauren Harris Teaching Objectives: Students will take measurements and record observations Students will understand the concept of density and states of matter Recommended Grade Level: Adaptable for K-8 (optimal with 3-7) Estimated Prep Time: 20 minutes Estimated Activity Run Time: 45 minutes Key concepts and definitions of terms: Mass: The amount of matter in an object Volume: How much space an object occupies Density: The measure of mass contained in a given unit of volume, or a measure of how tightly the stuff that there is in an object is packed together Materials: Warm water Salt Sugar 3 clear plastic cups per group 1 tall narrow clear plastic cup per group Red food coloring Blue food coloring Green food coloring Droppers (3 per group) Ice cubes Tablespoon measure (or a plastic spoon if tablespoon is not available) Stirrers 3 small plastic containers with lids (need to all be the same size) Beads (rice or marbles would also work) Funnel Preparation: Fill one small plastic container as much as you can with beads and label it high density. Fill another container halfway with beads and label medium density. Fill the last container about 1/8 of the way and label it low density Prepare the sets of 3 plastic cups for each group by labeling them salt red, sugar blue, pure green Fill all 3 cups with equal amounts of warm water. Warm from the faucet is sufficient, you don t need to heat it further. 1

2 Procedure: 1. Define density and use the small containers filled with beads to demonstrate density. Explain that the stuff inside the containers represents molecules. Pass around the low density container and explain that because there is a lot of space for the molecules to move around because they are not packed in tightly. 2. Divide class into groups of 3. Each student will either be a red and blue or a green and they should follow the instructions according to this. Each group should have 3 clear plastic cups, each labeled and filled with water. 3. Within each group assign one student to salt water, one student to sugar water, and one student to pure water. 4. Have the students measure 1 tablespoon of salt into the cup labeled salt red, 1 tablespoon of sugar into the cup labeled sugar blue and don t add anything to the cup labeled pure green. 5. Stir the solution until the salt and sugar have dissolved. Record any observations 6. Next have the students assigned to salt water add 2 drops of red food coloring to their salt water solution. Have everyone record and draw what happened. Repeat with 2 drops of blue food coloring to the sugar water and 2 drops of green food coloring to the pure water. 7. Based on the observations from adding food coloring can anyone make a prediction about which will liquid will have the highest density? The food dye in salt water will make swirls suspended in the water before very slowly spreading the color throughout the cup. The molecules have less freedom to move around so this should have the highest density. The food dye in the pure water will disperse evenly throughout the water almost immediately because the molecules are farther apart. The dye in the sugar water will disperse at a rate between the salt water and the pure water. The students should predict that the slower mixing of color indicates higher density. 8. Have the student assigned to salt water pour about ¼ of it into the tall, narrow cup 9. Use the dropper to SLOWLY!!!!! drop the blue sugar water in next. Have them do 10 droppers full of the water, down the side of the tall cup. Repeat with the green pure water again, SLOWLY!!!!! 10. The salt water should be on the bottom, the sugar water in the middle, and the pure water on top, clearly showing the differing densities. 11. Ask the students what they think will happen if they put an ice cube in the column? 12. Place an ice cube and observe that it floats, discuss the environmental implications of this, that ice floats on top of a frozen lake, allowing animals to live underneath. 2

3 This is what the column should look like: Clean-up: All cups should be washed out to re use, colored water can be poured in the sink. Why it works: Density is a measure that is established by comparing its mass to its volume. This is because of the atomic structure the more tightly molecules are packed together in an object the higher density it will have. Liquids that look the same can still have differing densities. When salt and sugar are dissolved in water it makes the water become more dense because there are more molecules. Supplemental activities: Try using varying amounts of sugar (2 tablespoons, 4 tablespoons, 6 tablespoons, etc) and color them with different colors. Make predictions about the densities (most concentrated with sugar should be the most dense) and add using the same procedure as described in this activity to see which actually has the highest density. References: Liquid Density Experiments, accessed January 9, Water Density Experiment, accessed January 9,

4 Handout: Name: Date: The great scientist, Doctor Smart E. Pahntz, has challenged you to have a container of salt water, sugar water, and pure water in which none of the three solutions mix together. You, being an up-and-coming scientist, know that you are up to the test. Using your knowledge of density you will be able to complete this seemingly impossible task! Instructions: 1. Red s: measure 1 tablespoon of salt and put it into the cup of water labeled Red - Salt water 2. Blue s: measure 1 tablespoon of sugar and put it into the cup of water labeled Blue Sugar water 3. Red s, Blue s and Green s: take turns stirring the salt and sugar into the water until most of the grains have dissolved 4. Green s: drop 2 drops of green food coloring into the cup labeled Green pure water 5. What do you see in the green cup? Draw it here: 4

5 Describe what happened: (how fast did the color mix in, did it sink?): 6. Blue s drop 2 drops of food coloring into the cup labeled Blue sugar water 7. What do you see? a. Draw it here: b. Describe it here: 5

6 8. Red s drop 2 drops of food coloring into the cup labeled Red salt water 9. What do you see? a. Draw it here: b. Describe it here: 6

7 Look back at your descriptions of all 3 colors mixing in: Which color water do you predict will have the highest density? Lauren Harris Which color water do you predict will have the lowest density? 10. Now create the column according to your instructor s description. Remember to go SLOWLY or it won t work!!! 11. Draw what happened: 7

8 12. Was your prediction correct? If not, what are your results? 13. Why do you think the different colors are layered in this order? 14. What do you predict will happen if we put in an ice cube? 15. What happened when we put in an ice cube? 8

9 16. Draw it here: 9