This short lesson is intended to be used as part of a unit on water or properties of matter, or simply as a fun and motivating lesson.

Transcription

1 Amazing Ice Cubes Floating and Sinking Brief description This short lesson is intended to be used as part of a unit on water or properties of matter, or simply as a fun and motivating lesson. Unlike nearly all other substances, water expands when it freezes, and shrinks when it melts. Students discover this unusual property by observing the mesmerising process of an ice cube melting in cooking oil. Simultaneously, a surprising teacher demonstration prepared at the beginning of the lesson is monitored and discussed at the end of the lesson. Duration: Year Level: Topics: Preparation: 30 to 60 minutes Middle to upper primary Water / Floating & sinking / Density / Buoyancy / Solids, liquids & gases 15 minutes (depending on availability of materials) Overview Whole class Introduce lesson and discuss procedure (10 min) Discuss and set up the Melting Ice Cubes demonstration Designate group work jobs Small groups Floating ice cubes in oil (15 25 min) Whole class Check results of teacher demonstration (5 min) Whole class Discuss activity and demonstrations (15 min) Materials and equipment Teacher Demonstration: Ice Cubes in Water Total Qty Description ice cubes 1 tall drinking glass 1 white plate or saucer water food colour Lesson 5 Amazing Ice Cubes Page 1

2 Ice Cube in Oil Activity: Total Qty Description 6 clear drinking glasses (1 per group) 12 coloured ice cubes (2 per group) 6 1 litre soft-drink bottles (1 per group) 2 litres cooking oil* (any type) (150ml per group) 1 kitchen tongs or similar water (500ml per group) 1 turkey baster / funnel (to re-bottle oil at end of lesson) * You can collect and rebottle the oil at the end of the lesson Preparation Collect and prepare materials for teacher demonstrations Collect sufficient quantities of materials for Ice Cube in Oil activity Prepare ice block, ice cubes and coloured ice cubes in school freezer Objectives Students prior knowledge Students are familiar with their group work job responsibilities. No prior knowledge is assumed for this lesson. You should decide if and how you wish to assess this lesson to decide how students record their observations and inferences. Science skills Students will: Science concepts carefully follow the instructions observe that water and oil do not mix, and oil floats on water observe that the ice cube floats in oil observe the formation of water droplets as the ice melts and that the droplets cause the ice cube to tilt down observe that the water droplets sink observe that the water droplets mix with the water in the bottom of the glass ice is less dense than water (ice floats on water) oil is less dense than water (oil floats on water) ice is less dense than oil (ice floats on oil) water expands when it freezes / water contracts when it melts Lesson 5 Amazing Ice Cubes Page 2

3 Positive attitudes Students will: Procedure work cooperatively in small groups ensuring each member has an opportunity to see the activity use water sparingly and dispose responsibly (eg pour onto school garden beds, not into sinks) collect the oil for re-bottling Introduction (Whole class / 5 10 min) Set up the teacher demonstration (see page 5) and ask the class if they think the glass will overflow as the ice melts. Ask questions such as: Q: What happens when you leave a cold drink in the open air? A: Condensation appears on the container. Q: How will we know if the glass has overflowed? A: If the water in the saucer is coloured, the glass overflowed. Q: Why do some things float while others sink? eg wood floats, rocks sink A: Things float if they are less dense than water and sink if they are more dense. Q: What is ice made of? why do you think it floats in water? A: Ice is frozen water. It floats because water expands as it freezes which makes it less dense than water. Leave the teacher demonstration in a visible spot and ask students not to touch the glass Introduce the activity by discussing student s observations of water and ice using questions such as: does oil float or sink in water? will an ice cube float or sink in oil? what else do you think you might see when we put an ice cube in oil? Instruct the class on how to conduct the activity with notes and a diagram of the glass on the whiteboard (see page 6). Hands-on activities (Small groups / min) Small group activities All group members cooperate to prepare a Work Station by grouping desks Equipment Managers collect materials required from Science Store Group Supervisors ensure group adheres to instructions and completes activities Equipment Managers clean and return equipment to the Science Store Remainder of group cleans Work Station and returns desks to normal locations Early finishers Early finishers can check progress of the teacher demonstration and/or continue with other work. Lesson 5 Amazing Ice Cubes Page 3

4 Conclusion (Whole class / min) Class discussion Lead a discussion about the activities by asking questions such as: why do you think the ice in the demonstration didn t overflow when it melted? what did you see happening in the glass? what do you think happens to water when it freezes? why did the water droplets sink while the ice cube kept floating? Plan next science lesson Ask students to collect and bring in any household items you might require for the next lesson you have planned Lesson 5 Amazing Ice Cubes Page 4

5 Teacher notes Teacher demonstration Description: A glass is filled to the brim with ice cubes and water so that ice cubes protrude above the rim of the glass. Surprisingly, no coloured water spills over onto the saucer below because the melting water contracts (becomes more dense) and fits perfectly into the glass. Instructions: 1. Set a glass on a white plate or saucer and fill with ice cubes 2. Add coloured water until the ice cubes begin to float. Add more ice cubes if possible but ensure that no ice cubes are touching the bottom of the glass. 3. Fill the glass to the brim with coloured water. If any coloured water is spilt onto the saucer, dry it with paper towel. Discussion: Water expands when it freezes because water forms a crystal structure which occupies a greater volume than the liquid state. Very few substances are less dense in the solid state as ice is (eg solid candle wax sinks in molten candle wax). If the water inside a living cell is frozen, the expansion and formation of sharp crystals can rupture the cell walls resulting in frostbite (when it occurs on a large scale). This property of water is extremely important for life in lakes which freeze over in winter however if the ice sank, it would squash and kill any life at the bottom. Lesson 5 Amazing Ice Cubes Page 5

6 Ice Cube in Oil Description: A glass is half filled with water and topped up with cooking oil. A coloured ice cube is carefully placed in the oil. The ice cube floats because it is less dense than oil. As the ice melts, drops of water collect at the bottom of the cube. The water droplet is more dense than the ice and causes the cube to tilt. Once the droplet is sufficiently large, it drops off the cube and sinks to the bottom of the oil layer. The droplet eventually penetrates the oil layer and mixes into the water. Instructions:. 1. Half fill the glass with water. Next, carefully top up with oil (hold the glass on an angle and pour slowly). 2. Carefully place the ice cube in the oil using tongs so the cube does not fall too deep 3. On completion of the activity, remove the remainder of the ice cube. Use a turkey baster to siphon of as much of the oil layer as possible (you may prefer to do this rather than leave it to the students) Lesson 5 Amazing Ice Cubes Page 6

7 Observations: 1. As the ice melts, a droplet collects at the bottom of the cube, causing it to tilt 2. Once the droplet is heavy enough, it sinks to the bottom of the oil layer several droplets may collect here before penetrating into the water layer 3. Eventually, the droplet penetrates the oil layer and mixes into the water layer Lesson 5 Amazing Ice Cubes Page 7