Freezing Point Through various experiments, students will investigate the properties of water and find out what changes it from one state to another Grade Level: 4th Grade Next Generation Science Excellence in Environmental Standards Education Guidelines Phenomena: 4-ESS3-2. Generate and compare Strand 2.1— the Earth as a How does water’s chemical multiple solutions to reduce the Physical System. structure change from a liquid impacts of natural Earth processes to solid? on humans. B) Changes in matter— Learners are able to identify Science and Engineering basic characteristics of and Objectives: Practices (SEP): changes in matter. Describe Students will state the Asking questions and defining objects in terms of the materials temperature at which problems. they are made of and their water freezes in both Analyzing and interpreting data. observable properties. Identify the effects of factors such as Fahrenheit and Celsius Disciplinary Core Ideas: heating, cooling, and moisture Students will explain why 4-LS1 From Molecules to on the properties of materials ice is less dense than Organisms: Structures and and how quickly change water Processes happens. For example, describe Students will evaluate the change of water from solid to Cross Cutting Concepts: liquid to gas in the environment. environmental Energy and matter. implications related to the Stability and change. density of ice. Materials: Ice 4-5 pieces per student Frozen bottle or jug of water Background state. Water is unique because Clear plastic cups it can be observed as a solid, Activity sheet (page 7) Ice plays an important role in liquid, and gas within a our everyday lives, especially relatively small temperature Time Considerations: during the long winter months range. (0-100 °C) Preparations: 20-25 min in northern Nevada. We use it Activity 1: 5-7 min When water cools to 0⁰C Activity 2: 5-7 min in our drinks, it forms on (32⁰F) It begins to solidify. Activity 3: 10 min sidewalks, allows us to skate Activity 4: 15 min on lakes and can ruin our fruit. This process is called freezing, Activity 5: 10 min Understanding the properties so the temperature at which Activity 6: 10 min of ice allows us to better something changes from a understand how it can affect liquid to a solid is called the Related Activities: our daily lives. freezing point. When ice Let it Snow! Let it Melt! warms up to 0⁰C and begins to Like all substances, water can melt that temperature is called exist as a solid, liquid, or gas. the melting point. Ice is the solid form of water while the term water vapor is When many substances freeze used to describe its gaseous the molecules pack together, 1 reducing the amount of empty A simple visual representation of taken up by a set number of space and making the solid this can be done using your molecules. Density can be form more dense than the liquid calculated using density =mass form. However, the shape of ÷ volume (or stuff ÷ space). water molecules causes ice When water freezes it takes up crystals to have more empty more space but no ‘stuff’ is space than liquid water. added. This causes ice to have a lower density than liquid water Water molecules consist of two so ice floats. hydrogen atoms bonded to a This reduced density has a profound effect on the environment. As water in lakes The structure of an ice crystal has more open space than a salt crystal. and ponds freeze, it floats to the surface and creates a layer of fingers. Hold your thumb and ice that insulates the rest of the forefinger into an ‘L’ shape, pond. This prevents the pond roughly modeling the water from freezing solid and allows molecule and the angle. The tip fish to swim around underneath. of your thumb and finger are the Freezing the water contained in hydrogen atoms while the skin fruit can have drastic between them represents the consequences. Plant cells are Atoms in a salt crystal are closely packed oxygen. filled with liquid, but have a fixed single oxygen atom. Due to In liquid water, the molecules volume. When the water in cells electronic forces, the molecule are free to slide past each other. freezes it expands and breaks is bent at an angle of 104.5⁰. It To model this, place the web open the cells destroying the is this angle which allows for the between your thumb and fruit. To prevent this from expansion of ice. When water forefinger nearly together and happening, farmers will spray exists in the liquid form, the twist or slide your hands. In their fruit with water in an molecules are free to move water, the molecules move extreme cold so the outside around and bump together. close together like this, yet do freezes. This creates an When the freezing point of a not actually join together. This insulation so the temperature of substance is reached, is due to the hydrogen bonds the fruit will not fall below 32 molecules begin to form bonds constantly being created and degrees, even if the outside with each other creating solid destroyed. temperature keeps decreasing. crystals. In water, a hydrogen Since more than half of the bond forms between the To model ice, connect your thumb or forefinger to the web of human body is water, our cells hydrogen of one molecule and can be damaged by the cold the oxygen of another. Since the your other hand. With your hands connected this way, they too. When human cells are molecules are bent, the forming damaged by freezing it is called of these bonds creates open take up much more space just like the molecules in ice. frostbite and severe cases might space in the crystal causing the require amputation to prevent water to expand as molecules Since water expands when it infection. become fixed in place. freezes, the density is affected. Density is the amount of space Ice also is a huge factor in weathering and the deterioration 2 of roads. When snowmelt or Where do we find ice in the Ask the students to hold up their runoff freezes on a roadway or world? (glaciers, icecaps, arctic, thumb and forefinger in an ‘L’ in a rock, the water that is Antarctica, your freezer, etc) shape. The tips of their thumb trapped in the cracks will and finger represent the expand, causing more cracking What is the process by which hydrogen and the web of skin to occur. This process is called water turns into a solid? between them represents the ice wedging. (freezing) oxygen. The angle is about the same as a water molecule. Prior to the lesson, freeze a At what temperature does this sealed plastic bottle or milk jug occur? (32⁰ For 0⁰ C) Demonstrate how the water filled with water. This temperature is called the molecules are arranged by freezing point, because it is interlocking your two Preparation the point at which liquid water ‘molecules’. turns into solid ice. In any liquid, the molecules Gather all lesson materials. Activity 2: What is Water? move freely and bump into each other. (move your “molecules”) Introduction: Before we can take a closer look at what happens when water At the freezing point, the Begin the lesson by holding up a molecules slow down and bind jug of water that has been freezes, we must understand water a bit more. together. In water, each frozen solid. Ask the students hydrogen bonds with an oxygen. what they notice about the jug. Ask the class what water is. (stick one thumb to the web of (the sides are bulging or broken) (Water molecules, H2O, your other hand) hydrogen and oxygen) Doing the Activity Show the difference between ice Ask the students why they think Write H2O on the board and ask and water a few times with your the sides of the jug are bulging. hands, having the students (Do not give answer, allow follow along. But don’t mention students just to brainstorm that the ice has expanded. ideas). Explain that today we are going to learn about some Activity 3: What is Ice? unique properties of ice that (NOTE: This activity builds off of explain what happened to the the December mineral/crystal jug. lesson for fourth grade). Activity 1: Ice brainstorm Ask the students how many of Ask students to list some things what it means. What does the them think ice is a mineral. they already know about ice. ‘H’ stand for? The ‘O’? What about the ‘2’? (2 hydrogen Ask the students what all The following questions may be minerals have in common and used to help guide discussion: atoms and one oxygen atom) These are the parts of every write these characteristics on What is ice? (the solid form of water molecule. the board: water) Draw the molecule on the board, Non-living (inorganic) What are the other forms water making sure you mark the Naturally occurring can take? (Liquid water, solid angle. ice, gaseous water vapor) 3 Definite crystalline when we place them in water? Tell the students that the structure Why does ice float? temperature is dropping to the freezing point and have them Definite chemical Activity 5: Why Ice Floats or bond by placing one hand gently composition Density on a classmate’s head without With the students, compare Ask the students why the ice is moving their arms. each property to the properties floating. ( it is NOT lighter, it is Ask students to look at the of ice. (ice has all four less dense than the water) amount of space their “ice” properties) Ask the students to hold up their takes up.