Observe liquid water freezing and ice melting

Learning goal (for the adult): Recognize liquid water and solid ice as forms of water and describe changes caused by warming or cooling. This lesson focuses on freezing and melting. Water vapor and the full water cycle belong to later instruction, so they are not needed to explain the observations here.

Look at an adult-provided ice cube and a small amount of liquid water in separate safe containers. The ice keeps a shape of its own while it remains solid. Liquid water can flow and takes the shape of the part of a container it occupies. Changing the container changes the liquid's shape without turning the water into a different material.

An ice cube left in a sufficiently warm place begins to melt. Its edges may become rounded and liquid water collects around it. During part of the change, solid ice and liquid water are present together. Do not label that mixed stage “all liquid” while a visible piece of ice remains. When the last solid piece has melted, the sample is liquid water.

The diagram shows three observations of the same sample at different times: ice, some ice with liquid water, and liquid water. It does not represent three independent samples or three different substances. Its shapes are simplified and are not measurements of the sample's volume. The arrows represent the observation order during melting; they do not say the change happens instantly.

Cooling liquid water sufficiently can make it freeze into solid ice. An adult can place water in a suitable freezer-safe container, record its starting condition, and show the later frozen result. Do not use a sealed glass container. A classroom freezer demonstration takes time, and an adult handles cold equipment and chooses the container. Compare the frozen sample with the starting liquid rather than inventing intermediate observations while the door was closed.

Melting involves energy entering the ice from warmer surroundings; freezing involves energy leaving the water to colder surroundings. First graders can describe this as warming and cooling while retaining the connection to energy. Merely moving a cup into another room does not guarantee freezing or melting: the conditions must be suitable. Ice does not turn into a new substance when it melts, and cold water is not necessarily solid.

Water on Earth is found in many places, not only in classroom cups. Liquid water is in puddles, ponds, lakes, streams, rivers, wetlands and the ocean, and it falls from the sky as rain. Solid water falls as snow, sleet or hail, and it forms as ice on puddles and ponds. On a cold winter day, cold air can cool the water in a puddle or pond until ice forms on its top; when warmer days return, that ice and the snow on the ground melt back into liquid water. The classroom ice cube shows the same two changes, freezing and melting, on a small scale. Look at outdoor water and ice only from a safe place with an adult: never walk on ice or go near deep or fast water.

Read aloud to the children: Ice is water. It is solid water. Solid ice keeps its own shape. Liquid water flows. It takes the shape of its cup. When ice gets warm, it melts. It turns into liquid water. When liquid water gets very cold, it freezes. It turns into ice. Outside, water is in puddles, ponds, lakes, rivers and the ocean. Rain is liquid water. Snow is solid water. Look at ice from a safe place. Never walk on ice.

Worked example 1: Name the mixed stage. A cube sits in a shallow puddle inside a bowl. The cube is solid water and the puddle is liquid water. Both forms are present. The observation supports “some ice has melted,” not “all the ice is gone.” Point to each form as you explain.

Worked example 2: Change the container. An adult pours liquid water from a round cup into a rectangular container. The liquid's shape changes, but it remains liquid water. That is different from freezing, where water changes from liquid to solid.

Worked example 3: Reverse the change. Water made by melting an ice cube is put in a freezer-safe tray. Later it has frozen. The sequence is solid ice to liquid water to solid ice. The final piece may have a different shape because the tray gives the freezing water a different boundary.

Guided investigation: Observe one ice sample in a clear, shallow container at several recorded times. Draw what is actually visible, naming solid and liquid where present. Keep the same sample label throughout. Ask whether the drawing shows a stage or a new sample. Compare with an adult's before-and-after freezing demonstration.

Independent tasks: Describe one property that distinguishes solid ice from liquid water, explain the mixed middle stage, and put melting and freezing observations in order. Explain whether pouring liquid into a differently shaped container counts as freezing. Use drawings and oral explanations if writing would hide the learner's scientific understanding.

Feedback: If the child says the ice disappeared without becoming anything, trace the water collecting around it. If they say all cold water is ice, compare a cold liquid sample with a solid cube. Do not infer that water has vanished when an observation record is incomplete. Assess the change supported by the actual sample.