Diffusion is the process through which molecules, or tiny particles of a substance, move from an area of high concentration to an area of low concentration. It explains why a spoonful of sugar dissolves evenly in a cup of tea, sweetening the entire beverage. The sugar molecules spread over time and distribute themselves evenly among the water molecules. This concept provides several fascinating projects to monitor and test diffusion in liquids with students of all ages.
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Food Coloring and Water
Use food colouring and water to introduce diffusion of liquids to elementary students. Students observe what happens when a drop of food colouring is placed in a container of water. They monitor how long it takes for the food colouring to spread throughout the water and record the results. Students should note how long it takes the food colouring to spread if they do not stir the water and record the resulting colour, comparing it to the colour of the original drop of food colouring.
Sugar and Water Temperature
Introduce elementary students to the diffusion of solids into a liquid with water and sugar cubes. Students should perform a variety of experiments using sugar and water and record the results. Tests could include timing the rate of diffusion of a sugar cube in cold water versus hot water, recording how quickly the cube dissolves if the water is left alone or if it is stirred and comparing which dissolves faster: a solid sugar cube or a crushed one.
Corn Syrup and Water
One middle school project studying the diffusion of liquids uses corn syrup and water. Adding food colouring to the water helps make the diffusion more obvious. Students can test varying thicknesses of syrup in the water to see whether a thicker or thinner syrup diffuses faster. Another variation involves keeping the syrup type constant but changing the water temperature to see whether cold, room temperature or hot water diffuses the syrup faster. Alternately, students can attempt this project using different liquids with the syrup, such as vinegar or rubbing alcohol, to see which liquid allows for the fastest diffusion rate.
Lead Nitrate and Potassium Iodide
Experiment with high school students using lead nitrate and potassium iodide in water. Students should wear eye protection and use forceps when working with lead nitrate as it is toxic. For this project, students fill a dish with deionised water and then use forceps to carefully place a crystal of lead nitrate in one side of the dish and a crystal of potassium iodide in the other side of the dish. As the two solids begin to diffuse in the water, their molecules will combine to form two new compounds: lead iodide and potassium nitrate. The lead iodide will be visible as solid yellow particles that collect together in a formation similar to a miniature sandbar in the dish.
Copper Sulfate and Water
Study the rate of diffusion with high school students by diffusing copper sulphate in distilled water. The copper sulphate, when diffused in water, creates a blue colour. Students should experiment to see which produces a faster rate of diffusion: cold water, room temperature water, or water heated over a Bunsen burner. Before beginning the experiment, the teacher can demonstrate by dropping a crystal of copper sulphate into a beaker of distilled water to show the students the desired blue colour produced as the copper sulphate diffuses into the water. Students can then form a hypothesis, or educated guess, as to which temperature of distilled water will lead to the fastest rate of diffusion. While performing the experiment, students should record their observations.
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