Tell students that they will add soap to hard water to create soap scum. Explain that hard water is water that contains dissolved minerals, such as calcium, iron, and magnesium. Tell students that they are going to make “hard water” and see how it reacts with soap. Sink or plastic bucket with water (to wash out and reuse the cups)Įxplain that “soap scum” is a common example of a precipitate that forms when certain minerals in water react with soap molecules.2 Empty disposable water bottles (8-oz) with caps.Have students combine a soap solution with an Epsom salt solution to form a soap scum precipitate. Follow all safety precautions regarding the use, storage, and disposal of sodium carbonate.Įxplore Question to investigate: What happens when soap is mixed with “hard” water? Avoid contact of the solid with eyes and skin. SAFETY NOTES: Sodium carbonate may cause skin and serious eye irritation. These same reactants will be used in Lesson 4.1 to study the conservation of mass. Explain that when substances are mixed and a new substance is formed, a chemical reaction has occurred.ĭemonstrate the production of a precipitate using magnesium sulfate (Epsom salt) and sodium carbonate. This solid is a new substance, and it’s called a precipitate. Tell students that sometimes when two liquids are mixed, a solid forms. So far, students have observed a gas produced when certain solids and liquids are mixed. Remind students that they have seen that mixing certain substances can result in a chemical reaction that produces a new substance. Cut one or two bars of Ivory soap so that each group gets about 1/4 of a bar.Place 2 teaspoons of Epsom salt in its labeled cup.Label 1 small cup Epsom salt for each group.One or two bars of soap is enough for an entire class to do this activity. 2 Empty 8-oz disposable water bottles with lids.Materials Materials for the demonstration All common household or classroom materials can be saved or disposed of in the usual manner. Remind students to wash their hands after completing the activity. Follow all safety precautions regarding the use, storage, and disposal of sodium carbonate. Sodium carbonate, also called soda ash or washing soda, is available at many hardware stores and may also be purchased from various chemical suppliers, such as Carolina Biological Supply Company or Flinn Scientific. Sodium carbonate may cause skin and serious eye irritation. Do not handle solid sodium carbonate with bare hands. Make sure you and your students wear properly fitting safety goggles. The activity sheet will serve as the Evaluate component of the 5-E lesson plan. Evaluationĭownload the student activity sheet (PDF) and distribute one per student when specified in the activity. The two main ideas for students to understand from this activity are that mixing substances can result in the formation of a new substance, and that the way different substances react is a characteristic property that can be used to identify a substance. Students then carry out a bubble test on the solid soap scum and Ivory soap to determine if they are different.Students combine the soap solution with the Epsom salt solution to produce a solid “soap scum” precipitate.Students also make an Epsom salt solution to simulate hard water.Students prepare a soap solution by dissolving Ivory soap in water.NGSS 5-PS1-4: Conduct an investigation to determine whether the mixing of two or more substances results in new substances.NGSS 5-PS1-3: Make observations and measurements to identify materials based on their properties.Designing a fair test to study chemical reactions requires keeping everything the same except for the one thing you want to know about.Substances have characteristic chemical reactions that can be used to identify a substance.Two liquids can chemically react to produce a solid.Mixing substances can result in a chemical reaction that produces new substances. Students will also be able to explain that different substances react in a characteristic way that can be used to identify a substance. Students will be able to plan and carry out an investigation to compare the amount of bubbles produced by a solid “soap scum” precipitate with the bubbles produced from soap. Students will be able to explain that mixing substances can cause a chemical reaction that results in the formation of a new substance.
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