Leschild Outline for Teachers

View the video listed below to see what you and your students will carry out in this lesboy.

You are watching: Why does adding a salt solution cause soap to precipitate


Lesboy Plan (PDF)|Student Activity Sheet (PDF)|Student Reading (PDF)|Teacher Background (PDF)|Connections to NGSS (PDF)


Students will certainly be able to describe that mixing substances deserve to reason a chemical reaction that results in the development of a brand-new substance. Students will certainly be able to plan and also carry out an investigation to compare the amount of bubbles created by a solid “soap scum” precipitate via the bubbles developed from soap. Students will certainly likewise be able to explain that different substances react in a characteristic way that deserve to be offered to recognize a substance.

Key Concepts

Mixing substances have the right to cause a chemical reaction that produces brand-new substances.Two liquids deserve to chemically react to produce a solid.Substances have characteristic chemical reactions that have the right to be provided to determine a substance.Designing a fair test to research chemical reactions requires maintaining every little thing the same other than for the one thing you desire to recognize about.

NGSS Alignment

NGSS 5-PS1-3:
Make observations and also measurements to determine products based on their properties.NGSS 5-PS1-4:Conduct an examination to recognize whether the mixing of two or more substances outcomes in brand-new substances.


Students prepare a soap solution by disaddressing Ivory soap in water.Students additionally make an Epsom salt solution to simulate difficult water.Students combine the soap solution via the Epsom salt solution to produce a solid “soap scum” precipitate.Students then bring out a bubble test on the solid soap scum and also Ivory soap to recognize if they are different.

The two major ideas for students to understand from this task are that mixing substances deserve to bring about the formation of a brand-new substance, and also that the way various substances react is a characteristic building that have the right to be provided to recognize a substance.


Downpack the student activity sheet (PDF)and also distribute one per student when specified in the activity. The activity sheet will certainly serve as the Evaluate component of the 5-E lesboy plan.


Make certain you and also your students wear appropriately fitting safety goggles. Do not handle solid sodium carbonate via bare hands. Sodium carbonate might cause skin and also serious eye irritation. Sodium carbonate, likewise called soda ash or washing soda, is easily accessible at many hardware stores and also may additionally be purchased from various chemical providers, such as Carolina Biological Supply Company type of or Flinn Scientific. Follow all safety and security prewarns regarding the usage, storage, and also disposal of sodium carbonate.

Clean-up and also Disposal

Remind students to wash their hands after completing the task. All widespread family members or classroom materials have the right to be saved or disposed of in the usual manner.


Materials for the demonstration2 clear plastic cupsSodium carbonateMagnesium sulfate (Epsom salt)WaterGraduated cylinderTeaspoonKnife (to cut soap)Materials required for each groupWaterEpsom salt1 piece of Ivory soapPaper towel2 Popsicle sticks2 Empty 8-oz disposable water bottles through lids4 Clear plastic cups1 Small cup1 Tablespoon1 TeaspoonNotes about the materials

One or 2 bars of soap is sufficient for an entire class to do this activity.

Teacher Preparation

Label 1 little cup Epsom salt for each group.Place 2 teaspoons of Epsom salt in its labeled cup.Cut one or two bars of Ivory soap so that each group gets around 1/4 of a bar.

Remind students that they have actually watched that mixing particular substances have the right to result in a chemical reaction that produces a new substance. So much, students have actually oboffered a gas produced as soon as certain solids and liquids are mixed. Tell students that occasionally once 2 liquids are blended, a solid develops. This solid is a brand-new substance, and also it’s dubbed a precipitate. Explain that when substances are combined and also a brand-new substance is developed, a chemical reactivity has actually arisen.

Demonstprice the production of a precipitate making use of magnesium sulfate (Epsom salt) and also sodium carbonate. These very same reactants will be provided in Lesboy 4.1 to research the conservation of mass.

Materials for the demonstration2 Clear plastic cupsSodium carbonateMagnesium sulfate (Epsom salt)WaterGraduated cylinderTeaspoonPopsicle sticks for stirring

SAFETY NOTES: Sodium carbonate might cause skin and severe eye irritation. Avoid call of the solid with eyes and also skin. Follow all safety and security preadvises concerning the use, storage, and also disposal of sodium carbonate.


Procedure In a clear plastic cup add 50 mL of water and also 1 teaspoon of Epsom salt. Swirl or stir till the Epsom salt dissolves.To an additional cup, include 50 mL of water and also 1 teaspoon of sodium carbonate. Swirl or stir until the sodium carbonate dissolves.Hold the cups up so the students deserve to watch them. Slowly add the sodium carbonate solution to the Epsom salt solution.Expected results: 

White solid particles will form and also deposit as a precipitate. 

Tell students that a chemical reaction took location and that a solid was created. When a solid creates from two options in this means, the solid is called a precipitate. A characteristic home of these options is that they form a precipitate when combined. Tell students they will certainly likewise make a precipitate called soap scum by mixing a soap solution through an Epsom salt solution.

Give each student an Activity Sheet (PDF). Students will record their observations and answer inquiries about the activity on the task sheet. 


Inquiry to investigate:What happens when soap is combined via “hard” water?

Have students integrate a soap solution via an Epsom salt solution to create a soap scum precipitate.

See more: Which Of The Following Characteristics Applies To Process Costing

Materials needed for each groupWaterEpsom saltPiece of Ivory soapPaper towels2 Popsicle sticks2 Empty disposable water bottles (8-oz) through caps4 Clear plastic cups1 Small cup1 Tablespoon1 TeaspoonSink or plastic bucket with water (to wash out and also reuse the cups)

Explain that “soap scum” is a widespread instance of a precipitate that develops once particular minerals in water react through soap molecules. Tell students that they are going to make “hard water” and see exactly how it reacts via soap. Explain that hard water is water that includes dissolved minerals, such as calcium, iron, and also magnesium. Tell students that they will certainly add soap to difficult water to develop soap scum. Then they will compare the bubbling capability of soap and also soap scum to discover out whether soap scum is a new substance or the very same as soap.