Precipitation Reactions Activity
(Replaces Activities of Metals Lab)
SC.A.1.4.2 The student knows that the vast diversity of the properties of materials is primarily due to variations in the forces that hold molecules together. SC.A.1.4.5 The student knows that connections (bonds) form between substances when outer-shell electrons are either transferred or shared between their atoms, changing the properties of substances.
Purpose of Lab/Activity:
* To introduce students to precipitation reactions, a type of double displacement reactions * To practice nomenclature of ionic compounds and formula writing * To create a particle level model to explain precipitation reactions * To identify the parts of a chemical equation and the state subscripts
Prerequisite: Students should already be familiar with ionic compounds and electrolytes. They should have a clear model of how a solid dissolves in a solvent to produce an aqueous solution. They should also be aware of basic nomenclature of ionic compounds including polyatomic ions.
0.1M solutions of the following in Beral pipettes or bottles with droppers *
* Glass spot plate or well plate
Procedures: Day of Activity
| What the teacher will do: a. Prepare all solutions. Bottles with droppers work well and can be used for many groups and years to follow. Upside down beral pipettes work well too. Label the bottles or pipettes with the formula of the compound only to make students practice nomenclature. b. Ask students how soluble solids dissolve when placed in a solvent such as water. Review the particle level model that explains this situation. Stress that water molecules separate the ions in the solid until they become invisible. There is a force that allows the water molecules to overcome the attraction between the ions in the solid. c. Show students the containers of the solids that you used to make the solutions. The nickel chloride and potassium chromate are both colorful enough for them to see what the chemical looks like in the solid state and then show them the solutions they will be using. d. Explain students the procedure and stress that they don’t use more than two drops of reactant. Some of these chemicals such as the chromates and lead salts are toxic and harmful for the environment. So to reduce waste the amounts must be small. e. Warn students not to mix anything other than what is described in the activity. f. This activity works best when students work in pairs. g. Groups can work in any order they prefer. If all groups work in order they will all need the same bottles at the same time. Working out of order will minimize this delay. Another solution is to make enough solutions for every group.
| During activity:
| What the teacher will do: a. Students will be very surprised to see what happens when they start combining the solutions. Some precipitates are white and others are black or colored. Therefore, student should have a white piece of paper under the glass spot plate and a dark surface to see the colors well. b. Students may not realize that the color change occurs because a solid is forming. You may need to point out that at the bottom they can see some flecks of solid collecting as the mixture settles. c. Ask the students what they think it is happening or where the solid is coming from. d. Watch students write some of the formulas for the products and reactants. Correct mistakes in nomenclature as you observe them e. Follow appropriate disposal procedure for the chemicals used in this experiment.
| After activity:
| What the teacher will do: a. Bring the students together for class discussion. b. Ask students to explain what they think is happening at the particle level that makes a solid form out of...
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