5 E Lesson Plan Title: Precipitates: A Clue to Chemical Reactions Grade Level and Course: 8 th Grade Physical Science Materials: Epsom salt solution

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1 5 E Lesson Plan Title: Precipitates: A Clue to Chemical Reactions Grade Level and Course: 8 th Grade Physical Science Materials: Epsom salt solution Household ammonia Water 50 ml beaker Spoon to stir Balance Eye protection 25 ml graduated cylinder Teacher prep-prepare Epsom salt solution by dissolving 15 g Epsom salt per 100 ml distilled H2O Instructional Resources Used: Video clips: Think-pair-share o Divide students into predetermined groups. Show one of the videos above, then ask students to discuss their observations of the video in their groups. Students will then participate in an all class discussion about those observations. California State Standards: 8 th Grade Physical Science: 5. Chemical reactions are processes in which atoms are rearranged into different combinations of molecules. As a basis for understanding this concept: o a: Students know reactant atoms and molecules interact to form products with different chemical properties. o b. Students know the idea of atoms explains the conservation of matter: In chemical reactions the number of atoms stays the same no matter how they are arranged, so their total mass stays the same. 9. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will: o a. Plan and conduct a scientific investigation to test a hypothesis. o b. Evaluate the accuracy and reproducibility of data Lesson Objectives: Students will be able to explain that for a chemical reaction to take place, the reactants interact, bonds between certain atoms in the reactants are broken, the

2 atoms rearrange, and new bonds between the atoms are formed to make the products. Students will also be able to explain that this definition applies to the production of a solid called a precipitate. Differentiation Strategies to meet the needs of diverse learners: English Learners: In mixed ability groupings, students will be ask to define the terms reactant, product, solution, ions and precipitate prior to this lesson. After defining the terms have the students identify where they are in the reaction: AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq). Special Education: Have students watch you tube video which shows multiple precipitation reactions. o As the reactions are performed, write the equations on the board, reinforcing the terms reactant, product, precipitate and solution. o Place students into pre-arranged in lab groups that have been designed to maximize student time on task and understanding. GATE: While performing the lab, students will record masses of all reactants and products to prove conservation of mass in a precipitate reaction. ENGAGE Describe how the teacher will capture the students interest. What kind of questions should the students ask themselves after the engagement? Demonstration: Prior to class, prepare the following: o 25 ml NaOH mixed with 25 ml CuCl2. o Ask students: What has happened, especially at the level of the atoms? (Ions of the particles present have formed new bonds creating a substance with different properties, i.e., cannot dissolve.) If we were to weigh the reactants and the products, what would we find? (The masses would be the same.) Why it is important to understand precipitate reactions? o Show Ammonia Deposition in Rocky Mountain National Park : EXPLORE Describe the hands-on laboratory activity that the students will be doing. List the big idea conceptual questions that the teacher will ask to focus the student exploration. a. Students will have prepared a lab write-up prior to class. Students will draw the procedure, labeling all material in the lab write up. Drawing the lab will assist the English Language Learner and Special Ed student by having them understand the materials being used (terminology) as well as making sure that the lab procedure is understood. Copying the procedure may or may not mean the student understands the procedure. b. Students will then follow the procedure, creating the precipitate and then filtering it.

3 c. Students will record both volume and mass of the two solutions they will use. Big Idea Conceptual Questions: a. What relationship is found between the mass of the reactant solutions and the product solutions and solid product? (They are the same even thought a solid was produced.) b. How do you know that a reaction has occurred? (The formation of a precipitate solid is one clue that a chemical reaction has occurred.) EXPLAIN What is the big idea concept that students should have internalized from doing the exploration? List the higher order questions that the teacher will ask to solicit student explanations for their laboratory outcomes, and justify their explanations. Big Idea Concept: Solutions are homogenous mixtures of ions, both positive and negative. When two solutions are mixed, it is possible that the ions from one solution will form bonds with the ions from the other solution. This is a precipitation reaction. While some ions don t bond, others will. This is called being insoluble or insoluble. Higher Order Questions: What does the presence of a precipitate indicate? Why is this important? What forces are involved in this type of reaction? How can we use this knowledge in the treatment or non-treatment of waste? EXTEND Explain how students will develop a more sophisticated understanding of the concept. How is this knowledge applied in our daily lives? a. Groups of two will research precipitate reactions in nature, either natural or manmade, and present a PowerPoint presentation on their findings. (Pouring certain chemicals down drains or in gutters could produce solids that are toxic to the environment. This theme can extend to air pollution as a result of gas mixtures interacting to form precipitates. An example is smog.) b. Additionally, for GATE students: 1. Using the knowledge gained in this lab and using the following solubility rules chart, lists three solution combinations that will create a precipitate and three that won t. (This is not an 8th grade standard. However, higher level students should be challenged with this concept using the appropriate information.) All compounds containing alkali metal cations and the NH4 + ion are soluble. All compounds containing NO3 -, ClO4 -, ClO3 -, and C2H3O2 - anions are soluble. All chlorides, bromides, and iodides are soluble except those

4 containing Ag +, Pb 2+, or Hg2 2+. All sulfates are soluble except those containing Hg2 2+, Pb 2+, Sr 2+, Ca 2+, or Ba 2+. All hydroxides are insoluble except compounds of the alkali metals, Ca 2+, Sr 2+, and Ba 2+. EVALUATE How will the student demonstrate their new understanding and/or skill? What is the learning product for the lesson? Along with answering the questions attached to the lab, students will answer the following questions to show understanding of the key concepts in the lab. When chemical relations occur, atoms rearrange to produce new substances with different chemical properties. In all chemical reactions, mass is conserved. 1. What are the reactants in this reaction? 2. Is it possible to have a product that does not contain the atoms that are present as reactants? Why or why not? 3. If bubbles are created in the reaction, will the mass of the products equal the mass of the reactants? Why or why not? Background Knowledge for the Teacher: Some chemical compounds will dissolve in water, and some will not. If the molecule is made up of insoluble ion combinations then the substance will not dissolve in water. It is said to be insoluble. If the molecule is made up of soluble ion combinations, it will dissolve in water and is said to soluble. Two solutions of soluble molecules can be added to each other and the introduction of ions that are not soluble with each other will create a precipitate. This precipitate will be a molecule that is insoluble. For example, AgNO3 and NaCl are both soluble molecules, each one dissolving to produce their appropriate ions. In this case, AgNO3 dissolves into Ag + and NO 3 - ions and NaCl dissolves into Na + and Cl - ions. When these two clear solutions are mixed together and since Ag+ and Cl - are not soluble, a yellow precipitate of AgCl will form. As always, there are limits and exceptions but these are not addressed until high school chemistry. D. Ryan Costa Mesa High School, Costa Mesa, CA Student pages are attached.

5 Reacting Two Compounds to Form a Precipitate INTRODUCTION: In this lab, you will react solutions Epsom salt with ammonia. These are both compounds that dissolve in water. Household ammonia contains ammonium hydroxide, and the chemical name for Epsom salt is magnesium sulfate. Mixing ammonia and Epsom salt causes a reaction that produces magnesium hydroxide as one of the products. Magnesium hydroxide is a white substance that does not dissolve well in water. After standing awhile, the white precipitate will settle to the bottom of the jar. Objective: Observe the formation of a precipitate, and explain that the presence of that precipitate indicates that a chemical reaction has occurred. Materials: Materials: Epsom salt solution Household ammonia Water 50 ml beaker Spoon to stir Balance Eye protection 25 ml graduated cylinder Procedure: 1. Find the mass of a 50 ml beaker and a 25 ml graduated cylinder and record them in your data table. 2. Using the 25 ml graduated cylinder, measure out 10 ml of Epsom salt solution, weigh it and pour it into the 50 ml beaker. Rinse out the graduated cylinder. 3. Using the 25 ml graduated cylinder, measure out 20 ml of ammonia and weigh it. 4. Add the ammonia to the beaker. 5. Record what you observe for 5 minutes. 6. Weigh the beaker.

6 Data Table: Mass of 50 ml beaker (g) Mass of 25 ml graduated cylinder Mass of cylinder and Epsom salt solution Mass of cylinder and ammonia solution Mass of 50 ml beaker after reaction Analysis: 1. What is the mass of the Epsom salt solution? Show your calculations. (Mass of cylinder and Epsom salt solution mass of cylinder = mass of Epsom salt solution) 2. What is the mass of the ammonia solution? Show your calculations. (Mass of cylinder and ammonia solution mass of cylinder = mass of ammonia solution) 3. What is the mass of your products? Show your calculations. (Mass of 50 ml beaker and products mass of beaker = mass of products) 4. Did a reaction occur? What evidence do you have? 5. Was mass conserved? Why or why not? 6. Is possible to find the mass of the solid precipitate only? Propose a way. Taken from