The Eight Solution Problem Exploring Reactions of Aqueous Ionic Compounds

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1 15 Exploring Reactions of Aqueous Ionic Compounds INTRODUCTION Your goal in this lab is to identify eight unknown solutions. You and your partner will first collect data by observing reactions between various known ionic compounds. You will then use this data to determine the identity of the unknowns. This type of lab requires organization, clear logical thinking, and excellent observation/data-taking skills. PURPOSE In this activity you will observe a variety of double replacement reactions, identify their solubilities and write net ionic equations for all reactions producing precipitates. You will also use your observation and data-taking skills to identify 8 unknown solutions. MATERIALS 96 well plate cotton swabs solutions of the following: Pb(NO 3 ) 2, small scale pipets of all solutions Na 2 CO 3, CaCl 2, HCl, H 2 SO 4, AgNO 3, goggles HNO 3, NaOH, KI, Na 3 PO 4, FeCl 3, CuSO 4 black paper or surface lab aprons Safety Alert 1. Wear your safety goggles and lab aprons. 2. If your hands come in contact with any of the chemicals make sure to rinse them under water and dry. 3. If the chemicals come in contact with your eyes, please use the eye wash according to your teacher s instructions. 428 Laying the Foundation in Chemistry

2 15 PROCEDURE PART I 1. Obtain your 96-well plate and orient it on the table so that the long edge is at the top. You might find it helpful to put piece of black or dark paper behind the plate to make any precipitates more visible. 2. You will place 2 drops of each horizontal and vertical reactant listed on data table 1 into each well. To begin, place 2 drops of iron (III) chloride in each of 11 wells across the first row. As you begin to add the second solution, make sure not to touch the pipet tip to the well or its contents. Any contamination of the pipet will cause error in subsequent reactions. 3. To the first well add two drops of lead (II) nitrate. Use a toothpick and swirl the solutions together until mixed. Take care not to scratch the bottom of the well plate. Record your observations in data table 1 on the student answer page. 4. Continue in the same fashion by observing all of the combinations listed on your data table. 5. When you have finished, carefully rinse the microplate with water and use cotton swabs to clean any wells that have remaining precipitate. PART II 1. Obtain the eight unknown solutions as directed by your teacher. These 8 unknown solutions came from the original 12 you have already tested. Write the numbers for each of your unknowns horizontally on data table 2. Reverse the order of the numbers as you write them down the vertical column. Mix two drops of each solution in a well just as you did in part I. Stir them with a toothpick and then record your observations in data table 2. Take care not to scratch the bottom of the well plate. 2. Analyze the results of your unknown mixings by comparing them with the results recorded in part I. Identify all of the unknowns which had distinct reactions. 3. You may need to mix a few of the original 12 known solutions to correctly identify all of your unknowns. Make a plan before mixing. 4. Once you have identified the eight unknown solutions, write the number, name, and formula in data table 2 in the spaces provided on the student answer page. Laying the Foundation in Chemistry 429

3 15 Name Period Reactions of Aqueous Ionic Compounds Page DATA AND OBSERVATIONS 430 Laying the Foundation in Chemistry

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5 15 CONCLUSION QUESTIONS 1. On a sheet of paper write the full chemical equation, including state symbols for each of the reactions you observed. If there was no reaction place the symbol NR for no reaction in front of the reaction. Be careful here, just because no precipitate was formed doesn t mean there was no reaction; some reactions produce gases or other molecular compounds. For all reactions producing a precipitates, gases or other molecular compounds, write the net ionic equation. Be sure that all formulas are correct and that all equations are balanced. When writing the chemical equations start with the box labeled (1) on data table 1 and proceed in numerical order. Skip lines between equations. You may wish to type the equations for neatness. 2. Which reactions formed gas? What do they all have in common? Write a net ionic equation for one of the reactions. 3. Some of the reactions produced distinct color changes but did not produce a precipitate. Does this mean that a reaction did not take place? Explain your answer. 4. Were there any neutralization reactions? If so, write them below. What do they all have in common? 432 Laying the Foundation in Chemistry

6 15 5. Many of the equations you wrote earlier were labeled NR for no reaction. Choose one of the reactions and explain the NR by showing ion cancellation leaving no net reaction. Laying the Foundation in Chemistry 433