Intro to Chemistry Chem 1020 Lab Ionic Precipitation

Intro to Chemistry Chem 1020 Lab Ionic Precipitation Reactions in Aqueous Solutions Chemistry Department Minneapolis Community & Technical College 1

Overview • Part I: Procedure Introduction Station setup Mixing Waste disposal • Part II: Lab report 2

Part I. Procedure You will be mixing 14 pairs of chemicals in aqueous solutions. Observe whethere is a precipitation reaction between the two solutions in each pair. Write the chemical equations for the reactions. This part is discussed in Chapter 7. 2 & 7. 3 in textbook. The 14 test tubes provided for you will be used for the 14 pairs of chemicals. Make sure to use the correct test tubes. For example: test tube #5 needs to be used for the reaction #5: strontium chloride solution with aluminum sulfate solution. 3

Station Setup There will be 14 stations. A typical station looks like this: Used and rinsed test tubes (pointing up) Waste container Water for rinsing used test tubes A pair of chemicals 4

Mixing Chemicals 1. Choose the correct test tube. Add 3 drops of each of the two chemicals in that reaction. 2. Make sure not to let the tip of the dropper touch the test tube (especially the inside) to avoid contamination. Put the dropper back to its original container. 3. Mix the chemicals by gently plucking the bottom of the test tube. Do you observe any signs of a precipitation reaction? If yes, record the color and form of the precipitate, e. g. white gel-like. 5

Waste Disposal • Don’t mix wastes, or dump them into the sink!!! • Dispose of the waste from a reaction into the waste container located in the station designated for that reaction. • Rinse the test tube with water and dispose of the rinse into the same waste container. Please restock your test tube rack with 14 clean and dry test tubes for the next section. Thanks! 6

Part II. Lab Report This lab report takes a significant amount of time to finish unless you are very proficient in writing formulas and chemical equations. Make sure to start early, and work on one part at a time. Review the formulas of the polyatomic ions before you start. Try not to refer to textbook or lecture notes, and use the periodic table and solubility rules only. 1. Complete the names of the products: 1) Switch the two cations 2) Check the solubility rules for the solubilities of the two products Example: Reaction #14: Sodium hydroxide and magnesium chloride sodium hydroxide + magnesium chloride magnesium hydroxide (s) + sodium chloride 7

2. Balanced molecular equation: 1) From the above equation with names of compounds, translate the names of the ions into their formulas 2) Determine the formula of each compound based on the charges of its cation and anion 3) Balance the equation 4) Indicate the physical state of each compound based on the solubility rules. “s” for solid (insoluble), and “aq” for soluble. *To receive points for this part, you need to have correct formulas for all reactants and products, their physical states, and coefficients. Example: 1) sodium hydroxide + magnesium chloride magnesium hydroxide (s) + sodium chloride Na+ OH- Mg 2+ 2) Na. OH + Mg. Cl 2 3) 2 Na. OH + Mg. Cl 2 4) 2 Na. OH (aq) + Cl- Mg. Cl 2 (aq) Mg 2+ OH- Na+ Cl- Mg(OH)2 + Na. Cl Mg(OH)2 + 2 Na. Cl Mg(OH)2 (s) + 2 Na. Cl (aq) The parts in green are the ones being accomplished in that step. You are only required to show the final balanced equation. 8

3. Net ionic equation: 1) From the above balanced molecular equation, select the insoluble product (having “s” as its physical state). Write down its formula on the right side of the equation 2) Write the formulas of its cation and anion on the left side of the equation. 3) Balance the equation 4) Indicate the physical state of ions as “aq” and that of the product as “s” *To receive points for this part, you need to have correct formulas for all reactants and products, their physical states, and coefficients. Example: Mg(OH)2 1) Mg(OH)2 3) Mg 2+ + 2 OH Mg(OH)2 4) Mg 2+ (aq) + 2 OH- (aq) Mg(OH)2 (s) 2) Mg 2+ + OH- The parts in green are the ones being accomplished in that step. You are only required to show the final balanced equation. 9