EXPERIMENT 17. Oxidation-Reduction Reactions INTRODUCTION

Transcription

1 EXPERIMENT 17 Oxidation-Reduction Reactions INTRODUCTION Oxidizing agents are compounds or ions that contain an element capable of achieving a lower oxidation state by gaining electrons The stronger the tendency for a compound or ion to acquire electrons, the stronger oxidizing agent it is This experiment will look at four reactions that involve strong oxidizing agents Colors of various transition metal ions will aide you in predicting the products of the oxidation-reduction reactions you will be carrying out involving metals and metal ions Transition metal ions with a partially filled d sublevel are usually colored, whereas ions from non-transition metals or those with filled d sublevels are not This is because the electron transitions between orbitals in ions with partially filled d sublevels absorb some of the visible spectrum In solution, copper (II) ions show a blue or green color The permanganate ion in solution shows a purple color In solution, the dichromate ion is orange while chromium (III) ions show a blue or green color Iron (III) ions are yellowish-orange in solution Metal ions without a partially filled d sublevel, such as sodium ions, potassium ions, or zinc ions, are colorless Colors of various elemental halogens will aide you in predicting the products of the oxidation-reduction reactions you will be carrying out involving halogens and halide ions Colors of the halogens have been seen in earlier experiments In the nonpolar liquid hexane, bromine shows a red to light orange color depending on its concentration, and iodine shows a violet color The halogens dissolve slightly in water, with bromine showing a pale brown color and iodine showing a pale orange color PROCEDURE 1 Except for the laboratory handout, remove all books, purses, and such items from the laboratory bench top, and placed them in the storage area by the front door For laboratory experiments you should be wearing closed-toe shoes Tie back long hair, and do not wear long, dangling jewelry or clothes with loose and baggy sleeves Open you lab locker Put on your safety goggles, your lab coat, and gloves REACTION 1 - NITRIC ACID AS AN OXIDIZING AGENT 2 Position the snorkel hood so that it is about 15 inches above the lab bench Obtain a one-hole rubber stopper equipped with a glass bend from the back of the lab room Select a test tube that fits the one-hole stopper Under the snorkel hood support the test tube with a clamp on a ring stand at a 45 angle Attach the one-hole rubber stopper equipped with a glass bend Half fill a 400-mL beaker with water and place it under the snorkel hood Place the end of the glass bend in the beaker of water 3 Disconnect the stopper from the test tube, and add the two or three pieces of copper metal Measure out about 5 ml of concentrated nitric acid, add it to the test tube, and quickly reconnect the stopper CAUTION: Concentrated nitric acid causes severe burns If the nitic acid spills on the benchtop or on the ring stand, neutralize it with sodium bicarbonate before cleaning it up 169

2 4 Observe and record the color of the gas in the test tube Name the colored gas in your Data Table After several minutes observe and record the color of the resulting solution in the test tube Name the colored chemical species in your Data Table Disconnect the stopper from the large test tube under the snorkel hood at your lab station to release the poisonous gas into the hood The water from the 400- ml beaker can be poured down the sink The solution in the test tube should be disposed of in the Liquid Waste bottle in the Fume Hood A Rinse out the glass bend and the rubber stopper with water, and return it to the back of the lab room Work out the balanced ionic equation in the Reaction Work box following the Data Table and write the balanced net ionic equation in the Reaction 1 box of the Final Equations section on page 173 REACTION 2 - PERMANGANATE AS AN OXIDIZING AGENT 5 Place 5 ml of sodium bromide solution in a medium test tube and add 2 drops of concentrated nitric acid Add about 20 drops of the immiscible liquid hexane, which will form a clear layer on top of the aqueous solution of sodium bromide The hexane is not involved in the chemical reaction, but one of the products of the reactions readily dissolves in it upon mixing 6 Record the color of the potassium permanganate solution and name the colored chemical species in your Data Table Add ten drops of the potassium permanganate solution and mix the contents of the test tube with the vortex mixer Record the color in the hexane layer If no color is present in the hexane layer, add ten more drops of the potassium permanganate solution, mix as before and record the color in the hexane layer Name the colored chemical species in your Data Table The solution in this reaction should be disposed of in the Liquid Waste bottle in the fume hood Work out the balanced ionic equation in the Reaction Work box following the Data Table and write the balanced net ionic equation in the Reaction 2 box of the Final Equations section on page 173 REACTION 3 - DICHROMATE AS AN OXIDIZING AGENT 7 Record the color of the potassium dichromate solution and name the colored chemical species in your Data Table Place 20 drops of the potassium dichromate solution in a medium test tube and add 2 drops of concentrated nitric acid Add 10 drops of hydrogen peroxide solution, shake the test tube, and looking for any sign of chemical action other than a color change Name the product giving you the sign of chemical action your Data Table Add 10 drops of the hydrogen peroxide solution twice more, shaking after each addition Record your observations, including the final color of the solution and name the colored chemical species in your Data Table The solution in this reaction should be disposed of in the Liquid Waste bottle in the fume hood Work out the balanced ionic equation in the Reaction Work box following the Data Table and write the balanced net ionic equation in the Reaction 3 box of the Final Equations section on page 173 REACTION 4 - METAL IONS AS OXIDIZING AGENTS 8 Record the color of the iron (III) nitrate solution and name the colored chemical species in your Data Table Place 20 drops of the iron (III) nitrate solution in a medium test tube Add 20 drops of sodium iodide solution to the same test tube 9 Add about 20 drops of the immiscible liquid hexane, which will form a clear layer on top of the aqueous solution The hexane is not involved in the chemical reaction, but one of the products of the reactions readily dissolves in it upon mixing Mix the contents of the test tube with the vortex mixer Record the color in the hexane layer and name the colored chemical species in your Data Table The solution in this reaction should be disposed of in the Liquid Waste bottle in the fume hood Work out the balanced ionic equation in the Reaction Work box following the Data Table and write the balanced net ionic equation in the Reaction 4 box of the Final Equations section on page Once your working area has been checked your lab report can then be turned in to the instructor 170

3 EXPERIMENT 17 LAB REPORT Name: Student Lab Score: Date: Lab Station Number: DATA TABLE REACTION 1 OBSERVATIONS IDENTITY OF SPECIES Gas Solution after Reaction REACTION 2 OBSERVATIONS IDENTITY OF SPECIES Potassium Permanganate Solution Hexane Layer after Reaction REACTION 3 OBSERVATIONS IDENTITY OF SPECIES Potassium Dichromate Solution Signs of Chemical Action Solution after Reaction REACTION 4 OBSERVATIONS IDENTITY OF SPECIES Iron (III) Nitrate Solution Hexane Layer after Reaction 171

4 REACTION WORK Rxn 1 Rxn 2 172

5 Rxn 3 Rxn 4 FINAL EQUATIONS RXN 1 RXN 2 RXN 3 RXN 4 173

6 QUESTIONS 1 When dilute nitric acid is used as an oxidizing agent instead of concentrated nitric acid, nitrogen monoxide gas is produced rather than nitrogen dioxide gas Assuming in Reaction 1 that dilute nitric acid was used instead of concentrated nitric acid, predict the products and write the balanced net ionic equation 2 Assuming the reaction conditions for Reaction 2 were a basic solution instead of an acidic solution, predict the products and write the balanced net ionic equation 174