AP Chemistry By Satellite Laboratory Manual Instructor's Edition EXPERIMENT 6: CONDUCTIVITY Contents Page Reagents...........................................................................6-2 Equipment........................................................................6-4 Useful Experimental Comments..........................................6-5 Pre–laboratory Questions...................................................6-7 Experimental Write–up .....................................................6-8 Post–laboratory Questions.................................................6-24 Instructor Evaluation Sheet...............................................6-28 AP CHEMISTRY BY SATELLITE 6 - 1 INSTRUCTOR LAB MANUAL Reagents CHEMICAL Quantity CHEMICAL Quantity acetic acid, 0.1 M 15 mL methanol 15 mL acetic acid, 1.0 M 50 mL nickel chloride hexahydrate, 0.1 M 15 mL ammonium acetate, 0.1 M 15 mL nickel nitrate hexahydrate, 0.1 M 15 mL ammonium chloride,0.1 M 15 mL nitric acid, 0.1 M 15 mL ammonium hydroxide, 0.1 M 15 mL potassium chloride, 0.1 M 15 mL ammonium sulfate, 0.1 M 15 mL potassium iodide 1 g ammonium thiocyanate 1 g potassium iodide, 0.1 M 15 mL barium hydroxide octahydrate, 0.1 M 15 mLpotassium nitrate, 0.1 M 15 mL calcium carbonate (ppt. chalk) 9 g silver nitrate, 0.1 M 15 mL calcium hydroxide, sat'd 15 mL sodium acetate trihydrate, 0.1 M 15 mL cobalt chloride hexahydrate, 0.1 M 15 mL sodium carbonate 1 g cupric chloride dihydrate, 0.1 M 15 mL sodium chloride 1 g ethanol 15 mLsodium chloride, 0.1 M 15 mL ferric nitrate nonohydrate 1 g sodium hydroxide, 0.1 M 15 mL hydrochloric acid, 1.0 M 50 mL sucrose 1 g hydrochloric acid, 0.1 M 5 mL sulfuric acid, 0.5 M 50 mL lead (II) nitrate 1 g sulfuric acid, 0.1 M 5 mL lead (II) nitrate, 0.1 M 15 mL Solution Preparation Use the table below to prepare the solutions of acids and bases. For general instructions on how to prepare solutions of dilute acids (or bases) from more concentrated solutions, see Appendix III. Some of the volumes of concentrated acid may be too small to measure accurately. It is recommended larger amounts of the dilute solutions be prepared. These reagents can be used in subsequent experiments. Conc. of dilute Vol. of dilute Conc. of concentrated Vol. of concentrated Acid or base acid or base acid or base acid or base acid or base NH3 (ammonium hydroxide) 0.1 M 15 mL 6 M 0.25 mL HCl (hydrochloric acid) 1.0 M 50 mL 12 M 4.2 mL HCl (hydrochloric acid) 1.0 M 50 mL 6 M 8.3 mL HCl (hydrochloric acid) 0.1 M 5 mL 1 M 0.5 mL H2SO4 (sulfuric acid) 0.5 M 50 mL 18 M 1.4 mL H2SO4 (sulfuric acid) 0.5 M 50 mL 3 M 8.3 mL H2SO4 (sulfuric acid) 0.1 M 5 mL 0.5 M 1 mL HNO3 (nitric acid) 0.1 M 15 mL 16 M 0.1 mL HNO3 (nitric acid) 0.1 M 15 mL 6 M 0.25 mL HC2H3O2 (acetic acid) 1.0 M 50 mL 17.3 M 2.89 mL HC2H3O2 (acetic acid) 0.1 M 15 mL 1 M 1.5 mL AP CHEMISTRY BY SATELLITE 6 - 2 INSTRUCTOR LAB MANUAL Use values from the table below to prepare the solutions of the salts needed in this experiment. (See Appendix I & III. for more detail.) To facilitate dispensing these solutions, each should be placed in dropper bottles. Since the experiment is performed at the microscale level students will only require a few drops of each solution. 15 mL is an estimate of the amount of each solution needed for every 5 students. Conc. of Weight Vol. of Salt salt of salt solution NH4C2H3O2 (ammonium acetate) 0.1 M 0.116 g 15 mL NH4C1 (ammonium chloride) 0.1 M 0.080 g 15 mL (NH4)2SO4 (ammonium sulfate) 0.1 M 0.198 g 15 mL . Ba(OH)2 8H2O (barium hydroxide octahydrate) 0.1 M 0.473 g 15 mL Ca(OH)2 (calcium hydroxide) 0.1 M 0.111 g 15 mL CoCl2·6H2O (cobalt (II) chloride hexahydrate) 0.1 M 0.357 g 15 mL CuCl2·2H2O (cupric chloride dihydrate) 0.1 M 0.256 g 15 mL Pb(NO3)2 (lead nitrate) 0.1 M 0.497 g 15 mL NiCl2·6H2O (nickel (II) chloride hexahydrate) 0.1 M 0.357 g 15 mL . Ni(NO3)2 6H2O (nickel (II) nitrate hexahydrate) 0.1 M 0.436 g 15 mL KCl (potassium chloride) 0.1 M 0.112 g 15 mL KI (potassium iodide) 0.1 M 0.249 g 15 mL KNO3 (potassium nitrate) 0.1 M 0.152 g 15 mL AgNO3 (silver nitrate) 0.1 M 0.255 g 15 mL NaC2H3O2·3H2O (sodium acetate trihydrate) 0.1 M 0.204 g 15 mL NaCl (sodium chloride) 0.1 M 0.088 g 15 mL NaOH (sodium hydroxide) 0.1 M 0.060 g 15 mL Since the amounts of reagents used are so small, disposal problems are minimized. The test solution for the conductivity apparatus should be 1 M HCl. Place about 15 mL in a dropper bottle labeled 'Test Solution.' Students will use this solution at the beginning of the experiment to check that their conductivity apparatus is working. If the conductivity apparatus is not working, you should replace the battery. AP CHEMISTRY BY SATELLITE 6 - 3 INSTRUCTOR LAB MANUAL Equipment PART I: Introduction to Conductivity EQUIPMENT Quantity EQUIPMENT Quantity beaker, 50 mL......................... petri dish.............................1 conductivity apparatus................1 plate, 96-well .......................1 dropper.................................1 spatula or microspatula ............2 paper towels...........................several watch glass..........................2 PART II: Strong and Weak Electrolytes EQUIPMENT Quanti ty beaker, 50 mL.........................1 conductivity apparatus................1 dropper.................................1 paper towels...........................several plate, 96-well..........................1 PART III: Electrolyte Strength and Reaction Rate EQUIPMENT Quantity EQUIPMENT Quantity laboratory balance.....................1 paper towels.........................3 beaker, 50 mL.........................2 plate, 96-well .......................1 capillary tube ..........................1 ring stand............................2 conductivity apparatus................1 spatula ...............................1 dropper.................................1 stopper, 1-hole #6..................1 flask, Erlenmeyer, 250 mL..........1 trough or pan........................1 glass bend..............................1 tubing,1' rubber....................1 glass tubing............................1 utility clamps........................2 graduated cylinder, 50 mL...........1 weighing paper .....................3 PART IV: Chemical Reactions EQUIPMENT Quantity EQUIPMENT Quantity beaker, 50 mL.........................1 paper towels......................several conductivity apparatus................1 plate, 96-well .......................2 dropper.................................1 spatula ...............................1 For information on building the conductivity apparatus, see Appendix IV. For information on obtaining well plates, see Appendix VI. AP CHEMISTRY BY SATELLITE 6 - 4 INSTRUCTOR LAB MANUAL Useful Experimental Comments Experiment Scheduling This experiment will require approximately 5 hours to complete. The experiment is organized to easily stop and start at almost any point. A discussion is needed at Expl. #1 in the experiment. It is intended the Expl. (explanations) portions of the experiment be completed while students are working in the laboratory. Depending on how far students progress each day, students could be assigned to complete some Expl. sections outside of class. However, students should not be encouraged to proceed too far beyond the uncompleted Expl. sections while working in the laboratory. The Expl. sections are intended to make the students address and formulate ideas based on their experimental observations. The experiment is long and will require a great deal of preparation time. You may decide to omit some portions of the experiment or to have students do different parts and then report their data to the rest of the class. Part III can be easily omitted. College Board Recommendations: This experiment is not of the type specifically suggested by the College Board, but it does require careful recording and analysis of experimental observation. The descriptive chemistry included in the experiment and the practice in writing chemical equations should prove to be very useful to those students taking the AP Examination. The experiment is intended to familiarize students with ideas such as conductivity and net ionic equations which will be included on the examination. The basic approach students are expected to follow in the laboratory is to do the experiments and then immediately answer the questions. If students have trouble answering questions, they should discuss the ideas with you or their classmates. Many of the important ideas will not be clear to students if they delay answering these questions. PART I: Introduction to Conductivity The test solution for the conductivity apparatus should be 1 M HCl. Place about 15 mL in a dropper bottle labeled 'Test Solution.' Students will use this solution at the beginning of the experiment to check that their conductivity apparatus is working. If the conductivity apparatus is not working, you should replace the battery. Remind students to clean the electrodes between tests. If the potentiometer is set too low on the conductivity apparatus, some electrolysis may occur in some of the solutions. To prevent this from happening adjust the potentiometer or use stainless steel wire for electrodes. If copper wire is used, cover the end of the wire with solder. The first nine observations are intended to familiarize the students with the conductivity apparatus and to introduce the kind of observations they will make in the laboratory. The students should briefly summarize their observations following each experiment. Remind the students they will need to return to these observations later in the experiment. The point of the petri dish experiment is to introduce the idea that species can migrate in water and that the migration is slow. You need to take some time to discuss the observations with your students. Careful discussion at this time will help students understand the rest of the experiment. The article by Vos and Verdonk from the Journal of Chemical Education 62(8), 649 includes an excellent model for the needed discussion.