# When an electric potential, or voltage is applied

Oakland UniversityDepartment of ChemistryCHM 147Experiment 4Conductivity of SolutionsIntroductionConductanceWhen an electric potential, or voltage is applied across a conductor, an electric current flows.The magnitude of the current is determined by the resistance of the conductor. The relationshipbetween the voltage (V), the current (i), and the resistance (R) is given by Ohm’s law_V=iR(3.1)The unit of voltage is the volt, V; 1 volt = 1 Joule/coulomb, where the coulomb is the unit ofelectric charge. The unit of electric current is the ampere, A; 1 ampere = 1 coulomb/second. Theunit of resistance is the ohm, ; 1 = 1 V/A. A related quantity is the conductance, L, which isthe reciprocal of the resistance:=1=(3.2)The unit of conductance is 1/ohm, or ohm1; this is sometimes called the mho, but the official unitis the siemen, S; 1 ohm1 = 1 mho = 1 siemen. Thus, to measure the conductance (or resistance)of a conductor, one simply measures the current that results from the application of a given electricpotential V. These relationships apply to all conductors – metal wires, silicon computer chips, andsolutions of ions in water. The charge carriers in metals, and in semiconductors such as silicon,are electrons. In aqueous solutions, however, the charge carriers are ions. The conductance of anaqueous solution depends on the configuration of the measurement cell, the temperature of thesolution, and the concentration of the ions present as well as their charges and mobilities. In thisexperiment you will measure the conductance of a series of solutions in order to explore the natureof the aqueous solutions formed from strong electrolytes, weak electrolytes, and nonelectrolytes.The configuration of the measurement cell and the solution temperature will be kept constant, sothat the solution conductance will be determined only by the identity and concentration of thesolute particle in solution.1Exp #4Conductivity of SolutionsOakland UniversityDepartment of ChemistryThe solutions analyzed in this experiment are composed of acids, bases and salts. Acids, bases,and salts dissolve in water to give solutions that contain ions, which conduct electricity. Manysalts when dissolved in water dissociate completely into hydrated ions, and are known as strongelectrolytes. Some acids and bases react completely with water resulting with only the ionizedspecies in solution. These acids are also strong electrolytes. Others acids and bases react only toa small extent with water, therefore only a small amount of the ionized species are found insolution. This results with much of the solute found in solution as the neutral molecule and someas the ionized species. Those which react completely with water are called strong acids and bases,and are also strong electrolytes, while those that do not react completely are called weak acids andbases, and are weak electrolytes. The conductance of a solution in part depends on theconcentration of ions dissolved in it, so when comparing solutions of the same concentration, aweak electrolyte results in a solution with a low conductivity compared to the high conductivity ofa solution of a strong electrolyte. Nonelectrolytes do not ionize at all in an aqueous solution, andthese solutions have extremely low or zero conductivities. The conductance of aqueous solutionformed from various substances allows us to distinguish between strong electrolytes, weakelectrolytes and nonelectrolytes. In theory conductance values of 1.0 mS or greater are consideredto be strong electrolytes, conductance values that fall between 0.1 – 1.0 mS are considered to beweak electrolytes, and conductance values below 0.1 mS are considered nonelectrolytes.As stated above, the conductance of a solution depends on the concentration of ions dissolved in it.There is a relationship between the concentration of ions in solution and conductivity. Whencomparing solutions of the same solute with varied concentrations, a trend in the difference inconductivities should be observed. In this experiment you will measure the conductivity ofsolutions of HCl at various concentrations. To observe the relationship between the concentrationof solute ions in solution and conductivity, a graph of Conductance versus Concentration will begenerated using data collected in the lab.In addition, the conduction of electric current in an aqueous solution is due to the motion of ions ormobility. The mobility is linked to the identity of the dissolved particles. For example, in asolution of sodium chloride, the charge carriers are sodium ions and chloride ions—the current iscarried partly by Na+(aq) ions and partly by Cl(aq) ions. In dilute solutions, the cations (positiveions) and anions (negative ions) act as independent entities with each ion making a characteristiccontribution to the overall conductance. For example, a comparison of isomolar solutions(solutions with the same molarity) of NaCl(aq) and KCl(aq). Even though the overallconductance will be different due to the different cations which are present, the contribution to theoverall conductance value from Cl(aq) is the same.This means that the conductivities due todifferent ions are additive. From this we can write, LNaCl(aq)=LNa+(aq)+LCl(aq). It also means thatwe can predict the conductivity of a solution we haven’t yet measured using conductivity valuesfrom other solutions. For example, suppose we have measured the conductivity of solutions of theionic substances AC, DB, and DC, and we wish to know the conductivity of a solution of the ionicJBTRev 2-7-152Exp #4Conductivity of SolutionsOakland UniversityDepartment of Chemistrysubstance AB. We can theoretically calculate the conductivity of AB using the measuredconductance values of AC, DB, and DC. The conductivity of AB is= + + −(3.3)Using the conductance values of the salts AC, DB and DC, all of which contain either A+ or B−, theconductance of AB can be predicted. The conductance values should be added or subtracted toend up with A+ and B− ions left in the equation. (The conductance values for each substance are:= [ + + − ]; = [ + + − ]; = [ + + − ])To calculate the conductance of AB, the values of AC and DB, and DC are combined as follows:= + −or= [ + + − ] + [ + + − ] − [ + + − ](3.4)The conductivity of DC is subtracted because the contribution from the ions D+ and C− needs to beeliminated. If you rearrange the ions, then the contribution from the unwanted cations (D+) andanions (C-) will cancel out.= [ + + − ] + [ + − + ] + [ − − − ]You are left with = [ + + − ]. Therefore, the conductance of AB in solution can bepredicted using the conductance values of AC, DB, and DC in the following equation.= + −In this experiment you will test that the conductivity of a solution can be predicted using theconductivities of other solutions. The conductivity of a KNO3 solution will be predicted using themeasured conductivities of solutions of KCl, HCl, and HNO3, and then your prediction will becompared with the measured conductivity.Preparing solutions of known concentrationChemists frequently use the concentration unit known as molarity, or molar concentration, whichis defined as moles of solute per liter of solution; the solution is the entire mixture, not just thewater solvent. The equation for molarity is=(3.5)where M is the molar concentration, n is the number of moles of solute, and V is the volume of thesolution in liters. The units of molarity (mol/L) are frequently written as “M”, so for example, asolution of 0.5 mol/L is written as “0.5 M”. In laboratory work with solutions, we can measureout a particular number of moles of solute by measuring out a particular volume of solution or aJBTRev 2-7-153Exp #4Conductivity of SolutionsOakland UniversityDepartment of Chemistrymass of a solid. For example, suppose we have a 0.25 M solution of acetic acid, and we want tomeasure out 0.050 mol of acetic acid. Using the equation, = , where M = 0.25 mol/L and n =0.050 mol, we can rearrange the molarity equation to solve for the required volume:==0.050= 0.20 2000.250DilutionsA very common procedure in the laboratory is the preparation of a solution of lower concentrationby dilution of a solution of higher concentration. This is done by accurately measuring out avolume of the more concentrated solution, and then transferring it quantitatively to a volumetricflask which has the desired total volume required for the final solution. To calculate the quantityof the more concentrated solution needed to make a solution of a desired volume andconcentration, the following equation is used. (M1 is molarity of the more concentrated solution,V1 is the volume needed of the more concentrated solution, M2 is the molarity of the dilutesolution, and V2 is the final volume of the dilute solution)1 1 = 2 2(3.6)Note: A quantitative transfer is one where none of the original solution, solid or any of therinse water is lost, i.e. all of the sample is transferred to the flask.To make solutions in concentrations of molarity, a volumetric flask should be used. A volumetricflask is a container which has been calibrated to contain a particular volume of liquid. Whensolvent is added to the mark etched on the neck of the volumetric flask, then the flask is known tocontain the indicated volume to high precision, typically on the order of 0.01 mL. Whenpreparing a solution by dilution, one adds the carefully measured volume using a pipet of the moreconcentrated solution to the volumetric flask first, and then adds water or solvent to the mark onthe neck of the flask second, giving a solution of the desired total volume. Note that volumes arenot always additive. For example, mixing 20 mL of 1.0 M HCl solution with 30 mL of water mayresult in a solution with a volume somewhat different from 50 mL. Because of this, it is importantto prepare solutions of the required total volume as described above, using a volumetric flask.Solid Solute Solution PreparationWhen making solutions using a solid solute, gram quantities of solute is needed. If we need tomake a 0.25 M solution from a solid salt, then we will need to determine how much in grams of thesolid is needed to have the ratio0.025. In order to do this, the final volume of thesolution is necessary. We can calculate the amount in grams of solid needed to make the solutionas by multiplying molarity times volume, and then the calculated moles by the molar mass.JBTRev 2-7-154Exp #4Conductivity of SolutionsOakland UniversityDepartment of Chemistry× =×=For example, if we were trying to make 25 mL of a 0.25 M KCl solution, then the process tocalculate the number of grams needed to make the solution is as follows:0.25 0.025×= 0.00630.0063×74.55= 0.47Note: When preparing a solution by dissolving a solid in water, the solid is first weighedaccurately in a tared beaker. Then, a small volume of deionized water is added to thebeaker and stirred to dissolve the solid completely. This mixture is then transferredquantitatively to a volumetric flask of the desired total volume required for the solution.Water or solvent is added to the mark etched on the neck of the volumetric flask to makethe desired final volume of the solution. Mix the solution thoroughly.Chemicals & Equipment1.00 M HCl1.0 M HNO31.0 M KOH1.0 M EthanolGlacial acetic acidConcentrated ammoniaKNO3KClCa(NO3)2 •4H2OAl(NO3)3•9H2OCuSO4•5H2O100 mL Volumetric flask50 mL Volumetric flask25 mL Volumeric pipet10 mL Graduate pipet1 mL Volumetric pipetPipet bulb4 Beakers (100 mL or larger)50 mL BeakerTDS testerKimwipesProcedurePreparation of solutionsUse pipets (volumetric and graduated) and volumetric flasks to provide the desired precision forthe preparation of the solutions needed for this experiment. A kit containing the glassware andJBTRev 2-7-155Exp #4Conductivity of SolutionsOakland UniversityDepartment of Chemistryinstruments needed for this experiment is available in the stockroom. Please read the sections inyour Laboratory Skills titled “How to use a Pipet” and “Volumetric Flask”. Make sure you rinsethe volumetric glassware provided in the kit well with deionized water before and between uses.Also don’t forget to rinse the pipets with the desired solution that will be used to make the newsolution. It is important to make sure each solution is thoroughly mixed before using ormeasuring the solution – for thorough mixing, invert the volumetric flask and swirl it gently for ashort time. Repeat swirling process multiple times to ensure a homogeneous solution. Transferthe well mixed solution to a labelled beaker to measure the conductivity.The conductance for the following solutions will be measured:0.025 M HCl0.025 M Al(NO3)30.0125 M HCl0.025 M Ca(NO3)20.00625 M HCl0.025 M KNO30.025 M HNO30.025 M CuSO40.025 M KOH0.025 M KCl0.025 M NH30.025 M HC2H3O21.0 M ethanoltap waterdeionized water.Before measuring any conductance values, you must prepare the following solutions:1. 0.0250 M HCl, 0.0125 M HCl, 0.00625 M HClPrepare 100 mL of the 0.0250 M solution by dilution of the 1.00 M HCl solution provided inthe lab. Then prepare 100 mL of the 0.0125 M solution by dilution of the 0.0250 M solution.Finally, prepare 50 mL of the 0.00625 M solution by an appropriate dilution of the 0.0125 Msolution.2. 100 mL each of 0.025 M HNO3, and 0.025 M KOHPrepare these by dilution from the 1.0 M solutions provided in the lab.3. 100 mL each of 0.025 M CH3CO2H (acetic acid), and 0.025 M NH3 (ammonia) (Share databetween 2 groups)Prepare these solutions by method of serial dilution from the commercial “glacial” aceticacid and concentrated ammonia provided in the lab. See prelab items 6 and 7 (Pre-lab page2 – 3) for serial dilution procedure. These solutions should be prepared in the fumehood. Both glacial acetic acid and ammonia produce vapors that have strong odors and areirritants.4. 100 mL each of 0.025 M KNO3, 0.025 M Ca(NO3)2, 0.025 M Al(NO3)3, 0.025 M CuSO4,and 0.025 M KCl (Share data between 2 groups)Prepare these by dissolving the appropriate mass of the solid salts in water.Conductance measurementsThe conductance measurements will be done using an instrument called the TDS Tester 4, which isa hand-held conductivity meter with a digital readout. Its range is from 0–19.90 millisiemensJBTRev 2-7-156Exp #4Conductivity of SolutionsOakland UniversityDepartment of Chemistry(mS), or 0–0.01990 ohms 1 . Before each conductance measurement, rinse the conductivitymeter’s electrodes well with deionized water, and then dry carefully with a Kimwipe. To use themeter, simply turn it on, immerse the electrodes in the solution to be measured, and read the valueof the conductance from the meter. Before using the meter to measure the conductance of yoursolutions, make sure the electrodes have been rinsed adequately by measuring the conductance of afresh sample of deionized water—the conductance should be zero on the scale of the meter.Note: If your TDS tester is battery operated, please turn off the TDS tester when you arenot making a measurement to maximize the battery life.Measure and record the conductance of each of the solutions listed above. In addition, measurethe conductance of deionized water, tap water, and a solution of 1.0 M CH 3CH2OH(aq) (ethanol),which will be supplied in the lab. Take 15 mL of the ethanol solution in a 50 mL beaker tomeasure the conductance. You only need enough solution to cover the electrode to take ameasurement using the TDS tester.How to Use TDS Tester:1. Turn TDS tester on2. Remove the electrode cover.3. Rinse TDS tester with deionized water and then blot dry with a Kimwipe.4. Check conductance of water.5. Blot dry with a Kimwipe6. Place TDS tester in the solution to be measured only far enough to submerge the electrodes.7. Record the measurement including all significant figures and units.8. Rinse electrode again with deionized water, blot dry, and then replace electrode cover.Waste DisposalAll liquid waste can be disposed of down the drain.Laboratory ReportYour report should consist of the following sections, in order:1.2.3.4.The summary page.Data pagesPlot of conductance of HCl(aq) solutions vs. concentration.Post-Laboratory QuestionsJBTRev 2-7-157CHM 147Oakland UniversityDepartment of ChemistryName _____________________________________________Conductivity of SolutionsPartner’s Name______________________________________Exp #4Pre-laboratory Assignment(page 1 of 4)1. View the laboratory technique videos associated with this experiment in Moodle:1) Preparation of Standard Solutions from Solids, 2) Preparation of Standard Solutions byDilution and 3) Use of the Conductivity Meter. If needed review the videos associatedwith Experiment 1 on use of pipets and volumetric flasks.2. View the two tutorials:Conductivity Values.1) Solution Preparation Calculations and 2) Predicting3. Complete the calculation on pages 2 – 3 of the pre-lab assignment associated with thetutorials. Pages 2 – 3 are to be turned in to your instructor at the beginning of lab. Youwill want to have these pages available to reference when taking the Pre-lab quiz.4. Record on page 4 of the Pre-lab the masses and volumes needed (your answers from pages2 – 3 of the pre-lab) to prepare the solutions measured in this experiment. Bring page 4with you to lab to use when preparing the solutions analyzed in this experiment.5. Prepare a procedure outline on a separate 8.5” x 11” piece of paper for this experiment. Itis recommended to not prepare the outline until after you have viewed the videos andtutorials. Some of the details of the procedure will be clarified after viewing the videosand tutorials.6. Complete the Pre-laboratory Quiz in Moodle. Reminder, the Pre-lab quiz should becompleted before 7:30 AM on the day your laboratory meets unless otherwise indicatedby your instructor. The quiz has a 45 minute time limit with only one attempt allowed, soonly take the quiz after completing all the above pre-lab assignments. Once you open thequiz, you must complete the quiz. The instructor will review the quiz scores prior to thebeginning of the laboratory.JBTRev 2-7-158CHM 147Oakland UniversityDepartment of ChemistryName _____________________________________________Conductivity of SolutionsPartner’s Name______________________________________Exp #4Pre-laboratory Assignment(page 2 of 4)Show all calculations for the following solution preparations for full credit. Transfer allcalculated volumes and masses to page 4 of the pre-lab.1. 100 mL of the 0.0250 M HCl solution by dilution of the 1.00 M HCl solution provided in thelab.2. 100 mL of the 0.0125 M HCl solution by dilution of the 0.0250 M HCl solution.3. 50 mL of the 0.00625 M HCl solution by an appropriate dilution of the 0.0125 M HCl solution.4. 100 mL of 0.025 M HNO3 prepared from 1.0 M HNO3 solution.5. 100 mL of 0.025 M KOH prepared from 1.0 M KOH solutions.6. For part of the experiment, you will need to prepare 100 mL of 0.025 M CH 3CO2H (aceticacid), starting from commercial “glacial” acetic acid, which has a concentration of 17.4 M.Devise a method using a two-step serial dilution to make 100 mL of 0.025 M acetic acidsolution. The glassware available is a 100 mL volumetric flask, 50.00 mL volumetric flask,1.00 mL volumetric pipet, and a 10 mL graduated pipet. For the first step, dilute 1.00 mL ofglacial acetic acid to 50.00 mL to produce “Solution 1”. You will then use Solution 1 to makethe 0.025 M concentration for step 2. Determine the volume of Solution 1 needed to make 100mL of 0.025 M acetic acid. (View the serial dilution tutorial.)JBTRev 2-7-159CHM 147Oakland UniversityDepartment of ChemistryName _____________________________________________Conductivity of SolutionsPartner’s Name______________________________________Exp #4Pre-laboratory Assignment(page 3 of 4)7. Devise a method (two-step serial dilution) similar to that in the previous question to make100.00 mL of 0.025 M NH3 (ammonia), from concentrated ammonia, which has aconcentration of 15.28 M.8. Calculate the masses of the solids you must measure out to prepare 100 mL each of 0.025 MKNO3, 0.025 M CuSO4, 0.025 M Ca(NO3)2 , 0.025 M Al(NO3)3, and 0.025 M KCl. (Note thatsome of these salts are hydrates; their formulas are: Ca(NO3)2 •4H2O, Al(NO3)3•9H2O, andCuSO4•5H2O). You must include the waters of hydration when calculating the formulaweights. Show all your calculations for full credit.A. 0.025 M KNO3B. 0.025 M CuSO4C. 0.025 M Ca(NO3)2D. 0.025 M Al(NO3)3E. 0.025 M KCl.JBTRev 2-7-1510CHM 147Oakland UniversityDepartment of ChemistryName _____________________________________________Conductivity of SolutionsPartner’s Name______________________________________Exp #4Pre-laboratory Assignment(page 4 of 4)Record the masses of solids or volumes of more concentrated solutions required to prepare 100 ml(50 ml of 0.00625 M HCl) of the following solutions. Bring this sheet to the laboratory the day ofthe experiment.1. 0.0250 M HCl – _______________________________2. 0.0125 M HCl – ______________________________3. 0.00625 M HCl – ______________________________4. 0.025 M HNO3 – ______________________________5. 0.025 M KOH – ______________________________6. 0.025 M CH3CO2Ha. _____________________________b. _____________________________7. 0.025 M NH3 (ammonia)a. _____________________________b. _____________________________8. 0.025 M KNO3 – ______________________________9. 0.025 M CuSO4 – ______________________________10. 0.025 M Ca(NO3)2 – ______________________________11. 0.025 M Al(NO3)3 – ______________________________12. 0.025 M KCl – ______________________________Before you prepare solutions, the instructor or TA should check your calculated quantities.JBTRev 2-7-1511CHM 147Oakland UniversityDepartment of ChemistryExperiment 4 Conductivity of SolutionsSummary PageDate:Name:Partner:Summary StatementDescribe, briefly, the aim of this experiment, what quantities you measured, what quantities (ifany) you determined using your experimental data, and what you learned from doing thisexperiment.JBTRev 2-7-1512CHM 147Oakland UniversityDepartment of ChemistryExperiment 4 Conductivity of SolutionsData sheet #1Date:Name:Partner:For each solution, record the measured value of the conductance.0.0250 M HClConductance: _______________0.0125 M HClConductance: _______________0.00625 M HClConductance: _______________0.025 M HNO3Conductance: _______________0.025 M KOHConductance: _______________0.025 M CH3CO2H (acetic acid)Conductance: _______________0.025 M NH3 (ammonia)Conductance: _______________0.025 M KNO3Conductance: _______________0.025 M Ca(NO3)2Conductance: _______________0.025 M Al(NO3)3Conductance: _______________0.025 M CuSO4Conductance: _______________0.025 M KClConductance: _______________Deionized waterConductance: _______________Tap waterConductance: _______________1.0 M CH3CH2OH(aq) (ethanol)Conductance: _______________JBTRev 2-7-1513CHM 147Oakland UniversityDepartment of ChemistryExperiment 4 Conductivity of SolutionsData sheet #2Date:Name:Partner:For select solutions, record how you prepared the solution. Make sure to include the volumes,masses and which pieces of glassware you used to prepare the solution. (2 pts each)a. Solution Preparation Procedure for 0.025 M HCl.b. Solution Preparation Procedure for 0.025 M NH3 from concentrated ammonia.c. Solution Preparation Procedure for 0.025 M Ca(NO3)2.JBTRev 2-7-1514CHM 147Oakland UniversityDepartment of ChemistryName _____________________________________________CHM 147Partner’s Name______________________________________Exp #4Post-Laboratory Questions(page 1 of 2)1. On an 8.5” x 11” piece of graph paper, graph Conductance versus Concentration of HClusing your data collected in the lab. Make sure to draw a best fit line (trend line), the graphhas a title, and the axes are labeled properly. For full credit the graph MUST be on graphpaper. (Include the graph in your lab report.)2. Using you data, what is the relationship between conductance and concentration for theHCl(aq) solutions?3. From your measurements, characterize each of the following as a strong electrolyte (SE),weak electrolyte (WE), or nonelectrolyte (NE):a. H2Og. CH3CO2Hb. HClh. CuSO4c. HNO3i. NH3d. KClj. Ca(NO3)2e. KNO3k. Al(NO3)3f. KOH4. From your me…

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