Conductivity Lab ReviewConductivity Lab Review

Configuration of the Lab StationConfiguration of the Lab Station

The left side image shows the entire station including the The left side image shows the entire station including the reagentsreagents, , the the buretteburette for water and the for water and the computercomputer required for the required for the data data acquisition and analysisacquisition and analysis. The right side image provides a closer . The right side image provides a closer look at the required reagents and hardware.look at the required reagents and hardware.

Conductivity of NaCl SolutionConductivity of NaCl Solution

After we delivered After we delivered 25 ml of distilled water25 ml of distilled water to the beaker to the beaker we then tested for the we then tested for the conductivity of the controlconductivity of the control (only (only water). After the data was water). After the data was recorded by the computerrecorded by the computer we we then then delivered 5 dropsdelivered 5 drops of the of the NaCl solution to the test NaCl solution to the test samplesample..

NaCl Test ContinuedNaCl Test Continued

The above images show from left to right the conductivity The above images show from left to right the conductivity of the test solution after 5 drops, 10 drops and 30 drops of of the test solution after 5 drops, 10 drops and 30 drops of the NaCl reagent were added respectively. The linearity of the NaCl reagent were added respectively. The linearity of the data confirms the increase in conductivity as the the data confirms the increase in conductivity as the concentration of ions increases.concentration of ions increases.

Molecular PotentialMolecular Potential

Before we tested NaCl we Before we tested NaCl we speculatedspeculated on the on the expected performance. The expected performance. The molecular profilemolecular profile for this for this substance is one of an substance is one of an ionic compoundionic compound. When NaCl . When NaCl (which is a salt) is dissolved in water we expect the (which is a salt) is dissolved in water we expect the “liberation”“liberation” of the ions by what we like to think of as of the ions by what we like to think of as our our water taxiwater taxi..

NaClNaCl(S)(S) + H-O-H + H-O-H Na Na1+1+(aq) (aq) + Cl + Cl1-1-

(aq)(aq)

Since Since conductivity requires the movement of chargeconductivity requires the movement of charge

and these liberated ions are now and these liberated ions are now free to movefree to move the increase in the increase in conductivity conductivity confirmedconfirmed our our predictionprediction. .

Conductivity of CaClConductivity of CaCl22

Before we test CaClBefore we test CaCl22 we will again we will again speculatespeculate on on the expected performance. The the expected performance. The molecular profilemolecular profile for this substance is again for this substance is again ionicionic. When CaCl. When CaCl22 (which is again a salt) is dissolved in water we (which is again a salt) is dissolved in water we expect the expect the “liberation”“liberation” of the ions by the of the ions by the water taxiwater taxi..

CaClCaCl2 2 (S)(S) + H-O-H + H-O-H Ca Ca2+2+(aq) (aq) + 2 Cl + 2 Cl1-1-

(aq)(aq)

Since Since conductivity requires the movement of chargeconductivity requires the movement of charge

the reaction the reaction should liberate the captive ionsshould liberate the captive ions an increase in an increase in conductivity is conductivity is expectedexpected. .

CaClCaCl22 Data Data

From the image of the From the image of the datadata it is clear that it is clear that CaClCaCl22 is is

conductiveconductive. The . The slopeslope of the graph shows the solution to of the graph shows the solution to be be more conductivemore conductive than the similarly profiled NaCl. than the similarly profiled NaCl.

CaClCaCl22 Data Continued Data Continued

After the final 5 drops were added the After the final 5 drops were added the appearanceappearance of the of the graphs graphs suggested further analysissuggested further analysis. . BothBoth of the graphs were of the graphs were linearlinear with fantastic C.O.R. values. The question that plagued us was why with fantastic C.O.R. values. The question that plagued us was why the two ionic compounds were not identical. They were the two ionic compounds were not identical. They were both “binary” both “binary” ionic compoundsionic compounds and both “liberated” metallic ions and chloride ions. and both “liberated” metallic ions and chloride ions.

It’s a Question of NumberIt’s a Question of Number

When we considered the reactions we noted that the When we considered the reactions we noted that the number of ions number of ions liberated by the salts was not the sameliberated by the salts was not the same. A . A ratio of 3:2ratio of 3:2 is observed for is observed for the CaClthe CaCl22 salt compared to the NaCl salt. When we salt compared to the NaCl salt. When we compared the compared the slopesslopes of the graphs we obtained a value of of the graphs we obtained a value of 1.51.5. Since the conductivity . Since the conductivity is generated by the movement of ions and the ions are “liberated” in a is generated by the movement of ions and the ions are “liberated” in a ratio of 3:2 the slope of ratio of 3:2 the slope of 1.5 strongly supports the model1.5 strongly supports the model. .

Molecular Profile of HClMolecular Profile of HCl

To assist in generating a molecular profile for a To assist in generating a molecular profile for a substance we generally substance we generally consult ASIMSconsult ASIMS. Hydrogen . Hydrogen presents a presents a half filled energyhalf filled energy level so it is level so it is not not expectedexpected to form to form ionic compoundsionic compounds. We expect this . We expect this binary compound (HCl) to be binary compound (HCl) to be molecular with bonds molecular with bonds that are polar covalentthat are polar covalent. The reagent list noted the . The reagent list noted the HCl system as HCl system as hydrochloric acidhydrochloric acid. The . The behavior of behavior of this system may well help us to understandthis system may well help us to understand the the important components of the important components of the acid profileacid profile..

HCl ResultsHCl Results

The 5 drops of HCl had a very steep slope. By the The 5 drops of HCl had a very steep slope. By the time 30 drops were added the relationship was time 30 drops were added the relationship was clearly established.clearly established.

NaOH ResultsNaOH Results

The The NaOH graph is the lowerNaOH graph is the lower of the two presented in the of the two presented in the image. Although both were made at the same time and at the same image. Although both were made at the same time and at the same concentration the “years” of storage has caused the NaOH to become concentration the “years” of storage has caused the NaOH to become less basic. less basic. Over time bases absorb COOver time bases absorb CO22 (which forms carbonic acid). (which forms carbonic acid). What is important to noteWhat is important to note is that the is that the ionic compound NaOHionic compound NaOH is is conductive as expected.conductive as expected.

The Magic of TitrationThe Magic of Titration

When Mr. Zachmann asked the class to speculate on the When Mr. Zachmann asked the class to speculate on the conductivity of a system where a conductor like HCl is added to conductivity of a system where a conductor like HCl is added to another conductor like NaOH. Many suggested an another conductor like NaOH. Many suggested an increase in increase in conductivityconductivity would occur. The would occur. The datadata however, however, does not confirmdoes not confirm this this hypothesis. During the titration of the basic solution we noted a hypothesis. During the titration of the basic solution we noted a decrease in the conductivitydecrease in the conductivity. This observation helps us to . This observation helps us to understand at the molecular level the act of understand at the molecular level the act of “neutralization“neutralization” when ” when acids and bases interact.acids and bases interact.

NeutralizationNeutralization

As we consider the act of neutralization we see the As we consider the act of neutralization we see the reformation of reformation of waterwater by the liberated by the liberated HH++ ion ion and and OHOH1-1- ions ions. . The remaining NaThe remaining Na1+ 1+ and Cland Cl1- 1- ions continue to support ions continue to support conductivity.conductivity.

NaOHNaOH(S)(S) + H-O-H + H-O-H NaNa1+1+(aq)(aq) + + OHOH1-1-

(aq)(aq)

HCl HCl (aq)(aq) + H-O-H + H-O-H HH1+1+(aq)(aq) + + ClCl11--(aq)(aq)

__________________________________________________________________________________________________

NaOHNaOH(S)(S) + HCl + HCl (aq)(aq) NaNa1+1+(aq)(aq) + + ClCl11--(aq)(aq)

Titration ReviewTitration Review

The beaker shows the The beaker shows the titration 1 drop before titration 1 drop before equivalence. Notice the equivalence. Notice the slight pink color. The graph slight pink color. The graph shows the same system shows the same system one drop past equivalence one drop past equivalence (the pink color left the (the pink color left the system). Notice what system). Notice what happens to the graph happens to the graph when more titrant is added when more titrant is added (see next slide)(see next slide)

Titration Review ContinuedTitration Review Continued

The left image was taken at five drops past end point and The left image was taken at five drops past end point and the right image was for 10 drops past end point. the right image was for 10 drops past end point. Remember that indicators Remember that indicators rely on colorrely on color to convey data and to convey data and this can be ambiguousthis can be ambiguous. In the next slide we used an . In the next slide we used an algebraic approach to determine the equivalencealgebraic approach to determine the equivalence point for point for the titration.the titration.

Algebraic Approach to EquivalenceAlgebraic Approach to Equivalence

The ambiguity of the colorimetric determination of The ambiguity of the colorimetric determination of equivalence can be eliminated by finding the common equivalence can be eliminated by finding the common (x, y) coordinate for the intersection of the two lines.(x, y) coordinate for the intersection of the two lines.

The Algebraic SolutionThe Algebraic Solution

For the declining line For the declining line yy = -19.6 x + 742 and for the ascending line = -19.6 x + 742 and for the ascending line yy = 55.4 = 55.4 x -749.5. x -749.5.

If we If we equate the two respective expressionsequate the two respective expressions for the common y value we for the common y value we get:get:

-19.6 x + 742 = 55.4 x – 749.5.-19.6 x + 742 = 55.4 x – 749.5.Collecting termsCollecting terms we get: we get:75 x = 1491.575 x = 1491.5Solving for xSolving for x we get: we get:XX = 19.89 drops = 19.89 drops

Can we use this information to compute the concentration of the base? If Can we use this information to compute the concentration of the base? If you remember from our solutions unit VM = VM. Therefore the molarity you remember from our solutions unit VM = VM. Therefore the molarity of the base would be:of the base would be:

MM(Base) (Base) =(V=(VAcidAcidMMAcidAcid)/ V)/ VBaseBase = ( = (19.89 drops19.89 drops)(.10M)/(30.0 drops) = )(.10M)/(30.0 drops) = .066 M.066 M

Applied ResearchApplied Research

Using the Using the same techniquesame technique we measured we measured the conductivity of solutions made from the conductivity of solutions made from some some common chemicalscommon chemicals found in the found in the home. Through the exercise we tried to use home. Through the exercise we tried to use ASIMS or deductive processASIMS or deductive process to to make make predictionspredictions. The data provided in the . The data provided in the following slides will often following slides will often retain the recordretain the record of of previously tested materials. This is done to previously tested materials. This is done to remind you of the remind you of the deductive processdeductive process..

ApplicationsApplications

The substances which appear in The substances which appear in the image to the right were the image to the right were assessed for conductivityassessed for conductivity. Methanol . Methanol solution was tested first. This test solution was tested first. This test was followed by ethanol solution, was followed by ethanol solution, ammonia solution, sugar in solution ammonia solution, sugar in solution and finally baking soda (AKA and finally baking soda (AKA sodium bicarbonate). Each sodium bicarbonate). Each substance was also tested with substance was also tested with phenolphthaleinphenolphthalein. As the testing . As the testing progressed progressed deductivedeductive and and inductiveinductive process was used to help with the process was used to help with the predictive process.predictive process.

Methanol AssessmentMethanol Assessment

The top image shows that The top image shows that the the methanol was not methanol was not conductiveconductive. The bottom . The bottom image indicates that the image indicates that the phenolphthaleinphenolphthalein did notdid not have a have a positive reactionpositive reaction. . We conclude from this We conclude from this result that the result that the OHOH attached attached to the carbon of methanol to the carbon of methanol was not liberatedwas not liberated by the by the water solvent.water solvent.

Ethanol AssessmentEthanol Assessment

Because ethanol was Because ethanol was structured very much like structured very much like methanol we methanol we expected expected the same behaviorthe same behavior. From . From the images to the right the images to the right we can see that there we can see that there was no difference in their was no difference in their respective behavior. We respective behavior. We conclude that conclude that alcohols alcohols are not conductiveare not conductive..

Ammonia AssessmentAmmonia Assessment

The structure of ammonia The structure of ammonia is interesting as it presents is interesting as it presents a nonbonding electron a nonbonding electron pair. The conductivity test pair. The conductivity test was positive as was the was positive as was the phenolphthalein test. We phenolphthalein test. We conclude ammonia was conclude ammonia was able to attack water or able to attack water or water attacked ammonia water attacked ammonia and as a result liberated and as a result liberated the OHthe OH1-1- ion. ion.

Sugar AssessmentSugar Assessment

Like methanol and ethanol Like methanol and ethanol solution the solution the sugar did not sugar did not conductconduct nor did it present a nor did it present a positive positive phenolphthaleinphenolphthalein response. The structural response. The structural formula for the glucose showed formula for the glucose showed numerous numerous OH groupsOH groups attached attached to the carbon backbone. The to the carbon backbone. The tests indicate that these groups tests indicate that these groups stay attachedstay attached..

Sodium Bicarbonate AssessmentSodium Bicarbonate Assessment

The photo to the right The photo to the right shows the response to the shows the response to the addition of the sodium addition of the sodium bicarbonate. bicarbonate. The early The early spike in conductivity is the spike in conductivity is the sodium bicarbonatesodium bicarbonate. The . The later response was the later response was the ammonia responseammonia response that that was not removed so that was not removed so that we could compare the we could compare the magnitude of the magnitude of the response. Again, we had a response. Again, we had a positive phenolphthaleinpositive phenolphthalein response.response.

Lab Report ExpectationsLab Report Expectations In class In class we outlined the talking pointswe outlined the talking points that that must appearmust appear in the in the

report. I expect to see several paragraphs dedicated to these various report. I expect to see several paragraphs dedicated to these various talking points. I talking points. I expect a drawing with suitable developmentexpect a drawing with suitable development to support to support your paragraph on the nature of conductivity. As you discuss the your paragraph on the nature of conductivity. As you discuss the molecular potentialmolecular potential of the various tests I expect you to of the various tests I expect you to write the write the reactions and make clear supporting commentsreactions and make clear supporting comments that illuminate the that illuminate the components of the written reaction which support conductivity (or do components of the written reaction which support conductivity (or do not support conductivity). The not support conductivity). The titration deserves a separate paragraphtitration deserves a separate paragraph in the introduction. Be sure to explain the titration process and our in the introduction. Be sure to explain the titration process and our expectations with respect to the conductivityexpectations with respect to the conductivity of the system as the of the system as the titration progresses. Again you will need to write chemical equations to titration progresses. Again you will need to write chemical equations to support your writing.support your writing. The The discussion part of the report should have equal attentiondiscussion part of the report should have equal attention. . Again, I expect well constructed paragraphs. I certainly expect to see Again, I expect well constructed paragraphs. I certainly expect to see downloaded images with supporting statementsdownloaded images with supporting statements. This is particularly . This is particularly important for the titration part of the lab. important for the titration part of the lab.

The highly motivated student will The highly motivated student will devote a separate paragraphdevote a separate paragraph to each of the to each of the assessment substancesassessment substances. Again I expect to see . Again I expect to see downloaded results followed by a discussion of the formula that I downloaded results followed by a discussion of the formula that I provided on the board and how this formula interacted to provide or not provided on the board and how this formula interacted to provide or not provide conductivity.provide conductivity.