Lab Two Conductivity of Solutions PDF

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The conductivity of Solutions Lab...

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Chem 101-094 Lab John-Paul Marrazzo 10/21/2018

Conductivity Lab

I.

Written Experimental Procedure Materials: Laptop and Vernier Conductivity Sensor, Ten 6-inch test tubes, Gloves, 0.05M: Ethylene Glycol, Acetic Acid, Hydrochloric Acid, Methanol, Ammonia, Potassium Bromide. 1.0M: Sodium Chloride, Aluminum Chloride, Methanol, Calcium Chloride, Ammonium Nitrate. Distilled Water. Procedure:

A. Classes of Compounds 1. Log onto the computer provided using Drexel ID. Set the switch on the conductivity sensor for the 0-20000 range. Open Chem 101_102 Conductivity (A) file from the computer. 2. Place distilled water in the first test tube. Place conductivity sensor in the tube, liquid level will rise and cover the sensor. Once the conductivity has stabilized record it on the data page. 3. Clean the sensor with distilled water, blot the outside with paper towel. 4. With a new clean test tube, fill with

0.05 M C H 3 OH

❑

and record the

conductivity using the conductivity sensor. Once stabilized record data. 5. Repeat steps 3-4 with the remaining solutions listed on the data page, making sure to clean the sensor between each test with distilled water. 6. Also for comparison sake measure the conductivity of tap water.

B. Effect of Concentration

1. Change the switch on the conductivity sensor to the 0-2000.Open Chem 101_102 Conductivity (B) file from the computer. 2. In a 150 mL beaker fill about 70 mL of distilled water. 3. Use the conductivity sensor, and once the conductivity has stabilized click collect at the top of the screen. Press keep and enter 0 in the edit box because there are zero drops added to the solution. 4. Obtain a plastic piper and place some

1.0 M C H 3 OH

❑

5. Add one drop of the solution, use the sensor to stir and then repeat step number three, but this time enter 1 as this is the total number of drops added. Repeat this procedure until eight total drops have been added to the solution. 6. Click Stop and Export as CSV. 7. Repeat this study using clean materials. Repeat steps 2-6 using

1.0 M NaCl ,

1.0 M CaC l2 , and 1.0 M AlC l3

C. Effect of Polyatomic 1. Using the same procedure as in Part B repeat the study using

1.0 M N H 4 N O 3

II.

Signed Data Page

III.

Introduction

A. The purpose of this experiment was to use conductivity to better understand the difference between ionic and molecular compounds. In Part A of this experiment the conductivity of solutions is measured in order to determine if the compound is ionic, molecular or a midgroup. In Part B the effect of concentration as well as the amount of ions present is examined. Lastly in the third part Part C the effect of a polyatomic versus monatomic ions.

B. An aqueous solution is a solution in which the solvent is water. Ionic compounds that are dissolved in water fragment into ions. Ions are a charged species that enable the solution to conduct electricity. An electrical circuit can be completed with the use of a conductivity sensor, which also measures the amount of conductivity. A “high” conductivity is termed an electrolyte, whereas a “low” conductivity is termed a nonelectrolyte.

C. Molecular compounds do not dissociate into charged ions but instead remain as molecules. These molecules do not conduct electricity to a notable extent, but

there is residual conductivity from a small concentration of

+¿ −¿ H ¿ and O H ¿

ions.

D. Conductivity helps determine the class of compound, either ionic or molecular. There is a gray area in this measurement as there are “medium” conductivities that are measured. Here there is partial dissociation, as well as chemical equilibrium because there is a balance between the “little bit” of dissociation and the non-dissociation.

E. As stated, conductivity is a measure of the concentration of ions in a solution. The more ions present, the higher the expected concentration yield. In Part B the

impact ionic charge has on conductivity will be measured. It is expected that for aqueous solutions, the higher the concentration of ions lead to a higher conductivity.

F. In Part B only monatomic ions are measured, but in Part C a polyatomic ion is measured

N H 4 N O 3 . When the solution dissociations, it becomes two ions

each composed of multiple atoms. Since there are more atoms, and more ions, it can be expected that polyatomic ions exhibit greater conductivity than the monatomic ions.

G. In Parts B and C graphic methods were used to determine the impact on conductivity. Linear regression was used to determine the slope, which was used for comparison of the impact on conductivity.

IV.

Calculation and Discussion

A. Part A Solution

Concentration

Strong, Weak, Non-Electrolyte

μ S /cm Distilled Water

60

Non-Electrolyte

0.05M CH3OH

64

Non-Electrolyte

0.05M C2H6O2

64

Non-Electrolyte

0.05 NH3

385

Weak Electrolyte

0.05M CH3COOH

525

Weak Electrolyte

Tap Water

715

Weak Electrolyte

0.05M KBr

6260

Strong Electrolyte

0.05M HCl

24825

Strong Electrolyte

Although both are water, tap and distilled water have noticeably different concentrations. Tap water contains elements such as

Na, K , Ca, Mg and Fe at high concentrations. These

elements form positive ions when aqueous, therefore it would make sense that tap water has a higher concentration than distilled water.

B. Part B

Solution

Slope

Impact on Conductivity

Ionic Makeup

NaCl

71

Highest Impact

−¿ ¿ +¿ , C l N a¿

CaCl2

132

High Impact

−¿ ¿ −¿ ,C l ¿ 2+¿ , C l ¿ Ca

AlCl3

195

Median Impact

−¿ ¿ −¿ ,C l ¿ −¿ ,C l ¿ 3+¿ , C l ¿ Al ❑

CH3OH

-0.1084

No Impact

-----

From Part B it can be concluded that the ionic concentration does have an effect on conductivity. The higher ionic concentration, the higher the conductivity.

C. Part C

Solution

Slope

Impact on Conductivity

NH4NO3

93.9

Highest Impact

Makeup Nitrate Ion:

+¿ ¿ NH

Ammonium Ion:

−¿ N O3¿ NaCl

71

High Impact

−¿ ¿ +¿ , C l ¿ Na

From Part C it can be concluded that the polyatomic ion NH4NO3 which has more atoms has a higher impact on conductivity than NaCl, a monatomic ion.

V.

Conclusion

A. The purpose of this experiment was to use conductivity to better understand the difference between ionic and molecular compounds. In Part A of this experiment the conductivity of solutions is measured in order to determine if the compound is ionic, molecular or a midgroup. In Part B the effect of concentration as well as the amount of ions present is examined. Lastly in the third part Part C the effect of a polyatomic versus monatomic ions.

B. The results did confirm the expected results, the more ions present in an aqueous solution, the higher the expected concentration yield which was determined In Part B. In Part C it was determined that the presence of more atoms, and more ions, polyatomic ions exhibit greater conductivity than the monatomic ions.

C. Errors that could have occurred to skew the results of this experiment were technical. The conductivity sensor obviously had some faults, as the results for distilled water rendered a notable level of conductivity when it should have been zero. Although this does skew the data, because the same sensor was used throughout the results are controlled. All of the data was collected with the same

amount of “skewness” and therefore the qualitative data is accurate even though the quantitative may be off.

D. From this experiment I learned about strong electrolytes, weak electrolytes and nonelectrolytes. I also learned about plotting data collected from lab in a graph using excel, and reading said graph to make conclusions about the data....