Each pair of students will check out from the instructor a Vernier conductivity probe and a LabQuest 2. The conductivity probe is sensitive and must be calibrated before using.
Before performing this part, you will need to calibrate the LabQuest 2 as follows:
1. Make sure to have a beaker of DI water ready (enough in small beaker so tip of electrode is
immersed in DI water)
2. Plug in the power supply to the LabQuest 2.
3. Turn on the LabQuest 2.
4. On the sensitivity switch on the side of the LabQuest, move the switch to 0-2000
µS if this is not
set here.
5. Connect the conductivity probe to the LabQuest.
6. Click on Sensors on the top of the screen.
7. Click Calibrate.
8. Select CH1: Conductivity 2000 MICS.
9. Click one point calibrate.
10. Immerse conductivity probe into beaker of DI water.
11. Enter in 0 for the Known value.
12. Press Keep (on bottom left of screen).
13. You will now return to the previous screen. Press OK (on bottom left of screen).
14. LabQuest will now show 0
µS/cm.
15. You are now ready to take conductivity measurements of your solutions.
16. Make sure you fill the spot plate all the way to the top without spilling solution all over the plate.
This ensures that the electrode tip is in contact and immersed within the solution.
17. Conductivity may fluctuate. Choose the measurement that stays around a value that is constant.
You are now ready to perform taking conductivity measurements of solutions from table B page 7. a. Take a clean spot plate to the reagent bench. Fill each separate well of the spot plate all the way to the
top with each solution listed on table B-page 7.
b. Immerse the ‘tip’ of the conductivity probe in each solution to be tested. Before testing each solution,
rinse the probes by immersing them in distilled water placed in a small beaker. To prevent contamination,
do not allow a solution from one well to mix with a solution of another well. The measured conductivity
(in units of
µS/cm) of the tested solution will be recorded in table B, page 7 and will indicate one of the
following types of electrical conductivity:
i. Strong conductor- very high measured conductivity values in the range of 1000 – 5000 µS/cm . ii. Weak conductor- low to high measured conductivity values in the range of 100 – 1000 µS/cm . iii. Non-conductor- essentially zero or very low conductivity values in the range of 0 – 100 µS/cm . c. Record the measured conductivity value for each of the solutions from the LabQuest 2 as described
above onto table B, page 7 .
d. Classify each solution as weak-, strong-, or as a non-electrolyte based on your measurement and the
ranges given above.
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e. Write the formulas of all solute particles (ions and/or molecules) present, listing the most abundant kind
of particle first.
3. EFFECT OF MIXING REAGENTS
a. Take a clean spot plate to the reagent bench. Fill each separate well of the spot plate all the way to the
top with each of the solutions listed in part 3(a) on page 8. For the pairs of reagents listed, you will test
the conductivity of each solution separately by using the conductivity probe. Then, you will mix the pair
of solutions by using a clean medicine dropper to transfer the contents of one well into the other. Measure
the conductivity after mixing. You should be able to recognize the changes in the number of ions present.
i. Record your observations.
ii. Write molecular-, total ionic-, and net ionic equations
iii. Explain the observed electrical conductivity by listing the formulas of the ions present in
solution after the reaction has taken place. Note: The ions listed as products in the total ionic equations are responsible for the observed electrical conductivity. These include the spectator ions(ions that do not participate in the chemical reactions) and the ions produced in the chemical reactions. b. Again take a clean spot plate to the reagent bench. Fill each separate well of the spot plate all the way to the top with each of the solutions listed in part 3(b) on page 8. Measure the conductivity and proceed as
you did in part 3(a) above.
4. DETECTING THE END POINT OF AN ACID-BASE REACTION BY MEASURING THE
ELECTRICAL CONDUCTIVITY
Take a clean spot plate to the reagent bench. Fill a separate well of the spot plate all the way to the top
with 0.10 M Ba(OH)
2
. Into another well of the spot plate fill all the way to the top with 0.10 M H
2
SO
4
.
Measure the conductivity of each solution by using the conductivity probe. Record your observations.
Now, in a clean small beaker fill it with 5 mL of 0.10 M H
2
SO
4
, place the conductivity probe into the
solutionand then slowly add the 0.10 M Ba(OH)
2
solution drop by drop. Mix well after the addition of
each drop by gently swirling the beaker. Monitor the electrical conductivity until the conductivity
measurement shows no conductivity. Show the non-conducting mixture with your measured conductivtiy
to your instructor and get his/ her initial on page 9. Write your explanation on page 9 based on the
chemical equations for the reaction.
Now add more drops of Ba(OH)
2
to the non-conducting mixture until the electrical conductivity is
resumed. Explain in terms of the ions present.
Dispose of the Barium mixture in a special waste container labeled: BaSO 4 waste Dispose of the calcium chloride/sodium carbonate mixture in a special waste container labeled: CaCO 3 waste. Dispose of your solutions by pouring them in the sink and washing them down with water.
Dispose of the solutions by pouring them in the sink and washing them down with water.
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5. CONDUCTIVITY OF WATER
a. Test the conductivity of water, using the conductivity probe. Notice that the conductivity you will
observe for tap water is due to the presence of dissolved minerals.
b. Record the response of the conductivity probe on table C, page 9.
6. CONDUCTIVITY OF IONIC COMPOUNDS AND METALS
Test the conductivity of solids listed on page 10 using the LED conductivity indicator. Be sure that “both”
probes are dry and in contact with the material being tested. To dry the probes, blot the excess water with
a tissue. Record the response of the LED on table D, page 10.
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Report- Electrical Conductivity
Name__________________________________
Last
First
Instructor’s initial ___________
1. SOLVENT EFFECT ON THE ELECTRICAL CONDUCTIVITY