Computer
Saltwater Conductivity:
The Effect of Concentration
17
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If an ionic solid is dissolved in water, ions are released and the resulting solution will conduct
electricity. Dissolving solid sodium chloride (table salt) in water releases ions according to the
equation
→ Na+(aq) + Cl-(aq)
NaCl(s) 
OBJECTIVES
In this experiment, you will
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Use a computer to measure conductivity.
Record data.
Graph this data.
Use the data and graph to make conclusions about conductivity.
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In this experiment, you will study the effect on electrical conductivity of increasing sodium
chloride concentration. Electrical conductivity will be measured as the ion concentration of the
solution being monitored is gradually increased by the addition of concentrated NaCl drops. A
Conductivity Probe, attached to a computer, will be used to measure electrical conductivity.
Conductivity is measured in microsiemens (µS/cm).
MATERIALS
utility clamp
100 mL beaker
distilled water
sodium chloride solution (salt water)
Ev
al
computer
Vernier computer interface
Logger Pro
Vernier Conductivity Probe
ring stand
Figure 1
Physical Science with Vernier
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Computer 17
PROCEDURE
1. Obtain and wear goggles.
2. Get 60 mL of distilled water in a clean 100 mL beaker.
3. Your experiment setup should look like Figure 1. Your teacher will have connected the
Conductivity Probe and interface to the computer. The Conductivity Probe should be set on
the 0–2000 µS/cm position.
4. Prepare the computer for data collection by opening the file “17 Saltwater” from the Physical
Science w Vernier folder.
5. Before adding any salt solution
a. Click
.
b. Raise the beaker until the hole in the probe end is completely submerged in the water.
Swirl the water briefly.
c. Monitor the conductivity of the distilled water until the conductivity reading stabilizes.
, and then lower the beaker away from the probe.
d. Click
e. Type 0 in the edit box (for 0 drops added). Press ENTER to store this data pair. This gives
the conductivity of the water before any salt solution is added.
6. You are now ready to begin adding salt solution.
a. Add 1 drop of salt solution to the distilled water.
b. Swirl to ensure thorough mixing.
c. Raise the beaker until the hole in the probe end is completely submerged in the solution.
Swirl the solution briefly.
d. Monitor the conductivity of the solution until the reading stabilizes.
e. Click
, and then lower the beaker away from the probe.
f. Type 1 (the total drops added) in the edit box and press ENTER.
7. Repeat the Step 6 procedure, entering 2 this time.
8. Continue this procedure, adding 1-drop portions of salt solution, measuring conductivity, and
entering the total number of drops added—until a total of 10 drops have been added.
to end data collection. Record the conductivity values displayed in the table in
9. Click
your data table.
10. Print copies of the graph as directed by your teacher.
11. Dispose of the beaker contents as directed by your teacher.
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Physical Science with Vernier
Saltwater Conductivity: The Effect of Concentration
DATA
Drops
Conductivity
(µS/cm)
Drops
Conductivity
(µS/cm)
0
______
6
______
1
______
7
______
2
______
8
______
3
______
9
______
4
______
10
______
5
______
OBSERVATIONS
PROCESSING THE DATA
1. Describe the appearance of the curve on your graph.
2. Describe the change in conductivity as the concentration of the NaCl solution was increased
by the addition of NaCl drops.
Physical Science with Vernier
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Computer 17
3. Why are drops of NaCl solution graphed on the horizontal axis?
4. Why is conductivity graphed on the vertical axis?
EXTENSION
1. Investigate the effect of concentration on conductivity using other solutes.
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Physical Science with Vernier
Vernier Lab Safety Instructions Disclaimer
THIS IS AN EVALUATION COPY OF THE VERNIER STUDENT LAB.
This copy does not include:
z
Safety information
z
Essential instructor background information
z
Directions for preparing solutions
z
Important tips for successfully doing these labs
The complete Physical Science with Vernier lab manual includes 40 labs and essential
teacher information. The full lab book is available for purchase at:
http://www.vernier.com/cmat/psv.html
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