Name:
________________________________
Blk: ______ Date:
Purpose: To connect chemistry bonding and polarity concepts_______________
to measured values
of conductivity and concentration for a wide variety of reagents.
Materials:
Reagents:
- 1 small jar of sodium chloride
- solid calcium carbonate
- 0.10 M hydrochloric acid
- 2.0 M hydrochloric acid
- Methanol (CH3OH)
- distilled water (dH2O)
Apparatus:
- electronic balance (set on side)
- Stir rod / scoopula
- (2) weigh boats
- (1) 250 mL beaker
- (4) 50 mL or 100 mL beakers
- (1) 50 mL Graduated cylinder
- Multimeter + ‘How to Use’ sheet
- Light bulb
- 4 wires with alligator clips
- (2) 1.5VBattery + holder
- small piece of sand paper
- Hot plate + mat + tongs
- 2 pieces of thick copper wire (copper electrodes)
Procedure and Results:
1. Put on your safety equipment (goggles and apron)
2. Write a brief description of the safety hazards for the above chemicals:
Sodium chloride:
Calcium carbonate:
Hydrochloric acid:
Methanol:
3. Once safety concerns have been noted, obtain all of the above apparatus (not the
reagents). Make sure the copper electrodes are sanded to reveal ‘fresh’ copper.
4. One of the main properties you will be testing is electrical conductivity. You will first
need to construct a series circuit involving 2-1.5V battery, multimeter (set to read DC
Amperage), and a light bulb (optional). Draw a schematic diagram involving these
materials which will attach to the copper electrodes in the beaker:
Schematic
5. Build the circuit. Make sure you do NOT complete the circuit unless you are sure the
multimeter is connected correctly. Note: the circuit should not be left connected as
it will drain the batteries altering your results.
6. What is electricity? (make sure to use ‘conducting’ in your definition)
__________________________________________________________________________________
7. Since there are generally only 2 types of substances which can
conduct electricity: (i) Metals and (ii) Charged particles. Let’s start
the data/observation collection by completing the circuit by
touching the two copper electrodes together. You are measuring
current to show the conductivity!
8. Fill one of the beakers with about 50mL
of dH2O and measure the conductivity
of water by placing the copper
electrodes into the water (make sure
the electrodes do not touch, or else
you will be testing the copper and not
the water!).
Predict!!! What do you think the current will
be in comparison to the reading you found
in step 7?
Copper: current (DCA):
Water: current (DCA):
Let’s use the above results as our controls for the experiment!
Note: After each conductivity test that follows, make sure the copper
electrodes are washed, dried and sanded (if necessary). You should use the
250mL beaker as a ‘wash’ container for the electrodes!
Now test several different items in the classroom to have an idea of what can
conduct (ex. Air, a beaker etc.)
End of Day 1
Day 2 – Begin by completing step 7 and 8 as your controls!!!
Testing Ionic compounds:
9. Obtain one of the jars of sodium
chloride. Make a prediction of the
conductivity of NaCl(s); then test the
conductivity by placing the electrodes
in the jar (of course making sure the
electrodes do not touch each other)
NaCl(s) : current (DCA):
Prediction:
10. Place precisely 30mL of dH2O in one of the
beakers. Predict what will happen to the
conductivity if a small amount of NaCl(s) is
added to the water. Add a small ‘scoop’
of NaCl to the water and stir. Make
observations and then test for conductivity.
Note: let’s be precise, measure out
0.0050mol! Do NOT discard this solution!
Observations:
Prediction:
NaCl(aq) : current (DCA):
Show the calculation here for 0.0050mol:
11. Predict what will happen to the
conductivity as more NaCl is added to the
solution in step 10. Now, using the solution
from step 10, add small scoops of NaCl until
a saturated solution is formed and then test
this solution for conductivity. Make sure you
discuss the appearance of a saturated
solution. Do NOT discard this solution!
12. Using the saturated solution
from step 11, add one more
scoop of NaCl to the solution.
What do you notice? Test the
conductivity. Do NOT discard!
13. Now you want to make a
supersaturated solution of
sodium chloride. What do
you need to do to
complete this? Test the
conductivity of your
supersaturated solution.
Repeat step 10 with calcium
carbonate (0.0050mol) instead
of sodium chloride. First, make
your predictions!
Observations:
Prediction:
Prediction:
Procedure to make a Supersaturated solution:
Saturated NaCl: current
(DCA):
Observations:
current (DCA):
Observations:
Supersaturated NaCl: current:
Prediction:
Observations:
current (DCA):
Testing Covalent molecules:
14. Place 20mL of the 0.10 M HCl solution into a 50 or
100 mL beaker and test the conductivity.
15. Place 20mL of the 2.0M HCl
solution into a beaker.
Predict the difference
between the two HCl
solutions. Test the
conductivity. Do NOT
discard this solution!
16. Using the solution from step
16, add 20mL of dH2O to the
solution. Predict what will
happen to the conductivity
and then test for the
conductivity.
17. Place 20 mL of the
methanol into a 100mL
beaker. Predict what the
comparison would be to
water (step 8) and NaCl(aq)
(step 10). Test the
conductivity of the
methanol liquid.
18. Now add 20mL of water to
the methanol solution.
Predict the conductivity
and then test for it.
Prediction:
0.10M HCl : current:
Observations:
2.0M HCl : current:
Prediction:
______M HCl : current:
Prediction:
Observations:
Methanol: current (DCA):
Prediction:
Observations:
Methanol: current (DCA):
19. Clean-up and make sure all solutions are properly disposed of!
What’s the deal with Conductivity – Post Lab Questions
Name: __________________________
Blk: _____ Date: ________________
1) a) What can you conclude about the conductivity of metals (ex. Copper)
compared to all other substances tested?
b) Give an explanation to why metals conduct electricity. (you must cite
your resource!)
2) Compare the conductivity of water (step 8) to the unsaturated NaCl (aq) (step
10). Is there a significant difference? Explain why
3) Why do you think the solid NaCl (step 9)did NOT conduct any electricity?
4) Explain the conductivity difference between an unsaturated solution of NaCl
(step 10) to a saturated one (step 11).
5) Explain why the conductivity did not change from the solution in step 11 to
the solution in step 12.
6) Explain why a supersaturated solution conducts more electricity than a
saturated one.
7) Explain the conductivity difference between step 10 and step 14. Both
solutions contain very similar amounts of different salts, so why the difference
in conductivity? Make sure to use your observations to help explain your
answer.
8) In the beakers below, draw the structure for all particle(s) which exist in the
following: the second beaker is completed for you!
Water
Unsaturated NaCl(aq)
Saturated NaCl(aq)
9) Explain the conductivity differences between acidic solutions:
a) step 15 and step 16
b) step 16 and step 17
10) Compare and explain the conductivity results for:
H2O(l) (step 8) vs CH3OH(l) (step 18) vs CH3OH(aq) (step 19)
Although the data results are small values, there are still major differences
between them!
Conclusion: Why can liquids and solutions allow electrons to flow through them as a
conducting circuit?