| Short Description: |
Using conductivity probes to find the different electric conductivity of some electrolytes and non-electrolytes by observing the behavior of these substances in aqueous solutions. |
| Duration of Lesson: |
2 Class Periods |
| Grade Levels: |
High 9-12 |
| Subjects: |
Chemistry |
| Technologies used in Lesson: |
Computer, Probe |
|
Online Tutorial: |
|
STUDENT GRADE: 11 and 12
DURATION: 90
minutes (double periods)
OBJECTIVES: After students have completed this lesson,
they will be able to:
1. Discover
some properties of electrolytes and non-electrolytes by observing the behavior
of these substances in aqueous solutions.
2. Know how to
determine those properties by using a conductivity probe.
3. Learn the
conductivity value depending on the ability of aqueous solution to conduct
electricity
4. Observe
the relative magnitude of the conductivity of different compounds dissolving in
water
5. Learn three types
of compounds and their aqueous solutions.
6. Learn
how to read the graph of conductivity and compare the values.
RESOURCES/MATERIALS:
1. Students’ chemistry review book 2004 Edition.
2. Student journals.
3. A sheet of “Data Table”
4. Power Macintosh or Windows PC
5. Vernier computer interface
6. Logger Pro.
7. Vernier Conductivity Probe
8. 250-ml beakers
9. Wash bottle with distilled water
10. Tissues
11. Ring stand
12. Utility clamp
13. Tap water
14. Distilled water
15. 0.05 M NaCl
16. 0.05 M KCl
17. 0.05 M HCl
18. 0.05 M CH3OH
19. 0.05 M C12H22O11
20. 0.05 M CH3COOH
21. NaCl (s)
22. Sugar (s)
ACTIVITIES / PR0CEDURES
1. Warm-up / Do Now
Students respond to the following question written on the
board prior to the class:
Why is it dangerous to
swim outdoor in the storm with thunder and lightning?
2. Teacher’s Demonstration:
Using conductivity probe to measure the conductivity of:
(1) pure water
(2) tap water
(3) the same tap water used in (2) by adding some sugar (s)
(4) the same tap water used in (2) by adding some NaCl(s)
A projector connected with the computer reflects the
conductivity graph to a big screen on the wall in front of the class so that
all students will see the results.
Always ask students to predict the result by drawing a graph
on their paper before each demonstration and then ask them to compare their
prediction with the real experiment graph.
3. Class Discussion:
(1) What have you observed from the demonstration?
(2) Why does pure water have almost zero conductivity?
(3) Why does the conductivity of tap water with some sugar
dissolved not change?
(4) Why does the conductivity increase by adding some NaCl (s) in
the tap water
4. Divide students of the class into five or six groups. Each
group will do the demonstration for one solution and the other students predict
the results by drawing the graph of the conductivity on their paper and then
compare their predictions with the results of the demonstration. After the
activities of all the groups, the students will input the data on the “Data
Table” and prepare for the class discussion.
5. Data Table:
|
Group
|
Solution
|
Conductivity
|
|
A
|
KCl
|
|
|
|
MgCl2
|
|
|
|
NaCl
|
|
|
|
|
|
|
B
|
CH3OH
|
|
|
|
C12H22O11
|
|
|
|
H2O
(pure)
|
|
|
|
|
|
|
C
|
CH3COOH
|
|
|
|
HCl
|
|
6. Divide the students into small groups (5 to 6 students in each
group) to discuss:
(1) Which group (A, B or C) has higher conductivity?
(2) Which group (A, B or C) has lower conductivity?
(3) How do you explain the
relatively high conductivity of tap water compared to a low or zero
conductivity of distilled water
(4) How do you explain the
high conductivity of group A compared to the lower conductivity for group B
7. Teacher’s Explanation:
(1) The conductivity value depends on the ability of the aqueous
solution to conduct electricity.
(2) Larger numbers of ions in the solution will result in high
conductivity values.
(3) A substance, whose water solution conducts an electric
current, is called electrolytes. Strong electrolytes produce large number of
ions, resulting in high conductivity; weak electrolytes produce small number of
ions, resulting in low conductivity.
(4) A substance, whose water solution does not conduct an electric
current, is called non-electrolytes.
(5) There are three types
of compounds in the data table:
|
Group
|
A
|
B
|
C
|
|
Compounds
|
Ionic Compounds
|
Molecular Compounds
|
Molecular Acids
|
|
Type of
Electrolytes
|
Strong
|
Usually
Non-electrolytes
|
Some are strong;
some are weak
|
|
Bond Type
|
Ionic
|
Covalent
|
Covalent
|
|
Dissociate in Water
Solution
|
Almost 100%
|
Almost not
|
Wholly or partially
|
|
Conductivity in
Water Solution
|
High
|
Almost Zero
|
Some are high; some
are low
|
|
Example of
Ion-equation
|
NaCl(s)
---- Na(aq)+ +
Cl(aq)-
|
C12H22O11
_ C12H22O11
|
HCl (aq)
----H+(aq) + Cl-(aq) (strong acid)
CH3COOH
(aq) – H+(aq) + CH3COO-(aq) (weak acid)
|
8. Summary
|
|
Electrolytes
|
Non-electrolytes
|
|
|
Strong
|
Weak
|
|
|
Ions yielded in
water solution
|
Large
|
Small
|
Almost none
|
|
Conductivity value
|
High
|
Low
|
Almost zero
|
EVALUATION/ASSESSMENT
Students will be evaluated based on
initial journal response, participation in class and small group discussions,
completing of their data table and a small quiz.
QUIZ
(1) Based on your conductivity values in data table, explain the
differences occurred between NaCl and CH3OH. (Hint: Ionic or
molecular compounds; bonding type and how they dissociate in water)
(2) How do you explain the relatively high conductivity of tap
water compared to a low or zero conductivity of distilled water?
|
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