Name: ……………………………….
Practical No : ……….
Grade: ……….
Date: ……………..
The measurement of Avogadro’s Number. (SL/HL)
This is a demonstration experiment in which the educator conducts the experiment and learners
observe and record results.
Aims: 1. To demonstrate the electrolysis of a solution of copper sulphate
using copper electrodes.
2. To show an understanding of the chemical processes involved in electrolysis.
3. To use the results obtained to calculate Avogadro’s Number.
Instructions
1. Take notes when the procedure is explained to you in class so that you will be able to include
the theory in your write-up.
2. Record all the results obtained in the experiment.
3. Explain the theory of electrolysis in your write-up.
4. Calculate Avogadro’s Number.
5. Consult the rubrics to ensure that you have included all that is expected of you.
PROCEDURE
1. Describe the action plan, including a statement of the problem, the apparatus that you will use,
a sketch of the apparatus and circuit diagram and the method that you will follow.
2. Write a brief explanation of the electrolysis process that occurs in this experiment. Head this
section “Theory of Electrolysis”
3. Draw up a suitable table for the readings to be entered into, and enter these readings.
4. Establish the number of ions lost by the anode that account for the decrease in mass of the
anode.
5. Carry out the calculation of Avogadro’s Number, ensuring that full explanation has been given.
6. Indicate the equations for the reactions at the respective electrodes.
7. State the conclusion to the investigation, and discuss possible sources of error.
8. Attach the rubric sheet to the top of your write-up.
ASSESSMENT
The rubrics on the next page will be used to assess your work. The total number of marks for the
practical is given on the rubric sheet.
NAME: …………………………………….
CLASS: ………..
DATE …………………..
ASSESSMENT RUBRICS FOR MEASUREMENT OF AVOGADRO’S NUMBER
Prac No: …..
Assessment of investigative and manipulative skills
COMPETENCY LEVEL
Not achieved
CRITERIA
Achieved
1
Partially
Achieved
2
1
2
3
1
2
3
1
2
3
3
States the problem
Presents action plan
Presents list of apparatus and a
sketch with circuit diagram
(9)
Assessment of ability to explain electrolysis
CRITERIA
Competency level
Fully explained, including the half-reactions and full equation.
Clear understanding demonstrated
Fair explanation, but an error or omission.
4
3
A number of errors or omissions. Little real understanding
demonstrated.
Very poor explanation. No real understanding demonstrated.
2
1
(4)
Assessment of recording skill
CRITERIA
Competency level
All readings neatly tabulated in a neat, logical manner.
4
Readings tabulated, but not in a logical or clear manner
3
No structure shown in recording of readings.
2
Readings not recorded
1
(4)
Assessment of interpretation of data
CRITERIA
Competency level
Correctly uses data to calculate Avogadro’s number. Steps clearly
identifiable and explanation given where necessary.
Correct calculation of Avogadro’s number but weakness in
methodical setting out of the calculation.
Very poor setting out. Logical steps not evident, even though
calculation may be correct.
Calculation of Avogadro’s number not attempted.
4
3
2
1
(4)
TOTAL MARKS : 21
MARK ACHIEVED: ……………
Sample results obtained during this practical to measure the
Avogadro Number:
 Current allowed to run for 15 minutes.
 Strength of current flow = 0.7A
 Initial mass of Cu anode = 71.59 g
 Final mass of Cu anode = 71.39 g
Extra hints:
 Determine charge Q in circuit in 15 min. Q = I X t
 Find no. of electrons passed in this time: no. of electrons = Total charge Q
charge on electron



Charge on electron = 1.6 x 10-19C
Find no. of Cu atoms passing during this time:
No. Cu atoms removed = no. electrons/2
Thus find the Avogadro Number: i.e. no of Cu atoms lost x 63.5/ decrease in mass.