Download What are the factors affecting the electromotive force of a Daniell cell?

LLG
Paris–Abu Dhabi
Advanced Math and Science Pilot Class
Academic year 2014-2015
Lab work– Chemistry
What are the factors affecting the electromotive force of a
Daniell cell?
Purpose:
● Building a Daniell cell by associating the half-cells : Cu2+/Cu and Zn2+/Zn
● Using a voltmeter to measure the electromotive force (emf) of this cell
● Varying some factors of the cell and finding out how they affect the emf.
● Building a concentration cell.
I. Daniell cell and electromotive force
Reminder: Using a voltmeter to measure the electrical potential difference ( or voltage) between two
electrodes shows how strongly the anode reaction can push the electrons into the circuit and how
strongly the cathode reaction can pull them out. The maximum potential difference (measured when
no current is flowing in an external circuit) is called the electromotive force, abbreviated emf and
represented by the symbol E.
E1:Using the equipment available on your table, including two
ionic solutions of copper sulfate (Cu2+(aq), SO42-(aq)) and zinc
sulfate (Zn2+(aq), SO42-(aq)) whose molar concentration is C1 = 1.0
mol.L-1, create an electrochemical cell following the drawing
beside (each compartment has a 20.0 mL solution)
Q2: What is the use of the salt bridge?
E3: Study the cell in open circuit, with a voltmeter. Measure
and record the emf E
Q4: Identify the electrodes (which one is the anode and which
one the cathode?)
Q5: Write the half redox reaction occurring at each electrode.
Q6: Write the redox reaction occurring when this cell is
functioning .
II. Factors affecting the emf:
Q7: What factor of the Daniell cell could you think of modifying (using the available
equipment)?
E8: Conduct an experiment (after proposing a procedure to the teacher) to test this factor.
(Detailed report of this experiment is expected here)
Q9: Show your results in a table
Q10: Expose your result to the class and write a general conclusion (collaborative work).
III. Concentration cells:
A concentration cell is an electrolytic cell that is comprised of two half cells with the same
electrodes but differing in concentrations.
E11: Build a copper concentration cell, using the copper sulfate (Cu2+(aq), SO42-(aq)) solutions at 1.0
mol.L-1 and 1.0×10-2 mol.L-1 and then using the 1.0×10-1 mol.L-1 and 1.0×10-2 mol.L-1 solutions.
E12: Measure and record the emf of these cells
Q13: Identify the electrodes (which one is the anode and which one the cathode?)
Q14: Write the half redox reaction occurring at each electrode.
Q15: Write the redox reaction occurring when this cell is functioning
Q16: What can be the use of concentration cells?
LLG
Paris–Abu Dhabi
Advanced Math and Science Pilot Class
Equipment: (8 groups)
Students:
• distilled water
• 6 beakers 100 mL
• graduated cylinder 50 mL
• graduated pipette 10 mL + bulb
• 2 volumetric flasks 100 mL
• stripes of filter paper ( for salt bridge)
• copper and zinc plates
• voltmeter + 2 wires
Teacher:
• 250 mL of solution (Cu2+ + SO 24  ) at 1.0 mol/L
• 250 mL of solution (Zn2+ + SO 24  ) at 1.0 mol/L
• saturated solution of ammonium nitrate
Academic year 2014-2015
Lab work– Chemistry