Chemistry Project to Study the Change in EMF of a Daniel Cell

Study the Change in E.M.F of a Daniel Cell Due to Various Factors Such as Change in Concentration, Temperature and Area of Electrodes

Certificate

This is to certify that ROHIT SINGHAL, student of Class XII A, YUVA SHAKTI MODEL SCHOOL has completed the project titled “To Study the Change in E.M.F of a Daniel Cell due to Various Factors Such as Change in Concentration, Temperature and Area of Electrode” under my guidance and completed it to my total satisfaction.

Mrs. Shanthi Jaichandran Date: (Teacher’s Signature)

Acknowledgement

It gives me great pleasure to express my gratitude towards our chemistry teacher Mrs. Shanthi Jaichandran for her guidance, support and encouragement throughout the duration of the project. Without her motivation and help the successful completion of this project would not have been possible.

Rohit Singhal XII-A

Objective

The goal of this project is to study the change in E.M.F of a Daniel cell due to various factors such as change in concentration, temperature and area of electrodes.

Materials and Equipment

To do this experiment we will need the following materials and equipment:

• Two beakers
• Zinc and Copper plate
• Filter paper
• Voltmeter
• Connecting wires
• Card board
• KNO3 solution
• 1 M, 0.1 M, 0.01 M solution of:
  • a. CuSO4
  • b. ZnSO4

Introduction

It is an arrangement to convert the chemical energy of the redox reaction into electric energy.

Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s)

Daniel Cell

When an external circuit is connected, the chemical equation for the zinc side (anode) half cell is:

Zn (s) → Zn2+ (aq) + 2e-

For the copper sulphate side (cathode) half cell:

Cu2+ (aq) + 2e- → Cu (s)

Therefore, the overall reaction of the Daniel cell is:

Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s)

Features of Daniel Cell

• Zinc rod at which oxidation occurs is called the anode while the copper rod at which the reduction takes place is called cathode.
• The overall reaction occurring in electrochemical cell is due to two half-cell reactions, one occurring in each beaker.
• The half-cell reaction occurring at anode is called oxidation half-cell reaction while the one occurring at cathode is called reduction.
• The two half-cell reactions always take place simultaneously. A half-cell reaction cannot take place independently.
• Since electrons are produced at the zinc electrode, it is rich in electrons and pushes these electrons into the external circuit and hence acts as the negative pole. The copper electrode on the other hand is deficient in electrons and thus pulls the electrons from the external circuit and acts as positive pole.
• The electrons flow from negative pole to positive pole in the external circuit. However, conventionally the current is said to flow in the opposite direction, i.e. from positive pole to negative pole in the external circuit.
• The concentration of copper sulphate solution decreases with passage of time as the cell operates; consequently the current falls with passage of time.

Salt Bridge

It consists of a tube filled with semi-solid paste obtained by adding gelatine or agar to the solution of a strong electrolyte such as NaCl, NH4NO3, KNO3 etc., which does not change chemically during the process.

Function of Salt Bridge

• To complete the electrical circuit by allowing the solution to flow from one solution to another without mixing the two solutions.
• To maintain electrical neutrality of solution in the two half-cells.

EMF of Cells

The potential difference generated by a cell when the cell draws no current is called EMF.

Procedure

1. Take two beakers and pour the required chemicals in the respective beaker and mark them for identification.
2. Take two square plates, slide in the connecting wires and tighten their screws.
3. Connect the negative terminal of the voltmeter to the anode and its positive terminal to the cathode.
4. Take filter paper long enough to dip into both solutions. Dip the filter paper in KNO3 solution and place it as a salt bridge.
5. Set up the electrode-voltmeter setup. Note the reading quickly and then disconnect the setup.
6. For measuring variation with change in area of electrode, use different sizes of electrode and then repeat step 5.
7. For measuring variation with temperature, heat the solution and then repeat step 5.
8. For measuring variation with change in concentration of electrolyte, use electrolytes of different molarity and then repeat step 5.

Observations

Electrode Potential of Zinc = ………….. V

Electrode Potential of Copper = ………….. V

Variation with Concentration

Molarity of CuSO4 (M)	Molarity of ZnSO4 (M)	Voltmeter Reading (V)

Variation with Change in Area of Electrodes

With increase in area or decrease in area of electrode, EMF of cell remains the same.

Variation with Temperature

CuSO4 (°C)	ZnSO4 (°C)	Voltmeter Reading (V)

Conclusions

• The EMF varies non-linearly with change in concentration of reactants.
• Increase in concentration of ions in the anode half-cell decreases EMF and vice versa.
• The EMF is independent of area of electrode.
• The EMF increases with increase in temperature.