To Set Up Simple Daniell Cell Using Salt Bridge and Determine its Emf

Introduction

Daniell Cells are used to either generate or store electricity. Daniell Cells are used in the development of batteries and electrical telegraphy. Battery means collections of cells.

Table of Contents

• Aim of the Experiment

• Apparatus Required

• Theory

• Prodedure

• Observations

• Result

• Precautions

Aim of the Experiment

To set up simple Daniell cell using salt bridge and determine its emf

Apparatus Required

• One beaker

• a porous pot

• connecting wires

• milli voltmeter

• sand paper

• zinc strip

• copper strip

• 1 M ZincSulphate solution 

• 1 M CopperSulphate solution

Theory

When a copper electrode dipped in copper sulphate solution is connected to a zinc electrode dipped in zinc sulphate solution, electrons flow from zinc electrode to copper electrode and the following chemical reactions occur:

$${{Zn}}$$ $$\to$$ $${{Zn}^{2+}{+}{2}{e}^{-}}$$

$${{Cu}^{2+}{+}{2}{e}^{-}}$$ $$\to$$ $${{Cu}}$$

The overall reactions is $${{Zn}{+}{Cu}^{2+}}$$ $$\to$$ $${{Zn}^{2+}{+}{Cu}}$$

While doing the experiment you should assume that the beaker with a name. For example Beaker “A”. So as to avoid confusion.

Procedure

Daniell Cell with salt bridge

• Set up the apparatus as shown in the above figure.

• The flow of electrons will happen for sometime. Now note the readings of voltmeter.

Observations

Result

The EMF varies non-linearly as the concentration of reactants changes.

Precautions

• Copper sulphate and zinc sulphate concentrations should be neither too low nor too high.

• The porous pot should not be completely immersed in the copper sulphate solution, and no copper sulphate solution should enter the porous pot.

• Sand the zinc and copper strips before using them.

• Dilute the solution slowly and carefully.

• Only take note of the reading when the pointer becomes stable.

• Connect the copper strip to the voltmeter's positive terminal and the zinc strip to the negative terminal.

Lab Manual Questions

1. In this experiment, explain how le Chatelier's principle applies to your electrochemical cell.

Ans. Le Chatelier's principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change to reestablish equilibrium.

2. Is the Nernst law followed across the entire concentration range? 

Ans. The value of the equilibrium potential for any ion depends upon the concentration gradient for that ion across the membrane. If the concentrations on the two sides were equal, the force of the concentration gradient would be zero, and the equilibrium potential would also be zero.

3. Is Daniel cell a type of primary cell?

Ans. Daniel cell is a primary cell which produces an electromotive force between its two terminals by a series of chemical reactions. It is composed of copper and zinc with the cuprite sulphate as an electrolyte.

4. In Daniell's cell, which solution is used?

Ans. In a Daniell cell, the electrolytes are $${{Zn}{S}{O}_{4}}$$(aq) with a Zn anode in its half-cell and $${{Cu}{S}{O}_{4}}$$(aq) with a copper cathode in its half-cell.

Viva Questions

1. What are the two electrodes that are used in the Daniell cell?

Ans. Zinc and Copper Electrodes are used.

2. How does a Daniel cell function?

Ans. In a Daniell cell, electrons flow from zinc electrode to copper electrode through an external circuit, while metal ions form one half cell to the other.

3. How do you depict Daniell cell?

Ans. The symbol double vertical lines || represents the Daniell cell. The left part is oxidation half Cell and the right part is reduction half Cell.

4. Why can't Daniell cell be recharged?

Ans. Daniell Cell is not rechargeable, because recharge would much aggravate the Cu2+ crossover, indicating a battery-killing process.

5. Is Daniel cell a dry cell?

Ans. No. Daniell cell is a wet cell.

6. What is the Daniell cell Nernst equation?

Ans. $${{E}^{0}_{cell}{=}{\frac{0.0592}{n}}{log}{K}}$$

7. Is the galvanic cell and the Daniel cell the same thing?

Ans. A galvanic cell is one which converts the redox reaction chemical energy in to electrical energy through outside circuit. But a Daniel cell is the cell constructure by redox couple of Zn|$${{Zn}{S}{O}_{4}}$$ and Cu|$${{Cu}{S}{O}_{4}}$$. So Daniel cell is primarily a Galvanic cell but all the galvanic cells are not Daniel cell.

8. Which phenomena does not occur in Daniell cell?

Ans. There is no change in colour of the $${{Zn}{S}{O}_{4}}$$ solution.

9. Is a Daniel cell a spontaneous reaction?

Ans. The emf of the cell is +1.1V. hence the cell reaction is spontaneous.

10. What is Daniell's cell used for?

Ans. The Daniell cell can be used to 'generate' electricity by consuming an electrode or to store electricity. Although the Daniell cell was one of the early examples of a device for generating electricity, it is relatively difficult to analyse thermodynamically because it has electrodes of different materials.

Practical-Based Questions

1. An electrochemical cell is typically made up of a cathode and an anode. Which of the following statements about the cathode is correct?

a) Oxidation occurs at the cathode

b) Electrons move into the cathode

c) Usually denoted by a negative sign

d) Usually made up of insulating material

Answer: B

2. Cell emf is the sum of the electrode potentials of the two electrodes when no current is drawn through an electrochemical cell. True or False?

a) True

b) False

Answer: A

3. An electrochemical cell can convert electrical energy to chemical energy.

a) True

b) False

Answer: B

4. When equilibrium is reached inside the two half-cells of the electrochemical cells, what is the net voltage across the electrodes?

a) > 1

b) < 1

c) = 0

d) Not defined

Answer: C

5. Which of the following statements is correct regarding Electrochemical cells?

a) Cell potential is an extensive property

b) Cell potential is an intensive property

c) The Gibbs free energy of an electrochemical cell is the intensive property

d) Gibbs free energy is undefined for the electrochemical cell

Answer: B

6. Which of the following factors does not affect the electrode potential of an electrode?

a) Nature of the electrode (metal)

b) Temperature of the solution

c) Molarity of the solution

d) Size of the electrode

Answer: D

7. Why are the saturated solutions of electrolytes for the salt bridge prepared in agar-agar jelly or gelatin?

a) The jelly acts as an electrolyte

b) It help the electrolytes to mix with the contents of the half cells

c) It help maintain the electrical polarity between the two half-cell solutions

d) It keep the electrolyte in semi-solid phase and prevents it from mixing with the two half-cell solutions

Asnwer: D

8. Which of the following is not a type of electrochemical cell?

a) Voltaic cell

b) Photovoltaic cell

c) Electrolytic cell

d) Fuel Cell

Answer: B

9. EMF of Daniell cell is

a)1.1 volts

b)2.1 volts

c)1.0 volts

d)1.5 volts

Answer: A

10. What is the observation when the opposing external applied potential to an electrochemical cell is greater than the cell’s potential?

a) The electrochemical cell behaves like an electrolytic cell

b) The electrochemical cell stops functioning

c) Only oxidation reactions occur in the cells

d) Only reduction reactions occur in the cells

Answer: A

Conclusion

• A Daniell Cell is an ElectroChemical Cell that performs chemical reactions to generate electricity. The anode in the Daniell Cell is zinc metal, and the cathode is copper.

• Daniell Cells are used to either generate or store electricity. Daniell Cells are used in the development of batteries and electrical telegraphy. Battery means collections of cells.