Step-by-Step Guide to Performing the Daniell Cell EMF Experiment for Class 12 Chemistry
Daniell Cells are used to 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
Procedure
Observations
Result
Precautions
Aim of the Experiment
To set up a simple Daniell cell 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”. To avoid confusion.
Procedure
Fill a clean beaker halfway with copper sulphate solution.
Clean the copper strip with sandpaper before dipping it in copper sulphate.
Fill a porous pot halfway with zinc sulphate solution.
Clean the zinc strip with sand paper before dipping it in zinc sulphate solution.
Maintain the porous pot in the beaker.
Connect the copper strip to the positive terminal of a voltmeter and the zinc strip to the negative terminal.
Take note of where the pointer is.
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 an 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 Daniell cell a type of primary cell?
Ans. Daniell cell is a primary cell which produces an electromotive force between its two terminals by a series of chemical reactions. It is essentially made up of copper and zinc with 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 Daniell 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 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 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 metal.
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.
FAQs on CBSE Class 12 Chemistry 2025-26: Setting Up Daniell Cell & Finding EMF
1. From an exam perspective for the CBSE Class 12 Chemistry Board Exam 2025-26, what are the most important aspects to cover when explaining the setup and working of a Daniell cell for 3 marks?
For a 3-mark question on the Daniell cell, you must include the following points:
- Anode Half-Cell: A zinc rod dipped in a 1M zinc sulphate (ZnSO₄) solution. Mention that oxidation occurs here (Zn → Zn²⁺ + 2e⁻).
- Cathode Half-Cell: A copper rod dipped in a 1M copper sulphate (CuSO₄) solution. Mention that reduction occurs here (Cu²⁺ + 2e⁻ → Cu).
- Salt Bridge: Describe its function – to connect the two half-cells, maintain electrical neutrality by allowing ion flow, and complete the internal circuit.
- Electron Flow: Clearly state that electrons flow from the zinc electrode (anode) to the copper electrode (cathode) through the external wire.
2. What is the standard EMF of a Daniell cell and how is it calculated from the standard electrode potentials?
The standard EMF (Electromotive Force) of a Daniell cell is +1.1V. This value is a crucial one-mark point in many numerical problems. It is calculated using the formula:
E°cell = E°cathode - E°anode
For a Daniell cell:
- The standard reduction potential of the copper half-cell (cathode) is E°(Cu²⁺/Cu) = +0.34 V.
- The standard reduction potential of the zinc half-cell (anode) is E°(Zn²⁺/Zn) = -0.76 V.
Therefore, E°cell = (+0.34 V) - (-0.76 V) = 1.1 V.
3. What are the two primary functions of a salt bridge in a Daniell cell? What happens if it is removed?
The two primary functions of a salt bridge, often asked for 2 marks, are:
- It completes the electrical circuit by connecting the electrolytes in the two half-cells, allowing the flow of ions.
- It maintains electrical neutrality in both half-cells by providing ions to counteract the charge build-up. Anions from the salt bridge move to the anode compartment, and cations move to the cathode compartment.
If the salt bridge is removed, the flow of ions between the half-cells stops. This leads to an accumulation of positive charge (Zn²⁺ ions) in the anode half-cell and negative charge (SO₄²⁻ ions) in the cathode half-cell. This charge separation creates an opposing potential that stops the electron flow, and the cell stops working instantly.
4. Write the cell notation for a standard Daniell cell and state the reactions occurring at the anode and cathode.
The correct cell notation for a standard Daniell cell is a frequently asked 1-mark question:
Zn(s) | Zn²⁺(aq, 1M) || Cu²⁺(aq, 1M) | Cu(s)
The reactions are:
- Anode (Oxidation): Zn(s) → Zn²⁺(aq) + 2e⁻
- Cathode (Reduction): Cu²⁺(aq) + 2e⁻ → Cu(s)
5. How does the EMF of a Daniell cell change when the concentration of Cu²⁺ ions is increased? Justify your answer with the Nernst equation.
This is a high-order thinking question. When the concentration of Cu²⁺ ions is increased, the EMF of the Daniell cell increases.
Justification using the Nernst Equation:
The Nernst equation for a Daniell cell at 298 K is:
Ecell = E°cell - (0.0591/2) * log([Zn²⁺]/[Cu²⁺])
As you increase the concentration of Cu²⁺, the value of the ratio [Zn²⁺]/[Cu²⁺] decreases. Consequently, the value of log([Zn²⁺]/[Cu²⁺]) also decreases. This means a smaller value is subtracted from E°cell, which results in a larger value for Ecell (the cell's EMF).
6. What is the role of the copper sulphate (CuSO₄) solution in the Daniell cell? Is it a depolariser?
Yes, in the context of the Daniell cell, the copper sulphate solution acts as the depolariser at the cathode. Its role is to provide Cu²⁺ ions. These ions accept the electrons coming from the anode, preventing the accumulation of negative charge on the copper electrode and allowing the reduction reaction (Cu²⁺ + 2e⁻ → Cu) to proceed smoothly. This prevents cell polarisation and ensures continuous current flow.
7. An external opposing potential is applied to a Daniell cell. What is the expected effect on the cell reaction and current flow when this external potential is (i) less than 1.1 V, (ii) equal to 1.1 V, and (iii) greater than 1.1 V?
This is a critical concept for the CBSE 2025-26 exam. The effects are as follows:
- (i) When Eext < 1.1 V: The cell functions as a normal galvanic cell. Electrons flow from Zn to Cu, Zn dissolves at the anode, and Cu deposits at the cathode.
- (ii) When Eext = 1.1 V: The opposing potential exactly balances the cell potential. There is no flow of current or electrons, and no chemical reaction occurs. The system is at equilibrium.
- (iii) When Eext > 1.1 V: The cell behaves as an electrolytic cell. The direction of the current reverses. Electrons flow from Cu to Zn, so copper dissolves and zinc gets deposited. The overall cell reaction is reversed.
8. Why can't we use an electrolyte like KCl in the salt bridge if one of the half-cells uses a silver (Ag) electrode?
This is a conceptual trap question. We cannot use KCl in a salt bridge with a silver electrode because the chloride ions (Cl⁻) from the KCl would react with the silver ions (Ag⁺) from the half-cell solution to form a precipitate of silver chloride (AgCl).
Reaction: Ag⁺(aq) + Cl⁻(aq) → AgCl(s)
The formation of this precipitate would block the flow of ions, disrupt the electrical neutrality, and cause the cell to stop working. The key principle is that the electrolyte in a salt bridge must be inert and not react with the ions in either half-cell.
