Electrochemical Cells - Galvanic Cell - UNSOLVED PRACTICE SET

Q7. Draw a labelled diagram of a Daniel cell showing the anode, cathode, electrolytes, salt bridge, and direction of electron flow.

Q8. Write the half-cell reactions and overall cell reaction for a Daniel cell (Zn | Zn²⁺ || Cu²⁺ | Cu).

Q9. Why is a salt bridge necessary in a galvanic cell? What would happen if it were removed?

Q10. Differentiate between a galvanic cell and an electrolytic cell with respect to:

(a) Energy conversion

(b) Spontaneity of reaction

(c) Polarity of electrodes

Q11. Your school science fair project involves making a lemon battery using a zinc nail and a copper coin. Explain which metal acts as the anode, which as the cathode, and why electrons flow from one to the other.

Q12. Why is platinum or graphite used as an inert electrode in some galvanic cells? Give one example where an inert electrode is necessary.

Q13. Describe the construction and working of a galvanic cell (Daniel cell) in detail:

(a) Components: electrodes, electrolytes, salt bridge, external circuit

(b) Half-cell reactions at anode and cathode

(c) Overall cell reaction

(d) Direction of electron and ion flow

(e) Function of the salt bridge and why KCl or KNO₃ is commonly used

(f) Cell representation (cell notation)

Q14. Explain the different types of electrodes used in galvanic cells:

(a) Metal-metal ion electrodes (e.g., Zn | Zn²⁺)

(b) Gas-ion electrodes (e.g., hydrogen electrode, Pt | H₂ | H⁺)

(c) Metal-insoluble salt electrodes (e.g., calomel electrode, Ag | AgCl | Cl⁻)

(d) Redox electrodes (e.g., Pt | Fe²⁺, Fe³⁺)

(e) Inert electrodes — when and why they are used

Give one example of each type with half-cell reaction.

Q15. Galvanic cells power countless devices in modern India. Discuss:

(a) How the principle of galvanic cells is used in medical devices like pacemakers and hearing aids

(b) Why zinc-carbon dry cells are still widely used in rural India's torches and radios

(c) The role of galvanic cells in corrosion protection of India's railway bridges and pipelines

(d) How understanding galvanic cells helps design better batteries for India's electric vehicle revolution

Q16. In a galvanic cell, the following half-reactions occur:

Anode: Zn → Zn²⁺ + 2e⁻

Cathode: Cu²⁺ + 2e⁻ → Cu

(a) Calculate the standard cell potential if E°(Zn²⁺/Zn) = -0.76 V and E°(Cu²⁺/Cu) = +0.34 V.

(b) Calculate the standard Gibbs free energy change for the cell reaction.

(c) Is the cell reaction spontaneous under standard conditions? Justify.

[Given: F = 96500 C/mol]

Q17. A student constructs a galvanic cell using magnesium and silver electrodes.

(a) Write the cell notation and identify the anode and cathode.

(b) Calculate the standard EMF of the cell. [E°(Mg²⁺/Mg) = -2.37 V, E°(Ag⁺/Ag) = +0.80 V]

(c) If the cell delivers a current of 0.5 A for 2 hours, calculate the mass of magnesium dissolved at the anode.

[Given: Atomic mass of Mg = 24 g/mol, F = 96500 C/mol]

Q18. A lemon battery is made by inserting a zinc nail and a copper wire into a lemon.

(a) Write the half-cell reactions occurring at each electrode.

(b) If the measured voltage is 0.9 V, and the pH of lemon juice is 2.0, calculate the approximate concentration of Zn²⁺ ions using the Nernst equation. [E°(Zn²⁺/Zn) = -0.76 V, E°(H⁺/H₂) = 0 V, assume PH₂ = 1 atm]

(c) If 10 such lemon cells are connected in series, what total voltage would be obtained? Could this power an LED requiring 2.5 V?