Definitions [7]
Define cathode
The electrode at which the reduction occur is called cathode.
Define anode
The electrode at which the oxidation occur is called anode.
Define the following term:
Fuel cell
Fuel cells are the galvanic cells in which the energy of combustion of fuels like hydrogen, methanol, etc., is directly converted into electrical energy.
Define cell constant.
Cell constant is the ratio of the distance between the electrodes divided by the area of cross-section of the electrode. It is denoted by b.
Thus, Cell constant = b =`l/a`. It is expressed in unit m−1.
Define limiting molar conductivity.
The limiting molar conductivity of an electrolyte is defined as its molar conductivity when the concentration of the electrolyte in the solution approaches zero.
When the concentration of an electrolytic solution placed between electrodes of a conductivity cell placed at a unit distance having an area of cross-section sufficient to accommodate enough volume of solution containing one mole of electrolyte approaches zero, then the conductance of the solution is known as limiting molar conductivity.
Define “Molar conductivity”.
Molar conductivity is the conductance of a volume of solution containing 1 mole of dissolved electrolyte when placed between two parallel electrodes 1 cm apart and large enough to contain between them all the solution.
The conductivity, which is shown by all the ions when 1 mol of electrolyte is dissolved in the solution, is called molar conductivity; it is expressed by ∧m (lambda). If 1 mol of electrolyte is present in Vm cm3 of electrolyte solution, then ∧m = κ × V
= `(kappa xx 1000)/"Molarity" = (kappa xx 1000)/M`
Its unit is ohm−1 cm2 mol−1 or S cm2 mol−1.
Any reaction that involves both oxidation and reduction occurring simultaneously is called an oxidation-reduction reaction or simply a redox reaction.
Formulae [1]
Write the Nernst equation and explain the terms involved.
Nernst equation can be given as,
`E = E^circ - (2.303 RT)/(nF) log_10 [["Products"]]/[["Reactants"]]`
where,
E° = Standard potential of electrode or cell,
n = Number of moles of electrons used in reaction,
F = Faraday = 96500 C/mol e−,
[Products] = Concentration of products,
[Reactants] = Concentration of reactants,
T = Temperature in K and
R = Gas constant = 8.314 J K−1 mol−1
Theorems and Laws [2]
State Kohlrausch Law.
Kohlrausch law states that at infinite dilution of the solution, each ion of electrolyte migrates independently of its co-ions and contribute independently to the total molar conductivity irrespective of the nature of other ion.
State Kohlrausch’s law of independent migration of ions.
Kohlrausch’s law states that the molar conductivity of an electrolyte at infinite dilution is the same as the sum of the anions' and cations' limited molar conductivities.
`∧_m^° = v_+ λ_+^° + v_- λ_-^°`
Here `λ_+^°` and `λ_-^°` are limiting molar conductivities of cations and anions.
Key Points
| Type | Electrolytic Cell | Galvanic (Voltaic) Cell |
|---|---|---|
| Energy conversion | Electrical → Chemical | Chemical → Electrical |
| Nature of reaction | Non-spontaneous | Spontaneous |
| Anode | Positive | Negative |
| Cathode | Negative | Positive |
| Electron flow | Cathode → Anode | Anode → Cathode |
| Salt bridge | Not required | Required |
Electrolysis of NaCl
1. Molten NaCl:
-
Oxidation: Cl⁻ → Cl₂ (gas)
-
Reduction: Na⁺ → Na (metal)
-
Products: Na (cathode), Cl₂ (anode)
2. Aqueous NaCl:
-
Oxidation: Cl⁻ → Cl₂
-
Reduction: H₂O → H₂ + OH⁻
-
Products: H₂ (cathode), Cl₂ (anode), NaOH formed
Components of a Galvanic Cell
| Component | Key Points |
|---|---|
| Electrodes | Surfaces where oxidation and reduction occur may be inert or active |
| Anode | Electrode where oxidation occurs; in a galvanic cell → negative electrode |
| Cathode | Electrode where reduction occurs; in a galvanic cell → positive electrode |
| Electrolyte | Substance that ionises in solution or molten state; provides ions for conduction; placed in separate containers (half-cells) |
| Salt Bridge (Structure) | U-shaped tube with electrolyte |
| Salt Bridge (Functions) | Completes electrical circuit; maintains electrical neutrality; prevents mixing of solutions |
6. Cell Notation
-
Anode written on the left, cathode on the right
-
Example:
Cu(s) | Cu²⁺(aq) || Ag⁺(aq) | Ag(s)
-
Single line (|) → phase boundary
-
Double line (||) → salt bridge
Redox Reactions:
- A substance that oxidises another substance (and is itself reduced) is called an oxidising agent.
- A substance that reduces another substance (and is itself oxidised) is called a reducing agent.
What is Oxidation and Reduction?
| Perspective | Oxidation | Reduction |
|---|---|---|
| In terms of oxygen | Gain of one or more O atoms | Loss of one or more O atoms |
| In terms of hydrogen | Loss of hydrogen | Gain of hydrogen |
| In terms of electropositive element | Loss of electropositive element | Gain of electropositive element |
| In terms of electronegative element | Gain of electronegative element | Loss of electronegative element |
| In terms of electrons | Loss of electrons | Gain of electrons |
| In terms of oxidation number | Increase in oxidation number | Decrease in oxidation number |
Redox in Terms of Electron Transfer:
A reaction in which electrons are lost by one substance and gained by another is called a redox reaction.
- Oxidising agent = electron acceptor
- Reducing agent = electron donor
Example:
(Hg₂²⁺ gains electrons → reduced; Sn²⁺ loses electrons → oxidised)
Important Questions [43]
- Construct a Labelled Diagram for the Following Cell
- Derive a Relation Between δH and δU for a Chemical Reaction. Draw Neat Labelled Diagram of Calomel Electrode.
- How Many Faradays of Electricity Are Required to Produce 6 G of Mg from Mgcl2?
- Write Cathode and Anode Reaction in a Fuel Cell.
- Conductivity of a solution is 6.23 x 10-5 Ω-1cm-1 and its resistance is 13710Ω. If the electrodes are 0.7cm apart, calculate the cross-sectional area of electrode
- Define Cell Constant.
- The molar conductivity of cation and anion of salt BA are 180 and 220 mhos respectively. The molar conductivity of salt BA at infinite dilution is
- The S.I. Unit of Cell Constant for Conductivity Cell is __________.
- Define “Molar conductivity.
- State Kohlrausch Law.
- Resistance of Conductivity Cell Filled with 0.1 M Kcl Solution is 100 Ohms. If the Resistance of the Same Cell When Filled with 0.02 M Kcl Solution is 520 Ohms, Calculate the Conductivity and Molar Conductivity of 0.02 M Kcl Solution.
- State Kohlrausch’s law of independent migration of ions.
- 10.0 Grams of Caustic Soda When Dissolved in 250 cm^3 of Water, the Resultant Gram Molarity Of Solution is
- Write mathematical expression of molar conductivity of the given solution at infinite dilution.
- The Conductivity of 0.02m Agno3 at 25°C What is Its Molar Conductivity?
- How much electricity in terms of Faraday is required to produce 40.0 g of Al from molten Al2O3? (Given: Molar mass of Aluminium is 27 g mol−1.)
- On Calculating the Strength of Current in Amperes If a Charge of 840c (Coulomb) Passes Through an Electrolyte in 7 Minutes, It Will Be
- The charge of how many coulomb is required to deposit 1.0 g of sodium metal (molar mass 23.0 g mol-1) from sodium ions is
- 96500 Coulombs Correspond to the Charge on How Many Electrons?
- Write Any Four Applications of Electrochemical Series
- How much electricity in terms of Faraday is required to produce 20 g of Ca from molten CaCl2? (Given: Molar mass of Calcium is 40 g mol−1.)
- Number of faradays of electricity required to liberate 12g of hydrogen is 12
- On Passing 1.5 F Charge, the Number of Moles of Aluminium Deposited at Cathode Are
- Write Any ‘Two’ Uses of Each of the Following Sulphuric Acid
- Draw Neat Labelled Diagram of Electrolytic Refining of Blis Ter Copper
- What is the ratio of volumes of H2 and O2 liberated during electrolysis of acidified water?
- State Second Law of Electrolysis
- Explain Faraday’S Second Law of Electrolysis
- How Many Faradays of Electricity Are Required to Produce 13 Gram of Aluminium from Aluminium Chloride Solution?
- How Much Quantity of Electricity in Coulomb is Required to Deposit 1.346 × 10-3 Kg of Ag in 3.5 Minutes from Agno3 Solution? ( Given: Molar Mass of Ag is 108 × 10-3 Kg Mol-1 )
- Write Cell Reaction in Lead Storage Battery During Discharge.
- Draw Neat and Labelled Diagram of Dry Cell.
- What is a salt bridge?
- What are the functions of a salt bridge in a galvanic cell?
- Answer the following in one or two sentences. Write any two functions of salt bridge.
- Write the Nernst equation and explain the terms involved.
- Write Any ‘Two’ Advantages of Calomel Electrode.
- What is the ‘Ellingham Diagram’? Write Any ‘Two Points’ of Its Significance.
- Potential of Saturated Calomel Electrode Is-
- What is the value of for the following reaction at 298 K
- With the help of the equation ΔG° = - nFEocell. Explain that cell potential is an intensive property
- In the Hydrogen-oxygen Fuel Cell, the Carbon Rods Are Immersed in the Hot Aqueous Solution of __
- Write Electrode Reaction and Net Cell Reaction for Fuel Cell. Calculate E.M.F. of the Following Cell at 25 °C
Concepts [12]
- Electrochemical Cells
- Conductance of Electrolytic Solutions - Introduction
- Variation of Conductivity and Molar Conductivity with Concentration
- Electrolytic Cells and Electrolysis - Introduction
- Primary Batteries
- Lead Accumulator
- Galvanic or Voltaic Cell
- Nernst Equation - Introduction
- Relation Between Gibbs Energy Change and Emf of a Cell
- fuel cell
- Factors Affecting Corrosion
- Concept of Redox Reactions
