Given below are two statements: Statement I: Mohr's salt is composed of only three types of ions-ferrous, ammonium and sulphate. Statement II: If the molar conductance at infinite dilution of ferrous, ammonium and sulphate ions are mathbfx_1, mathbfx_2 and mathbfx_3 mathrmS\ cm^2\ mathrmmol^-1, respectively then the molar conductance for Mohr's salt solution at infinite dilution would be given by mathbfx_1 + mathbfx_2 + 2mathbfx_3. In the light of the given statements, choose the correct answer from the options given below:

Solution & Explanation

### Related Formula lambda_m^infty = nu_+ lambda_+^infty + nu_- lambda_-^infty ### Core Logic Statement I: Mohr's salt is a double salt with chemical formula: mathrmFeSO_4 cdot (NH_4)_2SO_4 cdot 6H_2O When dissolved in water, it completely dissociates into three distinct ionic species: mathrmFe^2+ text (ferrous), quad mathrmNH_4^+ text (ammonium), quad textand mathrmSO_4^2- text (sulphate) Thus, Statement I is true. Statement II: According to Kohlrausch's law of independent migration of ions: lambda_m^infty(textMohr's Salt) = 1 cdot lambda_m^infty(mathrmFe^2+) + 2 cdot lambda_m^infty(mathrmNH_4^+) + 2 cdot lambda_m^infty(mathrmSO_4^2-) lambda_m^infty = x_1 + 2x_2 + 2x_3 Statement II claims the expression is x_1 + x_2 + 2x_3 (missing the coefficient 2 for ammonium). Thus, Statement II is false. ### Pattern Recognition Kohlrausch's law matches stoichiometric coefficients directly to the ion quantities released. Mohr's salt formula contains (NH_4)_2, requiring a multiplier of 2 for ammonium ion conductance. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: Electrochemistry Class 12 Chemistry: d- and f-Block Elements

Reference Study Guides

More Electrochemistry Previous-Year Questions — Page 4

Q26 jee_main_2025_24_jan_morning Galvanic Cells and Standard Cell Potential
For the given cell: Fe^2+(aq) + Ag^+(aq) rightarrow Fe^3+(aq) + Ag(s) The standard cell potential of the above reaction is given by: Ag^+ + e^- rightarrow Ag quad E^0 = xtext V Fe^2+ + 2e^- rightarrow Fe quad E^0 = ytext V Fe^3+ + 3e^- rightarrow Fe quad E^0 = ztext V
  • A. x + y - z
  • B. x + 2y - 3z
  • C. y - 2x
  • D. x + 2y

Solution

### Related Formula Delta G^0 = -nFE^0 ### Core Logic Using Gibbs free energy changes for individual steps to find the target reduction potential: 1. Ag^+ + e^- rightarrow Ag quad Delta G_1^0 = -1Fx 2. Fe^2+ + 2e^- rightarrow Fe quad Delta G_2^0 = -2Fy 3. Fe^3+ + 3e^- rightarrow Fe quad Delta G_3^0 = -3Fz For the conversion of Fe^2+ rightarrow Fe^3+ + e^-, we compute the free energy change as: Delta G^0 = Delta G_2^0 - Delta G_3^0 = -2Fy - (-3Fz) = 3Fz - 2Fy Thus, E^0_Fe^2+/Fe^3+ = 2y - 3z Combining with silver reduction: E^0_cell = E^0_Ag^+/Ag + E^0_Fe^2+/Fe^3+ = x + 2y - 3z ### Step 1: Final Calculation The overall potential equals x + 2y - 3z.
Galvanic Cells and Standard Cell Potential diagram for Q26 - JEE Main 2025 Morning
Galvanic Cells and Standard Cell Potential diagram for Q26 - JEE Main 2025 Morning
### Pattern Recognition Direct application of Delta G^0 summation. Remember that standard cell potentials cannot be added directly unless the number of electrons involved is identical. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: Electrochemistry
Q48 jee_main_2025_28_jan_evening Faraday's Laws of Electrolysis
Electrolysis of 600mathrm~mL aqueous solution of NaCl for 5mathrm\ min changes the mathrmpH of the solution to 12. The current in Amperes used for the given electrolysis is ______ (Nearest integer).
Numerical Answer. Answer: 2 to 2

Solution

### Related Formula Faraday's law of electrolysis equation: textMoles of electrons (equivalents) = fracI cdot tF Water ion product relation: textpH + textpOH = 14 ### Core Logic During the electrolysis of brine (NaCl(aq)), hydroxide ions (OH^-) are generated at the cathode: 2H_2O + 2e^- rightarrow H_2 + 2OH^- Given metrics: - Final textpH = 12 implies textpOH = 14 - 12 = 2 - [OH^-] = 10^-2mathrm\ M - textVolume = 600mathrm\ mL = 0.6mathrm\ L - textTime = 5mathrm\ min = 300mathrm\ s ### Step 1: Calculate Moles of Hydroxide Produced Find the absolute moles of OH^- ions generated: textMoles = textMolarity times textVolume (L) = 10^-2 times 0.6 = 6 times 10^-3text moles ### Step 2: Relate to Electrical Current Since 1 mole of electrons produces 1 mole of OH^-, the moles of charge equals 6 times 10^-3. Applying Faraday's equation: 6 times 10^-3 = fracI times 30096500 I = frac6 times 10^-3 times 96500300 = 1.93mathrm\ A Rounding to the nearest integer gives 2. ### Pattern Recognition Always convert a given textpH value into [OH^-] concentration when dealing with cathodic water reduction. Tracking the relationship where 1\ e^- equiv 1\ OH^- provides a direct shortcut to link textpH changes to current flow. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: Electrochemistry
Q jee_main_2025_29_jan_morning Standard Reduction Potential and Oxidising Power
The standard reduction potential values of some of the p-block ions are given below. Predict the one with the strongest oxidising capacity.
  • A. mathrmE_mathrmSn^4+/mathrmSn^2+^ominus = +1.15mathrmV
  • B. mathrmE_mathrmTl^3+/mathrmTl^ominus = +1.26mathrmV
  • C. mathrmE_mathrmAl^3+/mathrmAl^ominus = -1.66mathrmV
  • D. mathrmE_mathrmPb^4+/mathrmPb^2+^ominus = +1.67mathrmV

Solution

### Related Formula textOxidising Capacity propto textStandard Reduction Potential (E^ominus) ### Core Logic A higher positive value of standard reduction potential (E^ominus) indicates a stronger tendency to undergo reduction, hence behaving as a stronger oxidising agent. Comparing the given values: * mathrmE_mathrmSn^4+/mathrmSn^2+^ominus = +1.15mathrmV * mathrmE_mathrmTl^3+/mathrmTl^ominus = +1.26mathrmV * mathrmE_mathrmAl^3+/mathrmAl^ominus = -1.66mathrmV * mathrmE_mathrmPb^4+/mathrmPb^2+^ominus = +1.67mathrmV Since +1.67mathrmV is the highest value, mathrmPb^4+ possesses the strongest oxidising capacity. ### Pattern Recognition Strongest oxidising agent = Most positive reduction potential. Weakest oxidising agent = Most negative reduction potential. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: Electrochemistry Class 12 Chemistry: p-Block Elements
Q jee_main_2025_29_jan_morning Variation of Molar Conductivity with Concentration
The molar conductivity of a weak electrolyte when plotted against the square root of its concentration, which of the following is expected to be observed?
  • A. A small decrease in molar conductivity is observed at infinite dilution.
  • B. A small increase in molar conductivity is observed at infinite dilution.
  • C. Molar conductivity increases sharply with increase in concentration.
  • D. Molar conductivity decreases sharply with increase in concentration.

Solution

### Related Formula For weak electrolytes, the degree of dissociation alpha increases sharply near infinite dilution according to Ostwald's Dilution Law: alpha = sqrtfracK_aC ### Core Logic When a weak electrolyte is diluted (concentration C rightarrow 0), its molar conductivity increases steeply. Conversely, when plotted against sqrtC, as concentration increases, the degree of dissociation drops rapidly, causing a sharp decrease in molar conductivity. This matches the curve given below:
Variation of Molar Conductivity with Concentration diagram for Q28 - JEE Main 2025 Morning
Variation of Molar Conductivity with Concentration diagram for Q28 - JEE Main 2025 Morning
### Pattern Recognition Weak electrolyte plots feature a steep asymptotic exponential-like rise towards the y-axis as C rightarrow 0, meaning a sharp decrease occurs with increasing concentration. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: Electrochemistry
Q jee_main_2025_29_jan_morning Nernst Equation
For a mathrmMg mid mathrmMg^2+ (aq) parallel mathrmAg^+(mathrmaq) mid mathrmAg the correct Nernst Equation is :
  • A. mathrmE_cell = E_cell^o - fracRT2Flnfrac[Ag^+][Mg^2 + ]
  • B. mathrmE_mathrmcell = mathrmE_mathrmcell^circ + fracmathrmRT2 mathrm~F ln frac[mathrmAg^+]^2[mathrmMg^2+]
  • C. mathrmE_cell = E_cell^o - fracRT2Flnfrac[Mg^2 + ][Ag^+]
  • D. mathrmE_cell = E_cell^o - fracRT2Flnfrac[Ag^+]^2[Mg^2 + ]

Solution

### Related Formula E_textcell = E_textcell^circ - fracRTnF ln Q ### Core Logic Let us explicitly formulate the complete chemical oxidation-reduction equations : Anode oxidation: mathrmMg_(s) rightarrow mathrmMg^2+_(aq) + 2e^- Cathode reduction: 2mathrmAg^+_(aq) + 2e^- rightarrow 2mathrmAg_(s) Net total equation : mathrmMg_(s) + 2mathrmAg^+_(aq) rightleftharpoons mathrmMg^2+_(aq) + 2mathrmAg_(s) Total transferred moles of electrons n = 2 . Reaction quotient : Q = frac[mathrmMg^2+][mathrmAg^+]^2 Substituting into Nernst form : E_textcell = E_textcell^circ - fracRT2F lnleft( frac[mathrmMg^2+][mathrmAg^+]^2 right) Inverting the inside quotient changes the sign of the logarithm term from negative to positive: E_textcell = E_textcell^circ + fracRT2F lnleft( frac[mathrmAg^+]^2[mathrmMg^2+] right) ### Pattern Recognition A standard negative logarithmic quotient can always toggle into an addition configuration by inverting the products/reactants variables concentration ratio.

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