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Saturday, 31 October

JEE Main 2021 · ChemistryNumerical answerNumerical valueHardCalculation

JEE Main 25 February 2021, Shift 2, Chemistry Q56

Question 56 of 90 in this shift, Chemistry question 26 of 30, Section B.

Copper reduces NO3−\mathrm{NO_3^-} into NO and NO2\mathrm{NO_2} depending upon the concentration of HNO3\mathrm{HNO_3} in solution. (Assuming fixed [Cu2+]\mathrm{[Cu^{2+}]} and PNO=PNO2\mathrm{P_{NO}=P_{NO_2}}), the HNO3\mathrm{HNO_3} concentration at which the thermodynamic tendency for reduction of NO3−\mathrm{NO_3^-} into NO and NO2\mathrm{NO_2} by copper is same is 10x10^x M. The value of 2x is ________. (Rounded-off to the nearest integer) [Given, ECu2+/Cuo=0.34\mathrm{E^o_{Cu^{2+}/Cu}}=0.34 V, ENO3−/NOo=0.96\mathrm{E^o_{NO_3^-/NO}}=0.96 V, ENO3−/NO2o=0.79\mathrm{E^o_{NO_3^-/NO_2}}=0.79 V and at 298 K, RTF(2.303)=0.059\frac{RT}{F}(2.303)=0.059]

Official answer

4

NTA final key.

Chapter
Electrochemistry
Topic
Nernst Equation
Idea tested
pH Dependence of Electrode Potential

Same idea in other shifts

Asked 6× in all
  1. 8 Apr 2025, Shift 2 · Q75Consider the following half cell reaction Cr2O72−(aq)+6e−+14H+(aq)⟶2Cr3+(aq)+7H2O(l)\mathrm{Cr_2O_7^{2-}(aq) + 6e^- + 14H^+(aq) \longrightarrow 2Cr^{3+}(aq) + 7H_2O(l)} The…MediumNumerical value
  2. 29 Jun 2022, Shift 2 · Q84The cell potential for the given cell at 298 K Pt∣H2 (g,1 bar)∣H+ (aq)∣∣Cu2+ (aq)∣Cu(s)\mathrm{Pt|H_2\,(g,1\ bar)|H^{+}\,(aq)||Cu^{2+}\,(aq)|Cu(s)} is 0.31V. The pH of the…MediumNumerical value
  3. 30 Jun 2022, Shift 1 · Q65In which of the following half cells, electrochemical reaction is pH dependent ?EasySingle correct
  4. 24 Feb 2021, Shift 2 · Q56The magnitude of the change in oxidising power of the MnO4−/Mn2+\mathrm{MnO_4^-/Mn^{2+}} couple is x×10−4x \times 10^{-4} V, if the H+\mathrm{H^+}…MediumNumerical value
  5. 8 Jan 2020, Shift 1 · Q48What would be the electrode potential for the given half cell reaction at pH=5 ? ______.…MediumNumerical value

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.