Science (English Medium) Class 12 - CBSE Important Questions

Why does the cell potential of mercury cell remain constant throughout its life?

Define the following terms: Molar conductivity (⋀_m)

Define the following terms: Secondary batteries

Calculate the standard cell potential of a galvanic cell in which the following reaction takes place:

\[\ce{2Cr_{(s)} + 3Cd{^{2+}_{(aq)}} -> 2Cr{^{3+}_{(aq)}} + 3Cd_{(s)}}\]

Calculate the Δ_rG° and equilibrium constant of the reaction.

Define conductivity for the solution of an electrolyte.

Write the name of the cell which is generally used in transistors. Write the reactions taking place at the anode and the cathode of this cell.

The cell in which the following reaction occurs:

`2Fe^(3+) (aq) + 2I^(-) (aq) ---> 2Fe^(2+) (aq) + I_2 (s)` has `E_"cell"^@` = 0.236 V at  298 K. Calculate the standard Gibbs energy of the cell reaction. (Given : 1 F = 96,500 C mol⁻¹)

How many electrons flow through a metllic wire if a current of 0·5 A is passed for 2 hours? (Given : 1 F = 96,500 C mol⁻¹)

 Following reactions occur at cathode during the electrolysis of aqueous copper(II) chloride solution :

On the basis of their standard reduction electrode potential (E°) values, which reaction is feasible at the cathode and why ?

Although chlorine is an electron withdrawing group, yet it is ortho-, para- directing in electrophilic aromatic substitution reactions. Why?

 Write the reaction that occurs at anode on electrolysis of concentrated 2 4 H SO using platinum electrodes. 

 Following reaction takes place in the cell: 
`Zn(s) + Ag_2O(s)+H_2O(l) -> Zn^{2+}(aq) + 2Ag (s) + 2OH^- (aq)`
Calculate `Delta_r G^0` of the reaction

[Given ; `E^0_(Zn^{2+}//Zn)` = -0.76V

`E_((Zn^{2+}//Zn)) = 0.76V`

`E_(Ag^4//Ag)^0 = 0.80V, 1F = 96,500 C mol^-1 ]`
          

 How can you determine limiting molar conductivity,   0 m for strong electrolyte and weak electrolyte?

A steady current of 2 amperes was passed through two electrolytic cells X and Y connected in series containing electrolytes FeSO₄and ZnSO₄ until 2.8g of Fe deposited at the cathode of cell X. How long did the current flow? Calculate the mass of Zn deposited at the cathode of cell Y. 
(Molar mass: Fe=56g mol^-1,Zn=65.3g mol^-1,1F=96500C mol^-1)

In the plot of molar conductivity (∧_m) vs square root of concentration (c^1/2) following curves are obtained for two electrolytes A and B : 

Answer the following:
(i) predict the nature of electrolytes A and B.
(ii) What happens on the extrapolation of ∧_m to concentration approaching for electrolytes A and B?

E°_cell for the given redox reaction is 2.71 V
Mg_(s) + Cu²⁺ _{(0.01 M)} → Mg²⁺ (0.001 M) + Cu_(s)

Calculate E_cell for the reaction. Write the direction of flow of current when an external opposite potential applied is
(i) less than 2.71 V and
(ii) greater than 2.71 V

Solve the following question.
A steady current of 2 amperes was passed through two electrolytic cells X and Y connected in series containing electrolytes FeSO₄ and ZnSO₄ until 2.8 g of Fe deposited at the cathode of cell X. How long did the current flow? Calculate the mass of Zn deposited at the cathode of cell Y.
(Molar mass : Fe = 56 g mol^–1, Zn = 65.3 g mol^–1, 1F = 96500 C mol^–1)

In the plot of molar conductivity (∧_m) vs square root of concentration (c^1/2), following curves are obtained for two electrolytes A and B:

Answer the following:
(i) Predict the nature of electrolytes A and B.
(ii) What happens on extrapolation of ∧_m to concentration approaching zero for electrolytes A and B?

Why on dilution the m Λ_m of \[\ce{CH3COOH}\] increases very fast, while that of \[\ce{CH3COONa}\] increases gradually?

Solutions of two electrolytes ‘A’ and ‘B’ are diluted. The Λ_m of ‘B’ increases 1.5 times while that of A increases 25 times. Which of the two is a strong electrolyte? Justify your answer. Graphically show the behavior of ‘A’ and ‘B’.