Redox Reactions and Electrochemistry
- In the electrochemical cell :Zn|ZnSO_4(0.01\ M)||CuSO_4(1.0\ M)|Cu, the emf of this Daniel cell is E_1. When the concentration of ZnSO_4 is changed to 1.0 M and that of CuSO_4 changed to 0.01 M, the emf changes to E_2. From the followings, which one… Answer: 2. E₁ > E₂ Key idea: apply the Nernst equation, E = E^° - 0.059/2logdfrac[Zn²⁺][Cu²⁺] . E₁ : log0.01/1=-2 , so E₁ = E^° + 0.059 . E₂... 1
- If the E^°_cell for a given reaction has a negative value, which of the following gives the correct relationships for the values of Δ G^° and K_eq? Answer: 4. Δ G^° > 0 ; K_eq < 1 Key idea: Δ G^°=-nFE^°_cell=-RTln K . If E^°_cell<0 , then Δ G^°>0 , so ln K<0 and K_eq<1 . The reaction is... 1
- The molar conductivity of a [obscured] solution of AgNO_3 with electrolytic conductivity of 5.76×10^-3 S cm^-1 at 298 K is Answer: 1. 11.52 S cm ² /mol Key idea: molar conductivity Lambda_m=kappa×1000/M (S cm ² mol ⁻¹ , kappa in S cm ⁻¹ , M in mol/L). Lambda_m=fr... 1
- During the electrolysis of molten sodium chloride, the time required to produce 0.10 mol of chlorine gas using a current of 3 amperes is Answer: 1. 110 minutes Key idea: 2Cl^-→ Cl₂+2e^- , so 1 mol Cl₂ needs 2 F. Q=0.10×2×96500=19300\ C t=Q/I=19300/3≈6433\ s≈107\ min≈110\ min T... 1
- The number of electrons delivered at the cathode during electrolysis by a current of 1 ampere in 60 seconds is (charge on electron = 1.60×10^-19 C) Answer: 2. 3.75×10²⁰ Key idea: charge Q=It , and number of electrons =Q/e . Q=1×60=60\ C n=frac601.60×10⁻¹⁹=3.75×10²⁰ Option 4 ( 6×10²³ ) is... 1
- Zinc can be coated on iron to produce galvanized iron but the reverse is not possible. It is because Answer: 3. zinc has higher negative electrode potential than iron Key idea: a more electropositive metal can protect a less electropositive... 1
- The pressure of H_2 required to make the potential of H_2 - electrode zero in pure water at 298 K is : Answer: 1. 10⁻¹⁴ atm Key idea: for the half cell 2H^++2e^-→ H₂ , the Nernst equation is E=0-0.059/2logfracP_(H_2)[H^+]² In pure water [H^+]=... 1