Question

State true or false for the folloing statements.

1. The Faraday constant equals the charge of one proton.

2. In the spontaneous chemical reaction of an electrochemical cell, electrons flow from the anode to the cathode.

3. Increasing the activity of a reactant in the cell's chemical reaction must increase the cell potential.

4. If we double all the coefficients in a cell's reaction, the number of electrons transferred, n, is doubled but the cell potential is unchanged.

5. The standard cell potential E° of an electrochemical cell is the limiting value of E taken as all molalities go to zero.

Calculate the followings:

6. Calculate the ionic strength of a solution that is 0.18 mol/kg in KCl (aq) and 0.40 mol/kg in CuSO₄ (aq).

7. Using the Debye-Hückel limiting law, estimate the mean ionic activity coefficient for CaCl₂ in an aqueous solution that is 0.016 mol/kg CaCl₂ (aq) and 0.025 mol/kg NaF (aq).

8. Calculate the standard potential of the following cell:

Zn|ZnSO₄(aq)||AgNO₃(aq)|Ag

9. Calculate the equilibrium constant of the following reaction at 25°C from standard potential data:

Sn(s) + Sn⁴⁺(aq) ↔ 2Sn²⁺(aq)

Answer 1

1. False

2. True

3. True

4. True

5. False

6. Ionic sterngth , I = 1/2(c1* z1² + c2* z2² + .... )

c1 , c2 .... are concentration of ions 1,2 , .....

z1,z2 .... are charges of ions 1,2 .......

= 1/2( 0.18m * (+1)² + 0.18 *(-1)² + 0.40m*(-2)² + 0.40m * (-2)²)

= 1.78m

= 1.78mol/kg

8. Oxida halftion half cell

Zn(s) -----> Zn²⁺(aq) + 2e E⁰_red = -0.762V Anode

Reduction half cell  

Ag(aq) + 2e -----> Zn(s) E⁰_red = +0.800V Cathode

Overall reaction

Zn(s) + Ag(aq) -------> Ag(s) + Zn(aq)

E⁰_cell = E⁰red (cathode) - E⁰red( anode)

= 0.800V -(-0.762V)

= 1.56V

9) Sn(s) -----> Sn2+(aq) + 2e E⁰red = -0.13V

Sn4+(aq) + 2e ----> Sn2+(aq) E⁰red = +15V

E⁰cell = 0.15V -(-0.13V) = 0.28V

  G⁰ = -nFE⁰cell

= - 2*96485C/mol * 0.28V

= - 54032J/mol

G⁰= - RTlnK

logK = - G^0/(/2.303RT)

= - (-54032J/mol)/(2.303*8.314(J/mol K) * 298K)

= 54032/5706

= 9.47

K = 2.95*10⁹