Lecture 5: Revison

Match the items of Column I and Column II.
Column I                                                         Column II
(i) Lead storage battery                                   (a) maximum efficiency


(ii) Mercury cell                                                (b) prevented by galvanisation
(iii) Fuel cell                                           (c) gives steady potential
(iv) Rusting                                                (d) Pb is anode, PbO2 is cathode

Note : Match the items of Column I and Column II in the following questions.

Match the terms given in Column I with the units given in Column II.
Column I                                     Column II
(i) ∧m                                     (a) S cm–1
(ii) ECell                                    (b) m–1
(iii) κ                                   (c) S cm2 mol–1
(iv) G*                                    (d) V

Write the cell reaction of a lead storage battery when it is discharged. How
does the density of the electrolyte change when the battery is discharged?

What advantage do the fuel cells have over primary and secondary batteries?

Write the Nernst equation for the cell reaction in the Daniel cell. How will the
ECell be affected when concentration of Zn2+ ions is increased?

Which reference electrode is used to measure the electrode potential of other
electrodes?

In an aqueous solution how does specific conductivity of electrolytes change
with addition of water?

When acidulated water (dil.H2SO4 solution) is electrolysed, will the pH of the
solution be affected? Justify your answer.

Unlike dry cell, the mercury cell has a constant cell potential throughout its
useful life. Why?

How will the pH of brine (aq. NaCl solution) be affected when it is electrolysed?

A galvanic cell has electrical potential of 1.1V. If an opposing potential of 1.1V
is applied to this cell, what will happen to the cell reaction and current flowing
through the cell?

Why is alternating current used for measuring resistance of an electrolytic
solution?

What is electrode potential?

Value of standard electrode potential for the oxidation of Cl– ions is more
positive than that of water, even then in the electrolysis of aqueous sodium
chloride, why is Cl– oxidised at anode instead of water?

Depict the galvanic cell in which the cell reaction is Cu + 2Ag+ ⎯→ 2Ag + Cu2+

Aqueous copper sulphate solution and aqueous silver nitrate solution are
electrolysed by 1 ampere current for 10 minutes in separate electrolytic cells.
Will the mass of copper and silver deposited on the cathode be same or
different? Explain your answer.

Can absolute electrode potential of an electrode be measured?

What is the effect of temperature on molar conductivity?

Why is it not possible to measure single electrode potential?

Name the factor on which emf of a cell depends:- 

Write Nernst equation –

For the general cell reaction

aA+bB→cC+dD

 What is the EMF of the cell when the cell reaction attains equilibrium? 

What is the electrolyte used in a dry cell? 

How is cell constant calculated from conductance values?

What flows in the internal circuit of a galvanic cell. 

Define electrochemical series.

Calculate emf of the following cell at 298K

Zn/Zn2+ (10-4 M) || Cu2+ (10-2M)/Cu

Given E0 Zn2+/Zn=-0.76V E0Cu2+/Cu=+0.34V

Electrolysis of KBr(aq) gives Br2 at anode but KF(aq) does not give

F2. Give reason.

Write any three differences between potential difference and e.m.f.

E.M.F                                                           POTENTIAL DIFFERENCE

Why an electrochemical cell stops working after sometime?

The reduction potential of an electrode depends upon the concentration of solution with which it is in contact.

for the standard cell

Cu(s)/Cu+(aq)|| Ag+(aq)/Ag(s) E0 cell 2+/Cu = +0.34 V

E0 cell 2+ =+0.34 V

E0 Ag+/Ag =+0.80 V

i.         identify the cathode and the anode as the current is drawn from the cell. ii.        Write the reaction taking place at the electrodes.

iii.        Calculate the standard cell potential. 

Can we store copper sulphate in (i)Zinc vessel (ii) Silver vessel? Give reasons.

Given E0 Cu2+/Cu = +0.34V, E0Zn2+/Zn= -0.76V) , E0Ag+/Ag = +0.80V

Predict the products of electrolysis in each of the following:

(i) An aqueous solution of AgNO₃ with silver electrodes.

(ii) An aqueous solution of AgNO₃with platinum electrodes.

(iii) A dilute solution of H₂SO₄with platinum electrodes.

(iv) An aqueous solution of CuCl₂ with platinum electrodes

Using the standard electrode potentials given in Table 3.1, predict if the reaction between the following is feasible:

(i) Fe³⁺(aq) and I^-(aq)

(ii) Ag⁺ (aq) and Cu(s)

(iii) Fe³⁺ (aq) and Br^- (aq)

(iv) Ag(s) and Fe³⁺ (aq)

(v) Br₂ (aq) and Fe²⁺ (aq).

Three electrolytic cells A,B,C containing solutions of ZnSO₄, AgNO₃ and CuSO₄, respectively are connected in series. A steady current of 1.5 amperes was passed through them until 1.45 g of silver deposited at the cathode of cell B. How long did the current flow? What mass of copper and zinc were deposited?

A solution of Ni(NO₃)₂ is electrolysed between platinum electrodes using a current of 5 amperes for 20 minutes. What mass of Ni is deposited at the cathode?

How much electricity is required in coulomb for the oxidation of

(i) 1 mol of H₂O to O₂.

(ii) 1 mol of FeO to Fe₂O₃.

How much electricity in terms of Faraday is required to produce

(i) 20.0 g of Ca from molten CaCl₂.

(ii) 40.0 g of Al from molten Al₂O₃.

How much charge is required for the following reductions:

(i) 1 mol of Al³⁺ to Al.

(ii) 1 mol of Cu²⁺ to Cu.

(iii) 1 mol of  to Mn²⁺.

Conductivity of 0.00241 M acetic acid is 7.896 × 10 ^{- 5} S cm ^{- 1}. Calculate its molar conductivity and if for acetic acid is 390.5 S cm² mol ^{- 1}, what is its dissociation constant?

The conductivity of sodium chloride at 298 K has been determined at different concentrations and the results are given below:

Concentration/M 0.001 0.010 0.020 0.050 0.100

102 × κ/S m - 1 1.237 11.85 23.15 55.53 106.74

Calculate for all concentrations and draw a plot between and c ½. Find the value of.

The resistance of a conductivity cell containing 0.001M KCl solution at 298 K is 1500 Ω. What is the cell constant if conductivity of 0.001M KCl solution at 298 K is 0.146 x 10^-3 S cm^-1.

The conductivity of 0.20 M solution of KCl at 298 K is 0.0248 Scm^-1. Calculate its molar conductivity.

In the button cells widely used in watches and other devices the following reaction takes place:

Zn(s) + Ag₂O(s) + H₂O(l) → Zn²⁺(aq) + 2Ag(s) + 2OH ^- (aq)

Determine and  for the reaction.

Write the Nernst equation and emf of the following cells at 298 K:

(i) Mg(s) | Mg²⁺(0.001M) || Cu²⁺(0.0001 M) | Cu(s)

(ii) Fe(s) | Fe²⁺(0.001M) || H⁺(1M)|H₂(g)(1bar) | Pt(s)

(iii) Sn(s) | Sn²⁺(0.050 M) || H⁺(0.020 M) | H₂(g) (1 bar) | Pt(s)

(iv) Pt(s) | Br₂(l) | Br^-(0.010 M) || H⁺(0.030 M) | H₂(g) (1 bar) | Pt(s).

Calculate the standard cell potentials of galvanic cells in which the following reactions take place:

(i) 2Cr(s) + 3Cd²⁺(aq) → 2Cr³⁺(aq) + 3Cd

(ii) Fe²⁺(aq) + Ag⁺(aq) → Fe³⁺(aq) + Ag(s)

Calculate the Δ_rG^θ and equilibrium constant of the reactions.

Depict the galvanic cell in which the reaction Zn(s) + 2Ag⁺(aq) → Zn²⁺(aq) + 2Ag(s) takes place. Further show:

(i) Which of the electrode is negatively charged?

(ii) The carriers of the current in the cell.

(iii) Individual reaction at each electrode.

Given the standard electrode potentials,

K⁺/K = -2.93V, Ag⁺/Ag = 0.80V,

Hg²⁺/Hg = 0.79V

Mg²⁺/Mg = -2.37 V, Cr³⁺/Cr = - 0.74V

Arrange these metals in their increasing order of reducing power.

Arrange the following metals in the order in which they displace each other from the solution of their salts.

Al, Cu, Fe, Mg and Zn

Explain how rusting of iron is envisaged as setting up of an electrochemical cell.

Suggest two materials other than hydrogen that can be used as fuels in fuel cells.

Write the chemistry of recharging the lead storage battery, highlighting all the materials that are involved during recharging.

What is the quantity of electricity in coulombs needed to reduce 1 mol of

? Consider the reaction:

Suggest a list of metals that are extracted electrolytically.

If a current of 0.5 ampere flows through a metallic wire for 2 hours, then how many electrons would flow through the wire?

The molar conductivity of 0.025 mol L-1 methanoic acid is

46.1 S cm2 mol^-1.

Calculate its degree of dissociation and dissociation constant. Given λ ^°(H⁺)

= 349.6 S cm² mol^-1 and λ ^°(HCOO-) = 54.6 S cm² mol

Suggest a way to determine the value of water

Why does the conductivity of a solution decrease with dilution?

The cell in which the following reactions occurs:

has = 0.236 V at 298 K.

Calculate the standard Gibbs energy and the equilibrium constant of the cell reaction.

Calculate the emf of the cell in which the following reaction takes place:

Calculate the potential of hydrogen electrode in contact with a solution whose pH is 10.

Consult the table of standard electrode potentials and suggest three substances that can oxidise ferrous ions under suitable conditions.

Can you store copper sulphate solutions in a zinc pot?

How would you determine the standard electrode potential of the systemMg²⁺| Mg?