Chemistry

Electrochemistry

Question:

Why on dilution the Am of CH3COOH increases drastically, while that of CH4COONa increases gradually?

Answer:

In the case of CH3COOH, which is a weak electrolyte, the number of ions increase on dilution due to an increase in degree of dissociation.
ncert-exemplar-problems-class-12-chemistry-electrochemistry-47
In the case of strong electrolyte such as CH3COONa, the number of ions remains the same but the interionic attraction decreases.

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Electrochemistry

Q 1.

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

Q 2.

Three electrolytic cells A, B, C containing solutions of ZnS04, AgNO3 and CuS04, respectively are connected in series. A steady current of 1.5 amperes was passed through them until 45 g of silver deposited at the cathode of call B. How long did the current flow? What mass of copper and zinc were deposited?

Q 3.

The positive value of the standard electrode potential of Cu+2/Cu indicates that
(a) this redox couple is a stronger reduction agent than the H/H2  couple
(b) this redox couple is a stronger oxidizing agent than H+/H2
(c) Cu can displace  H2 from acid
(d) Cu cannot displace  H2   from acid

Q 4.

Assertion (A): E , increases with increase in concentration of  Ag+ ions.
Ag /  Ag+
Reason (R): E + has a positive value.
Ag /Ag

Q 5.

Use the data given in Q. 8 and find out the most stable ion in its reduced form.
ncert-exemplar-problems-class-12-chemistry-electrochemistry-13

Q 6.

Match the items of Column I and Column II.
ncert-exemplar-problems-class-12-chemistry-electrochemistry-52

Q 7.

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 andλ °(HCOO-) = 54.6 S  cm2 mol-1

Q 8.

Match the items of Column I and Column II.
ncert-exemplar-problems-class-12-chemistry-electrochemistry-51

Q 9.

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

Q 10.

What does the negative sign in the expression ncert-exemplar-problems-class-12-chemistry-electrochemistry-38 mean? Zn /Zn

Q 11.

ncert-exemplar-problems-class-12-chemistry-electrochemistry-27

Q 12.

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

Q 13.

Use the data given in Q.8 and find out the most stable oxidized species.
ncert-exemplar-problems-class-12-chemistry-electrochemistry-14

Q 14.

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?

Q 15.

Match the terms given in Column I with the items given in Column II.
ncert-exemplar-problems-class-12-chemistry-electrochemistry-49

Q 16.

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.

Q 17.

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 Mn04- to Mn2+?

Q 18.

What will happen during the electrolysis of aqueous solution of CuSO4 in the presence of Cu electrodes?
(a) Copper will deposit at cathode.
(b) Copper will dissolve at anode.
(c) Oxygen will be released at anode.
(d) Copper will deposit at anode.

Q 19.

Conductivity K, is equal to
ncert-exemplar-problems-class-12-chemistry-electrochemistry-31

Q 20.

Can ncert-exemplar-problems-class-12-chemistry-electrochemistry-34for cell reaction ever be equal to zero?

Q 21.

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.

Q 22.

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

Q 23.

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

Q 24.

Can you store copper sulphate solutions in a zinc pot?

Q 25.

The cell in which the following reaction occurs:  2Fe3+ (aq) + 2I(aq) —> 2Fe2+ (aq) +I2 (s)  has E °cell=0.236 V at 298 K. Calculate the standard Gibbs energy and the equilibrium constant of the cell reaction.

Q 26.

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

Q 27.

Predict the products of electrolysis in each of the following.
(i) An aqueous solution of AgNO3 with silver electrodes.
(ii) An aqueous solution of AgNO3 with platinum electrodes.
(iii) A dilute solution of H2S04 with platinum electrodes.
(iv) An aqueous solution of CuCl2 with platinum electrodes.

Q 28.

Consider a cell given below:
Cu |Cu2+ || Cl |Cl2, Pt
Write the reactions that occur at anode and cathode.

Q 29.

Write the Nemst equation for the cell reaction in the Daniell cell. How will the Ecell be affected when concentration of Zn2+ ions is increased?

Q 30.

Consider the figure given below and answer the questions (i) to (vi) that follow.
ncert-exemplar-problems-class-12-chemistry-electrochemistry-57
(i) Redraw the diagram to show the direction of electron flow.
(ii) Is silver plate anode or cathode?
(iii)What will happen if salt bridge is removed?
(iv)When will the cell stop functioning?
(v)How will concentration of Zn+2  cell functions?
(vi)How will the concentration of Zn+2 ions and Ag+ ions be affected after the cell becomes ‘dead'?

Q 31.

In the button cells widely used in watches and other devices the following reaction takes place:
ncert-solutions-for-class-12-chemistry-electrochemistry-9

Q 32.

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 Al203?

Q 33.

How would you determine the standard electrode potential of the system Mg2+1  Mg?

Q 34.

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

Q 35.

Why does the conductivity of a solution decrease with dilution?

Q 36.

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

Q 37.

How much electricity is required in coulomb for the oxidation of (i) 1 mol of H2O to 02 (ii) 1 mol of FeO to Fe203

Q 38.

In the electrolysis of aqueous sodium chloride solution, which of the half-cell reaction will occur at anode?
ncert-exemplar-problems-class-12-chemistry-electrochemistry-20

Q 39.

E °en = 1.1 V for Daniell cell. Which of the following expressions are correct description of state of equilibrium in this cell?
ncert-exemplar-problems-class-12-chemistry-electrochemistry-25

Q 40.

Can absolute electrode potential of an electrode be measured?

Q 41.

Match the terms given in Column 1 with the units given in Column II.
ncert-exemplar-problems-class-12-chemistry-electrochemistry-48

Q 42.

Given the standard electrode potentials, K+/K=-2. 93 V, Ag+/Ag = 0.80 V, Hg2+/Hg =0.79V, Mg2+/Mg=-2.37V, Cr3+/Cr=0.74V.
Arrange these metals in their increasing order of reducing power.

Q 43.

Which of the following statements is correct?
ncert-exemplar-problems-class-12-chemistry-electrochemistry-6

Q 44.

What is electrode potential?

Q 45.

What is the relationship between Gibbs free energy of the cell reaction in a galvanic cell and the emf of the cell? When will the maximum work be obtained from a galvanic cell?

Q 46.

An electrochemical cell can behave like an electrolytic cell when
ncert-exemplar-problems-class-12-chemistry-electrochemistry-7

Q 47.

Using given below find strongest reduction agent.
ncert-exemplar-problems-class-12-chemistry-electrochemistry-8

Q 48.

Under what condition is
ncert-exemplar-problems-class-12-chemistry-electrochemistry-36

Q 49.

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- oxidized at anode instead of water?

Q 50.

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