Class 12 Chemistry · 68 questions · 67 with answers
Which cell will measure standard electrode potential of copper electrode? +
(iii) Pt(s) H2 (g, 1 bar) H (aq.,1 M) Cu2+ (aq.,1 M) Cu +
Electrode potential for Mg electrode varies according to the equation 0 .0 5 9 1 E = E V 2+ – log . The graph of E 2 + vs 2+ Mg | Mg Mg | Mg 2 [Mg 2 + ] Mg | Mg log [Mg2+] is
(ii)
Which of the following statement is correct?
(iii) ECell is an intensive property while ∆rG of cell reaction is an extensive property.
The difference between the electrode potentials of two electrodes when no current is drawn through the cell is called ___________.
(ii) Cell emf
Which of the following statement is not correct about an inert electrode in a cell?
(iv) It provides surface for redox reaction.
An electrochemical cell can behave like an electrolytic cell when ____________.
(iii) Eext > Ecell
Which of the statements about solutions of electrolytes is not correct?
(iii) Conductivity does not depend upon solvation of ions present in solution.
Using the data given below find out the strongest reducing agent. V V E E Cr2O72– /Cr 3+ = 1.33V Cl2 /Cl– = 1.36V V V E = 1.51V E = – 0.74V MnO4– /Mn2+ Cr 3+ /Cr –
(ii) Cr
Use the data given in Q.8 and find out which of the following is the strongest oxidising agent. –
(iii) MnO4
Using the data given in Q.8 find out in which option the order of reducing power is correct. 3+ – 2+
(ii) Mn < Cl < Cr < Cr 3+ – 2– –
Use the data given in Q.8 and find out the most stable ion in its reduced form. –
(iv) Mn2+
Use the data of Q.8 and find out the most stable oxidised species.
(i) Cr3+ –
The quantity of charge required to obtain one mole of aluminium from Al2O3 is ___________.
(iii) 3F
The cell constant of a conductivity cell _____________.
(iv) remains constant for a cell.
While charging the lead storage battery ______________.
(i) PbSO4 anode is reduced to Pb.
Λm (NH OH) is equal to ______________. 0 0 0
(ii) Λm (NH Cl) + Λm (NaOH) – Λ(NaCl) 0 0 0
In the electrolysis of aqueous sodium chloride solution which of the half cell reaction will occur at anode?
(ii) 2H2O (l) → O2 (g) + 4H (aq) + 4e– ; E Cell = 1.23V + 1 V
The positive value of the standard electrode potential of Cu2+/Cu indicates that ____________. +
(ii) this redox couple is a stronger oxidising agent than H /H2.
(iv) Cu cannot displace H2 from acid.
E Cell for some half cell reactions are given below. On the basis of these mark the correct answer. + 1 V (a) H (aq) + e– → H (g) ; E Cell = 0.00V 2 2 + V (b) 2H2O (l) → O2 (g) + 4H (aq) + 4e– ; E Cell = 1.23V 2– 2– V (c) 2SO4 (aq) → S2O8 (aq) + 2e– ; E Cell = 1.96 V
(i) In dilute sulphuric acid solution, hydrogen will be reduced at cathode.
(iii) In dilute sulphuric acid solution, water will be oxidised at anode. 2–
E Cell = 1.1V for Daniel cell. Which of the following expressions are correct description of state of equilibrium in this cell?
(ii) logK c =1.1 2F 2.2
(iii) log Kc = 0.059
Conductivity of an electrolytic solution depends on ____________.
(i) nature of electrolyte.
(ii) concentration of electrolyte.
Λm H2 O is equal to _______________. 0 0 0
(i) Λm (HCl) + Λm (NaOH) – Λm (NaCl) 0 0 0
(iv) Λm (NH OH) + Λm (HCl) – Λm (NH Cl) 4 4
What will happen during the electrolysis of aqueous solution of CuSO4 by using platinum electrodes?
(i) Copper will deposit at cathode.
(iii) Oxygen will be released at anode.
What will happen during the electrolysis of aqueous solution of CuSO4 in the presence of Cu electrodes?
(i) Copper will deposit at cathode.
(ii) Copper will dissolve at anode.
Conductivity κ , is equal to ____________. 1 l
(i) R A *
(ii)
Molar conductivity of ionic solution depends on ___________.
(i) temperature.
(iii) concentration of electrolytes in solution.
For the given cell, Mg|Mg2+|| Cu2+|Cu
(ii) Cu is cathode
(iii) The cell reaction is Mg + Cu2+ → Mg2+ + Cu
Can absolute electrode potential of an electrode be measured? V V
No
Can E Cell or ∆r G for cell reaction ever be equal to zero?
No
Under what condition is ECell = 0 or ∆ rG = 0?
When the cell reaction reaches equilibrium.
What does the negative sign in the expression E = − 0.76 V mean? Zn2+/Zn
It means that Zn is more reactive than hydrogen. When zinc electrode will be connected to SHE, Zn will get oxidised and H+ will get reduced.
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.
Different, see the NCERT textbook, page no. 84.
Depict the galvanic cell in which the cell reaction is Cu + 2Ag+ → 2Ag + Cu2+ –
Cu|Cu2+|| Ag+|Ag
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?
Under the conditions of electrolysis of aqueous sodium chloride, oxidation – of water at anode requires overpotential hence Cl is oxidised instead of water.
What is electrode potential?
See NCERT textbook, page no. 65
Consider the following diagram in which an electrochemical cell is coupled to an electrolytic cell. What will be the polarity of electrodes ‘A’ and ‘B’ in the electrolytic cell? Fig. 3.1
This question refers to a figure in the original PDF.
‘A’ will have negative polarity ‘B’ will have positive polarity
Why is alternating current used for measuring resistance of an electrolytic solution?
Alternating current is used to prevent electrolysis so that concentration of ions in the solution remains constant.
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?
See NCERT textbook, page no. 64
How will the pH of brine (aq. NaCl solution) be affected when it is electrolysed?
The pH of the solution will rise as NaOH is formed in the electrolytic cell.
Unlike dry cell, the mercury cell has a constant cell potential throughout its useful life. Why?
Ions are not involved in the overall cell reaction of mercury cells.
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. 39 Electrochemistry
Electrolyte ‘B’ is strong as on dilution the number of ions remains the same, only interionic attraction decreases therefore increase in ∧m is small. +
When acidulated water (dil.H2SO4 solution) is electrolysed, will the pH of the solution be affected? Justify your answer.
pH of the solution will not be affected as [H ] remains constant. + At anode : 2H2O → O2 + 4H + 4e– + At cathode 4H + 4e– → 2H2
In an aqueous solution how does specific conductivity of electrolytes change with addition of water?
Conductivity decreases because number of ions per unit volume decreases.
Which reference electrode is used to measure the electrode potential of other electrodes?
Standard hydrogen electrode is the reference electrode whose electrode potential is taken to be zero. The electrode potential of other electrodes is measured with respect to it.
Consider a cell given below — Cu|Cu2+||Cl |Cl2,Pt Write the reactions that occur at anode and cathode
Anode : Cu → Cu2+ + 2e– – Cathode : Cl2 + 2e– → 2Cl Cu is anode as it is getting oxidised. Cl2 is cathode as it is getting reduced.
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?
Zn + Cu2+ → Zn2+ + Cu 2+ V 0.059 [Zn ] ECell = E Cell – log 2+ 2 [Cu ] 2+ ECell decreases when concentration of Zn ions, [Zn2+] increases.
What advantage do the fuel cells have over primary and secondary batteries?
Primary batteries contain a limited amount of reactants and are discharged when the reactants have been consumed. Secondary batteries can be recharged but take a long time to recharge. Fuel cell runs continuously as long as the reactants are supplied to it and products are removed continuously.
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?
Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O Density of electrolyte decreases as water is formed and sulphuric acid is consumed as the product during discharge of the battery.
Why on dilution the Λ m of CH3COOH increases drastically, while that of CH3COONa increases gradually?
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. — + CH3COOH + H2O CH3COO + H3O In the case of strong electrolyte the number of ions remains the same but the interionic attraction decreases. IV. Matching Type
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
(c) S cm2 mol–1 (iv) G*
(b) m–1 (iii) κ
(d) V
Match the terms given in Column I with the items given in Column II. Column I Column II (i) Λm
(a) intensive property (ii) E Cell
(d) increases with dilution
(b) depends on number of ions/volume (iii) κ
(c) extensive property (iv) ∆rGCell
Match the items of Column I and Column II. Column I Column II (i) Lead storage battery
(a) maximum efficiency (ii) Mercury cell
(d) Pb is anode, PbO2 is cathode
(b) prevented by galvanisation (iii) Fuel cell
(c) gives steady potential (iv) Rusting
Match the items of Column I and Column II. Column I Column II (i) κ
(a) I×t (ii) Λm
(d)
(b) Λm / Λ0 κ (iii) α
(c) G* (iv) Q
Match the items of Column I and Column II. Column I Column II (i) Lechlanche cell
(a) cell reaction 2H2 + O2 → 2H2O (ii) Ni–Cd cell
(d) reaction at anode, Zn → Zn2+ + 2e– (e) converts energy of combustion into electrical energy
(b) does not involve any ion in solution and is used in hearing aids. (iii) Fuel cell
(c) rechargeable (iv) Mercury cell
Match the items of Column I and Column II on the basis of data given below: V V V E = 2.87V , E V + = −3.5V , E = 1.4V , E Br /Br – = 1.09V F /F – Li /Li Au3+/Au 2 Column I Column II (i) F2
(a) metal is the strongest reducing agent (ii) Li
(c) non metal which is the best oxidising agent – (iv) Br
(b) metal ion which is the weakest oxidising agent (iii) Au3+
(d) unreactive metal (v) Au (e) anion that can be oxidised by Au3+ + (vi) Li (f) anion which is the weakest reducing agent – (vii) F (g) metal ion which is an oxidising agent 41 Electrochemistry
Assertion (A): Cu is less reactive than hydrogen.
Reason (R): E is negative. Cu2+ /Cu
Assertion (A): E Cell should have a positive value for the cell to function.
Reason (R): Ecathode < Eanode
Assertion (A): Conductivity of all electrolytes decreases on dilution.
Reason (R): On dilution number of ions per unit volume decreases.
Assertion (A): Λm for weak electrolytes shows a sharp increase when the electrolytic solution is diluted.
Reason (R): For weak electrolytes degree of dissociation increases with dilution of solution.
Assertion (A): Mercury cell does not give steady potential.
Reason (R): In the cell reaction, ions are not involved in solution.
(v)
Assertion (A): Electrolysis of NaCl solution gives chlorine at anode instead of O2.
Reason (R): Formation of oxygen at anode requires overvoltage.
Assertion (A): For measuring resistance of an ionic solution an AC source is used.
Reason (R): Concentration of ionic solution will change if DC source is used.
Assertion (A): Current stops flowing when ECell = 0.
Reason (R): Equilibrium of the cell reaction is attained.
Assertion (A): E + Ag+/Ag increases with increase in concentration of Ag ions.
Reason (R): E Ag+/Ag has a positive value.
Assertion (A): Copper sulphate can be stored in zinc vessel.
Reason (R): Zinc is less reactive than copper.
Consider the Fig. 3.2 and answer the following questions. Fig. 3.2
This question refers to a figure in the original PDF.
(i) Cell ‘A’ has ECell = 2V and Cell ‘B’ has ECell = 1.1V which of the two cells ‘A’ or ‘B’ will act as an electrolytic cell. Which electrode reactions will occur in this cell?
(ii) If cell ‘A’ has ECell = 0.5V and cell ‘B’ has ECell = 1.1V then what will be the reactions at anode and cathode?
Consider Fig. 3.2 and answer the questions
This question refers to a figure in the original PDF.
Hint : (i) Electrons move from Zn to Ag. (ii) Ag is the cathode. (iii) Cell will stop functioning. (iv) When E Cell = 0. (v) Concentration of Zn2+ ions will increase and concentration of Ag+ ions will decrease (vi) When E cell = 0 equilibrium is reached and concentration of 2+ Zn ions and Ag + ions will not change.
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? 43 Electrochemistry