Download electrochemistry and electrode reaction and more Essays (university) Chemistry in PDF only on Docsity!
- Which cell will measure standard electrode potential of copper electrode?
(i) Pt (s) H 2 (g,0.1 bar) H+^ (aq.,1 M) Cu2+^ (aq.,1M) Cu (ii) Pt(s) H 2 (g, 1 bar) H+^ (aq.,1 M) Cu2+^ (aq.,2 M) Cu (iii) Pt(s) H 2 (g, 1 bar) H+^ (aq.,1 M) Cu 2+^ (aq.,1 M) Cu (iv) Pt(s) H 2 (g, 1 bar) H+^ (aq.,0.1 M) Cu2+^ (aq.,1 M) Cu
- Electrode potential for Mg electrode varies according to the equation
E (^) Mg 2 +| Mg = (^) E Mg (^) 2 +| Mg
V – 0 .0 5 9
2 2
log [Mg +^ ].^ The^ graph^ of^^ E Mg^^2 +| Mg^ vs log [Mg 2+^ ] is
(i) (ii)
(iii) (iv)
I. Multiple Choice Questions (Type-I)
UnitUnitUnit UnitUnit
ELECELECELECTRELECELECELECTRELECELECELECELECTRTRTROCHEMISTRTRTROCHEMISTRTROCHEMISOCHEMISOCHEMISOCHEMISOCHEMISOCHEMISTRYOCHEMISOCHEMISTRYTRYTRYTRYTRYTRYTRYTRYTRY
© NCERT
not to be republished
Exemplar Problems, Chemistry 34
- Which of the following statement is correct? (i) E Cell and Δ r G of cell reaction both are extensive properties. (ii) E Cell and Δ r G of cell reaction both are intensive properties. (iii) E Cell is an intensive property while Δ r G of cell reaction is an extensive property. (iv) E Cell is an extensive property while Δ r G of cell reaction is an intensive property.
- The difference between the electrode potentials of two electrodes when no current is drawn through the cell is called ___________. (i) Cell potential (ii) Cell emf (iii) Potential difference (iv) Cell voltage
- Which of the following statement is not correct about an inert electrode in a cell? (i) It does not participate in the cell reaction. (ii) It provides surface either for oxidation or for reduction reaction. (iii) It provides surface for conduction of electrons. (iv) It provides surface for redox reaction.
- An electrochemical cell can behave like an electrolytic cell when ____________. (i) E cell = 0 (ii) E cell > E ext (iii) E ext > E cell (iv) E cell = E ext
- Which of the statements about solutions of electrolytes is not correct? (i) Conductivity of solution depends upon size of ions. (ii) Conductivity depends upon viscosiy of solution. (iii) Conductivity does not depend upon solvation of ions present in solution. (iv) Conductivity of solution increases with temperature.
- Using the data given below find out the strongest reducing agent.
E Cr O (^) 2 2– 7 /Cr3+ V = 1.33 V E Cl 2 /Cl–
V = 1.36 V
EMnO 4 – (^) / Mn2+ V = 1.51 V ECr3+ /Cr
V = – 0.74 V
(i) Cl– (ii) Cr (iii) Cr3+ (iv) Mn2+
© NCERT
not to be republished
Exemplar Problems, Chemistry 36
(iii) PbSO 4 cathode is oxidised to Pb. (iv) PbSO 4 anode is oxidised to PbO 2.
0 Λ m (^) (NH OH) is equal to ______________.
(i) (^4 )
0 0 0 Λ m (^) (^) (NH OH) + Λ m (^) (NH Cl) – Λ(HCl)
(ii) (^4)
0 0 0 Λ m (^) (^) (NH Cl) + Λ m (^) (NaOH) – Λ(NaCl)
(iii) (^4)
0 0 0 Λ m (^) (^) (NH Cl) + Λ m (^) (NaCl) – Λ(NaOH)
(iv) (^4)
0 0 0 Λ m (^) (^) (NaOH) + Λ (^) m (NaCl) – Λ(NH Cl)
- In the electrolysis of aqueous sodium chloride solution which of the half cell reaction will occur at anode?
(i) Na +^ (aq) + e –^ ⎯→ Na ( s ); E Cell V^ = –2.71V
(ii) 2H 2 O ( l ) ⎯→ O 2 (g) + 4H +^ (aq) + 4e –^ ; E Cell V^ = 1.23V
(iii) H +^ (aq) + e –^ ⎯→
1 2
H 2 (g); E (^) CellV^ = 0.00 V
(iv) Cl–^ (aq) ⎯→
1 2
Cl 2 (g) + e–^ ; (^) E (^) CellV^ = 1.36 V
II. Multiple Choice Questions (Type-II)
Note : In the following questions two or more than two options may be correct.
- The positive value of the standard electrode potential of Cu 2+^ /Cu indicates that ____________. (i) this redox couple is a stronger reducing agent than the H+/H 2 couple.
(ii) this redox couple is a stronger oxidising agent than H+/H 2.
(iii) Cu can displace H 2 from acid.
(iv) Cu cannot displace H 2 from acid.
- E Cell V^ for some half cell reactions are given below. On the basis of these mark the correct answer.
(a) H +^ (aq) + e –^ ⎯→
1 2
H 2 (g) ; E Cell V^ = 0.00V
© NCERT
not to be republished
37 Electrochemistry
(b) 2H 2 O (l) ⎯→ O 2 (g) + 4H +^ (aq) + 4e –^ ; (^) E Cell V^ = 1.23V
(c) 2SO 4 2–^ (aq) ⎯→ S 2 O 8 2–^ (aq) + 2e –^ ; E Cell V^ = 1.96 V
(i) In dilute sulphuric acid solution, hydrogen will be reduced at cathode. (ii) In concentrated sulphuric acid solution, water will be oxidised at anode. (iii) In dilute sulphuric acid solution, water will be oxidised at anode. (iv) In dilute sulphuric acid solution, SO 4 2–^ ion will be oxidised to tetrathionate ion at anode.
- E Cell^ V^ =1.1 V for Daniel cell. Which of the following expressions are correct
description of state of equilibrium in this cell?
(i) 1.1 = K c
(ii) (^) c
2.303R logK =1. 2
T F
(iii) log K c =
(iv) log K c = 1.
- Conductivity of an electrolytic solution depends on ____________.
(i) nature of electrolyte. (ii) concentration of electrolyte.
(iii) power of AC source.
(iv) distance between the electrodes.
- Λ m 0 H O 2 is equal to _______________.
(i)
0 0 0 Λ m (^) (^) (HCl) + Λ m (^) (^) (NaOH) – Λ m (NaCl)
(ii) (^3 )
0 0 0 Λ m (^) (^) (HNO ) + Λ (^) m (^) (NaNO ) – Λ m (NaOH)
(iii) (^3 )
0 0 0 Λ(HNO (^) ) + Λ m (^) (^) (NaOH) – Λ m (NaNO )
(iv) (^4 )
0 0 0 Λ m (^) (^) (NH OH) + Λ m (^) (^) (HCl) – Λ m (NH Cl)
- What will happen during the electrolysis of aqueous solution of CuSO 4 by using platinum electrodes?
(i) Copper will deposit at cathode.
(ii) Copper will deposit at anode.
© NCERT
not to be republished
39 Electrochemistry
- What does the negative sign in the expression E Zn^ V2+ /Zn = −0.76 V mean?
- 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.
- Depict the galvanic cell in which the cell reaction is Cu + 2Ag+^ ⎯→ 2Ag + Cu2+
- 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?
- What is electrode potential?
- 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.
- Why is alternating current used for measuring resistance of an electrolytic solution?
- 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?
- How will the pH of brine (aq. NaCl solution) be affected when it is electrolysed?
- Unlike dry cell, the mercury cell has a constant cell potential throughout its useful life. Why?
- 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.
© NCERT
not to be republished
Exemplar Problems, Chemistry 40
- When acidulated water (dil.H 2 SO 4 solution) is electrolysed, will the pH of the solution be affected? Justify your answer.
- In an aqueous solution how does specific conductivity of electrolytes change with addition of water?
- Which reference electrode is used to measure the electrode potential of other electrodes?
- Consider a cell given below Cu|Cu2+^ ||Cl—|Cl 2 ,Pt Write the reactions that occur at anode and cathode
- Write the Nernst equation for the cell reaction in the Daniel cell. How will the E (^) Cell be affected when concentration of Zn2+^ ions is increased?
- What advantage do the fuel cells have over primary and secondary batteries?
- 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?
- Why on dilution the Λ m^ of CH 3 COOH increases drastically, while that of CH 3 COONa increases gradually?
IV. Matching Type
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– (ii) E Cell (b) m– (iii) κ (c) S cm 2 mol – (iv) G* (d) V
- Match the terms given in Column I with the items given in Column II.
Column I Column II
(i) (^) Λ m (a) intensive property
(ii) E Cell V^ (b) depends on number of ions/volume (iii) κ (c) extensive property (iv) Δr G Cell (d) increases with dilution
- Match the items of Column I and Column II.
Column I Column II (i) Lead storage battery (a) maximum efficiency
© NCERT
not to be republished
Exemplar Problems, Chemistry 42
V. Assertion and Reason Type
Note : In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices. (i) Both assertion and reason are true and the reason is the correct explanation of assertion. (ii) Both assertion and reason are true and the reason is not the correct explanation of assertion. (iii) Assertion is true but the reason is false. (iv) Both assertion and reason are false. (v) Assertion is false but reason is true.
- Assertion : Cu is less reactive than hydrogen.
Reason :^ E Cu2+ /Cu
V is negative.
- Assertion : E Cell should have a positive value for the cell to function. Reason : E cathode < E anode
- Assertion : Conductivity of all electrolytes decreases on dilution. Reason : On dilution number of ions per unit volume decreases.
- Assertion : Λ m for weak electrolytes shows a sharp increase when the electrolytic solution is diluted. Reason : For weak electrolytes degree of dissociation increases with dilution of solution.
- Assertion : Mercury cell does not give steady potential. Reason : In the cell reaction, ions are not involved in solution.
- Assertion : Electrolysis of NaCl solution gives chlorine at anode instead of O 2. Reason : Formation of oxygen at anode requires overvoltage.
- Assertion : For measuring resistance of an ionic solution an AC source is used. Reason : Concentration of ionic solution will change if DC source is used.
- Assertion : Current stops flowing when E Cell = 0. Reason : Equilibrium of the cell reaction is attained.
- Assertion :^ E^ Ag /Ag+ increases with increase in concentration of Ag+^ ions.
Reason :^ E^ Ag /Ag+ has a positive value.
- Assertion : Copper sulphate can be stored in zinc vessel. Reason : Zinc is less reactive than copper.
© NCERT
not to be republished
43 Electrochemistry
VI. Long Answer Type
- Consider the Fig. 3.2 and answer the following questions.
Fig. 3.
Fig. 3.
(i) Cell ‘A’ has ECell = 2 V and Cell ‘B’ has ECell = 1.1 V 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 E Cell = 0.5V and cell ‘B’ has E Cell = 1.1 V then what will be the reactions at anode and cathode?
- Consider Fig. 3.2 and answer the questions (i) to (vi) given below.
(i) Redraw the diagram to show the direction of electron flow. (ii) Is silver plate the 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+^ ions and Ag+^ ions be affected when the cell functions? (vi) How will the concentration of Zn2+^ ions and Ag+^ ions be affected after the cell becomes ‘dead’?
- 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?
© NCERT
not to be republished
45 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.
- pH of the solution will not be affected as [H+] remains constant.
At anode : 2H 2 O ⎯→ O 2 + 4H+^ + 4e– At cathode 4H+^ + 4e–^ ⎯→ 2H 2
- Conductivity decreases because number of ions per unit volume decreases.
- 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.
- Anode : Cu ⎯→ Cu2+^ + 2e – Cathode : Cl 2 + 2e –^ ⎯→ 2Cl–
Cu is anode as it is getting oxidised. Cl 2 is cathode as it is getting reduced.
- Zn + Cu 2+^ ⎯→ Zn2+^ + Cu
E Cell = (^) E CellV^ –
2+ 2+
0.059 (^) log[Zn ] (^2) [Cu ]
E Cell decreases when concentration of Zn2+^ ions, [Zn2+] increases.
- 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.
- Pb + PbO 2 + 2H 2 SO 4 ⎯→ 2PbSO 4 + 2H 2 O Density of electrolyte decreases as water is formed and sulphuric acid is consumed as the product during discharge of the battery.
- In the case of CH 3 COOH, which is a weak electrolyte, the number of ions increase on dilution due to an increase in degree of dissociation. CH 3 COOH + H 2 O CH 3 COO—^ + H 3 O+ In the case of strong electrolyte the number of ions remains the same but the interionic attraction decreases.
IV. Matching Type
- (i) → (c) (ii) → (d) (iii) → (a) (iv) → (b)
- (i) → (d) (ii) → (a) (iii) → (b) (iv) → (c)
- (i) → (d) (ii) → (c) (iii) → (a) (iv) → (b)
© NCERT
not to be republished
Exemplar Problems, Chemistry 46
- (i) → (d) (ii) → (c) (iii) → (b) (iv) → (a)
- (i) → (d) (ii) → (c) (iii) → (a), (e) (iv) → (b)
- (i) → (c) (ii) → (a) (iii) → (g) (iv) → (e)
(v) → (d) (vi) → (b) (vii) → (g) (f)
V. Assertion and Reason Type
- (iii) 57. (iii) 58. (i) 59. (i) 60. (v)
- (i) 62. (i) 63. (i) 64. (ii) 65. (iv)
VI. Long Answer Type
- (i) Cell ‘B’ will act as electrolytic cell as it has lower emf ∴ The electrode reactions will be: Zn 2+^ + 2e–^ ⎯→ Zn at cathode Cu ⎯→ Cu2+^ + 2e–^ at anode
(ii) Now cell ‘B’ acts as galvanic cell as it has higher emf and will push electrons into cell ‘A’. The electrode reaction will be: At anode : Zn ⎯→ Zn2+^ + 2e – At cathode : Cu2+^ + 2e–^ ⎯→ Cu
- 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 Zn2+^ ions and Ag +^ ions will not change.
© NCERT
not to be republished
