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Chemistry NCERT Exemplar Solutions Class 12th Chapter Three

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3 months ago

Chemistry NCERT Exemplar Solutions Class 12th Chapter Three Electrochemistry

Assertion: Electrolysis of NaCl solution gives chlorine at anode instead of ?2 .

Reason: Formation of oxygen at anode requires overvoltage

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Vishal Baghel

Contributor-Level 10

This is a Assertion and Reason Type as classified in NCERT Exemplar

Ans: Correct Option: (i)

(i) Electrolysis of sodium chloride is represented by the following equations

H⁺ (aq)+ e⁻→12H₂ (g)

At the anode, the reaction goes this way,

Cl⁻ (aq)→12Cl₂ (g) + e⁻ E $°$ _cell =1.36V

2H₂O (aq)→O₂ (g) + 4H⁺ (aq)+ 4e− E $°$ _cell =1.23V

The reaction with the lower value E_cell is preferred but the formation of oxygen requires overpotential

Therefore, the assertion is correct, the reason is correct and the reason is the correct explanation for assertion. Therefore, this option is correct

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Chemistry NCERT Exemplar Solutions Class 12th Chapter Three Electrochemistry

Assertion: Mercury cell does not give steady potential.

Reason: In the cell reaction, ions are not involved in the solution.

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Vishal Baghel

Contributor-Level 10

This is a Assertion and Reason Type as classified in NCERT Exemplar

Ans: Correct Option: (i)

(i)Mercury cells give a steady potential. The reason is that the ions are not involved in this reaction. The assertion is incorrect and the reason is correct so this option is incorrect

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Chemistry NCERT Exemplar Solutions Class 12th Chapter Three Electrochemistry

Assertion: Λm Weak electrolytes show a sharp increase when the electrolytic solution is diluted.

Reason: For weak electrolytes degree of dissociation increases with the dilution of solution

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Vishal Baghel

Contributor-Level 10

This is a Assertion and Reason Type as classified in NCERT Exemplar

Ans: Correct Option: (i)

(i) Molar conductivity of weak electrolytes increases on dilution. In addition to solution the degree of dissociation increases leading to an increase in the number of ions produced. Therefore, Λm shows a sharp increase.

Therefore, the assertion is correct, the reason is correct and the reason is a correct explanation for assertion.

(ii) Assertion is correct, the reason is correct and the reason is the correct explanation of assertion. Therefore, this option is incorrect

(iii)Assertion and true both are correct therefore

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Chemistry NCERT Exemplar Solutions Class 12th Chapter Three Electrochemistry

Assertion: Conductivity of all electrolytes decreases on dilution

Reason: On dilution the number of ions per unit volume decreases.

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Vishal Baghel

Contributor-Level 10

This is a Assertion and Reason Type as classified in NCERT Exemplar

Correct Option: (i)

Ans: (i) Conductivity is due to the movement of ions. The number of ions present per unit volume decides the conductivity. It decreases on dilution. The number of ions per unit volume decreases on dilution. So, the assertion is correct, the reason is correct and the reason is the correct explanation of the assertion. Therefore, this option is correct

(ii) Assertion is correct, the reason is correct and the reason is the correct explanation of assertion. Therefore, this option is incorrect

(iii) Assertion and true both are correct therefore this

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Chemistry NCERT Exemplar Solutions Class 12th Chapter Three Electrochemistry

Assertion: E_cell should have a positive value for the cell to function

Reason: E_cathode < E_annode

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Vishal Baghel

Contributor-Level 10

This is a Assertion and Reason Type as classified in NCERT Exemplar

Ans: Correct Option: (iii)

(i)A chemical reaction is spontaneous when the Gibbs free energy is negative. This is possible when E_cell is positive. E_cathode < E_{annode .}Therefore, the assertion is correct and the reason is incorrect and the reason is not a correct explanation of assertion. Therefore, this option is incorrect

(ii) E_cathode < E_annode reaction is spontaneous when the Gibbs free energy is negative. This is possible when E_cell is positive. E_cathode < E_annode . Therefore, the assertion is correct and the reason is incorrect. Therefore, this option is co

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Chemistry NCERT Exemplar Solutions Class 12th Chapter Three Electrochemistry

Assertion: Cu is less reactive than hydrogen.

Reason: E $°$ Cu²⁺/Cu is negative.

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Vishal Baghel

Contributor-Level 10

This is a Assertion and Reason Type as classified in NCERT Exemplar

Ans: Correct Option: (iii)

(i)The electrode potential of Cu²⁺/Cu is negative. The electrode potential of 2H⁺/H²is 0.00V. Therefore, the assertion is correct and the reason is incorrect and the reason is not a correct explanation of assertion. Therefore, this option is incorrect

(ii) E $°$ Cu²⁺/Cu is not negative so the reason is incorrect. Therefore, this option is incorrect

(iii) The electrode potential of Cu²⁺/Cu is negative. The electrode potential of 2H⁺/H² is 0.00V. Therefore, the assertion is correct and the reason is incorrect. Therefore, this opt

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This is a Assertion and Reason Type as classified in NCERT Exemplar

Ans: Correct Option: (iii)

(ii) E $°$ Cu²⁺/Cu is not negative so the reason is incorrect. Therefore, this option is incorrect

(iii) The electrode potential of Cu²⁺/Cu is negative. The electrode potential of 2H⁺/H² is 0.00V. Therefore, the assertion is correct and the reason is incorrect. Therefore, this option is correct

(iv) Assertion is true and the reason is false therefore this option is incorrect

(v)Assertion is true therefore this option is incorrect.

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Chemistry NCERT Exemplar Solutions Class 12th Chapter Three Electrochemistry

Match the items of Column I and Column II based on data given below:

Column I	Column II
(i)F₂	(a)metal is the strongest reducing agent
(ii)Li	(b)metal ion which is the weakest oxidizing agent
(iii)Au ³⁺	(c)non-metal which is the best oxidizing agent
(iv)Br ⁻	(d)unreactive metal
(v)Au	(e)anion that can be oxidized by Au ³⁺
(vi)Li⁺	(f)anion which is the weakest reducing agent
(vii)F⁻	(g)metal which is an oxidising agent

E $\frac{G}{R}$ _F2/F=2.87V E $\frac{K}{C}$ _Li/Li= 3.5V E_Au3+/Au = 1.4V E $\frac{Λ m}{Λ^{0} m}$ _Br2/Br^- = 1.09V

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Vishal Baghel

Contributor-Level 10

This is a Matching Type Questions as classified in NCERT Exemplar

Ans: (i) F₂is a non-metal which is the best oxidizing agent since the standard reduction potential of F₂ is 2.87V.

(ii)Liis a metal and the strongest reducing agent because the standard reduction potential of Li is −3.05V.

(iii)Au³⁺is a metal ion which is an oxidizing agent as standard reduction potential of Au³⁺ is 1.40V.

(iv) Br⁻is an anion that can be oxidized by Au³⁺ as standard reduction potential of Au³⁺is 1.40V which is more than that of Br⁻ which is E $Q$ _Br2/Br−0=1.09V.

(v)Auis an unreactive metal

(vi)Li⁺ is a metal ion having the least value

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This is a Matching Type Questions as classified in NCERT Exemplar

Ans: (i) F₂is a non-metal which is the best oxidizing agent since the standard reduction potential of F₂ is 2.87V.

(ii)Liis a metal and the strongest reducing agent because the standard reduction potential of Li is −3.05V.

(iii)Au³⁺is a metal ion which is an oxidizing agent as standard reduction potential of Au³⁺ is 1.40V.

(iv) Br⁻is an anion that can be oxidized by Au³⁺ as standard reduction potential of Au³⁺is 1.40V which is more than that of Br⁻ which is E $Q$ _Br2/Br−0=1.09V.

(v)Auis an unreactive metal

(vi)Li⁺ is a metal ion having the least value of standard reduction potential of 3.05V. Hence it is the weakest oxidizing agent

(vii)F⁻is an anion that is the weakest reducing agent as it has less oxidation potential.

Hence, the answer is:

(i)-c; (ii)-a; (iii)-g; (iv)-e; (v)-d; (vi)-b; (vii)-f

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Chemistry NCERT Exemplar Solutions Class 12th Chapter Three Electrochemistry

Match the items of column I and column II

Column I	Column II
(i)Lechlanche cell	(a)cell reaction
(ii)Ni−Cd	(b) does not involve any ion in solution and is used in hearing aids.
(iii)Fuel cell	(c)rechargeable
(iv)Mercury cell	(d)reaction at anode
	(e) converts energy of combustion into electrical energy

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Vishal Baghel

Contributor-Level 10

This is a Matching Type Questions as classified in NCERT Exemplar

Ans: (i)The reaction occurring at Lechlanche cells are

At anode: Zn→Zn²⁺ + 2e⁻

At cathode: MnO₂ + NH₄⁺+ e⁻→MnO (OH)+NH₃

(ii)Ni−Cd is rechargeable. So it has a longer lifetime.

(iii) Energy in the fuel cell is due to the combustion process. It converts combustion energy into electrical energy 2H₂ + O₂→2H₂O

(iv) Mercury cells don't involve any solution and are used in hearing aids.

Hence, the answer is:

(i)-d; (ii)-c; (iii)-a, e; (iv)-b

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Chemistry NCERT Exemplar Solutions Class 12th Chapter Three Electrochemistry

Match the terms given in Column I with the units given in Column II.

Column I	Column II
(i)k	*(a)I x T***
(ii)Λ_m	(b) $\frac{Λ m}{Λ^{0} m}$
(iii) $α$	(c) $\frac{K}{C}$
(iv) $Q$	(d) $\frac{G}{R}$

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Vishal Baghel

Contributor-Level 10

This is a Matching Type Questions as classified in NCERT Exemplar

Ans: (i)Conductivity k is defined as k = $°$

(ii)Molar conductivity is given by Λ_m = $* T$

(iii)Degree of dissociation is given by $\frac{Λ m}{Λ^{0} m}$ ? = $α$

(iv)Charge $\frac{K}{C}$ is the product of current and time $Q$ = I $\frac{G}{R}$

Hence, the answer is:

(i)-d; (ii)-c; (iii)-b; (iv)-a

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Chemistry NCERT Exemplar Solutions Class 12th Chapter Three Electrochemistry

Match the terms given in Column I with the units given in Column II.

Column I	Column II
(i)Lead storage battery	(a)Maximum efficiency
(ii)Mercury cell	(b)prevented by galvanization
(iii)Fuel cell	(c)gives steady potential
(iv)Rusting	(d)Pbis the anode,PbO₂ is cathode

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Vishal Baghel

Contributor-Level 10

This is a Matching Type Questions as classified in NCERT Exemplar

Ans: (i) The cell reaction of a lead storage battery is as follows;

Pb + PbO₂+ 2H₂SO₄→2H₂SO₄+ 2H₂O

At cathode:PbO₂ (s)+SO₄²⁻ (aq)+2e⁻→2PbSO₄ (s) + 2H₂O (l)

At anode:Pb (s)+SO₄²⁻ (aq)→PbSO₄ (s)+2e⁻

Therefore Pb is the anode and PbO₂ is cathode

(ii)Mercury cell doesn't contain ions so it gives steady potential.

(iii)Fuel cells have maximum efficiency as they produce energy due to the combustion reaction of fuel.

(iv)Rusting is prevented by galvanization.

Hence, the answer is:

(i)-d ; (ii)-c ; (iii)-a ; (iv)-b

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