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Published on: 04/12/2019
Electro Chemistry
Download Tamil Nadu 12th Standard Chemistry question papers, model tests, one-mark questions, important questions, and public exam papers in PDF format. Free study materials and answer keys for TN State Board students.
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1.
What happens during the electrolysis of molten sodium chloride?
Cl2 is released at the cathode
Liquid sodium is obtained at the anode
The emf of the overall reaction is -4.07 V
Cl2 is released at the cathode and Liquid sodium is obtained at the anode
2.
Which of the statements about electrolytic conductance is not true?
Conductivity increases with decrease in viscosity.
Higher dielectric constant shows lower conductance in solution.
Temperature increases, conductance also increases.
Molar conductance increases with increase in dilution.
3.
Which of the following electrolytic solution has the least specific conductance?
2N
0.002N
0.02N
0.2N
4.
Faraday constant is defined as_______.
charge carried by 1 electron
charge carried by one mole of electrons
charge required to deposit one mole of substance
charge carried by 6.22 ×1010 electrons
5.
6.
The equivalent conductances at infinite dilution of HCl, CH3COONa and NaCl are 42616, 91.0 and 126.45 ohm-1 cm2 gm equuivalent-1 respectively. Calculate the equivalent conductance (λ∞) of acetic acid.
7.
State Kohlrausch Law. How is it useful to determine the molar conductivity of weak electrolyte at infinite dilution.
8.
Define Faraday.
9.
Write the reactions taking place in anode and cathode of a mercury button cell. Give the over all redox reaction of the cell with the emf generation
10.
Answer the following question with regard to specific resistance.
(i) How is specific resistance represented?
(ii) What does specific resistance depend on?
(iii) What is the reciprocal of specific resistance? How is it denoted.
(iv) What is the unit of resitivity?
11.
A copper electrode is dipped in 0.1M copper sulphate solution at 25oC. Calculate the electrode potential of copper. [Given: E0Cu2+|Cu = 0.34V].
12.
0.1M NaCl solution is placed in two different cells having cell constant 0.5 and 0.25 cm-1 respectively. Which of the two will have greater value of specific conductance.
13.
Give the empirical relationship between molar conductance and concentration of the electrolyte.
14.
Derive the unit of specific conductance.
15.
Give a mathematical expression that relates I cell constant, specific conductance and specific resistance.
16.
A conductivity cell has two platinum electrodes separated by a distance 1.5 cm and the cross sectional area of each electrode is 4.5 sq cm. Using this cell, the resistance of 0.5 N electrolytic solution was measured as 15 Ω. Find the specific conductance of the solution.
17.
Reduction potential of two metals M1 and M2 are \(E^{0}_{M^{2+}_{1}|M_{1}} = -2.3V\) and \(E^{0}_{M^{2+}_{1}|M_{1}} = 0.2V\) Predict which one is better for coating the surface of iron. Given : \(\mathrm{E}_{\mathrm{Fe}^{2+} \mid \mathrm{Fe}}^{\circ}=-0.44 \mathrm{~V}\)
1.
(c)
The emf of the overall reaction is -4.07 V
2.
(b)
Higher dielectric constant shows lower conductance in solution.
3.
In general, specific conductance of an electrolyte decreases with dilution.So,0.002N solution has least specific conductance.
4.
IF = 96500 C = charge of one mole of e- charge of 6.022 x 10-23 electron
5.
(c)
6.
Given:
λ∞CH3COONa = 91.0 ohm-1 cm2g eq-1
Formula:
λ∞CH3COONa = λ∞CH3COONa + λ∞HCl - λ∞NaCl
λ∞HCl = 426.16 ohm-1 cm2g eq-1
λ∞NaCl = 126.45 ohm-1 cm2g eq-1
Solution: ∴ λ∞CH3COOH
= 91.0 + 426.16 - (126.45)
= 517.16 - 126.45
λ∞CH3COOH = 390.71 ohm-1cm2 g eq-1
7.
Kohlraush's law:
(i) At infinite dilution, the limiting molar conductivity of an electrolyte is equal to the sum of the limiting molar conductivities of its constituent ions. i.e., the molar conductivity is due to the independent migration of cations in one direction and anions in the opposite direction.
(ii) For a uni - univalent electrolyte such as NaCl, the Kohlraush's law is expressed as
\(\left(\Lambda_{\mathrm{m}}^{0}\right)_{\mathrm{NaCl}}=\left(\lambda_{\mathrm{m}}^{0}\right)_{\mathrm{Na}^{+}}+\left(\lambda_{\mathrm{m}}^{0}\right)_{\mathrm{Cl}}^{-}\)
(iii) In general, according to Kohlraush's law, the molar conductivity at infinite dilution for a electrolyte represented by the formula Ax By, is given below.
\(\left(\Lambda_{m}^{0}\right)_{A_{x} B_{y}}=x\left(\lambda_{m}^{0}\right)_{A^{y+}}+y\left(\lambda_{m}^{0}\right)_{B^{x-}}\)
b) Calculation of molar conductance at infinite dilution for weak electrolytes experimentally.
(i) However, the same can be calculated using Kohlraush's Law. For example, the molar conductance of CH3COOH, can be calculated using the experimentally determined molar conductivities of strong electrolytes HCl, NaCl and CH3COONa.
\(\Lambda_{\mathrm{CH}_{3} \mathrm{COONa}}^{0}=\lambda_{\mathrm{Na}^{+}}^{0}+\lambda_{\mathrm{CH}_{3} \mathrm{COO}^{-}}^{0} \) ..........(1)
\(\Lambda_{\mathrm{HCl}}^{0}=\lambda_{\mathrm{H}+}^{0}+\lambda_{\mathrm{Cl}^{-}}^{0} \) .........(2)
\(\Lambda_{\mathrm{NaCl}}^{0}=\lambda_{\mathrm{Na}^{+}}^{0}+\lambda_{\mathrm{Cl}^{-}}^{0}\) ...........(3)
(ii) Equation (1) + Equation (2) - Equation (3) gives,
\(\left(\Lambda_{\mathrm{CH}_{3} \mathrm{COONa}}^{0}\right)+\left(\Lambda_{\mathrm{HCl}}^{0}\right)-\left(\Lambda_{\mathrm{NaCl}}^{0}\right)=\lambda_{\mathrm{H}+}^{0}+\lambda_{\mathrm{CH}_{3} \mathrm{COO}-}^{0} \)
\(=\Lambda_{\mathrm{CH}_{2} \mathrm{COOH}}^{0}\)
8.
(i) Faraday is defined as the quantity of electricity required to liberate one gram equivalent of a substance and it is equal to 96,495 coulombs.
(ii) It is denoted by the symbol F Faraday is the quantity of electricity that contains 1 mole of electrons.
(iii) 1 Faraday = 96,495 coulombs = 1 Mole electron.
9.
(i) Oxidation occurs at anode:
(ii) Reduction occurs at cathode:
(iii) Overall reaction:
\({ Zn }_{ (s) }+{ HgO }_{ (s) }\rightarrow { ZnO }_{ (s) }+Hg(l)\)
(iv) Cell emf: about 1.35V.
10.
(i) Specific resistance is denoted by ρ(rho).
(ii) Specific resistance depends on the nature of the electrolyte.
(iii) Reciprocal is specific resistance \(\frac{1}{ρ}\) is specific conductance or conductivity denoted by K (Kappa).
(iv) ohm metre.
11.
Given: [Cu2+] = 0.1M; E0Cu2+|Cu = +0.34V
Cell reaction is: \(Cu^{2+}_{(aq)}+2e^{-}\rightarrow Cu_{(s)}\)
\(E_{cell}=E^{0}-\frac{0.0591}{n}\log\frac{[Cu]}{[Cu^{2+}]}\)
\(= 0.34\frac{0.0591}{2}\log\frac{1}{0.1}\)
Ecell = 0.34 - 0.0296 = +0.31V
12.
\(\kappa=\mathrm{C}\left(\frac{l}{\mathrm{~A}}\right)\) (or) k = 1/R.l/A
Where, C - Conductance
\(\frac{l}{A} \Rightarrow\) Cell constant (or)
Sp. Conductance \(\propto\) Cell constant
Sp. Conductance \(\propto\) Concentration
1. Sp. Conductance = concentration x cell constant
i) \(\kappa=0.1 \times 0.5=0.05=5 \times 10^{-2} \mathrm{Scm}^{-1}\)
ii) \(\kappa=0.1 \times 0.25=0.025=2.5 \times 10^{-2} \mathrm{Scm}^{-1}\)
2. So the first case will have greater specific conductance with cell constant 0.05.
13.
Kohlrausch deduced the following empirical relationship between the molar conductance (\({ \Lambda }_{ m }\)) and the concentration of the electrolyte (C).
\({ \Lambda }_{ m }={ \Lambda }_{ m }^{ o }-k\sqrt { C } \)
14.
Unit of x
\(k=\frac { 1 }{ \rho } .\frac { l }{ A } \left( \frac { 1 }{ ohm } .\frac { m }{ { m }^{ 2 } } \right) \)
= ohm-1 m-1 = mho m-1 (or) Sm-1
15.
k = \(\frac{1}{R}.\frac{1}{a}=\frac{1}{ρ}\)
Where K is specific conductance
R is resistance and \(\frac1a\) is cell constant.
ρ is specific resistance.
16.
l = 1.5 cm = 1.5 × 10-2m
A = 4.5 cm2 = 4.5 × (10-4)m2
R = 15Ω
\(\kappa = \frac{1}{R}(\frac{l}{A})\)
\(\kappa = \frac{1}{15\Omega}\times\frac{1.5\times10^{-2}m}{4.5\times10^{-4}m^2}\)
= 2.22 ohm-1 m-1
= 2.22 Sm-1
17.
The oxidation potential of M1 is more +ve than the oxidation potential of Fe which indicates that it will prevent iron from rusting.
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