#### 12th Standard Chemistry English Medium Electro Chemistry Reduced Syllabus Important Questions With Answer Key 2021

12th Standard

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Chemistry

Time : 01:00:00 Hrs
Total Marks : 100

Multiple Choice Questions

15 x 1 = 15
1. The number of electrons that have a total charge of 9650 coulombs is

(a)

6.22 ×1023

(b)

6.022 ×1024

(c)

6.022 ×1022

(d)

6.022 ×10−34

2. Faradays constant is defined as

(a)

charge carried by 1 electron

(b)

charge carried by one mole of electrons

(c)

charge required to deposit one mole of substance

(d)

charge carried by 6.22 ×1010 electrons

3. While charging lead storage battery

(a)

PbSO4 on cathode is reduced to Pb

(b)

PbSO4 on anode is oxidised to PbO2

(c)

PbSO4 on anode is reduced to Pb

(d)

PbSO4 on cathode is oxidised to Pb

4. Among the following cells
I) Leclanche cell
II) Nickel – Cadmium cell
III) Lead storage battery
IV) Mercury cell
Primary cells are

(a)

I and IV

(b)

I and III

(c)

III and IV

(d)

II and III

5. The equivalent conductance of M/36solution of a weak monobasic acid is 6mho cm2 and at infinite dilution is 400 mho cm2. The dissociation constant of this acid is

(a)

1.25 ×10−6

(b)

6.25 x 10-6

(c)

1.25 ×10−4

(d)

6.25 x 10 -5

6. For the cell reaction
2Fe3+(aq) + 2l(aq) $\rightarrow$2Fe2+ (aq) + 12 (aq)
Eocell=0.24V  = at 298K. The standard Gibbs energy (Δ, Go) of the cell reactions is :

(a)

-46.32 KJ mol−1

(b)

-23.16 KJ mol-1

(c)

46.32 KJ mol−1

(d)

23.16 KJ mol-1

7. Pick out the correct statement regarding resistance of an electrolytic solution

(a)

It is inversely proportional to the length (I)

(b)

It is inversely proportional to the cross sectional area (A)

(c)

It is directly proportional to the cross sectional area (A)

(d)

Resistivity is denoted by p (rho)

8. Using the data given below fmd out the strongest reducing agent
${ E }_{ { Cr }_{ 2 }{ O }_{ 7 }^{ 2- } }^{ o }{ Cr }^{ 3+ }=1.33V{ ,E }_{ { Cl }_{ 2 }{ / }{ Cl }^{ - } }^{ o }=1.36V$
${ E }_{ { Mn }O_{ 4 }^{ - } }^{ 0 }/{ Mn }^{ 2+ }=1.51V,{ E }_{ { Cr }^{ 3+ }/Cr }^{ o }=-0.74V$

(a)

Cr

(b)

Cr3+

(c)

Cl-

(d)

Mn2+

9. Faraday's laws of electrolysis are related to

(a)

atomic number of the cation

(b)

atomic number of the anion

(c)

equivalent weight of the electrolyte

(d)

speed ofthe cation

10. According to Faraday's first law m = ZIt, where Z is

(a)

reaction quotient

(b)

effective nuclear charge

(c)

atomic number

(d)

electrochemical equivalent

11. If 0.2 ampere can deposit 0.1978 g of copper in 50 minutes, how much of copper will be deposited by 600 coulombs ?

(a)

19.78g

(b)

1.978 g

(c)

0.1978 g

(d)

197.8 g

12. Calculate the standard emf of the cell, provided the standard reduction potentials of cathode and anode are -0.763 V and 0.80V.

(a)

- 1.563V

(b)

0.037V

(c)

- 0.610V

(d)

None of these

13. The electrical energy produced by a cell equals __________

(a)

Ecathode - Eanode

(b)

$\frac{Charge \ of \ electrons}{E_{cell}}$

(c)

Charge of electrons x Ecell

(d)

$\frac{E_{cell}}{Charge \ of \ electrons}$

14. The cell voltage depends on ______________

(a)

nature of the electrodes

(b)

concentration of the electrolytes

(c)

temperature

(d)

all the above

15. ${ \Lambda }_{ { NH }_{ 4 }OH }^{ o }$ is __________

(a)

${ \Lambda }_{ { NH }_{ 4 }OH }^{ o }={ \Lambda }_{ { NH }_{ 4 }Cl }^{ o }+{ \Lambda }_{ NaoH }^{ o }-{ \Lambda }_{ NaCl }$

(b)

${ \Lambda }_{ { NH }_{ 4 }OH }^{ o }={ \Lambda }_{ { NH }_{ 4 }Cl }^{ o }-{ \Lambda }_{ NaoH }^{ o }-{ \Lambda }_{ NaCl }$

(c)

${ \Lambda }_{ { NH }_{ 4 }OH }^{ o }={ \Lambda }_{ NaOH }^{ o }+{ \Lambda }_{ NaCl }^{ o }-{ \Lambda }_{ { NH }_{ 4 }Cl }^{ o }$

(d)

${ \Lambda }_{ { NH }_{ 4 }OH }^{ o }={ \Lambda }_{ NaOH }^{ o }+{ \Lambda }_{ NaCl }^{ o }-{ \Lambda }_{ { NH }_{ 4 }Cl }^{ o }$

1. 2 Marks

10 x 2 = 20
16. Why does conductivity of a solution decrease on dilution of the solution

17. Describe the electrolysis of molten NaCl using inert electrodes

18. Why is anode in galvanic cell considered to be negative and cathode positive electrode?

19. The resistance of a conductivity cell is measured as 190 Ω using 0.1M KCl solution (specific conductance of 0.1M KCl is 1.3 Sm-1) . When the same cell is filled with 0.003 M sodium chloride solution, the measured resistance is 6.3KΩ. Both these measurements are made at a particular temperature. Calculate the specific and molar conductance of NaCl solution. Given that

20. Derive the unit of specific conductance.

21. For a uni - univalent electrolyte) write the Debye - Huckel Onsagar equation

22. Molar conductivity increases with dilution. Is the above statement true? Justify your answer

23. Apply Kohlraush's law and determine the limiting molar conductivity of
(i) BaCl2
(ii) AI2(SO4)3

24. What is the emf developed by a single lead storage battery?

25. The standard reduction potentials of Fe3+ / Fe and Fe2+ / Fe electrode system are -0.035 V and -0.44 V respectively. Predict which of the two oxidations is easy. Fe3+ / Fe and Fe2+ / Fe

1. 3 Marks

10 x 3 = 30
26. The conductivity of a 0.01M solution of a 1 :1 weak electrolyte at 298K is 1.5$\times$10-4 S cm−1.
i) molar conductivity of the solution
ii) degree of dissociation and the dissociation constant of the weak electrolyte
Given that
$\lambda^{0}_{catlon}=248.2\quad S$ cm2 mol-1
$\lambda^{0}_{anlon}=51.8\quad S$ cm2 mol-1

27. Why is AC current used instead of DC in measuring the electrolytic conductance?

28. Can Fe3+ oxidises Bromide to bromine under standard conditions?
Given: ${ E }_{ { Fe }^{ 3+ }|{ Fe }^{ 2+ } }^{ 0 }=0.771$
$\\ { E }_{ { Br }_{ 2 }|{ Br }^{ - } }=1.09V$.

29. Two metals M1 and M2 have reduction potential values of -xV and +yV respectively. Which will liberate H2 and H2SO4.

30. Define molar conductance.

31. What is the oxidation and reduction half cell in a Daniel cell?

32. Give the oxidation and reduction half cell reaction taking place in the Daniel cell.

33. Explain the reactions taking place in the anode and cathode of a lead storage battery.

34. Define Faraday.

35. Draw a neat diagram of Leclanche cell and mark the parts.

1. 5 Marks

7 x 5 = 35
36. Derive an expression for Nernst equation

37. 0.5 F of electric current was passed through 5 molar solution of AgNO3, CuSO4 and AICl3 connected in series. Find out the concentration of each of the electrolyte after the electrolysis.

38. Write the Nernst equation for the half cell Zn2+(aq)/ Zn(s)

39. If E1 = 0.5 V corresponds to Cr3++ 3e- ➝ Cr(s) and E= 0.41V corresponds to Cr3++ e- ➝ Cr2+ reactions, calculate the emf (E3) of the reaction Cr2++ 2 e- ➝ Cr(s)

40. Calculate the emf of the cell having the cell reaction 2Ag+ + Zn ⇌ 2Ag + Zn2+ and Eocell= 1.56 V at 25°C when concentration of Zn2+ = 0.1 M and Ag+ = 10 M in the solution.
$[{ E }_{ cell }={ E }_{ cell }^{ o }-\frac { RT }{ nF } In\frac { [{ Zn }^{ 2+ }] }{ [{ Ag] }^{ 2 } } ]$

41. Derive a relationship between dissociation constant Ka and molar conductivity ${ \Lambda }_{ m }$

42. Write an account on cell terminology.