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Class First year MCQs on Electrochemistry

1. The electrode through which the electron enter the electrolytic solution is





... Answer is b)
Explanation: The elctrode at which electron enter electrolytic solution is called cathod. At cathode, cations from electrolytic solution, take up elctron and get reduced.

42. Oxidation number of S in Na2S2O3





... Answer is b)
Explanation: Suppose, oxidation state of S in Na2S2O3 is X.
Sum of oxidation numbers of all atoms present in a neutral compound is zero.
2(Oxidation No. of Na) + 2(Oxidation No. of S) + 3(Oxidation No. of O ) = 0
2(+1) + 2 (x) + 3(-2) = 0
+2 + 2x -6 = 0
+2x -4 = 0
+2x = 4
x = 4/2 = +2

3. In the electrolysis of molten ZnCl2, the cathode reaction is Zn+2 +2e- ---------> Zn. What quantity of electricity is used up for the production of half mole of Zn





... Answer is b)
Explanation: From reaction, Zn+2 +2e- ---------> Zn,
Reduction of 1 mole of Zn+2 requires = 2 moles of electrons.
Reduction of 1/2 mole of Zn+2 will require = 1/2× 2F = 1F
1 hence, 1F = 1 mole of electrons

4. How many moles of Cr will be produced by 1.5 Faraday of electricity by the following reaction: Cr+3 + 3e- ---> Cr





... Answer is d)
Explanation: From reaction, Cr+3 + 3e- ---> Cr,
3 Farady or 3 moles of electrons produce = 1 mole of Cr
1 F will will produce = 1/3 moles of Cr
1.5 F will proudue = 1.5 x 1/3 mole of Cr = 0.5 moles of Cr

5. E0Sn = -0.14V, E0Pb = -0.13V





... Answer is b)
Explanation: Hence, reduction potential of Pb+ is greater than that of Sn+, So, Pb+ will oxidize Sn.

6. A fuel cell operates at ------temperature





... Answer is d)
Explanation: A fuel cell uses hydrogen gas as a fuel and oxidizing agent like Oxygen to generate electricity along with formation of water as a product. The chemical reactions in fuel cell occurs at very high temperature.

7. The oxidation number of Cl in HClO4 is





... Answer is d)
Explanation: Let, oxidation state of Cl in HClO4 is X.
Sum of oxidation numbers of all atoms present in a neutral compound is zero.
Oxidation No. of H + Oxidation No. of Cl + 4(Oxidation No. of O ) = 0
+1 + x + 4(-2) = 0
+1 + x -8 = 0
x -7 = 0
x = +7
Oxidation No. of Cl in HClO4 is +7.

8. In which of the following compounds oxidation number of N is +5





... Answer is d)
Explanation: To determine the compound with nitrogen with +5 oxidation number, we are to calculate the oxidation number of nitrogen in each compound.
Let, oxidation state of N in NO2 is X.
Sum of oxidation numbers of all atoms present in a neutral compound is zero.
Oxidation No. of N + 2(Oxidation No. of O ) = 0
X + 2(-2) = 0
X -4 = 0
X = +4
Oxidation No. of N in NO2 is +4
Let, oxidation state of N in N2O4 is X.
Sum of oxidation numbers of all atoms present in a neutral compound is zero.
2(Oxidation No. of N) + 4(Oxidation No. of O ) = 0
2X + 4(-2) = 0
2X -8 = 0
X = +8/2 = +4
Oxidation No. of N in N2O4 is +4
Let, oxidation state of N in N2O4 is X.
Sum of oxidation numbers of all atoms present in a neutral compound is zero.
2(Oxidation No. of N) + 3(Oxidation No. of O ) = 0
2X + 3(-2) = 0
2X -6 = 0
X = +6/2 = +3
Oxidation No. of N in N2O4 is +3
Let, oxidation state of N in N2O5 is X.
Sum of oxidation numbers of all atoms present in a neutral compound is zero.
2(Oxidation No. of N) + 5(Oxidation No. of O ) = 0
2X + 5(-2) = 0
2X -10 = 0
X = +10/2 = +5
Oxidation No. of N in N2O5 is +5
So, option d is the correct answer.

9. The passage of current through an electrolyte is due to the movement of





... Answer is d)
Explanation: The current pass through an electrolyte due to movement of cations and anions. So, most suitalble option is ions(cations and anions).

10. Oxidation number of an element in free state is





... Answer is c)
Explanation: Oxidation number of an element in free state is zero.

11. Which of these is not true for an electrolyte?





... Answer is c)
Explanation: An electrolyte is the substance which can conduct electricity in molten form or in aqueous solution form. However, it cannot conduct electricitysolid form because in solid form ions are tightly held together and cannot move freely.

12. Corriosion is an electrochemical process which requirs :

    a. Oxygen
    B. Water
    c. Acidic vapours
    d. Basic vapours




... Answer is 3)
Explanation: Corrision occurs when electrons move from the surface of metal such as Fe (anode) to is an electron acceptor specie (cathod) such as oxygen, acid or cations less reactive metals. Wate acts an medium to transport the ios. So, option 3 is correct.

13. A fuel cell is based upon the reaction between

    a. Oxygen
    B. Gaseous fuel
    c. KOH
    d. Pt




... Answer is d)
Explanation: Fuel cell consists of three compartments separated by carbon electrod. To produce electric current, oxygen is passed through cathod compartment, fuel gases such as hydrogen is passed through anode compartment.These elctrodes use pt as a catalyts. Middle compartment contains KOH as an electrolyte.
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