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Electrochemistry is a branch of Chemistry that deals with the relationship between electrical energy and chemical changes. Electrochemistry also studies the inter-conversion of electrical energy and chemical energy. The chemical reactions that lead to the generation of electric current are called electrochemical reactions. Electrochemical reactions are classified into two broad categories:
- Electrolysis: It is the production of chemical change by electrical energy.
- Generation of Electricity by Spontaneous Redox Reactions: It involves the conversion of chemical energy into electrical energy.
Spontaneous Chemical Reaction refers to a reaction that takes place on its own. In a spontaneous chemical reaction, Gibbs free energy of a system decreases. The reverse of this reaction is also possible where a non-spontaneous chemical reaction occurs by supplying electricity. All these interconversions are carried out in an electrochemical cell. Galvanic Cells and Electrolytic Cells are the two types of electrochemical cells.
Electrochemical Cells
MCQs on Electrochemistry
Ques 1. How much copper will CuSO4 solution release when 96500 coulombs of electricity are passed through it?
- 61.5 gm of Cu
- 31.76 gm of Cu
- 96500 gm of Cu
- 101 gm of Cu
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Ans. b) 31.76 gm of Cu
Explanation: The explanation for the answer is as follows:
At cathode, the reaction is: Cu2+(aq) + 2e- à Cu (s)
At anode, the reaction is: 4OH- (aq) à 2H2O (l) + O2 + 4e-
Faraday’s constant is 96500 C/mol
Thus, to deposit 1 mole of copper, we require 2 X 96500 C.
Thus, 96500 C will deposit ½, i.e. 0.5 moles of copper.
= 0.5X 63.5 = 31.75 gms
Ques 2. The two most frequent elements of an electrochemical cell are a cathode and an anode. Which of the aforementioned statements regarding the cathode is true?
- The cathode is where oxidation happens.
- Electrons enter the cathode.
- Typically indicated by a minus sign
- Typically contains insulating material
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Ans. b) Electrons enter the cathode
Explanation: Cathodes are frequently made of metal electrodes. Reduction takes place on this electrode. The cathode is the positive electrode in a galvanic cell, whereas it is the negative electrode in an electrolytic cell. Electrons are drawn to the cathode.
Ques 3. The half-cell reactions' common electrode potentials are as follows:
- Zn → Zn2-– 2e– (E° = 0.76 V)
- Fe → Fe2- + 2– (E° = – 0.41 V)
The emf of the cell reaction: Fe2- + Zn → Zn2- + Fe is
- - 0.35 V
- + 0.35 V
- - 1.17 V
- + 1.17 V
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Ans. b) +0.35 V
Explanation: These are potentials for oxidation.
Potentials for reduction are symmetrical and equal.
Zn serves as the anode and Fe as the cathode.
E- cell = (E- red)c + (E- oxd)a
-0.41 V + 0.76 V = +0.35 V
Ques 4. Electrochemical cells follow one of the following rules:
- The cell potential is a broad characteristic.
- Cell potential is an important independent characteristic.
- An electrochemical cell's Gibbs free energy is an intense attribute.
- Gibbs’s free energy for an electrochemical cell is undetermined.
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Ans. b) Cell potential is an important independent characteristic.
Explanation: Cell potential is a prominent characteristic because it is unaffected by the volume of material present. Because it is based on the quantity of material present, Gibbs free energy, a property that is defined for an electrochemical cell, is a broad feature.
Ques 5. If the molar conductance of a 0.15 M KCl solution at 298 K is 0.0152 S cm-1, then
- 124 Ω-1 cm2 mol-1
- 204 Ω-1 cm2 mol-1
- 101 Ω-1 cm2 mol-1
- 300 Ω-1 cm2 mol-1
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Ans. c) 101 Ω-1 cm2 mol-1
Explanation: The conductivity of an electrolyte solution divided by the electrolyte's molar concentration is known as molar conductivity.
M= 0.15 M
Ð = 0.0152 Scm-1
Λm = (k X 1000)/M = 101 Ω-1 cm2 mol-1
Ques 6. Which of the following is not a member of the electrochemical cell family?
- Voltaic cell.
- Photovoltaic cell
- Electrolytic cell
- Fuel Cell
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Ans. b) Photovoltaic cell
Explanation: Galvanic or voltaic cells are electrochemical devices that convert chemical energy into electrical energy. Photovoltaic cells are used to turn light energy into electrical energy. An electrolytic cell is a form of an electrochemical cell that converts electrical energy into chemical energy. A fuel cell is an electrochemical device that generates electricity from the chemical energy of a fuel and an oxidizing agent.
Ques 7. How long would it take a 105 ampere current to deposit 50 g of aluminum from an electrolytic cell containing Al2O3?
- 1.54 h
- 1.42 h
- 1.32 h
- 2.15 h
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Ans. b) 1.42 h
Explanation: Al3+ + 3e-
Equivalent weight of aluminum is = 27/3 = 9
W = Z X I X t
Z = Eq wt/96500
t = W X 96500/ Eq wt X I
= 5105.82 s or 1.42 hours
Ques 8. Which of the following is the electrolyte in a dry cell?
- Potassium hydroxide
- Sulfuric acid
- Ammonium chloride
- Manganese dioxide
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Ans. c) Ammonium chloride
Explanation: In a dry cell, ammonium chloride acts as the electrolyte and is placed as a wet paste in close proximity to the zinc anode. In some "heavy-duty" dry cells, zinc chloride substitutes sodium chloride for ammonium chloride.
Ques 9. Electrolytic conductors' conductivity is caused by which of the following?
- The movement of free, movable electrons.
- Ions moving about
- Either electron or ion movement
- Difficult to say
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Ans. b) Ions moving about
Explanation: The movement of ions in a fused electrolyte solution causes conductance in electrolytic conductors, whereas the flow of free mobile electrons causes conductance in metallic conductors.
Ques 10. Which of the following is not true with a lead storage cell or lead-acid battery?
- It is the main cell.
- Lead (IV) oxide makes up the cathode.
- Lead makes up the anode.
- Sulfuric acid in an aqueous solution is the electrolyte that is employed.
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Ans. a) It is the main cell.
Explanation: Lead storage cells are secondary cells that contain a grid of lead packed with lead (IV) oxide for the cathode and finely separated spongy lead for the anode. The electrolytic solution in a lead-acid battery is an aqueous solution of sulfuric acid.
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