Electrochemistry MCQs with Answers
What does the oxidation number represent?
The actual charge on an atom in a molecule.
The apparent charge on an atom of an element in a molecule or ion.
The number of valence electrons.
The number of protons in an atom.
What is the oxidation number of an element in its free or uncombined state?
+1
-1
Zero
Equal to its valency
What is the usual oxidation number of hydrogen in most of its compounds?
What is the usual oxidation number of oxygen in most of its compounds?
What is the oxidation number of Manganese (Mn) in KMnO₄?
What is the oxidation number of Sulfur (S) in the sulfate ion (SO₄²⁻)?
What is the first step in balancing a redox equation using the oxidation number method?
Balance the atoms other than oxygen and hydrogen.
Identify the atoms that undergo a change in oxidation number.
Add H₂O to balance oxygen atoms.
Add H⁺ to balance hydrogen atoms.
What is the initial step when balancing a redox equation using the ion-electron method?
Combine the two half-reactions.
Balance oxygen atoms by adding H₂O.
Split the overall reaction into two half-reactions (oxidation and reduction).
Add electrons to balance charges.
In the ion-electron method for an acidic medium, how are oxygen atoms balanced?
By adding OH⁻ ions.
By adding H₂O molecules to the side deficient in oxygen.
By adding O₂ molecules.
By adding O²⁻ ions.
After balancing oxygen atoms, how are hydrogen atoms balanced in the ion-electron method for an acidic medium?
By adding H₂O molecules.
By adding OH⁻ ions.
By adding H⁺ ions to the side deficient in hydrogen.
By adding H₂ gas.
In the ion-electron method for an acidic medium, how are charges balanced after balancing atoms?
By adding OH⁻ ions.
By adding electrons (e⁻).
By adding H₂O molecules.
By adding H⁺ ions.
In the ion-electron method for a basic medium, how are oxygen atoms balanced?
By adding H₂O molecules to the side deficient in oxygen.
By adding OH⁻ ions to the side deficient in oxygen.
By adding H₂O molecules to oxygen deficient and OH⁻ to opposite side.
By adding O₂ gas
In the ion-electron method for a basic medium, after balancing oxygen, how are hydrogen atoms balanced?
By adding H⁺ ions.
By adding H₂O to hydrogen deficient side and OH⁻ to opposite side.
By adding OH⁻ ions directly.
By adding H₂ gas.
According to the rules for assigning oxidation numbers, what is the sum of the oxidation numbers of all atoms in a neutral molecule?
Equal to the charge of the most electronegative atom.
Equal to the number of atoms.
Zero
Equal to the valency of the central atom.
For a polyatomic ion, what is the sum of the oxidation numbers of all atoms?
Zero
Equal to the number of atoms.
Equal to the charge on the ion.
Equal to the valency of the most common element.
What is the usual oxidation number of halogens (e.g., Cl, Br, I) in their compounds with less electronegative elements (like metals)?
Always +1.
Always -1.
Varies between -1 and +7.
Zero
Which of the following half-reactions represents an oxidation process?
MnO₄⁻ → Mn²⁺
Cu²⁺ → Cu
Fe²⁺ → Fe³⁺
Cr₂O₇²⁻ → Cr³⁺
Which of the following half-reactions represents a reduction process?
H₂S → S
Cl⁻ → Cl₂
Cr₂O₇²⁻ → Cr³⁺
SO₃²⁻ → SO₄²⁻
When balancing a redox reaction using the ion-electron method, what is the primary role of H₂O molecules?
To balance hydrogen atoms.
To balance oxygen atoms.
To balance charges.
To act as a spectator ion.
In the ion-electron method, what species are added to balance hydrogen atoms and/or charges, depending on the medium?
Spectator ions.
H₂O molecules.
H⁺ (acidic) or OH⁻ (basic) ions.
Metal ions.
What is the primary mechanism of conduction in metallic conductors?
Movement of ions.
Movement of free electrons.
Migration of protons.
Transfer of atoms.
In which state do electrolytes typically conduct electricity due to the movement of ions?
Solid state.
Gaseous state.
Fused state or aqueous solution.
Plasma state.
What type of reaction is driven by the passage of electricity in an electrolytic cell?
Spontaneous oxidation-reduction.
Non-spontaneous oxidation-reduction.
Acid-base neutralization.
Precipitation
In an electrolytic cell, which process occurs at the anode?
Reduction
Oxidation
Neutralization
Deposition
In an electrolytic cell, which process occurs at the cathode?
Oxidation
Reduction
Neutralization
Dissolution
In an electrolytic cell, towards which electrode do cations migrate?
Anode
Cathode
Salt bridge
Both anode and cathode equally
What are the main products obtained at the electrodes during the electrolysis of molten NaCl using inert electrodes?
Na and O₂
H₂ and Cl₂
Na and Cl₂
NaOH and H₂
The Hall-Heroult process is an industrially important electrolytic method for the extraction of which metal?
Which industrially important chemical is produced in the Nelson cell via an electrolytic process?
Sulfuric acid.
Nitric acid.
Caustic soda (NaOH).
Ammonia.
What is the electrolytic process used to form a protective oxide layer on aluminum, increasing its corrosion resistance?
Electroplating
Anodizing
Galvanizing
Electrowinning
What is the primary function of a galvanic (voltaic) cell?
To consume electrical energy to cause a non-spontaneous reaction.
To generate electrical energy from a spontaneous chemical reaction
To purify metals through electrolysis.
To balance redox equations
What is the main purpose of a salt bridge in a galvanic cell?
To provide a pathway for electron flow.
To allow for the mixing of solutions in the half-cells.
To maintain electrical neutrality and complete the circuit.
To prevent the spontaneous reaction from occurring.
In a galvanic cell, which electrode is typically considered the anode?
The electrode where reduction occurs.
The electrode where oxidation occurs.
The electrode with a positive charge.
The electrode where plating occurs.
In a galvanic cell, which electrode is typically considered the cathode?
The electrode where oxidation occurs.
The electrode where reduction occurs.
The electrode with a negative charge.
The electrode that dissolves.
In a standard zinc-copper galvanic cell, electrons flow from which electrode to which electrode in the external circuit?
From copper to zinc.
From zinc to copper.
From salt bridge to zinc.
From salt bridge to copper.
What is the overall spontaneous reaction occurring in a standard zinc-copper galvanic cell?
Cu(s) + Zn²⁺(aq) → Cu²⁺(aq) + Zn(s)
Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)
Zn²⁺(aq) + Cu²⁺(aq) → Zn(s) + Cu(s)
Zn(s) + Cu(s) → Zn²⁺(aq) + Cu²⁺(aq)
How can a galvanic cell be made to operate as an electrolytic cell?
None of these
By heating the cell.
By applying an external voltage greater than the cell's potential, in the opposite direction.
By removing the salt bridge.
When a galvanic cell is reversed to function as an electrolytic cell, what is the energy conversion?
Chemical to electrical.
Electrical to chemical.
Light to electrical.
Heat to chemical.
In a galvanic cell, the electrodes provide surfaces for:
Ion transport only.
Electron flow only.
Oxidation and reduction half-reactions.
Solution mixing.
What is the approximate standard cell potential (E°cell) of a standard zinc-copper galvanic cell, as mentioned in the document?
What is the electrode potential?
The potential difference between two different metals in contact.
The potential difference established between a metal and its ionic solution.
The potential difference between a metal and an external circuit.
The potential difference across a salt bridge.
What are the standard conditions for measuring standard electrode potential (E°)?
25°C, 0.1 M solution.
298 K, 1.0 M solution.
0°C, 1.0 M solution.
Any temperature, 1.0 M solution.
Why is the Standard Hydrogen Electrode (SHE) used as a reference electrode?
It produces the highest possible potential.
Its potential is arbitrarily set to zero volts.
It is the most reactive electrode.
It is easy to construct and maintain.
Which components are essential for a Standard Hydrogen Electrode (SHE)?
A silver wire immersed in silver nitrate solution
A copper wire in copper sulfate solution.
A platinum foil in 1M HCl solution with hydrogen gas at 1 atm.
A zinc rod in zinc sulfate solution.
How is the electrode potential of a given electrode measured?
By directly measuring the potential difference across the single electrode.
By connecting it to another standard electrode (like SHE) and measuring the potential difference.
By using a litmus paper.
By heating the electrode and measuring temperature change.
When an electrode potential is expressed as a reduction potential under standard conditions, it is called:
Standard oxidation potential.
Standard cell potential.
Standard reduction potential.
Standard absolute potential.
If the standard oxidation potential of Zn is +0.76 V, what is its standard reduction potential?
+0.76 V
-0.76 V
0.00 V
+1.52 V
What drives the flow of electrons from the anode to the cathode in an external circuit of a galvanic cell?
The salt bridge.
The potential difference between the two electrodes.
The concentration of ions.
The temperature of the cell.
A positive standard reduction potential indicates:
A strong tendency to be oxidized.
A strong tendency to be reduced.
A very reactive metal
A neutral solution.
A negative standard reduction potential indicates:
A strong tendency to be reduced.
A non-spontaneous reaction.
A strong tendency to be oxidized.
A basic solution.
Which industrial process utilizes an electrolytic cell to extract sodium metal?
Hall-Heroult process
Nelson cell
Down's cell
Contact process
What is the oxidation number of oxygen in peroxides (e.g., H₂O₂)?
Which type of electrochemical cell converts chemical energy into electrical energy?
Electrolytic cell
Fuel cell
Galvanic (voltaic) cell
Concentration cell
In balancing a redox equation in a basic medium using the ion-electron method, which species is added to balance hydrogen atoms?
H⁺ ions
Directly OH⁻ ions
H₂O molecules on one side and OH⁻ ions on the other
O₂ molecules
What is the arbitrarily assigned standard electrode potential of the Standard Hydrogen Electrode (SHE)?
+1.00 V
-1.00 V
+0.76 V
0.00 V
What is the primary purpose of anodized aluminum preparation?
To make it lighter.
To increase its electrical conductivity.
To enhance its corrosion resistance.
To make it more malleable.
What is the oxidation number of oxygen in OF₂?
Which of the following is an example of an electrolytic conductor?
Solid copper wire
Fused sodium chloride
Graphite electrode
Distilled water
The chemical reaction that takes place in a galvanic cell is always:
Endothermic
Exothermic
Non-spontaneous
Spontaneous
The potential of a single electrode cannot be measured directly. It is determined by forming a galvanic cell with a reference electrode and measuring the:
Resistance of the electrode.
Temperature change.
Potential difference (voltage).
pH change.
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