Most Important Electrochemistry Quiz Test Online

Electrochemistry Quiz Test Online

Electrochemistry Test. 1

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1) For a polyatomic ion, what is the sum of the oxidation numbers of all atoms?

Equal to the valency of the most common element.

Equal to the number of atoms.

Zero

Equal to the charge on the ion.

Explanation: The sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the net charge of that ion.

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2) When balancing a redox reaction using the ion-electron method, what is the primary role of H₂O molecules?

To balance charges.

To act as a spectator ion.

To balance oxygen atoms.

To balance hydrogen atoms.

Explanation: In both acidic and basic mediums, water molecules (H₂O) are added to the half-reactions to balance the oxygen atoms.

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3) What is the initial step when balancing a redox equation using the ion-electron method?

Add electrons to balance charges.

Split the overall reaction into two half-reactions (oxidation and reduction).

Balance oxygen atoms by adding H₂O.

Combine the two half-reactions.

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4) What is the oxidation number of Sulfur (S) in the sulfate ion (SO₄²⁻)?

Explanation: In SO₄²⁻, oxygen (O) has an oxidation number of -2. Let the oxidation number of S be x. The sum of oxidation numbers in a polyatomic ion equals its charge: x + 4(-2) = -2, which simplifies to x - 8 = -2, so x = +6.

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5) Which of the following half-reactions represents an oxidation process?

Fe²⁺ → Fe³⁺

MnO₄⁻ → Mn²⁺

Cu²⁺ → Cu

Cr₂O₇²⁻ → Cr³⁺

Explanation: Oxidation is defined as an increase in oxidation number or loss of electrons. In option C, the oxidation number of Iron (Fe) increases from +2 to +3, indicating oxidation.

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6) In the ion-electron method for an acidic medium, how are charges balanced after balancing atoms?

By adding H⁺ ions.

By adding electrons (e⁻).

By adding H₂O molecules.

By adding OH⁻ ions.

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7) What is the first step in balancing a redox equation using the oxidation number method?

Identify the atoms that undergo a change in oxidation number.

Balance the atoms other than oxygen and hydrogen.

Add H₂O to balance oxygen atoms.

Add H⁺ to balance hydrogen atoms.

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8) According to the rules for assigning oxidation numbers, what is the sum of the oxidation numbers of all atoms in a neutral molecule?

Zero

Equal to the number of atoms.

Equal to the valency of the central atom.

Equal to the charge of the most electronegative atom.

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9) In the ion-electron method for an acidic medium, how are oxygen atoms balanced?

By adding H₂O molecules to the side deficient in oxygen.

By adding OH⁻ ions.

By adding O₂ molecules.

By adding O²⁻ ions.

Explanation: In an acidic medium, oxygen atoms are balanced by adding water molecules (H₂O) to the side of the half-reaction that needs oxygen.

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10) What is the oxidation number of Manganese (Mn) in KMnO₄?

Explanation: In KMnO₄, potassium (K) has an oxidation number of +1, and oxygen (O) has -2. Let the oxidation number of Mn be x. The sum of oxidation numbers in a neutral molecule is zero: 1 + x + 4(-2) = 0, which simplifies to 1 + x - 8 = 0, so x = +7.

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11) After balancing oxygen atoms, how are hydrogen atoms balanced in the ion-electron method for an acidic medium?

By adding H₂O molecules.

By adding H₂ gas.

By adding H⁺ ions to the side deficient in hydrogen.

By adding OH⁻ ions.

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12) In the ion-electron method for a basic medium, after balancing oxygen, how are hydrogen atoms balanced?

By adding H₂ gas.

By adding H₂O to hydrogen deficient side and OH⁻ to opposite side.

By adding OH⁻ ions directly.

By adding H⁺ ions.

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13) What is the oxidation number of an element in its free or uncombined state?

Zero

Equal to its valency

-1

Explanation: According to the rules for assigning oxidation numbers, the oxidation number of all elements in their free or uncombined state is zero.

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14) In the ion-electron method, what species are added to balance hydrogen atoms and/or charges, depending on the medium?

Spectator ions.

Metal ions.

H⁺ (acidic) or OH⁻ (basic) ions.

H₂O molecules.

Explanation: Hydrogen ions (H⁺) are used to balance hydrogen atoms and charges in acidic solutions, while hydroxide ions (OH⁻) are used for the same purpose in basic solutions.

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15) In the ion-electron method for a basic medium, how are oxygen atoms balanced?

By adding OH⁻ ions to the side deficient in oxygen.

By adding H₂O molecules to oxygen deficient and OH⁻ to opposite side.

By adding H₂O molecules to the side deficient in oxygen.

By adding O₂ gas

Explanation: In a basic medium, oxygen atoms are balanced by adding H₂O molecules to the side lacking oxygen, and then adding an equal number of OH⁻ ions to the opposite side.

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16) Which of the following half-reactions represents a reduction process?

Cl⁻ → Cl₂

Cr₂O₇²⁻ → Cr³⁺

SO₃²⁻ → SO₄²⁻

H₂S → S

Explanation: Reduction is defined as a decrease in oxidation number or gain of electrons. In option C, Chromium (Cr) in Cr₂O₇²⁻ has an oxidation number of +6, which decreases to +3 in Cr³⁺, indicating reduction.

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17) What is the usual oxidation number of oxygen in most of its compounds?

-2

-1

Explanation: The oxidation number of oxygen is usually -2, except in peroxides (-1), OF₂ (+2), and superoxides (-1/2).

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18) 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.

Zero

Varies between -1 and +7.

Explanation: Halogens generally exhibit an oxidation number of -1 in most of their compounds, especially when combined with metals or less electronegative elements. (Note: Fluorine always has -1).

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19) What does the oxidation number represent?

The number of protons in an atom.

The apparent charge on an atom of an element in a molecule or ion.

The actual charge on an atom in a molecule.

The number of valence electrons.

Explanation: The oxidation number is defined as the apparent charge on an atom of an element in a molecule or an ion, which can be positive, negative, or zero, as stated in the document.

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20) What is the usual oxidation number of hydrogen in most of its compounds?

-1

Explanation: The oxidation number of hydrogen is usually +1, except in metal hydrides where it is -1.

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Electrochemistry Test. 2

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1) How can a galvanic cell be made to operate as an electrolytic cell?

None of these

By removing the salt bridge.

By heating the cell.

By applying an external voltage greater than the cell's potential, in the opposite direction.

Explanation: A galvanic cell's spontaneous reaction can be reversed by applying an external electrical potential that is greater than its own cell potential and in the opposite direction, forcing the non-spontaneous reaction to occur, thus operating as an electrolytic cell.

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2) In a galvanic cell, which electrode is typically considered the anode?

The electrode where oxidation occurs.

The electrode where reduction occurs.

The electrode where plating occurs.

The electrode with a positive charge.

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3) What is the primary mechanism of conduction in metallic conductors?

Transfer of atoms.

Movement of free electrons.

Movement of ions.

Migration of protons.

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4) Which industrially important chemical is produced in the Nelson cell via an electrolytic process?

Nitric acid.

Ammonia.

Caustic soda (NaOH).

Sulfuric acid.

Explanation: The Nelson cell is an industrial electrolytic cell used for the production of caustic soda (sodium hydroxide, NaOH) and chlorine gas from brine (aqueous sodium chloride).

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5) What is the primary function of a galvanic (voltaic) cell?

To purify metals through electrolysis.

To generate electrical energy from a spontaneous chemical reaction

To balance redox equations

To consume electrical energy to cause a non-spontaneous reaction.

Explanation: A galvanic cell is designed to convert chemical energy, released from a spontaneous oxidation-reduction reaction, into electrical energy.

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6) 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)

Zn(s) + Cu(s) → Zn²⁺(aq) + Cu²⁺(aq)

Zn²⁺(aq) + Cu²⁺(aq) → Zn(s) + Cu(s)

Explanation: In the zinc-copper cell, zinc metal is oxidized to zinc ions (Zn → Zn²⁺ + 2e⁻) and copper ions are reduced to copper metal (Cu²⁺ + 2e⁻ → Cu). The sum of these half-reactions gives the overall spontaneous reaction.

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7) What is the electrolytic process used to form a protective oxide layer on aluminum, increasing its corrosion resistance?

Galvanizing

Electroplating

Electrowinning

Anodizing

Explanation: Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of aluminum parts, thereby enhancing their corrosion resistance and wear resistance.

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8) What type of reaction is driven by the passage of electricity in an electrolytic cell?

Precipitation

Spontaneous oxidation-reduction.

Non-spontaneous oxidation-reduction.

Acid-base neutralization.

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9) When a galvanic cell is reversed to function as an electrolytic cell, what is the energy conversion?

Heat to chemical.

Electrical to chemical.

Light to electrical.

Chemical to electrical.

Explanation: When a galvanic cell is reversed to act as an electrolytic cell, it consumes electrical energy to drive a non-spontaneous chemical reaction, thereby converting electrical energy into chemical energy.

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10) In a galvanic cell, which electrode is typically considered the cathode?

The electrode where oxidation occurs.

The electrode where reduction occurs.

The electrode that dissolves.

The electrode with a negative charge.

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11) What is the approximate standard cell potential (E°cell) of a standard zinc-copper galvanic cell, as mentioned in the document?

0.34 V

0.76 V

1.5 V

1.1 V

Explanation: The document explicitly states that the standard cell potential of the zinc-copper galvanic cell is 1.1 V

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12) In an electrolytic cell, which process occurs at the anode?

Neutralization

Oxidation

Deposition

Reduction

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13) In a galvanic cell, the electrodes provide surfaces for:

Electron flow only.

Oxidation and reduction half-reactions.

Solution mixing.

Ion transport only.

Explanation: The electrodes in a galvanic cell serve as the sites where the oxidation and reduction half-reactions take place, facilitating the electron transfer.

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14) What are the main products obtained at the electrodes during the electrolysis of molten NaCl using inert electrodes?

NaOH and H₂

Na and Cl₂

Na and O₂

H₂ and Cl₂

Explanation: During the electrolysis of molten NaCl, sodium ions (Na⁺) are reduced to sodium metal (Na) at the cathode, and chloride ions (Cl⁻) are oxidized to chlorine gas (Cl₂) at the anode.

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15) In a standard zinc-copper galvanic cell, electrons flow from which electrode to which electrode in the external circuit?

From salt bridge to copper.

From copper to zinc.

From salt bridge to zinc.

From zinc to copper.

Explanation: Zinc is oxidized at the anode (loses electrons), and these electrons then flow through the external circuit to the copper cathode, where reduction occurs.

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16) In an electrolytic cell, towards which electrode do cations migrate?

Cathode

Salt bridge

Anode

Both anode and cathode equally

Explanation: Cations are positively charged ions, and in an electrolytic cell, they are attracted to and move towards the negatively charged cathode.

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17) In which state do electrolytes typically conduct electricity due to the movement of ions?

Fused state or aqueous solution.

Plasma state.

Solid state.

Gaseous state.

Explanation: Electrolytic conduction relies on the mobility of ions, which is achieved when the electrolyte is in a molten (fused) state or dissolved in a solvent to form an aqueous solution.

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18) The Hall-Heroult process is an industrially important electrolytic method for the extraction of which metal?

Sodium

Iron

Aluminum

Copper

Explanation: The Hall-Heroult process is a widely used electrolytic method for the large-scale production of aluminum from its ore, alumina.

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19) What is the main purpose of a salt bridge in a galvanic cell?

To maintain electrical neutrality and complete the circuit.

To allow for the mixing of solutions in the half-cells.

To provide a pathway for electron flow.

To prevent the spontaneous reaction from occurring.

Explanation: The salt bridge allows for the migration of ions between the two half-cells, which maintains electrical neutrality in the solutions and completes the electrical circuit, allowing current to flow.

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20) In an electrolytic cell, which process occurs at the cathode?

Neutralization

Oxidation

Reduction

Dissolution

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Electrochemistry Test. 3

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1) When an electrode potential is expressed as a reduction potential under standard conditions, it is called:

Standard absolute potential.

Standard reduction potential.

Standard oxidation potential.

Standard cell potential.

Explanation: Standard electrode potential is conventionally reported as the standard reduction potential, which indicates the tendency of a species to gain electrons (be reduced) under standard conditions.

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2) Which of the following is an example of an electrolytic conductor?

Graphite electrode

Solid copper wire

Fused sodium chloride

Distilled water

Explanation: Electrolytic conductors are substances that conduct electricity through the movement of ions when they are in a molten (fused) state or dissolved in a solvent (aqueous solution). Fused sodium chloride fits this description.

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3) The chemical reaction that takes place in a galvanic cell is always:

Endothermic

Spontaneous

Exothermic

Non-spontaneous

Explanation: Galvanic cells convert chemical energy into electrical energy through a spontaneous oxidation-reduction reaction that inherently proceeds without external energy input.

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4) 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 temperature of the cell.

The concentration of ions.

Explanation: The difference in electrode potentials between the two half-cells creates an electromotive force (EMF) or potential difference, which drives the flow of electrons through the external circuit.

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5) What is the oxidation number of oxygen in OF₂?

-1

-2

Explanation: In oxygen difluoride (OF₂), fluorine is more electronegative than oxygen. Therefore, oxygen exhibits a positive oxidation number of +2 to balance the two -1 oxidation states of fluorine.

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6) A negative standard reduction potential indicates:

A non-spontaneous reaction.

A strong tendency to be oxidized.

A basic solution.

A strong tendency to be reduced.

Explanation: A negative standard reduction potential suggests that the species has a greater tendency to undergo oxidation (lose electrons) compared to hydrogen under standard conditions

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7) Which components are essential for a Standard Hydrogen Electrode (SHE)?

A platinum foil in 1M HCl solution with hydrogen gas at 1 atm.

A silver wire immersed in silver nitrate solution

A copper wire in copper sulfate solution.

A zinc rod in zinc sulfate solution.

Explanation: The SHE consists of a platinum electrode immersed in a 1 M aqueous solution of H⁺ ions (e.g., HCl), with hydrogen gas at 1 atm pressure bubbled around the platinum electrode.

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8) What is the electrode potential?

The potential difference across a salt bridge.

The potential difference between a metal and an external circuit.

The potential difference established between a metal and its ionic solution.

The potential difference between two different metals in contact.

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9) 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.

Explanation: A positive standard reduction potential signifies that the species has a greater tendency to undergo reduction (gain electrons) compared to hydrogen under standard conditions.

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10) 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:

Temperature change.

Resistance of the electrode.

Potential difference (voltage).

pH change.

Explanation: To determine the potential of a single electrode, it is coupled with a reference electrode (like the SHE) to create a complete electrochemical cell, and the overall potential difference (voltage) of this cell is measured.

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11) Which type of electrochemical cell converts chemical energy into electrical energy?

Electrolytic cell

Fuel cell

Concentration cell

Galvanic (voltaic) cell

Explanation: Galvanic or voltaic cells are designed to generate electrical energy from spontaneous chemical (oxidation-reduction) reactions.

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12) What is the arbitrarily assigned standard electrode potential of the Standard Hydrogen Electrode (SHE)?

+0.76 V

0.00 V

+1.00 V

-1.00 V

Explanation: The Standard Hydrogen Electrode (SHE) serves as the reference electrode, and its standard electrode potential is, by convention, set to exactly zero volts.

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13) What is the oxidation number of oxygen in peroxides (e.g., H₂O₂)?

-2

-1

Explanation: While oxygen commonly has an oxidation number of -2, in peroxides, its oxidation number is -1.

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14) How is the electrode potential of a given electrode measured?

By heating the electrode and measuring temperature change.

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.

Explanation: The potential of a single electrode cannot be measured directly. It is determined by coupling it with a standard reference electrode (like the SHE) to form a galvanic cell and then measuring the overall potential difference (voltage) of that cell.

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15) 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.

Explanation: Standard electrode potential is measured at a temperature of 298 K (25°C), with the concentration of ions in the solution being 1.0 M (and 1 atm pressure for gases).

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16) If the standard oxidation potential of Zn is +0.76 V, what is its standard reduction potential?

+0.76 V

-0.76 V

+1.52 V

0.00 V

Explanation: The standard reduction potential for a half-reaction is equal in magnitude but opposite in sign to its standard oxidation potential.

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17) Why is the Standard Hydrogen Electrode (SHE) used as a reference electrode?

It is the most reactive electrode.

It produces the highest possible potential.

Its potential is arbitrarily set to zero volts.

It is easy to construct and maintain.

Explanation: The Standard Hydrogen Electrode (SHE) is assigned an arbitrary potential of exactly zero volts under standard conditions, serving as a universal reference point for measuring other electrode potentials.

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18) Which industrial process utilizes an electrolytic cell to extract sodium metal?

Nelson cell

Contact process

Down's cell

Hall-Heroult process

Explanation: The Down's cell is a specific electrolytic method used for the industrial production of sodium metal from molten sodium chloride.

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19) What is the primary purpose of anodized aluminum preparation?

To make it more malleable.

To increase its electrical conductivity.

To enhance its corrosion resistance.

To make it lighter.

Explanation: Anodizing is an electrolytic process that forms a thicker, more durable, and highly corrosion-resistant oxide layer on the surface of aluminum.

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20) In balancing a redox equation in a basic medium using the ion-electron method, which species is added to balance hydrogen atoms?

H⁺ ions

H₂O molecules on one side and OH⁻ ions on the other

O₂ molecules

Directly OH⁻ ions

Explanation: In a basic medium, hydrogen atoms are balanced by adding water molecules (H₂O) to the side deficient in hydrogen, and an equal number of hydroxide ions (OH⁻) to the opposite side.

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