Electrochemistry MCQ Quiz - Objective Question with Answer for Electrochemistry - Download Free PDF

Concept :

 Reaction of metals with air :

• All metals do not react with oxygen at the same rate.
• Different metals show different reactivities towards oxygen
• Almost all metals combine with oxygen to form metal oxides.
• Metal + Oxygen → Metal oxide

Explanation :

• Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open.
• They generate a lot of heat which may cause accidents.
• Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil.

​So, the correct answer is Sodium and Potassium.

Important Points

• Most metal oxides are insoluble in water but some of these dissolve in water to form alkalis.
• Sodium oxide and potassium oxide dissolve in water to produce alkalis as follows
• Na₂O(s) + H₂O(l) → 2NaOH(aq)

Additional Information

• At ordinary temperatures, the surfaces of metals such as magnesium, aluminum, zinc, and lead, are covered with a thin layer of oxide.
• The protective oxide layer prevents the metal from further oxidation.
• Iron does not burn on heating but iron filings burn vigorously when sprinkled in the flame of the burner.
• Copper does not burn, but the hot metal is coated with a black-colored layer of copper(II) oxide.
• Silver and gold do not react with oxygen even at high temperatures.

The correct answer is Ribosome.Key Points

• Ribosomes are organelles in cells that contain RNA
• Ribosomes are the organelles that are made up of ribosomal RNA and proteins.
• Ribosomes are responsible for the synthesis of proteins in the cell.
• Ribosomes can be found in both prokaryotic and eukaryotic cells.
• Ribosomes can be free in the cytoplasm or attached to the rough endoplasmic reticulum.

Additional Information

• Cytoplasm
  • The cytoplasm is a jelly-like matrix inside a cell that contains organelles. 
  • The plasma membrane, or cell membrane, is a selectively permeable membrane that surrounds the cytoplasm. 
  • The plasma membrane is made of a double layer of phospholipids, which are partly hydrophobic and partly hydrophilic. 
• Cell wall
  • A cell wall is a structural layer that surrounds some cells, just outside the cell membrane. 
  • It can be tough, flexible, and sometimes rigid. 
  • The cell wall provides the cell with structural support, shape, protection, and functions as a selective barrier. 
  • Cell walls are found in both prokaryotes and eukaryotes, although not all cells have cell walls. 
• Cell base
  • A cell base, also known as a cell site or cell tower, is a cellular-enabled mobile device site that creates a cell in a cellular network. 
  • Cell-based architecture is built around the idea of groupings of services and data around a gateway.

The correct answer is Copper sulphate.

Key Points

• Copper sulphate (CuSO₄) is commonly used as the electrolyte in the electrolytic refining of copper.
• In this process, impure copper is used as the anode, and a pure copper sheet is used as the cathode.
• When an electric current is passed through the electrolyte solution, copper ions from the anode dissolve into the solution and are deposited on the cathode.
• Impurities present in the impure copper either remain in the solution or fall to the bottom as anode sludge.
• This process helps in obtaining high-purity copper from impure copper.

Additional Information

• Electrolytic Refining
  • It is a process used to purify metals by electrolysis.
  • This method is used for metals like copper, zinc, and aluminum.
  • The process ensures the removal of impurities and produces high-purity metal.
• Copper Extraction
  • Copper is extracted from its ores through processes like smelting and electrolysis.
  • The extracted copper is further refined through electrolytic refining to achieve high purity.
• Applications of Copper
  • Copper is widely used in electrical wiring due to its excellent electrical conductivity.
  • It is also used in plumbing, roofing, and industrial machinery.
  • Copper alloys, such as bronze and brass, have various applications in decorative arts and manufacturing.

The correct answer is Copper sulphate.

Key Points

• Copper sulphate (CuSO₄) is commonly used as the electrolyte in the electrolytic refining of copper.
• In this process, impure copper is used as the anode, and a pure copper sheet is used as the cathode.
• When an electric current is passed through the electrolyte solution, copper ions from the anode dissolve into the solution and are deposited on the cathode.
• Impurities present in the impure copper either remain in the solution or fall to the bottom as anode sludge.
• This process helps in obtaining high-purity copper from impure copper.

Additional Information

• Electrolytic Refining
  • It is a process used to purify metals by electrolysis.
  • This method is used for metals like copper, zinc, and aluminum.
  • The process ensures the removal of impurities and produces high-purity metal.
• Copper Extraction
  • Copper is extracted from its ores through processes like smelting and electrolysis.
  • The extracted copper is further refined through electrolytic refining to achieve high purity.
• Applications of Copper
  • Copper is widely used in electrical wiring due to its excellent electrical conductivity.
  • It is also used in plumbing, roofing, and industrial machinery.
  • Copper alloys, such as bronze and brass, have various applications in decorative arts and manufacturing.

Explanation:-

As we know hydrogen's standard electrode potential is declared to be zero volts at all temperatures.

Hence using the relation,

ΔG0 = -nFE0

where,

-n=number of electrons transferred, F=Faraday's constant (96500),

E0= voltage of the cell

Now as we know that E0 = 0,

ΔG0 = -n × F× E0

ΔG0 = 0

Hence ΔGof (H+, aq) = 0

The correct answer is the negative terminal.

Key Points

• Cell Terminology:
  • The shorter, thicker vertical line in the symbol of a cell represents the negative terminal.
  • The longer, thinner vertical line in the symbol of a cell represents the positive terminal.
• ​A smaller line in the symbol for a cell represents its negative terminal.
• In the symbol for a cell, the positive terminal is a long line.
• A line connecting all the instruments indicates wire.
• Two/more cell symbols connected together indicate battery.

​

The correct answer is Lift system.

Key Points

• Solar cells:-
  • It is also known as photovoltaic cells, are devices that convert sunlight directly into electricity through a process called the photovoltaic effect.
  • They are a key technology in the field of renewable energy, as they provide a clean and sustainable way to generate electricity from sunlight.
  • Solar cells are widely used in various applications, including residential and commercial solar power systems, as well as in space exploration and remote power generation.
  • Solar cells are not used in Lift system.

The correct answer is Cathode.

Key Points:

• ​Impure metal will be utilized as an anode during the extraction process, and pure metal will be employed as a cathode to refine silver metal electrolytically.
• For electrolytic refinement, silver sulphate or silver nitrate makes appropriate electrolytes.
• The cathode produces pure silver.

Additional Information:

• Impure metals can be refined using electricity through a process called electrolytic refining.
• In this procedure, a strip of pure metal serves as the cathode while an anode is formed of impure metal.
• A soluble salt of the electrolyte's material is used to create a solution. Silver nitrate is employed as the electrolyte in this case.
• During the transmission of an electric current, metal ions from the electrolyte deposit as a pure metal in the cathode (refined silver), while the impure metal from the anode, which is the crude silver, dissolves as ions into the electrolyte.
• Metal impurities are gathered below the anode. It is known as a mud anode.
• The silver that is produced will be 99% pure.

The correct answer is Statement (i) and (ii) are true.

Fuel Cell:

• A device that converts the energy of combustion of fields like hydrogen and methane directly into electrical energy.
• It is an electrochemical reaction.
• It requires a continuous input of fuel and an oxidizing agent which is oxygen.
• Cathode Reaction of fuel cell 
  • O2 + 2H2O + 4e– → 4OH–
• Anode Reaction of fuel cell
  • 2H2 + 4OH– → 4H2O + 4e–
• Hence Statement (i) and (ii) are true while statement (iii) is false.

Applications of fuel cell:

• They are used to power many space expeditions including the Appolo space program.
• Electrical vehicles.
• Some military applications.

Explanation:-

• Conventional polishing: In conventional polishing, surface irregularities are removed from the workpiece by using abrasive particles which are glued to a flexible wheel or a belt
• Buffing: Buffing operation is carried out after polishing with a finer abrasive to further smoothen the surface and to provide the surface with a lustrous, grain less finish
• Barrel polishing or Tumbling: This is a deburring operation used for surface polishing
• Electropolishing: Electro polishing is a reverse process of electroplating

Additional Information

Lapping

• It is used to produce finished surfaces. It gives a very high degree of accuracy and smoothness.

Honing 

• is a finishing process, in which a tool called hone carries out a combined rotary and reciprocating motion while the workpiece does not perform any working motion. The surface finish of the cylindrical hole is maintained by honing.

The correct answer is Gold.

Key Points

• The least reactive metal is gold. The chemical element gold has the symbol Au and the atomic number 79.
• It is a bright, somewhat reddish yellow, dense, soft, malleable, and ductile metal in its purest form.
• Gold is a transition metal and a group 11 element chemically.
• A Reactivity series is an arrangement of metals in decreasing order of reactivity.
• In a displacement reaction, this series is used to assess if a given metal can displace another metal. 
• Based on their reactions with water and dilute acids, the metals potassium, sodium, lithium, calcium, magnesium, zinc, iron, and copper can be arranged in decreasing order of reactivity. Iron is more reactive than copper.
• Because iron has four unpaired shells in its three subshells, while copper only has one, according to the atomic structure. As a result, iron reacts more quickly than copper.

The correct answer is Roasting.

Concept:

• Mineral: A naturally occurring substance with uniform chemical composition is called a mineral.
• Ore: An ore is a mineral from which a metal can be extracted in a profitable way.

According to the reactivity of metals, different methods are employed to extract metals from their ores.

Reactivity series of metals:

• Metals of high reactivity; such as sodium, calcium, magnesium, aluminium, etc. are extracted from their ores by electrolytic reduction.
• Metals of middle reactivity, Iron, zinc, lead, etc. are found in the form of carbonate or sulfide ores. They are either calcinated or roasted.
• Metals of least reactivity, Mercury and copper, which belong to the least reactivity series, are often found in the form of their sulfide ores. They are roasted and then refined. 

Explanation:

• Cinnabar: It is an ore of Mercury. Its chemical formula is HgS. 
• Mercury is among the least reactive metals in the reactivity series.
• Its sulfide ore is roasted to extract the Mercury metal.
• Roasting: The heating of sulfide ores in the presence of excess air to convert them into oxides is known as Roasting.

Extraction of Mercury Metal:

• Cinnabar (HgS) is first heated in the air.
• This turns HgS (mercury sulfide or cinnabar) into HgO (mercury oxide) by liberation of sulfur dioxide.
  • 2HgS + 3O2 → 2HgO + 2SO2
• Mercury oxide so obtained is again heated strongly.
• This reduces mercury oxide to mercury metal.
  • 2HgO + 2Hg + O2 

So, Extracting a metal from cinnabar ore is through Roasting.

Additional Information

• Electrolytic reduction: Electric current is passed through the molten state of metal ores. Metal being positively charged is deposited over the cathode.
• Thermit process: It is a chemical reaction between metal and metal oxide. A lot of heat energy is liberated in this reaction. 
• Calcination: The heating of carbonate ores in the limited supply of air to convert them into oxides is known as Calcination.

Concept :

 Reaction of metals with air :

• All metals do not react with oxygen at the same rate.
• Different metals show different reactivities towards oxygen
• Almost all metals combine with oxygen to form metal oxides.
• Metal + Oxygen → Metal oxide

Explanation :

• Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open.
• They generate a lot of heat which may cause accidents.
• Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil.

​So, the correct answer is Sodium and Potassium.

Important Points

• Most metal oxides are insoluble in water but some of these dissolve in water to form alkalis.
• Sodium oxide and potassium oxide dissolve in water to produce alkalis as follows
• Na₂O(s) + H₂O(l) → 2NaOH(aq)

Additional Information

• At ordinary temperatures, the surfaces of metals such as magnesium, aluminum, zinc, and lead, are covered with a thin layer of oxide.
• The protective oxide layer prevents the metal from further oxidation.
• Iron does not burn on heating but iron filings burn vigorously when sprinkled in the flame of the burner.
• Copper does not burn, but the hot metal is coated with a black-colored layer of copper(II) oxide.
• Silver and gold do not react with oxygen even at high temperatures.

The correct answer is The colour of the solution changes from colourless to blue and a silver solid deposits on copper wire.

Concept:

Displacement reaction:

• It is a  chemical reaction wherein a more reactive element displaces the less reactive one from its salt solution.
• For example, CuSO4 + Fe → FeSO4 + Cu, here Fe is more reactive than Cu.

Explanation:

Reactivity series: It refers to the arrangement of metals in the descending order of their reactivities.

Copper is above silver in the reactivity series indicating that it is more reactive than silver. 

Thus, when a copper wire is dipped in silver nitrate solution, it will displace silver and form a blue-coloured copper nitrate solution. 

The correct answer is option 4 i.e., O2 and H2

Explanation:

• O₂ and H₂ are the gaseous products liberated at anode and cathode respectively when dilute aqueous solution of Sulphuric acid is electrolyzed.
• The cathode rode is the negatively charged electrode and the anode rod is the positively charged electrode.
• The reduction taken place at the cathode which means the electron is gained.
• In the aqueous solution of Sulphuric acid, the hydrogen ions are attracted to the cathode and give Hydrogen gas.
• Bubbles can be observed when hydrogen gas is produced.
• 2H⁺ (aq) + 2e^– → H₂(g)
• Oxygen ions are attracted to the anode rod.
• Oxidation takes place as the electron is lost.
• Please note that the sulphate ion is too stable and does not dissociate readily.
• Instead, either hydroxide ions or water molecules are discharged and oxidized to form oxygen gas.
• 2H₂O (l) – 4e^– → 4H⁺ (aq) + O₂(g) and 4OH^– (aq) – 4e^– → 2H₂O(l) + O₂(g)