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

CONCEPT:

Faraday's Laws of Electrolysis

• The amount of charge (in Faradays, F) required for a redox reaction depends on the number of electrons transferred per mole of species.
• The relationship is:

  Number of Faradays (F) = Number of moles of electrons transferred

• Key conversions:
  • For Cu²⁺ + 2e^- → Cu(s): 2 moles of electrons = 2F per mole of Cu²⁺
  • For 2Cl^- → Cl₂(g) + 2e^-: 1 mole of Cl₂ requires 2 moles of Cl^- ions, so 2 electrons total = 2F
  • For Al³⁺ + 3e^- → Al(s): 3 moles of electrons per mole, and since it's 2 moles of Al³⁺, total electrons = 6 moles = 6F
  • For Fe²⁺ → Fe³⁺ + e^-: 1 electron per Fe, so 2 mol Fe²⁺ needs 2F

EXPLANATION:

• Match each chemical conversion with the number of Faradays required:
  • A. Reduction of 1 mol of Cu²⁺ to Cu(s) → 2 electrons → 2F → II
  • B. Oxidation of 1 mol of Cl^- to Cl₂(gas) → 2 electrons from 2 Cl^- → 2F → IV
  • C. Reduction of 2 mol of Al³⁺ to Al(s) → 3 electrons per Al³⁺, total 6 electrons → 6F → III
  • D. Oxidation of 2 mol of Fe²⁺ to Fe³⁺ → 1 electron per Fe²⁺, total 1 electrons → F → I

Therefore, the correct matching is: A-II, B-IV, C-III, D-I.

CONCEPT:

Gibbs Free Energy and Standard Cell Potential

• The standard Gibbs free energy change (ΔG^o) of a reaction is related to the standard cell potential (E^o_cell) by the equation:

  ΔG^o = -n F E^o_cell

• Where,
  • ΔG^o = standard Gibbs free energy change (in J/mol)
  • n = number of moles of electrons exchanged in the reaction
  • F = Faraday constant = 96487 C mol^-1
  • E^o_cell = standard cell potential (in volts)

EXPLANATION:

• In the given reaction:

  Cu(s) + 2Ag⁺(aq) → Cu²⁺(aq) + 2Ag(s)

  • Cu is oxidized from Cu(s) to Cu²⁺, losing 2 electrons.
  • Ag⁺ is reduced to Ag(s), gaining 1 electron per ion. Since there are 2 Ag⁺ ions, n = 2.
• Given values:
  • E^o_cell = 0.76 V
  • F = 96487 C mol^-1
  • n = 2
• Applying the Gibbs free energy equation:
  • ΔG^o = -nFE^o_cell
  • = -2 × 96487 × 0.76
  • = -146265.44 J/mol
  • Convert to kJ: -146265.44 ÷ 1000 = -146.3 kJ/mol

Therefore, the standard Gibbs free energy change is -146.3 kJ mol^-1.

CONCEPT:

Calculation of Cell Potential using Nernst Equation

• The Nernst equation relates the cell potential (Ecell) to the standard cell potential (Ecello), the temperature, and the concentrations of the species involved in the electrochemical reaction.
• The Nernst equation is given by:

  Ecell = Ecello - (0.0592/n) log([Mn+]/[M])

  where:
  • Ecello is the standard electrode potential (in this case, 0.2 V)
  • n is the number of moles of electrons transferred (in this case, n = 2)
  • [Mn+] and [M] are the molar concentrations of the ions involved in the redox reaction.

EXPLANATION:
Overall reaction :–

\(\mathrm{H}_{2(\mathrm{~g})}+\mathrm{M}_{(\mathrm{aq})}^{3+} \longrightarrow \mathrm{M}_{(\mathrm{aq})}^{+}+2 \mathrm{H}_{(\mathrm{aq})}^{+} \)

\(\mathrm{E}_{\text {Cell }}=\mathrm{E}_{\text {Cathode }}^{\mathrm{o}}-\mathrm{E}_{\text {anode }}^{\mathrm{o}}-\frac{0.059}{2} \log \frac{\left[\mathrm{M}^{+}\right] \times 1^{2}}{\left[\mathrm{M}^{+3}\right] 1} \)

\(0.1115=0.2-\frac{0.059}{2} \log \frac{\left[\mathrm{M}^{+}\right]}{\left[\mathrm{M}^{+3}\right]} \)

\(3=\log \frac{\left[\mathrm{M}^{+}\right]}{\left[\mathrm{M}^{+3}\right]} \)

∴ a = 3

Therefore, the value of log([M3+]/[M]) is 3.

Explanation:

\(\frac{1}{2} \mathrm{H}_{2}(\mathrm{~g})+\mathrm{Fe}^{3+}(\mathrm{aq} .) \longrightarrow \mathrm{H}^{+}(\mathrm{aq})+\mathrm{Fe}^{2+}(\mathrm{aq} .)\)

\(\mathrm{E}=\mathrm{E}^{\circ}-\frac{0.059}{1} \log \frac{\left[\mathrm{Fe}^{2+}\right]}{\left[\mathrm{Fe}^{3+}\right]}\)

⇒ \(0.712=(0.771-0)-\frac{0.059}{1} \log \frac{\left[\mathrm{Fe}^{2+}\right]}{\left[\mathrm{Fe}^{3+}\right]}\)

⇒ \(\log \frac{\left[\mathrm{Fe}^{2+}\right]}{\left[\mathrm{Fe}^{3+}\right]}=\frac{(0.771-0712)}{0.059}=1\)

⇒ \(\frac{\left[\mathrm{Fe}^{2+}\right]}{\left[\mathrm{Fe}^{3+}\right]}=10\)

So, the correct answer is 10

CONCEPT:

Limiting Molar Conductivity of Anions in Aqueous Solution

• Limiting molar conductivity (Λ⁰) refers to the conductivity of an ion when its concentration approaches zero.
• The molar conductivity of anions in water depends on:
  • The size of the ion
  • The solvation effect (hydration)
  • The ion's charge and mobility in solution
• OH^- has exceptionally high conductivity due to the Grotthuss mechanism (proton hopping).
• Monovalent ions like NO₃^- and Cl^- have moderate conductivity, while F^- is smaller but more highly solvated, reducing its mobility. SO₄^2-, being divalent and larger, has the lowest mobility.

EXPLANATION:

• Comparing the limiting molar conductivities:
  • OH^- > NO₃^- > Cl^- > F^- > SO₄^2-
• Reasoning:
  • OH^- has the highest ionic mobility due to its special conduction mechanism.
  • NO₃^- is a relatively large, poorly hydrated ion, making it faster than Cl^-.
  • Cl^- is smaller but better hydrated than NO₃^-, so its conductivity is slightly lower.
  • F^- has a small size but strong hydration, reducing its mobility.
  • SO₄^2- is a large, doubly charged anion, making it the slowest due to greater solvation and ionic drag.

Therefore, the correct order of limiting molar conductivity for anions is: OH^- > NO₃^- > Cl^- > F^- > SO₄^2-.

The correct answer is Antipyretic.

• Antipyretic is a drug that reduces fever.
  • Antipyretics cause the hypothalamus to override a prostaglandin-induced increase in temperature.
  • The body then works to lower the temperature, which results in a reduction in fever. 

Additional Information

• Barbiturates are a type of central nervous system (CNS) depressant used to treat insomnia, seizures, and headaches​.
• Antiseptic slows or stops the growth of micro-organisms on external surfaces of the body and helps to prevent infections.
• Antibiotics include a range of powerful drugs that kill bacteria or slow their growth. 
  • They treat bacterial infections. 

The correct answer is Na2CO3.

Key Points

• The sodium compound is used for softening hard water. Washing soda or sodium carbonate is used for removing the permanent hardness of the water.
• Washing soda has a chemical formula Na₂CO₃.10H2O.
• It binds calcium and magnesium molecules in water.
• Water can be softened by adding sodium carbonate (washing soda) or bypassing the water through an ion-exchange column.
• For large-scale municipal operations, a process known as the lime-soda process is used to remove Ca²⁺ and Mg²⁺ from the water supply.
•  

Additional Information

The correct answer is E.

Key Points

• Vitamin E is tocopherol.
• Vitamin E represents a group of compounds that contain both tocopherol and tocotrienol.
  • It is good for the immune system and it fights toxins.
  • It is a fat-soluble vitamin.
  • It is a very powerful antioxidant.
  • Weak muscles and fertility problems are signs of deficiency of vitamin E.
  • Its deficiency also causes hair damage and skin problems.

Important Points

Bleaching powder by its nature is an Oxidising agent.

• Stable bleaching powder is widely used as a disinfectant in water purification, as well as in the textile and pulp and paper industries.
• "Bleaching powder" is made by the action of chloride gas on calcium hydroxide.
• The reaction being essentially:
• 2Ca (OH)₂ + 2Cl₂ → Ca(OCl)₂ + CaCl₂ + 2H₂O.
• In the production of bleaching powder, slaked lime spread on the floors of large rectangular chambers of lead or concrete is exposed to chlorine gas.
• Bleaching powder, a solid combination of chlorine and slaked lime, was introduced in 1799 by Scottish chemist Charles Tennant.

The correct answer is Sugar in water.

Key Points

• The physical properties help in separating the homogenous mixtures.
• Those mixtures in which the substances are completely mixed together and are indistinguishable from one another are called homogeneous mixtures.
• A homogeneous mixture is a mixture in which the composition is uniform throughout the mixture.
• Many homogeneous mixtures are commonly referred to as solutions.
• Some of the examples of homogeneous mixtures (or solutions) are Sugar solution, Salt solution, Copper sulphate solution, Seawater, Alcohol and water mixture, Petrol and oil mixture, Soda water etc.

• Heterogeneous mixture:
  • A heterogeneous mixture is a mixture with a non-uniform composition that contains components in different phases.
  • The composition varies from one region to another with at least two phases that remain separate from each other, with clearly identifiable properties.
  • Heterogeneous mixtures contain particles that retain their chemical properties when they are mixed and can be distinguished after they are mixed.
  • The components of heterogeneous mixtures can be separated by the filtration of chemical procedures.
  • The two types of heterogeneous mixtures are suspensions and colloids.
  • Sugar and sand form a heterogeneous mixture. If you look closely, you can identify tiny sugar crystals and particles of sand.
  • Ice cubes in cola form a heterogeneous mixture.

The correct answer is A reducing agent.

Key Points

• Hydrogen peroxide H₂O₂ is acting as a reducing agent here.
• A reducing agent is a compound that oxidises itself and reduces the other compound in a chemical reaction.
• A reducing agent will lose electrons in a chemical reaction, and thus get oxidized.
• Here, the charge on Chlorine (Cl) is earlier 0, but after reaction, the charge on each Cl atom is -1, this shows that it has been reduced. Thus, Hydrogen peroxide has worked as a reducing agent.
• Also, in terms of hydrogen, adding hydrogen is termed as reduction, whereas removing it is termed as oxidation. Since hydrogen is added to chlorine, chlorine is reducing, and hence we can say that Hydrogen peroxide has worked as a reducing agent.

The correct answer is Increase.

Concept:

• Molarity:
  • It is defined as the moles of a solute per litres of a solution.
  • It is also known as the molar concentration of a solution.
• Molality:
  • It is defined as the number of moles of solute per kilogram of solvent.
• Mole fraction:
  • It is the ratio of moles of a component with the total moles of solute and solvent.
• Mass%:
  • It is the percentage of the mass of solute or solvent w.r.t total mass of solution.
• Formulas:

Explanation:

• Molarity depends on the volume of the solution.
• And volume is directly proportional to temperature.
• And when we increase the temperature the volume will increase.
• So the increase in volume leads to a decrease in Molarity as Molarity is inversely proportional to the volume of solution.

​Additional Information

Notes:

• Normality:
  • It is defined as the number of gram equivalent per litre of solution.
  • Also known as equivalent concentration.
  • Normality = Number of gram equivalents / [volume of solution in litres]
• Normality is inversely proportional to temperature.
• ​Volume is directly proportional to temperature.
• Molarity is inversely proportional to volume.
• Molarity is inversely proportional to temperature.
• Molality is not dependent on temperature.

The correct answer is Bauxite.Key Points

• Bauxite is an aluminium-rich sedimentary rock formed from laterite soil.
• It is found in tropical or subtropical regions.
• Bauxite is used for the production of Aluminium.
• Bauxite is a non-ferrous metallic mineral that is used in the manufacturing of aluminium.
• Bauxite is found mainly in tertiary deposits and is associated with laterite rocks.

 Important Points

• Odisha is the largest bauxite-producing state in India.
• More than half of India's bauxite deposits are found in Odisha.
• Bauxite is an important mineral used in the production of aluminium.

 Additional Information

Important ores:

The correct answer is Nitric acid.

• Nitric acid is used in the purification of gold and silver.

Key Points

• Nitric acid is used in the purification of gold. The acid mixture aqua regia, or royal water, dissolves gold and is used to purify scrap alloy containing gold.
  • Aqua regia is a mixture of hydrochloric acid and nitric acid in a 3:1 ratio.
  • Nitric acid is a nitrogen oxoacid of formula HNO3 in which the nitrogen atom is bonded to a hydroxy group and by equivalent bonds to the remaining two oxygen atoms.

Important Points

The correct answer is Uracil.

Key Points

• In DNA, Adenine, Guanine, Thymine, and Cytosine are present.
• In RNA Adenine, Guanine, Cytosine, and Uracil are present.
• Uracil
  • It is one of the four nucleobases in nucleic acid RNA.
  • In DNA, Uracil nucleobases are replaced by thymine.
  • Its formula is C₄H₄N₂O_2.

_{Additional Information}

•  Guanine
  • It is one of the four main nucleobases found in the nucleic acids DNA and RNA.
  • It is used to make one of the building blocks of DNA and RNA.
• Adenine
  • It is also one of the four main nucleobases found in the nucleic acids DNA and RNA.
  • It is part of many substances in the body that give energy to cells.
• Cytosine
  • It is pyrimidine and one of the nitrogenous bases found in RNA and DNA acid for making genetic code.
  • It Plays an essential role in forming base pairs by bonding with guanine.