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

CONCEPT:

Determining Reaction Order from Experimental Data:

• For a rate law: Rate = k[X]m[Y]n
• Compare experiments where one reactant's concentration changes and the other remains constant.
• The rate change gives the exponent (order) for that reactant.

EXPLANATION:

•  Compare row 1 and row 2 (Y is constant):
  • [X] doubles from 0.1 → 0.2
  • Rate doubles from 1.5 × 10⁻³ → 3.0 × 10⁻³
  • ⇒ Order w.r.t X = 1
•  Compare row 2 and row 3 (X is constant):
  • [Y] doubles from 0.2 → 0.4
  • Rate doubles from 3.0 × 10⁻³ → 6.0 × 10⁻³
  • ⇒ Order w.r.t Y = 1

Therefore, the correct order of the reaction is 1 with respect to X and 1 with respect to Y.

EXPLANATION:

Arrhenius Equation and Its Graphical Form:

• The Arrhenius equation is:
  k = Ae^−E_a/RT
• Taking natural log on both sides gives:
  ln k = ln A − E_a / RT
• It can be rearranged as:
  ln k = −(E_a/R) × (1/T) + ln A

This is in the form of a straight-line equation:

y = mx + c, where

• y = ln k
• x = 1/T
• Slope m = −E_a/R (a negative value)
• Intercept c = ln A

• Since the slope is negative, the graph of ln k vs 1/T must be a straight line with a negative slope.
• Among the provided graphs, only the first option shows a line sloping downward as 1/T increases.

Therefore, the correct graph of ln k vs 1/T is the first graph.

CONCEPT:

Zero-Order Reaction Kinetics:

• In a zero-order reaction, the rate is independent of the concentration of the reactant.
• The concentration at any time is given by:

  [A] = [A]0 − kt

• Rearranging for time:

  t = ([A]0 − [A]) / k

EXPLANATION:

• Given:
  • Initial amount [A]0 = 10 µg
  • Final amount [A] = 5 µg
  • Rate constant k = 0.1 µg/year
• Using the formula:

  t = (10 − 5) / 0.1 = 5 / 0.1 = 50 years
  Therefore, the time required is 50 years.

CONCEPT:

Arrhenius Equation:

The Arrhenius equation is:

log(k2/k1) = (Ea / 2.303R) × (1/T1 − 1/T2)

EXPLANATION:

• Given:
  • k1 = 1.2 × 10−3 at T1 = 500 + 273 = 773 K
  • k2 = 3.6 × 10−1 at T2 = 700 + 273 = 973 K
  • R = 8.314 J K−1 mol−1
• Using the equation:

  log(3.6 × 10−1 / 1.2 × 10−3) = (Ea / 2.303 × 8.314) × (1/773 − 1/973)

  log(300) ≈ 2.477

  (1/773 − 1/973) ≈ 2.66 × 10−4

• 2.477 = (Ea / 19.147) × 2.66 × 10−4

  Ea = (2.477 × 19.147) / 2.66 × 10−4 ≈ 178000 J/mol

  Ea = 178 kJ/mol

 Therefore, the activation energy (Ea) is 178 kJ/mol.

EXPLANATION:

First-Order Reaction Kinetics

• In a first-order reaction, the time required for a certain percentage of the reactant to decompose depends only on the half-life.
• The relationship between time and completion percentage for a first-order reaction is:

  t75% = 2 × t1/2

  t87.5% = 3 × t1/2

  t99.9% = 10 × t1/2​

• To calculate time for 75% completion of the reaction:

  t75% = 2 × t1/2 = 2 × 30 = 60 min

Therefore, the time taken for 75% completion of the reaction is 60 minutes.

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.