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

CONCEPT:

Freezing Point Depression

• Freezing point depression occurs when a non-volatile solute is dissolved in a solvent, lowering the freezing point of the solution.
• The formula for freezing point depression is:
  • \(\Delta T_f = K_f \times m \)
• Here, \( K_f \) is the cryoscopic constant (1.86 K⋅kg/mol for water), and m is the molality of the solution.

CALCULATION:

• Step 1: Calculate the molality of the solution:
  • Moles of solute = 0.1 mol
  • Mass of solvent (water) = 1.0 kg
  • Molality \( m = \frac{\text{moles of solute}}{\text{mass of solvent in kg}} = \frac{0.1}{1.0} = 0.1 \, \text{mol/kg} \)
• Step 2: Apply the freezing point depression formula:
  • Given: \( K_f = 1.86 \, \text{K⋅kg/mol} \)
  • Molality \( m = 0.1 \, \text{mol/kg} \)
  • \(\Delta T_f = K_f \times m \)
  • \( \Delta T_f = 1.86 \, \text{K⋅kg/mol} \times 0.1 \, \text{mol/kg} \)
  • \( \Delta T_f = 0.186 \, \text{K} \)
• Thus, the freezing point depression \( \Delta T_f \) is 0.186 K.

CONCLUSION:

The correct freezing point depression is 0.186 K.

CONCEPT:

Drug Classes and Drug Molecules

• Antibiotics: These are drugs used to kill or inhibit the growth of bacteria. They are crucial in the treatment of bacterial infections. Penicillin is one of the earliest discovered antibiotics and is still widely used to treat a range of bacterial infections.
• Antipyretics: These are medications that are used to reduce fever by acting on the hypothalamus to regulate body temperature. Paracetamol is a commonly used antipyretic that helps in reducing fever as well as providing mild pain relief. It's widely used due to its safety profile.
• Tranquilizers: Tranquilizers are a class of drugs used to reduce tension and anxiety. These drugs can affect the central nervous system to induce a calming effect. Diazepam is a well-known tranquilizer used for the treatment of anxiety, muscle spasms, and seizures.
• Analgesics: Analgesics are drugs that relieve pain without causing a loss of consciousness. Aspirin is a commonly used analgesic that is also known for its anti-inflammatory and blood-thinning properties. It is often used to treat pain, inflammation, and to reduce the risk of heart attacks.

EXPLANATION:

• Antibiotics: The best-known example of an antibiotic is Penicillin, which works by inhibiting the synthesis of bacterial cell walls, ultimately killing the bacteria (a-ii).
• Antipyretics: Paracetamol is a widely used antipyretic that helps in reducing fever. It works by influencing the hypothalamic heat-regulating center to lower body temperature, making it a highly effective and safe choice for fever management (b-iv).
• Tranquilizers: Diazepam is a benzodiazepine tranquilizer that is commonly prescribed for anxiety disorders, muscle spasms, and seizures. It has a calming effect by enhancing the activity of the neurotransmitter GABA in the brain (c-iii).
• Analgesics: Aspirin is a non-steroidal anti-inflammatory drug (NSAID) that provides pain relief (analgesic effect) by inhibiting the enzyme COX, which reduces the production of prostaglandins responsible for pain and inflammation (d-i).

ADDITIONAL INFORMATION:

• Penicillin: It was discovered by Alexander Fleming in 1928 and was the first antibiotic used to treat infections caused by bacteria such as staphylococci and streptococci. Penicillin is still a cornerstone in the treatment of bacterial infections.
• Paracetamol: Known for its fever-reducing and mild pain-relieving effects, paracetamol (also known as acetaminophen) is commonly used worldwide. Unlike NSAIDs, paracetamol is not an anti-inflammatory, but it is preferred for patients who cannot tolerate NSAIDs.
• Diazepam: This tranquilizer is used in the management of anxiety, alcohol withdrawal symptoms, and seizures. It is a controlled substance because of its potential for dependence and abuse. Diazepam works by calming the brain through its effect on the neurotransmitter GABA.
• Aspirin: In addition to its use as an analgesic, aspirin is also used to prevent heart attacks and strokes due to its blood-thinning (antiplatelet) properties. It works by inhibiting the COX enzyme, reducing inflammation, pain, and clot formation.

CONCLUSION:

The correct answer is: Option 1.

CONCEPT:

Ozonolysis, Aldol Condensation, and NaBH₄ Reduction

• Ozonolysis:
  • Ozonolysis is a reaction in which ozone (O₃) cleaves the carbon-carbon double bond (C=C) in alkenes to form aldehydes or ketones. The reaction is carried out in the presence of a reducing agent like Zn/H₂O to prevent further oxidation.
  • In this reaction, the alkene breaks at the double bond, producing two carbonyl-containing compounds (either aldehydes or ketones) depending on the structure of the alkene.
• Aldol Condensation:
  • Aldol condensation is a base-catalyzed reaction between aldehydes or ketones with α-hydrogen atoms. The reaction forms a β-hydroxy aldehyde or ketone (aldol) as the initial product.
  • Further heating leads to the elimination of water (dehydration), resulting in the formation of an α,β-unsaturated aldehyde or ketone.
• Reduction by NaBH₄:
  • Sodium borohydride (NaBH₄) is a mild reducing agent commonly used in organic chemistry to reduce carbonyl compounds such as aldehydes and ketones to alcohols.
  • NaBH₄ selectively reduces aldehydes to primary alcohols and ketones to secondary alcohols without affecting other functional groups such as esters or carboxylic acids.

MECHANISM:

CONCLUSION:

• After ozonolysis, aldol condensation, and reduction with NaBH₄, the final products are identified as:
• O: The initial ketone formed after ozonolysis (cyclohexanone).
• P: The product of the aldol condensation, a conjugated α,β-unsaturated aldehyde.
• Q: The reduced product, an alcohol derived from the reduction of the aldehyde group.

The correct answer is: Cl₂ < HCl < NaCl < NaF

Explanation: The ionic character of a bond is determined by the difference in electronegativity between the two atoms forming the bond. The greater the electronegativity difference, the higher the ionic character of the bond.

• Cl₂: This molecule consists of two chlorine atoms, which have the same electronegativity, resulting in a purely covalent bond with no ionic character.
• HCl: Hydrogen and chlorine have a moderate difference in electronegativity, leading to a covalent bond with some ionic character.
• NaCl: Sodium and chlorine have a larger electronegativity difference, resulting in a bond with significant ionic character as sodium donates an electron to chlorine.
• NaF: Sodium and fluorine have the highest electronegativity difference among the compounds listed, resulting in a bond with the greatest ionic character, as sodium donates an electron to the highly electronegative fluorine.

Therefore, the order of increasing ionic character is: Cl₂ < HCl < NaCl < NaF

Additional Information:Ionic Character and Ionic Bonds:

• Electronegativity: This is a measure of an atom's ability to attract and hold onto electrons. The greater the difference in electronegativity between two bonded atoms, the more the bond will have ionic character.
• Covalent Bonds: These are bonds where electrons are shared between atoms. Pure covalent bonds occur when the atoms have identical or very similar electronegativities.
• Ionic Bonds: These occur when there is a significant difference in electronegativity between the bonded atoms, usually greater than 1.7 on the Pauling scale. In ionic bonds, electrons are transferred from one atom to another, leading to the formation of positive and negative ions.
• Polar Covalent Bonds: These are intermediate between purely covalent and purely ionic. They occur when the electronegativity difference is moderate, leading to unequal sharing of electrons and resulting in partial charges on the atoms.

 Factors Influencing Ionic Character:

• Electronegativity Difference: Larger differences lead to greater ionic character.
• Bond Length: Shorter bonds generally have higher covalent character, while longer bonds can have more ionic character.
• Polarizability: Larger, more polarizable atoms can facilitate partial electron transfer, affecting the ionic character.

The electronic configuration is an arrangement of electrons in various

shells of an atom of an element.

Key Points

Electronic configuration :

• The arrangement of electrons in the electronic levels of an atom is called its electronic configuration.
• The electrons are arranged according to their energies and space availability.
• The electrons in the completely filled shells are known as core electrons.
•  The electrons that are added to the electronic shell with the highest principal quantum number are called valence electrons.

Additional Information

There are a few sets of rules which we follow while arranging the electrons in an atom. They are-

• Aufbau principle-
  • ​It states that the atomic orbitals which have lower energies are filled first.
  • Then the electron goes to occupy the higher atomic energy levels.
  • This ruled is followed to write the electronic configuration of atoms in their ground state.
  • When in the excited state, the electrons might vacant the lower energy state and move on to a higher energy state.
  • The order in which atomic orbitals are filled are: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p.
  • The order follows that the lower ( n + l ) value of atomic orbital will have lower energy, where n = principal quantum number and l = azimuthal quantum number.
• Pauli's exclusion principle:
  • ​An electron is characterized by four quantum numbers n, m, l, and s.
  • Pauli's exclusion principle states that every electron must have its unique set of these four quantum numbers.
  • No two electrons can have the same set of quantum numbers.
  • Simplifying, we may say that an orbital can contain a maximum of two electrons and the two electrons should have opposite spins ( + ½, - ½ ).
• Hund's rule of maximum spin multiplicity:
  • ​While filling up the orbitals of the same energy, or degeneracy, electrons will first singly occupy the subshell.
  • After each subshell has been singly occupied, electron pairing will start.
  • This rule thus implies that maximum spin should be maintained while filling up electrons in a subshell.
  • The maximum spin state involves maximum exchange energy and yields a more stable state.
• Modern periodic law:
  • ​The modern period table involves the arrangement of the elements according to their increasing Atomic number.
  • The law states that the physical and chemical properties of an element are characteristics of its Atomic number.

The correct answer is Sodium carbonate.

Explanation:

• Washing soda is a chemical compound with the formula Na2CO3, known as sodium carbonate, and it's a salt of carbonic acid.
• Properties of a Washing soda:
  • It is a transparent crystalline solid.
  • It is one of the few metal carbonates which are soluble in water.
  • It is alkaline with a pH level of 11, it turns red litmus to blue.
  • It has detergent properties or cleansing properties because it can remove dirt and grease from dirty clothes, etc.
  • It attacks dirt and grease to form water-soluble products, which are then washed away on rinsing with water.

Important Points

Some common chemical compounds with their common names are:

K2CO3 or potassium carbonate is known as pearl ash.

• Pearl ash, in ancient times, was created by baking potash in a kiln in order to remove impurities. The remaining fine, white powder was pearl ash.
• Potassium carbonate is an inorganic compound and a white salt which is soluble in water.
• It is mainly used in the production of glass and soap.

Additional Information

The correct answer is increases.

Important Points

• In normal cases, the volume of substances increases on heating and decreases while cooling.
• When 1 litre of water is cooled from 4°C to 0°C volume of water will start increasing this due to water's unique property known as 'Anomalous Expansion of Water'.
• Anomalous Expansion of Water occurs between 4°C to 0°C.
• The density of water is a maximum at 4 °C.
• When water is cooled from 4°C to 0°C, its density decreases.
• The anomalous expansion of water helps preserve aquatic life during very cold weather.

Explanation:

• When water reaches 4°C the molecules have been pushed as close to one another as possible and the density of water becomes precisely 1.00 g/cm³
• When water freezes at 0°C due to the crystal structure the molecules arranged in some structured fashion so a little far apart ended up less dense - 0.93 g/cm³  - and so floats due to buoyancy.

As density decreases the volume increases.

Volume = mass /density.

The correct answer is Lactic Acid.

Key Points

• Lactic acid is present in Sour milk or curd.
• The sourness of the milk is due to the presence of lactic acid.
• Human beings feel tired due to the accumulation of lactic acid in the muscles.​

Additional Information

Explanation:

• Calcium hydroxide is sparingly soluble in water producing an alkaline solution known as limewater.
• Calcium Carbonate is a chemical compound found commonly in rocks as minerals and is the main component of pearls and the shells of marine organisms, eggs, etc.
• When carbon dioxide gas is passed through or over limewater, it turns milky due to the formation of calcium carbonate.
• In the chemical reaction it can be shown as :

\(\rm \underset{Lime\ water}{Ca (OH)_2} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{CaCO_3 \ (g)}\)Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" id="MathJax-Element-1-Frame" role="presentation" style="display: inline; position: relative;" tabindex="0">Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" role="presentation" style="display: inline; position: relative;" tabindex="0">Ca(OH)2

• However, when an excess of CO2 ​is passed through this solution, the milkiness disappears. This is due to the formation of calcium bicarbonate which is colorless and soluble in water.

Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" role="presentation" style="display: inline; position: relative;" tabindex="0">​\(\rm \underset{Lime\ water}{Ca (OH)_2} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{CaCO_3 \ (g)}\)​\(\rm \underset{Lime\ water}{Ca CO_3} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{Ca(HCO_3)_2 \ (g)}\)Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate\(\rm \underset{Calcium\ Carbonate}{Ca CO_3} \ \ +H_2O+ \ \underset{Carbon \ Dioxide}{CO_2 \ (g) } \ \longrightarrow \ \underset{Calcium \ bi\ Carbonate}{Ca(HCO_3)_2 \ (g)}\)

Additional Information Reaction involved-

CaCO₃ + 2HCl →  CaCl₂ + CO₂ + H₂O

• The evolved gas is carbon dioxide which then passes through lime water and turns it milky.

Ca(OH)₂ + CO₂ → H₂O + CaCO₃  

• Due to formation of these compounds
• when excess CO₂ is passed

CaCO₃ + H₂O + CO₂ →  Ca(HCO₃)₂ 

• Bicarbonate is formed which again clears the solution

Mistake Points

•  Do not confuse Calcium carbonate and calcium bicarbonate.
• One produces white colour while the other makes it colourless.

 Key Points

• Atomic Mass of the Hydrogen = 1
• Atomic Mass of the oxygen = 16

Explanation:

1 mole of hydrogen = 1gm

1 mole of oxygen = 16gm

Water (H2O) = 2 Hydrogen atoms + 1 Oxygen atom

2 mole of hydrogen = 2gm

1 mole of oxygen = 16 gm

The ratio of the mass of Hydrogen: Ratio of mass of Oxygen =  2/16 = 1/8 

The ratio of the mass of Hydrogen to the mass of Oxygen in water is always 1:8.

The correct answer is Zn.

Key Points

• Only a few elements have been found to be absolutely essential for plant growth and metabolism.
• These elements are further divided into two broad categories based on their quantitative requirements: (i) Macronutrients, and (ii) Micronutrients.
• Macronutrients are generally present in plant tissues in large amounts.
  • The macronutrients include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorous (P), sulphur (S), potassium (K), calcium (Ca) and magnesium (Mg).
  • Of these, carbon, hydrogen and oxygen are mainly obtained from CO₂ and H₂O, while the others are absorbed from the soil as mineral nutrition.
• Micronutrients or trace elements are needed in very small amounts.
  • These include iron, manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), boron (B), chlorine (Cl) and nickel (Ni).

Additional Information

• In addition to the 17 essential elements named above, there are some beneficial elements such as sodium (Na), silicon (Si), cobalt (Co) and selenium (Se). They are required by higher plants

The correct answer is Methanoic acid.

Key Points

• Nettle is an herbaceous plant that grows in the wild.
• Nettle leaves have stinging hair, which causes painful stings when touched accidentally. 
• This is due to the methanoic acid secreted by them. 
• A traditional remedy is rubbing the area with the leaf of the dock plant, which often grows beside the nettle.

Additional Information

• The number of water molecules present is washing soda is 10.
• We know the molecular formula for Washing Soda is Na₂CO₃.10H₂O.
• Recrystallisation of Sodium Carbonate (Na₂CO₃) gives washing soda.
• In a Washing soda, water is present in the form of crystals.

The correct answer is Vermilion.

• Mercury Sulfide is also known as Vermilion.
• It is a chemical compound composed of the chemical elements mercury and sulfur.
• The chemical formula of Mercury sulfide is HgS.
• It is dimorphic with two crystal forms:
  • Red cinnabar
  • Black metacinnabar

Additional Information

• Marsh Gas is the common name of Methane with the formula of CH₄.
• Mohr's Salt is the common name of Ammonium Ferrous Sulphate with the formula of (NH₄)2Fe(SO₄)₂(H₂O)₆.
• Potash Alum is the common name of Potassium Aluminium Sulphate with the formula of KAl(SO₄)₂.