Chemistry — Mixed Practice — Part 2: 40 MCQs with Explanations

Vitamin D is synthesized in skin upon exposure to UV radiation from sunlight.

Temporary hardness is due to Ca(HCO₃)₂ and Mg(HCO₃)₂; permanent hardness due to CaSO₄, MgSO₄, CaCl₂, etc. CaCO₃ causes scale formation but not directly hardness.

Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Oxygen is released as byproduct.

Penicillin is an antibiotic discovered by Alexander Fleming, used to treat bacterial infections.

Night blindness (nyctalopia) is caused by vitamin A deficiency, affecting rhodopsin production in retina.

Carbon dioxide is used in fire extinguishers as it displaces oxygen and cools the fire.

Helium is lighter than air and non-flammable, making it safe for filling balloons.

Sodium hypochlorite (NaOCl) is used as bleaching agent in household bleach and for disinfection.

Vitamin D is fat-soluble (stored in liver and fatty tissues). Vitamins B and C are water-soluble.

Temporary hardness is caused by bicarbonates of calcium and magnesium, removable by boiling.

The SI unit of pressure is pascal (Pa), defined as 1 newton per square meter (N/m²). Other units like atm, torr, and mmHg are non-SI units commonly used in chemistry.

Boiling point increases with molecular mass in homologous series due to stronger London dispersion forces. C₄H₁₀ (butane) has the highest molecular mass and boiling point.

Ionization energy generally increases across a period. Mg has higher IE than Na (due to increased nuclear charge) and Al (due to stable 3s² configuration vs. Al's 3s²3p¹).

Longest chain containing -CHO has 4 carbons (butanal) with methyl at carbon 3, so 3-methylbutanal.

CH₃CHOHCH₂CH₃ (butan-2-ol) has a chiral carbon (attached to H, OH, CH₃, and CH₂CH₃), so it exists as enantiomers and is optically active.

CH₃NH₂ (methylamine) has the -NH₂ group attached to one alkyl group, making it a primary amine.

FCC has 8 corner atoms (each shared by 8 cells: 8×1/8=1) and 6 face-centered atoms (each shared by 2 cells: 6×1/2=3), totaling 4 atoms per unit cell.

Compounds with CH₃CH(OH)- or CH₃CO- groups give positive iodoform test. Ethanol, acetaldehyde, and acetone all give this test.

Using Arrhenius equation approximation: ln(k₂/k₁) = (Ea/R)(1/T₁ - 1/T₂). ln(2) = (Ea/8.314)(1/298 - 1/308). 0.693 ≈ (Ea/8.314)(0.000109). Ea ≈ 52.9 kJ/mol ≈ 50 kJ/mol.

(CH₃)₂CHCl (2-chloropropane) has chlorine attached to a carbon bonded to two other carbon atoms, making it a secondary alkyl halide.

Cubic system has all sides equal (a = b = c) and all angles 90°. Tetragonal has a = b ≠ c, α = β = γ = 90°.

CH₃CH₂CHOHCH₃ (butan-2-ol) has a chiral carbon atom (C2 bonded to H, OH, CH₃, and CH₂CH₃), so it exists as enantiomers.

HCl has the lowest boiling point among hydrogen halides. HF has anomalously high bp due to hydrogen bonding. Boiling points: HF (19.5°C) > HI (-35.4°C) > HBr (-67°C) > HCl (-85°C).

BCC has 8 corner atoms (8×1/8=1) plus 1 body-centered atom (fully inside), totaling 2 atoms per unit cell.

Ethanol does not show tautomerism. Keto-enol tautomerism requires a carbonyl group with α-hydrogens (present in acetone, acetaldehyde, acetylacetone).

2,3-dichlorobutane has two chiral centers. The meso form (with plane of symmetry) and one pair of enantiomers give total 3 stereoisomers (2 optically active + 1 meso).

Tertiary carbocation (CH₃)₃C⁺ is most stable due to hyperconjugation and inductive effects of three methyl groups.

Longest chain has 4 carbons (butane) with two methyl groups at carbon 2: 2,2-dimethylbutane.

CsCl has a body-centered cubic structure where each Cs⁺ is surrounded by 8 Cl⁻ ions at cube corners, so coordination number is 8.

Nitrobenzene does not undergo Friedel-Crafts reactions because the nitro group strongly deactivates the ring toward electrophilic substitution.

The empirical formula represents the simplest whole number ratio of atoms. For H2O2, the ratio of H:O is 1:1, so the empirical formula is HO.

According to Charles's Law (V1/T1 = V2/T2). Remember to convert Celsius to Kelvin: T1 = 27+273 = 300K, T2 = 177+273 = 450K. V2 = (V1*T2)/T1 = (10*450)/300 = 15 L.

The units of the rate constant 'k' depend on the overall order of the reaction. For a first-order reaction, rate = k[A], so k = rate/[A] which has units of (mol L-1 s-1)/(mol L-1) = s-1.

The longest continuous carbon chain has 3 carbons (propane). There is a methyl (CH3) substituent on the second carbon. Therefore, the IUPAC name is 2-methylpropane.

By definition, one atomic mass unit (amu) is 1/12th the mass of one atom of Carbon-12. Therefore, the mass of one Carbon-12 atom is exactly 12 amu.

The overall order is the sum of the exponents in the rate law. Here, order with respect to A is 2 and with respect to B is 1, so the overall order is 2+1 = 3.

Spontaneity is determined by Gibbs Free Energy: ΔG = ΔH - TΔS. If ΔH is positive and ΔS is positive, the term -TΔS becomes more negative as T increases. At high temperatures, -TΔS will outweigh +ΔH, making ΔG negative.

Haematite (Fe2O3) is an ore of Iron. Bauxite (Al2O3.xH2O), Cryolite (Na3AlF6), and Corundum (Al2O3) are all ores of Aluminum.

Chlorination of methane proceeds via a free radical mechanism. In the propagation steps, chlorine free radicals (Cl•) and methyl free radicals (•CH3) are formed as intermediates.

The limiting reactant is the reactant that is completely consumed first in a chemical reaction and thus limits the amount of product that can be formed.