Chemistry — Mixed Practice — Part 3: 40 MCQs with Explanations

The Rydberg constant is a fundamental constant in atomic physics, with a value of approximately 1.097373 x 10^7 m^-1. It appears in the formula for hydrogen spectral lines.

Refining or fractional distillation is the process of separating crude petroleum into useful fractions (gasoline, kerosene, diesel, etc.) based on their different boiling points.

Salivary amylase (also known as ptyalin) is an enzyme in the mouth that catalyzes the hydrolysis of starch into simpler sugars like maltose.

According to de Broglie's hypothesis, matter has wave-like properties. The wavelength (λ) of a particle is inversely proportional to its momentum (p). The equation is λ = h / p, where h is Planck's constant.

The critical temperature (Tc) of a substance is the temperature above which distinct liquid and gas phases do not exist. No amount of pressure can liquefy a gas above its critical temperature.

Stainless steel is primarily an alloy of iron with a minimum of about 10.5% chromium. Nickel is also often added to improve properties like corrosion resistance and formability.

Empirical formula is the simplest whole number ratio of atoms. For glucose (C₆H₁₂O₆), dividing all subscripts by 6 gives CH₂O.

The Arrhenius equation is k = A e^{-Ea/RT}. A decrease in activation energy (Ea) makes the exponent less negative, thus increasing the value of k.

Antoine Lavoisier's Law of Conservation of Mass states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as the mass of the reactants equals the mass of the products.

Zymase is an enzyme complex found in yeast that catalyzes the fermentation of sugars into ethanol and carbon dioxide.

Molar mass of C₆H₁₂O₆ = (6×12) + (12×1) + (6×16) = 72 + 12 + 96 = 180 g/mol. Mass of carbon = 72 g/mol. % C = (72/180) × 100 = 40%.

Evaporation is the process of a substance in a liquid state changing to a gaseous state due to an increase in temperature and/or pressure. It occurs at the surface below the boiling point at a constant temperature.

Ethylene glycol (ethane-1,2-diol) is the main component of automotive antifreeze. It lowers the freezing point of the coolant in the radiator and also raises its boiling point.

Oxygen is the most abundant element in the Earth's crust, making up about 46.6% of the crust's mass. It is followed by silicon (27.7%) and aluminum (8.1%).

Baking soda is the common name for sodium bicarbonate, which has the chemical formula NaHCO₃. It is used as a leavening agent in baking.

Chromatography is a separation technique. The stationary phase is the phase that does not move and can be a solid (e.g., in adsorption chromatography) or a liquid supported on a solid (e.g., in partition chromatography).

Iodine is an essential component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Iodine deficiency can lead to goiter.

Galvanization is the process of applying a protective zinc coating to iron or steel to prevent rusting. The zinc acts as a sacrificial anode, corroding in place of the iron.

H₂SO₄: 2(1) + 32 + 4(16) = 2 + 32 + 64 = 98 amu.

Density ∝ molar mass at STP. Molar masses: H₂=2, N₂=28, O₂=32, Cl₂=71 g/mol. Chlorine has highest molar mass, hence highest density.

R = 8.314 J·mol⁻¹·K⁻¹ = 8.314 kg·m²·s⁻²·mol⁻¹·K⁻¹ in SI units.

v_rms = √(3RT/M) ∝ √T, where T is absolute temperature.

Z = PV/nRT. For ideal gas, PV = nRT, so Z = 1. For real gases, Z deviates from 1.

Gases with strong intermolecular forces (like NH₃ with hydrogen bonding) and larger molecular size show greater deviation from ideal behavior.

Above critical temperature, gas cannot be liquefied regardless of pressure applied.

l can have integer values from 0 to (n-1). For n=3, l = 0, 1, 2.

NaCl has face-centered cubic lattice where Cl⁻ ions form FCC lattice and Na⁺ ions occupy all octahedral voids.

FCC: 8 corners × 1/8 + 6 faces × 1/2 = 1 + 3 = 4 atoms per unit cell.

Viscosity is internal resistance to flow due to intermolecular forces and molecular entanglement.

Adhesive forces between water and glass exceed cohesive forces within water, causing water to climb walls (capillary action) forming concave meniscus.

Ag₂CrO₄(s) ⇌ 2Ag⁺(aq) + CrO₄²⁻(aq). K_sp = [Ag⁺]²[CrO₄²⁻].

Overall order = sum of exponents = 2 + 1 = 3 (third order).

For second-order: rate = k[A]² ⇒ k = rate/[A]² has units (mol·L⁻¹·s⁻¹)/(mol²·L⁻²) = L·mol⁻¹·s⁻¹.

Catalyst provides alternative reaction pathway with lower activation energy, increasing rate without being consumed.

For many reactions near room temperature, rate approximately doubles (factor of 2) for every 10°C rise in temperature.

Gibbs free energy criterion: ΔG = ΔH - TΔS < 0 for spontaneous process at constant T and P.

E°_cell = E°_cathode - E°_anode = E°_Cu - E°_Zn = +0.34 - (-0.76) = +1.10 V.

Li (Group 1, Period 2) shows diagonal relationship with Mg (Group 2, Period 3) due to similar charge/radius ratio and polarizing power.

Aluminum (Group 13) is p-block element. s-block includes Groups 1 and 2.

2Na + O₂ → Na₂O₂ (sodium peroxide). With limited oxygen: 4Na + O₂ → 2Na₂O.