Chemistry Q&A for Class 12
31 free answers in Chemistry for Class 12 students, across CBSE, ICSE and State boards. Covers 6 chapters, including Alcohols, Phenols and Ethers, Chemical Kinetics, Coordination Compounds.
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- ChemistryClass 12CBSE
P°(hexane) = 408 Torr, P°(heptane) = 141 Torr. x(hexane) = 0.300. Find Y₆ and Y₇.
Step-1: Partial pressures:P(hexane) = 0.300 × 408 = 122.4 TorrP(heptane) = 0.700 × 141 = 98.7 TorrStep-2: Total pressure:P_total = 122.4 + 98.7 = 221.1 TorrStep-3: Vapour mole fractions:Y₆ (hexane) = 122.4 / 221.1 ≈ 0.554Y₇ (heptane) = 98.7 / 221.1 ≈ 0.446Answer: Y₆ ≈ 0.554, Y₇ ≈ 0.446
- ChemistryClass 12CBSE
2N₂O₅(g) → 4NO₂(g) + O₂(g). Initial P = 50 mmHg; P at 30 min = 87.5 mmHg. Find P at 60 min.
Step-1: Let N₂O₅ decrease by 2p. Total pressure = 50 + 3p:50 + 3p = 87.5 ⇒ p = 12.5 mmHgP(N₂O₅) at 30 min = 50 − 2(12.5) = 25 mmHgStep-2: Rate constant (first order):k = (1/30) × ln(50/25) = ln(2)/30 = 0.02310 min⁻¹Step-3: P(N₂O₅) at 60 min (= two half-lives = 25% of initial):P(N₂O₅) at 60 min = 50/4 = 12.5 mmHgStep-4: Total pressure at 60 min:Decrease = 50 − 12.5 = 37.5
- ChemistryClass 12CBSE
P°A = 7×10³ Pa, P°B = 12×10³ Pa at 350 K. Liquid contains 40 mol% A. Find vapour composition.
Step-1: Partial pressures (Raoult’s Law):PA = 0.40 × 7000 = 2800 PaPB = 0.60 × 12000 = 7200 PaStep-2: Total pressure:P_total = 2800 + 7200 = 10000 PaStep-3: Vapour mole fractions (Dalton’s Law):yA = 2800 / 10000 = 0.28yB = 7200 / 10000 = 0.72Answer: Mole fraction of A in vapour = 0.28, B in vapour = 0.72The more volatile component (B, higher P°) is enriched in the
- ChemistryClass 12CBSE
O₂ at 293 K, partial pressure = 0.98 bar, KH = 34 kbar. Find solubility in g/L.
Step-1: Mole fraction:x(O₂) = 0.98 / 34000 = 2.882×10⁻⁵Step-2: Moles of O₂ in 1 L:n(O₂) ≈ 2.882×10⁻⁵ × 55.5 = 1.60×10⁻³ molStep-3: Mass (Mᵣ of O₂ = 32 g/mol):mass = 1.60×10⁻³ × 32 = 0.0512 gAnswer: Solubility of O₂ ≈ 0.0512 g/LO₂ has a smaller KH than N₂ (34 vs 76.48 kbar) meaning O₂ is more soluble, which is why aquatic life can survive using dissolved O₂.
- ChemistryClass 12CBSE
Find density (g/mL) of 3.60 M H₂SO₄ that is 29% by mass. (Mᵣ = 98 g/mol)
Formula linking molarity, density, and mass percent:M = (10 × d × w%) / Molar massSubstituting values:3.60 = (10 × d × 29) / 98d = (3.60 × 98) / (10 × 29) = 352.8 / 290 = 1.216 g/mLAnswer: Density = 1.216 g/mLNote: Memorise M = (10×d×w%)/Mᵣ. Always keep w% as a plain number (29, not 0.29) and density in g/mL.
- ChemistryClass 12CBSE
N₂ gas at 293 K, partial pressure = 0.987 bar, KH = 76.48 kbar. Find millimoles dissolved in 1 L water.
Step 1: Apply Henry’s Law (p = KH × x):x(N₂) = 0.987 / 76480 = 1.290×10⁻⁵Step 2: Moles of water in 1 L = 1000/18 = 55.5 molStep 3: Moles of N₂ (since x << 1):n(N₂) ≈ x × n(H₂O) = 1.290×10⁻⁵ × 55.5 = 7.16×10⁻⁴ mol = 0.716 mmolAnswer: ≈0.716 millimoles of N₂ dissolveKey Point: Henry’s Law: gas solubility ∝ partial pressure. The large KH for N₂ means it is only sparingly soluble a
- ChemistryClass 12CBSE
50 g of ethylene glycol (CH₂OH)₂ dissolved in 200 g water; cooled to −9.3°C. Find mass of ice that separates. (Kf = 1.86 K·kg/mol)
Molar mass of ethylene glycol (C₂H₆O₂) = 62 g/molStep 1 — Moles of solute:n = 50 / 62 = 0.8065 molStep 2 — Freezing point depression formula: ΔTf = Kf × m9.3 = 1.86 × (0.8065 / W_solvent_kg)Step 3 — Mass of liquid water remaining:W_solvent = (1.86 × 0.8065) / 9.3 = 0.1613 kg = 161.3 gStep 4 — Ice separated = total water − liquid water:Ice = 200 − 161.3 = 38.7 gAnswer: ≈38.71 g of ice separates outWhen a sol
- ChemistryClass 12CBSE
[Ni(NH₃)₆]²⁺ paramagnetic or diamagnetic?
Paramagnetic — Ni²⁺ is d⁸ with t₂g⁶ eg² configuration → 2 unpaired electrons in the eg orbitals.
- ChemistryClass 12All
What is the difference between order and molecularity?
It seems like there might be a slight confusion in your question. "Order" and "molecularity" are terms used in different contexts, particularly in chemistry and kinetics. Let me clarify the differences between them: Order: In the context of chemical kinetics, the term "order" refers to the power to which the concentration of a reactant is raised in the rate equation. The order of a reaction with respect to a specific reactant is determined experimentally and may be an
- ChemistryClass 12All
what is zero order reaction?
A zero-order reaction is a type of chemical reaction in which the rate of reaction is independent of the concentration of one or more of the reactants. In a zero-order reaction, the rate of reaction remains constant over time, and it is not influenced by changes in the concentration of the reactants. The general form of a zero-order reaction can be expressed as follows: Rate = k Where: "Rate" is the rate of the reaction (the change in concentration of a reactan
- ChemistryClass 12All
What is the name of H3PO3?
The chemical compound with the formula H₃PO₃ is named Phosphorous Acid. It's a phosphorus oxoacid and a weaker acid than the more well-known phosphoric acid (H₃PO₄). Phosphorous acid is often used as a reducing agent in chemical reactions and has significant applications in various industrial processes.
- ChemistryClass 12All
What is lanthanoid contraction?
Lanthanoid contraction refers to the steady decrease in the size of the atoms and ions of the elements in the lanthanide series (also known as lanthanoids) as one moves from left to right across the periodic table, from lanthanum (La, atomic number 57) to lutetium (Lu, atomic number 71). This phenomenon has significant implications in chemistry, particularly in the field of inorganic chemistry. Here are some key aspects of lanthanoid contraction: Cause of Lanthanoid Contraction: The c
- ChemistryClass 12All
what is non reducing sugar?
Non-reducing sugars are carbohydrates that do not have a free aldehyde or ketone functional group and, therefore, cannot act as reducing agents. In reducing sugars, the presence of a free aldehyde or ketone group allows them to participate in redox reactions, reducing other substances by donating electrons. Non-reducing sugars typically include disaccharides and polysaccharides that lack free aldehyde or ketone groups. Common examples of non-reducing sugars include sucrose and trehalo
- ChemistryClass 12All
What is the full form of pan in biology
Peroxyacyl nitrates are chemical compounds which are markedly present in photochemical smog. They irritate lung surfaces and also the eye. Besides they are believed to be mutagenic and a possible cause of skin cancer in people exposed to them. They are secondary pollutants meaning they are not emitted directly rather are released as volatile organic compounds from power plants or internal combustion engines. Ultra violet light catalyses the reaction that leads to formation of peroxyacyl nitra
- ChemistryClass 12All
What is electrode potential?
Electrode potential, also known as redox potential or electrode voltage, is a measure of the tendency of a chemical species to gain or lose electrons when it is involved in a redox (reduction-oxidation) reaction. In simpler terms, it represents the ability of a substance to be oxidized or reduced at an electrode. The electrode potential is typically measured in volts (V) and is defined with respect to a reference electrode. The standard hydrogen electrode (SHE) is often used as the re
- ChemistryClass 12All
what is water of crystallization?
Water of crystallization, also known as water of hydration or simply crystalline water, is water molecules that are structurally bound within the crystalline structure of a chemical compound. These water molecules are not just physically trapped or absorbed by the compound; instead, they are an integral part of the compound's crystal lattice. This means that they are chemically bonded to the compound, and their presence is essential for the compound's structure and stability. Water of
- ChemistryClass 12All
what is an intensive property?
An intensive property is a physical or chemical property of a substance that does not depend on the amount or quantity of the substance present. In other words, intensive properties are independent of the size or mass of the sample and remain constant regardless of how much of the substance you have. Intensive properties are intrinsic to the material itself and describe its inherent characteristics. Common examples of intensive properties include: Temperature</s
- ChemistryClass 12All
what is chlor alkali process?
The chlor-alkali process is an industrial chemical manufacturing process used to produce chlorine (Cl2), sodium hydroxide (NaOH, also known as caustic soda), and sometimes hydrogen gas (H2) from the electrolysis of sodium chloride (table salt) and water (H2O). This process is essential for various industries and has several applications, including in the production of chemicals, paper, textiles, and water treatment. The chlor-alkali process typically involves the following steps:
- ChemistryClass 12All
What is the Mass of 10 Mole of Sodium Sulphite
To find the mass of 10 moles of sodium sulphite, we first need to determine its molecular formula and calculate its molar mass. Sodium sulphite has the chemical formula Na₂SO₃, containing 2 sodium atoms, 1 sulfur atom, and 3 oxygen atoms. The molar mass is calculated by adding the atomic masses: (2 × 23) + 32 + (3 × 16) = 46 + 32 + 48 = 126 grams per mole. Therefore, the mass of 10 moles of sodium sulphite = 10 × 126 = 1,260 grams or 1.26 kilograms. This calculation
- ChemistryClass 12All
If the Value of CFSE for Ni is
Crystal Field Stabilization Energy (CFSE) represents the stabilization or destabilization that a metal ion experiences when surrounded by ligands in a coordination complex, arising from the splitting of d-orbitals in the presence of ligands' electric fields. For nickel in various oxidation states and geometries, the CFSE value varies depending on the specific coordination environment. For example, Ni²⁺ in an octahedral complex with weak field ligands has eight d-electrons configured as t