NCERT Solutions for Class 11 Chemistry Chapter 1 Some Basic Concepts of Chemistry

Short Note:

• Law of Conservation of Mass: matter can neither be created nor destroyed in a chemical reaction; total mass of reactants equals total mass of products.

• Law of Definite Proportions: a pure chemical compound always contains the same elements combined in a fixed ratio by mass, regardless of its source.

• Law of Multiple Proportions: when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers.

• Gay Lussac's Law of Gaseous Volumes and Avogadro's Law: equal volumes of all gases under the same conditions of temperature and pressure contain equal numbers of molecules.

Short Note:

• Atomic Mass is expressed in atomic mass units (u), based on the carbon-12 isotope as the standard (1 u = 1/12th the mass of one carbon-12 atom).

• Molecular Mass is the sum of atomic masses of all atoms present in a molecule of a substance.

• Formula Mass is used for ionic compounds that do not exist as discrete molecules, calculated similarly using the formula unit.

Short Note:

• One mole is the amount of substance that contains exactly as many elementary entities as there are atoms in 12 g of carbon-12, i.e. 6.022 × 10²³ entities (Avogadro's number, N_A).

• Molar Mass is the mass of one mole of a substance, expressed in g/mol, and is numerically equal to atomic/molecular mass in u.

Short Note:

• Empirical Formula shows the simplest whole-number ratio of atoms of each element in a compound; Molecular Formula shows the actual number of atoms.

• Molarity (M) = moles of solute / volume of solution in litres. Molality (m) = moles of solute / mass of solvent in kg. Mass percent = (mass of solute/mass of solution) × 100.