What is the mole concept in Class 9 Science?

A mole is the amount of substance containing 6.022 × 10²³ particles (Avogadro's number). 1 mole = molar mass in grams. Formula: Moles = Given mass ÷ Molar mass. Example: 18g of water = 1 mole = 6.022 × 10²³ molecules of H₂O.

What are the postulates of Dalton's Atomic Theory?

Key postulates: (1) All matter is made of atoms, (2) Atoms of the same element are identical, (3) Atoms of different elements have different properties, (4) Atoms combine in whole-number ratios to form compounds, (5) Atoms cannot be created or destroyed in chemical reactions.

How do you calculate molecular mass?

Molecular mass = sum of atomic masses of all atoms in the molecule. Example: H₂SO₄ = 2(H) + S + 4(O) = 2(1) + 32 + 4(16) = 2 + 32 + 64 = 98 u. Example: CO₂ = 12 + 2(16) = 44 u.

Dalton's Atomic Theory

Atoms and Molecules • Class 9 Science • NCERT • CBSE

Dalton's Atomic Theory proposed that all matter is made of atoms, which are indivisible and indestructible. Atoms of the same element are identical, while atoms of different elements differ in mass and properties. Chemical reactions involve rearrangement of atoms.

Key Formulas

Moles = Given mass / Molar mass
Number of particles = Moles × 6.022 × 10²³
Avogadro's number Nₐ = 6.022 × 10²³ mol⁻¹
Molar volume of gas at STP = 22.4 L/mol
Molecular mass of H₂O = 18 u
Molecular mass of CO₂ = 44 u

Frequently Asked Questions

What is the mole concept in Class 9 Science?: A mole is the amount of substance containing 6.022 × 10²³ particles (Avogadro's number). 1 mole = molar mass in grams. Formula: Moles = Given mass ÷ Molar mass. Example: 18g of water = 1 mole = 6.022 × 10²³ molecules of H₂O.
What are the postulates of Dalton's Atomic Theory?: Key postulates: (1) All matter is made of atoms, (2) Atoms of the same element are identical, (3) Atoms of different elements have different properties, (4) Atoms combine in whole-number ratios to form compounds, (5) Atoms cannot be created or destroyed in chemical reactions.
How do you calculate molecular mass?: Molecular mass = sum of atomic masses of all atoms in the molecule. Example: H₂SO₄ = 2(H) + S + 4(O) = 2(1) + 32 + 4(16) = 2 + 32 + 64 = 98 u. Example: CO₂ = 12 + 2(16) = 44 u.

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