Question

(a) Define atomic mass unit.

(b) Distinguish between molecular mass and molar mass.

(c) Give an example of (i) diatomic, and (ii) triatomic molecule of compounds.

Answer 1

A . atomic mass unit
a unit of mass used to express atomic and molecular weights, equal to one twelfth of the mass of an atom of carbon-12.
B. Molecular weight is defined as the sum of the atomic weights, or atomic mass units, of the atoms in one molecule of a molecular substance. A molecular substance can be a gas or a liquid composed of more than one atom of an element, or any chemical compound. Molecular weight is the same as “formula weight.” Chemists use a quantity called the “mole” as a convenient measure of substances in chemical calculations. A mole is defined as the “Avogadro number” of atoms of an element or molecules of a substance.

Answer 2

Atomic mass is the mass of an atom in relation to mass of one-twelfth part of C-12.


Molecular mass is the mass of all atoms in a molecule.

Molar mass is the same as molecular mass.


N2 is a diatomic molecule and O3 is a triatomic molecule.

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- Maheshwaran.