Chemistry ATOMIC AND MOLECULAR MASSES

Atomic mass

Atomic mass of an element is the number which indicates how many times the mass of one atom of the element is heavier in comparison to `1/12`th part of the mass of one atom of Carbon- 12. It is expressed in units of `am``u`.

1 amu =` 1.66 xx 10^-27` kg = `1.66 xx 10^-24` gm = `1/N_A` gm

Funda: Gram atomic mass is the mass of 1 mol atom of an element. Its unit is `gram`.

Conceptual Illustration:-
(a) What is the mass of one atom of `Cl`?

(b) What is the atomic mass of `Cl`?

(c) What is the gram atomic mass of `Cl`?

Sol. (a) Mass of one atom of Cl = `35.5` amu.

(b) Atomic mass of Cl = Mass of an atom in amu/ 1 amu

= `35.5` amu/1 amu =`35.5`

(c) Gram atomic massof Cl = Mass of one `Cl` atom x `N_A`

= `35.5` amu x `N_A`

= `35.5/N_A`x `N_A` gram = `35.5` gram

Molecular Mass

Molecular mass is the number which indicates how many times one molecule of a substance is heavier in comparison to `1/12`th of the mass of one atom of C-12.It is expressed in units of `am``u`.

Fundas:- 1.) Gram molecular mass is the mass of I mole of molecules. Its unit is `gram`.

2.) Molar mass is the mass of 1 mole particles of any substance.

Conceptual Illustration:-
(a)What is the mass of one molecule of `H_2SO_4`?

(b)What is the molecular mass of `H_2SO_4`?

(c) What is the gram molecular mass of `H_2SO_4`?

Sol. (a) Mass of one molecule of `H_SO_4` = `(1xx2 + 32 + 4 xx 16)` amu = `98` amu.

(b) Molecular mass of `H_2SO_4` = `98`

(c) Gram molecular mass of `H_SO_4` = Mass of one molccule of `H_2SO_4 xx N_A`

=`98` amu x `N_A` = `98/N_A` x `N_A` gm = `98` gram

ATOMIC AND MOLECULAR MASSES

Atomic mass

Molecular Mass

Basic of Mole Concept

1200