Define polyatomic ions. Write an example. Calculate the formula unit mass of CaCO3. (Atomic mass ofC = 12 u, Ca = 40 u, O = 16 u) Calculate the molecular mass of the following: (i) HNO3 (it) CH3COOH (Atomic mass of H = 1 u, N = 14 u, O = 16 u, C = 12 u)

CBSE Class 9 CBSE Class 9 Science
1

(a) Cluster of atoms that act as an ion are called polyatomic ions.
e.g., NH4, PO43-, SO42-, etc.

(b) CaC03 = Mass of Ca + Mass of C + Mass of O
=40 u + 12 u + 16 u x 3 = 100 u.

© (i) HNO3 = Mass of H + Mass of N + Mass of O
= 1 u + 14 u + 16 u x 3 = 63 u

(ii) CH3COOH = Mass of C + Mass of H + Mass of O
= 12 u x 2 + 1 u x 4 + 16 u x 2 = 24 u + 4 u + 32 u = 60 u