Science ·Class 9 Science

Determine the formula unit mass of the following substances. Class 9

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· Jul 06, 2026 · Reviewed & updated Sep 17, 2026 · 1 min read

Question 1.

(i) Ammonium nitrate (NH₄NO₃), used as a nitrogen fertiliser, which is essential for plant growth.

(ii) Phosphoric acid (H₃PO₄), used to make phosphate fertiliser and detergents.

(iii) Sodium hydrogencarbonate (NaHCO₃), used to relieve acidity and helps in digestion.

Answer:

(i) Ammonium nitrate (NH₄NO₃): NH₄NO₃

contains: N = 2, H = 4, O = 3

Formula unit mass = (14 × 2) + (1 × 4) + (16 × 3) .

= 28 + 4 + 48 = 80 u

(ii) Phosphoric acid (H₃PO₄): H₃PO₄

contains: H = 3,P = 1,O = 4

Formula unit mass

= (1 × 3) + (31 × 1) + (16 × 4)

= 3 + 31 + 64 = 98 u

(iii) Sodium hydrogencarbonate (NaHCO₃):

NaHCO₃ contains: Na = 1, H = 1, C = 12 u, O = 3

Formula unit mass

= (23 × 1) + (1 × 1) + (12 × 1) + (16 × 3)

= 23 + 1 + 12 + 48 = 84 u