Determine the formula unit mass of the following substances. (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.
The formula unit mass of an ionic compound is the sum of the atomic masses of all atoms in its formula unit. For Ammonium nitrate (NH₄NO₃), using atomic masses N = 14 u, H = 1 u, and O = 16 u: Calculation: Formula unit mass = (14 u × 2) + (1 u × 4) + (16 u × 3) = 28 u + 4 u + 48 u = 80 u.
For Phosphoric acid (H₃PO₄), using atomic masses H = 1 u, P = 31 u, and O = 16 u: Calculation: Formula unit mass = (1 u × 3) + (31 u × 1) + (16 u × 4) = 3 u + 31 u + 64 u = 98 u.
For Sodium hydrogencarbonate (NaHCO₃), using atomic masses Na = 23 u, H = 1 u, C = 12 u, and O = 16 u: Calculation: Formula unit mass = (23 u × 1) + (1 u × 1) + (12 u × 1) + (16 u × 3) = 23 u + 1 u + 12 u + 48 u = 84 u.
Explanation
The question requires calculating the formula unit mass, which is defined in the context as the mass of a formula unit of an ionic compound, calculated by summing the atomic masses of all constituent atoms. The atomic masses for N, H, O, Na, and C are explicitly provided in the context's examples (N=14u, H=1u, O=16u, Na=23u, C=12u). The atomic mass of Phosphorus (P=31u) is a standard NCERT value necessary to complete the calculation for part (ii), as it is not explicitly listed in the provided text chunks but is required to solve the textbook question.