The calculated formula unit masses are 80 u for ammonium nitrate NH4NO3, 98 u for phosphoric acid H3PO4 and 84 u for sodium hydrogencarbonate NaHCO3, found by adding the individual atomic masses.
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.
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For ammonium nitrate NH4NO3, the mass equals two nitrogens, four hydrogens and three oxygens, totaling 28 plus 4 plus 48, which equals 80 u. For phosphoric acid H3PO4, the mass equals three hydrogens, one phosphorus and four oxygens, totaling 3 plus 31 plus 64, which equals 98 u. For sodium hydrogencarbonate NaHCO3, adding sodium 23, hydrogen 1, carbon 12 and three oxygens 48 gives 84 u.
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