Theory Exercises

Introduction

Acid oxosalts (also called hydrogen salts) derive from oxyacids and, unlike neutral oxosalts, retain one or more hydrogen atoms. Because of these hydrogens the salts still display acidic character.

Traditional nomenclature

The anion is named similarly to neutral oxosalts (changing -ic to -ate or -ous to -ite as appropriate) and the prefix "hydrogen-" is added according to the number of hydrogens retained. Alternatively, the compound can be described as an "acid" followed by the anion name.

Examples:
  • NaHSO₄: hydrogensulfate of sodium (sodium bisulfate)
  • NaH₂PO₄: dihydrogenophosphate of sodium
  • Fe(HSO₄)₃: hydrogensulfate of iron(III)
  • Ca(HSO₃)₂: hydrogensulfite of calcium
  • Ca(H₂PO₄)₂: dihydrogenophosphate of calcium

Systematic additive nomenclature

The composition of the anion is described using prefixes that include hydrogen as a component. If multiple anions appear, use multiplicative prefixes such as bis-, tris-, tetrakis-, etc. The metal is then indicated, with multiplicative prefixes as needed.

Examples:
  • NaHSO₄: hydrogen tetraoxidosulfate of sodium
  • KHCO₃: hydrogen trioxidocarbonate of potassium
  • NaH₂PO₄: dihydrogen tetraoxidophosphate of sodium
  • Na₂HPO₄: hydrogen tetraoxidophosphate of disodium
  • Ca(HSO₃)₂: bis(hydrogen trioxidosulfate) of calcium
  • KH₂PO₄: dihydrogen tetraoxidophosphate of potassium

Systematic composition nomenclature

The number of atoms composing the anion (including hydrogen) and the overall charge are specified, followed by the metal and its charge if necessary.

Examples:
  • NaHSO₄: hydrogen tetraoxidosulfate(1-) of sodium
  • KHCO₃: hydrogen trioxidocarbonate(1-) of potassium
  • NaH₂PO₄: dihydrogen tetraoxidophosphate(1-) of sodium
  • Na₂HPO₄: hydrogen tetraoxidophosphate(2-) of sodium
  • Ca(HSO₃)₂: bis(hydrogen trioxidosulfate)(1-) of calcium
  • NaHS: hydrogensulfide(1-) of sodium

Common acid oxosalts

  • NaHCO₃ (hydrogenocarbonate of sodium / sodium bicarbonate): antacid, leavening agent in baking, household cleaner
  • NaHSO₄ (hydrogensulfate of sodium): pH regulator for pools, metal cleaning
  • KH₂PO₄ (dihydrogenophosphate of potassium): fertilizers, food supplements, pH regulator
  • Ca(H₂PO₄)₂ (dihydrogenophosphate of calcium): fertilizers, food supplements
  • NaHSO₃ (hydrogensulfite of sodium): food preservative, antioxidant in food industry