Frequently used reagents and their properties

Table of Contents

Nitric acid

  • Oxidizing acido
  • Mineralization of organic samples is accompanied by the formation of carbon dioxide (CH2)n+ 2HNO3 -> CO2 + 2NO + 2H2O
  • Often occurs in mixture with H2O2 or HCl, HF
  • Boiling point: 122°C (HNO3 65%)
  • Vapor pressure: ~25 bar (at ~225°C)
  • Easy purification by subboiling
  • Most nitrates are well soluble in water

Hydrogen peroxide

  • Increases oxidation potential by formation of oxygen during decomposition 2H2O2 -> 2H2O + O2
  • Reoxidizes NOX to NO3- and thereby suppresses formation of the yellow nitrogen oxides typical of nitric acid.
  • Typical mixture HNO3 : H2O2 = 4:1

Hydrochloric acid

  • Non-oxidizing acid
  • Boiling point: 84°C
  • Vapor pressure: ~25 bar (at ~205°C)
  • Dissolves salts of weak acids (carbonates, phosphates, borates)
  • Digestion of iron alloys
  • Easy purification by subboiling
  • Most chlorides are easily soluble in water

Aqua regia

  • HCl : HNO3 = 3:1
  • Forms NOCl and releases chlorine as active component: 2NOCl -> 2NO + Cl2
  • Vapor pressure: ~25 bar (at ~200°C)
  • Digestion of precious metals, sulfides
  • Should always be used fresh

Hydrofluoric acid

  • Non-oxidizing acid
  • Decomposition of silicates SiO2 + 6HF -> H2SiF6 + 2H2O
  • Boiling point: 108°C (HF 40%)
  • Vapor pressure: ~25 bar (at ~240°C)
  • Easy to purify by subboiling
  • Digestion of minerals, ores, soil, rocks and plants
  • Complexation necessary to mask free fluoride before further use of solutions

Boric acid

  • Complexation of free fluoride H3BO3 + 3 HF -> HBF3(OH) + 2 H2O
  • 6mL saturated boric acid solution per mL HF

Sulfuric acid

  • Strongly oxidizing acid
  • Dehydration of organic material, especially plastics
  • Boiling point: 340°C (H2SO4 98 %)
  • Vapor pressure: negligible
  • Digestion of plastics, ores, minerals
  • Sulphate salts of the alkaline earth elements hardly soluble

Phosphoric acid

  • Oxidizing acid
  • Boiling point: 296°C at 983 hPa
  • Vapor pressure: negligible
  • Higher digestion temperatures can be achieved by reducing the vapor pressure of the total acid mixture
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