Frequently used reagents and their properties
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