Perchloric acid



Perchloric acid
IUPAC name Perchloric acid; chloric(VII) acid
Identifiers
CAS number 7601-90-3
RTECS number SC7500000
SMILES OCl(=O)(=O)=O
Properties
Molecular formula ClO4
Molar mass 100.46 g/mol
Appearance colorless liquid
Boiling point

203 °C

Solubility in water Miscible
Hazards
EU classification Oxidant (O)
Corrosive (C)
NFPA 704
 
3
3
OX
R-phrases R5, R8, R35
S-phrases S45
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Perchloric acid, HClO4, is an oxoacid of pKa is −10.[1]

Anhydrous perchloric acid is an oily liquid. It forms a series of hydrates, several of which have been characterized hygroscopic, that is, if left unsealed, concentrated acid dilutes itself by absorbing water from the air.

A 0.100 molar solution in bases is made easier if the usual medium, water, is replaced by glacial acetic acid. Glacial acetic acid is a much weaker base than water, so the base being titrated appears to be stronger. As a counterpart, the strength of acids is reduced. This shows the difference in strength among the strong acids.

Laboratory preparation

The diluted acid can be prepared by perchlorate in concentrated sulfuric acid.

NaClO4 + H2SO4 → NaHSO4 + HClO4

In a related method, barium perchlorate reacts with dilute sulfuric acid to precipitate nitrous oxide and perchloric acid due to a concurrent reaction involving the ammonium ion..

Safety

Anhydrous and monohydrated perchloric acid can explode, and it slowly decomposes at normal temperature. According to the CRC "Handbook of Laboratory Safety", perchloric acid is extremely hazardous. It is very corrosive to skin and eyes and should be handled with the utmost care. It can also ignite or explode upon contact with organic material such as cloth or wood. The salts of perchloric acid are powerful oxidizers that are often used in explosive compositions. Perchlorate salts tend to be less reactive and more stable than their chlorate counterparts, which has led to their increased use in pyrotechnic compositions due to safety concerns.

References

  1. ^ dissociation constants
  2. ^ Almlöf, Jan; Lundgren, Jan O.; Olovsson, Ivar "Hydrogen Bond Studies. XLV. Crystal structure of perchloric acid 2.5 hydrate" Acta Crystallographica, Section B: Structural Crystallography and Crystal Chemistry (1971), 27(Pt. 5), 898-904.
 
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