What of acids is stronger? Answers to this question it is not so simple as it seems at first sight. Depending on what signs and in what environment to determine acid force. You should not confuse also oxidizing and acid properties of acid – sometimes they can coincide not absolutely. For example, mix of hydrochloric and nitric acid – "royal vodka" - one of the strongest oxidizers. But hydrochloric and nitric acids not the strongest.
It is required to you
- - help chemical tables.
Instruction
1. In terms of the theory of electrolytic dissociation acid is a connection which at dissociation in water breaks up to a positive ion of hydrogen and the negatively charged basis. From definition follows that extent of dissociation determines acid force.
2. Extent of dissociation depends on concentration and is set by the equation: a = Sdis/Sobshch, %; where Sdis – molar concentration of the pro-dissociating molecules, Sobshch – the general molar concentration of the substance taken for solution preparation. Strong acids dissociate almost completely, acids of average force – from 3 to 30%, weak – less than 3%. Apparently from the equation, the more concentration of substance in solution, the less size and. Knowing extent of dissociation you can judge acid force.
3. Acid force is also characterized by a constant of dissociation or a constant of acidity. It is set by expression: To = equilibrium concentration of not pro-dissociating molecules is [A+]*[B-]/[AB] = const where [A+], [B-] are equilibrium concentration of the pro-dissociating ions, [AB]. The constant of dissociation does not depend on the general molar concentration of substance. With temperature increase the degree and a constant of dissociation increase.
4. To determine acid force, find its constant of dissociation in help tables. The it is more, the acid is stronger. Strong acids have a constant from 43.6 (HNO3) and above. A part of mineral acids belongs to strong acids: chloric, salt, sulfuric and others. Organic acids (acetic, apple, etc.) and some from mineral belong to weak acids (coal, cyanic).
5. Along with a constant the indicator of acidity of pK which equal to a negative decimal logarithm from a constant is used: pK = - lgK. Strong acids have it negative.
6. But how to define what of strong acids is stronger if extents of their dissociation in water strive for infinity? Such acids are called superacids. To compare among themselves, they are considered on Lewis's theories as acceptors of electrons. Force of superacids is measured in other environments having in interaction of property of the weak reasons with them. These Wednesdays connect acid hydrogen protons.