Acid-base reactions

Acid-base reaction are reactions between acids and bases. They are also called neutralizing or protolytic. Definitions of acids and bases are based on different theories. They are Arrhenius theory of acids and bases, Brönsted theory of acids and bases, electron theory of acids and bases.

Theory of acids and bases[edit | edit source]

Arrhenius theory of acids and bases[edit | edit source]

Acids are electrolytes capable of splitting off the hydrogen cation H⁺.

Bases are electrolytes capable of cleaving the hydroxide anion OH − .

Brönsted-Lowry theory of acids and bases[edit | edit source]

Acids are electrolytes capable of splitting off a proton.

Bases are electrolytes capable of accepting a proton.

Electron theory of acids and bases[edit | edit source]

Acids are electrolytes capable of splitting off a proton .

Bases are electrolytes capable of removing an electron (electron donors).

Acid-base reactions[edit | edit source]

Autoprotolysis of water[edit | edit source]

Autoprotolysis of water is a reaction in which ions are formed from electrically neutral water molecules.

${2H_{2}O}\longrightarrow {H_{3}O^{+}}+{OH^{-}}$

The number of dissociated molecules compared to non-dissociated ones is very small or negligible. The concentration of hyroxide anion and oxonium cation is the same. The ionic product of water has a value of 10 −14 mol 2 ·l −2 . The concentration of individual dissociated ions is therefore 10 −7 mol·l −1 .

Calculation of pH

pH = – log [H₃O⁺]

At the above concentration, neutral pH is equal to 7. Acidic pH < 7 and basic pH > 7.

Protolysis of salts[edit | edit source]

Dissolved salts in water then behave as acids or bases. The result of other ongoing reactions is the formation of either a hydroxide anion or an oxonium cation.

Buffers[edit | edit source]

More detailed information can be found on the Buffer page.

Buffers are solutions that can buffer pH changes. This ability is necessary not only for the human organism by maintaining acid-base balance (ABR), but indirectly also for maintaining overall homeostasis. But even the buffering capacity has its limitations. For example, the buffer may run out. Then there is a disturbance of the acid-base balance.

Calculation of pH

The Henderson and Hasselbalch equation describes the relationship between buffer composition and its acidity . Under simplifying assumptions :

pH = pKa + log([cb]/[ca])

where

pH is the resulting pH of the buffer ,

pK A is the dissociation constant of the conjugate acid of the buffer,

c A and c B are the equilibrium concentrations of the conjugate acid and base forming the buffer.

Links[edit | edit source]

External links[edit | edit source]

Acid-base reactions and their use in volumetric analysis

References[edit | edit source]

DUCHOŇ, Jiří, et al. Medical Chemistry: Selected Chapters in General, Inorganic and Organic Chemistry for Medics and Physicians. 1st edition. Prague: 2nd Faculty of Medicine, Charles University in Prague, 1998.
- Acid-base reactions and their use in volumetric analysis [online]. ©2010. [feeling. 2010-12-12]. < http://users.prf.jcu.cz/sima/analyticka_chemie/volumacidobas.htm >.