In terms of the theory of electrolytic dissociation, acids are connections at which dissociation the positive ion of H+ hydrogen and a negative ion of the acid rest is formed. Lewis's acids are presented more generally: them are called all cations, anions or neutral molecules which are capable to accept electronic couples. Lewis's bases are capable to give electronic couples.
Instruction
1. For definition of acid in mix indicators are used. Reactions of acids with indicators lead to change of coloring of the last. High-quality detection of acids in solutions is based on this principle.
2. For example, litmus. Lower a small piece of a litmus piece of paper in solution. In the neutral environment it will become violet, in acidic environment will become red, in alkaline – blue. The intensity of coloring depends on concentration of solution. Litmus is the most widely applied acid osnovny indicator.
3. One more known indicator is methyl orange (methyl orange), organic synthetic dye. Methyl orange becomes red in acidic environment, orange in neutral and yellow in alkaline. When methyl orange reacts with substances, its structure changes, and from it the intensity of absorption of light beams by it changes.
4. Congo red will turn blue from strong acid. In the neutral and alkaline environment it will be red. For definition of the alkaline environment phenolphthalein which becomes crimson in such conditions is often used. At silnokisly reaction of the environment phenolphthalein orange. In subacidic, neutral and silnoshchelochny solutions it is colourless.
5. On separate acids the oxidation-reduction transformations leading to loss of a deposit are qualitative. So (+) + Cl (-) = AgCl ↓ can determine chlorohydrogen HCl acid as at addition in solution of cations of silver the white deposit of AgCl ↓ drops out by the ionic equation of Ag. The deposit of white color drops out also in the equation of Ba (2+) + SO4(2-) = BaSO4 ↓. Cations of silver it is possible to find also orthophosphoric H3PO4 acid: 3Ag (+) + PO4(3-) = Ag3PO4 ↓ (yellow deposit).