Phosphoric acid is strong acid in three yuan, three ionization, less volatile, not easy to decompose, almost no oxidation. Connectivity with acid.
PKa1:2.12
PKa2:7.21
PKa3:12.67
(1) concentrated phosphoric acid and sodium chloride were heat generated hydrogen chloride gas (with potassium iodide, sodium bromide, etc have similar reactions), belongs to the weak acid acid:
NaCl + H3PO4 (thick) = = delta = = NaH2PO4 + HCl write
Principle: difficult volatile acid volatile acid system
(2) phosphate ions have a strong cooperation ability, can generate soluble complexes with many metal ions. Such as Fe3 + and PO43 - generates colorless soluble complexes [Fe (PO4) 2] 3 - and [Fe (HPO4) 2] - and take advantage of this nature, PO43 - masking Fe3 + ions frequently used in analytical chemistry, concentrated phosphoric acid can dissolve tungsten, zirconium, silicon and iron silicide, and formed complexes with them.
(3) strong phosphoric acid by thermal dehydration, in turn, generate pyrophosphate, three phosphate and metaphosphoric acid polymers. Triphosphate chain structure, polymer metaphosphate is loop structure.
2 h3po4 = = = = 473-573 k H4P2O7 + H2O
More than 3 h3po4 = = 573 k = = H5P3O10 + 2 h2o
4 h3po4 temperature = = = = (HPO3) 4 + 4 h2o
(4) need to pay special attention to is, thick hot phosphoric acid may corrode silicon dioxide, heteropoly acid is generated. Due to the complex reaction principle too, so high school courses will be simplified as hydrofluoric acid is the only acid can react with silicon dioxide. Strong thermal phosphoric acid also can break down most of the minerals, such as chromite, rutile, ilmenite, etc.
Acid radical ion
salts
Phosphate has three types: normal salt (PO43 -), a hydrogen phosphate salt (including HPO42 -) and dihydrogen phosphate salt (H2PO4 -).
The relationship between the three kinds of salt as follows:
(1) the solubility
Normal salt and a hydrogen salt: except a few such as potassium, sodium, ammonium salt, the rest is poorly soluble in water, but soluble in acid.
Two hydrogen salt: they are soluble in water.
(2) transformation
To add lye in the phosphoric acid, and with the increasing of the lye, successively generated dihydrogen phosphate salt, a hydrogen phosphate salt, phosphate.
Against the phosphate solution strengthening acid, along with the increase in acid, has generated a hydrogen phosphate salt, dihydrogen phosphate salt, phosphate.
(3) ion coexist
1) H2PO4 -, HPO42 -, PO43 - and H + cannot coexist.
(2) H2PO4 -, HPO42 - and OH - cannot coexist.
(3) H2PO4 - and PO43 - cannot coexist (combined to generate HPO42 -).
(4) H2PO4 - and HPO42 - can coexist, HPO42 - and PO43 - can coexist.
inspection
Phosphate and excessive ammonium molybdate in nitric acid solution reaction has a pale yellow phosphorus ammonium molybdate crystals precipitation, this is the identification of the characteristics of the phosphate ion reaction:
PO43 - + 12 moo42-24 h + 3 NH4 + + + = = = = (NH4) [P (Mo12O40)] 3 · 6 h2o left + 6 h2o
PKa1:2.12
PKa2:7.21
PKa3:12.67
(1) concentrated phosphoric acid and sodium chloride were heat generated hydrogen chloride gas (with potassium iodide, sodium bromide, etc have similar reactions), belongs to the weak acid acid:
NaCl + H3PO4 (thick) = = delta = = NaH2PO4 + HCl write
Principle: difficult volatile acid volatile acid system
(2) phosphate ions have a strong cooperation ability, can generate soluble complexes with many metal ions. Such as Fe3 + and PO43 - generates colorless soluble complexes [Fe (PO4) 2] 3 - and [Fe (HPO4) 2] - and take advantage of this nature, PO43 - masking Fe3 + ions frequently used in analytical chemistry, concentrated phosphoric acid can dissolve tungsten, zirconium, silicon and iron silicide, and formed complexes with them.
(3) strong phosphoric acid by thermal dehydration, in turn, generate pyrophosphate, three phosphate and metaphosphoric acid polymers. Triphosphate chain structure, polymer metaphosphate is loop structure.
2 h3po4 = = = = 473-573 k H4P2O7 + H2O
More than 3 h3po4 = = 573 k = = H5P3O10 + 2 h2o
4 h3po4 temperature = = = = (HPO3) 4 + 4 h2o
(4) need to pay special attention to is, thick hot phosphoric acid may corrode silicon dioxide, heteropoly acid is generated. Due to the complex reaction principle too, so high school courses will be simplified as hydrofluoric acid is the only acid can react with silicon dioxide. Strong thermal phosphoric acid also can break down most of the minerals, such as chromite, rutile, ilmenite, etc.
Acid radical ion
salts
Phosphate has three types: normal salt (PO43 -), a hydrogen phosphate salt (including HPO42 -) and dihydrogen phosphate salt (H2PO4 -).
The relationship between the three kinds of salt as follows:
(1) the solubility
Normal salt and a hydrogen salt: except a few such as potassium, sodium, ammonium salt, the rest is poorly soluble in water, but soluble in acid.
Two hydrogen salt: they are soluble in water.
(2) transformation
To add lye in the phosphoric acid, and with the increasing of the lye, successively generated dihydrogen phosphate salt, a hydrogen phosphate salt, phosphate.
Against the phosphate solution strengthening acid, along with the increase in acid, has generated a hydrogen phosphate salt, dihydrogen phosphate salt, phosphate.
(3) ion coexist
1) H2PO4 -, HPO42 -, PO43 - and H + cannot coexist.
(2) H2PO4 -, HPO42 - and OH - cannot coexist.
(3) H2PO4 - and PO43 - cannot coexist (combined to generate HPO42 -).
(4) H2PO4 - and HPO42 - can coexist, HPO42 - and PO43 - can coexist.
inspection
Phosphate and excessive ammonium molybdate in nitric acid solution reaction has a pale yellow phosphorus ammonium molybdate crystals precipitation, this is the identification of the characteristics of the phosphate ion reaction:
PO43 - + 12 moo42-24 h + 3 NH4 + + + = = = = (NH4) [P (Mo12O40)] 3 · 6 h2o left + 6 h2o