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Chemical properties
Basic oxides
1. Interaction with water. Oxides of alkaline (Li2O, Na2O, K2O, Rb2O, Cs2O) and alkaline-earth (CaO, SrO, BaO) metals form soluble bases - alkalis:
Li2O + H2O = 2LiOH;
Rb2O + H2O = 2RbOH;
CaO + H2O = Ca(OH)2;
BaO + H2O = Ba(OH)2.
2. Interaction with acidic oxides forming the salts:
K2O + SO2 = K2SO3;
SrO + N2O5 = Sr(NO3)2;
CuO + SO3 = CuSO4;
3BaO + P2O5 = Ba3(PO4)2.
3. Interaction with acids forming the salts and water:
Na2O + 2HNO3 = 2NaNO3 + H2O
NiO + H2SO4 = NiSO4 + H2O
3MgO + 2H3PO4 = Mg3(PO4)2 + 3H2O.
Other basic oxides do not react with water directly.
Acidic oxides
1. The most of acidic oxides reacts with water forming the acids (except a few oxides like SiO2, MoO3, WO3):
SO3 + H2O = H2SO4;
N2O5 + H2O = 2HNO3;
P2O5 + 3H2O = 2H3PO4;
4NO2 + O2 + 2H2O = 4HNO3.
2. Interaction with basic acids with forming the salts:
N2O3 + Na2O = 2NaNO2;
P2O5 + 3CaO = 2Ca3(PO4)2;
SO3 + BaO = BaSO4.
3. Interaction with bases forming the salts and water:
SO3 + Ba(OÍ)2 = BaSO4 + H2O;
N2O5 + 2ÊOÍ = 2KNO3 + H2O;
SiO2+2NaOÍ = Na2SiO3 + H2O.
Amphoteric oxides
Term Amphoteric (from Greek) means double-sided, mutual. Therefore amphoteric oxides occupy a position between basic and acidic oxides and display corresponding chemical properties.
1. Interaction with basic and acidic oxides forming the salts:
PbO + SO3 = PbSO4;
PbO + N2O5 = Pb(NO3)2;
Cr2O3 + 3SO3 = Cr2(SO4)3;
Cr2O3 + 3N2O5 = 2Cr(NO3)3;
Li2O + PbO = Li2PbO2;
CaO + PbO = CaPbO2;
3Li2O + Cr2O3 = 2Li3CrO3;
Li2O + Cr2O3 = 2LiCrO2;
CaO + Cr2O3 = Ca3(CrO3)2;
CaO + Cr2O3 = Ca(CrO2)2.
2. Interaction with acids forming the salts and water:
PbO+ 2 HCl = PbCl2 + H2O;
Al2O3 + 2 H3PO4 = 2AlPO4 + 3H2O.
3. Interaction with alkalis forming the salts and water:
Cr2O3 + 6KOH = 2K3CrO3 + 3H2O;
MnO2 + 2NaOH = Na2MnO3 + H2O.
Peroxides may be shown as a peculiar group of Oxygen-contained compounds. Frequently peroxides are considered as salts of Hydrogen peroxide H2O2, where O2-2 (-O-O-) is an analogue of acid residue. For example, BaO2 - Barium peroxide includes Ba2+ and formally O-.
Bases
Bases are complex substances, in which atoms of metals or ionic groups (for example, NH4+) are bonded with one or several hydroxyls groups.
Classification of bases: they are divided into two groups - soluble in waters (alkalis - LiOH, NaOH, KOH, RbOH, CsOH, FrOH, Ca(OH)2, Ba(OH)2, Sr(OH)2) and insoluble (for example, Fe(OH)2, Cu(OH)2 etc.). Insoluble bases include amphoteric ones too (Al(OH)3, Cr(OH)3, Zn(OH)2 etc.).
According to quantity of OH- bases may be divided into:
One-acidic (NaOH);
Two-acidic (Ca(OH)2);
Three-acidic (Cr(OH)3) and so on.
Preparation
1. Interaction of alkaline and alkaline-earth metals and water forming alkalis and free Hydrogen:
2K + 2H2O = 2KOH + H2;
Âà + 2Í2Î = Âà(ÎÍ)2 + Í2;
2. Direct interaction of alkaline and alkaline-earth metals oxides and water forming the alkalis:
Na2O + H2O = 2NaOH;
CaO + H2O = Ca(OH)2;
3. Insoluble bases may be prepared by interaction between soluble salts of corresponding metals and alkali solution:
Cu(NO3)2 + 2LiOH = Cu(OH)2¯ + 2LiNO3;
Fe2(SO4)3 + 3Ca(OH)2 = 2Fe(OH)3¯ + 3CaSO4.
Date: 2015-01-12; view: 1713
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