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Alkaline earth metal salts also show characteristic colors in high-temperature flames (flame color test), such as orange-red for calcium flames, magenta for strontium flames, and green for barium flames
.
1.
Solubility of salt
Except for beryllium, alkaline earth metal salts are all ionic compounds, and salts formed with monovalent anions are generally soluble in water
.
Nitrate , chloride, acetate , bicarbonate , dihydrogen phosphate, etc.
Alkaline earth metal salt solubility and high negative charge of the anion generally small, such as carbonates, phosphates and oxalates are insoluble
.
BeSO 4 and MgSO 4 are easily soluble in water, CaSO 4 , SrSO 4 , and BaSO 4 are insoluble; BeCrO 4 and MgCrO 4 are easily soluble in water, and CaCrO 4 , SrCrO 4 , and BaCrO 4 are insoluble
The solubility of salts formed by complex anions with large radii and cations with large radii is generally small
.
The large cation radius can avoid contact between the anions in the crystal, and the crystal lattice energy is larger
2.
Salt crystal water and double salt
The charge of alkaline earth metal ions is higher than that of alkali metals, and the salt has a greater tendency to carry crystal water, such as MgCl 2 ·6H 2 O, CaCl 2 ·6H 2 O, MgSO 4 ·7H 2 O, CaSO 4 ·2H 2 O, BaCl 2 2H · 2 O
.
Anhydrous salts of alkaline earth metals have water absorption, such as anhydrous CaCl 2 is an important desiccant
3.
Thermal decomposition of oxo acid salt
The thermal stability of alkaline earth metal oxyacid salts is generally lower than that of alkali metal oxyacid salts
.
The reason is that alkaline earth metal cations have high charge, small radius, strong polarization ability, and lower decomposition temperature of oxyacid salt
The products of thermal decomposition of alkaline earth metal carbonates are metal oxides and carbon dioxide
MgCO 3 =MgO+CO 2
The products of thermal decomposition of alkaline earth metal nitrates are metal oxides, nitrogen dioxide and oxygen
2Mg(NO 3 ) 2 =2MgO+4NO 2 +O 2
The thermal decomposition products of alkaline earth metal sulfates are metal oxides and sulfur trioxide , and sulfur trioxide decomposes at higher temperatures
MgSO 4 =MgO+SO 3
