Hydroxide
The solubility in water of the other hydroxides in this group increases with increasing atomic number. Magnesium hydroxide Mg(OH) is a strong base (up to the limit of its solubility, which is very low in pure water), as are the hydroxides of the heavier alkaline earths: calcium hydroxide, strontium hydroxide, and barium hydroxide. A solution or suspension of calcium hydroxide is known as limewater and can be used to test for the weak acid carbon dioxide. The reaction Ca(OH) + CO Ca + + OH illustrates the basicity of calcium hydroxide. Soda lime, which is a mixture of the strong bases NaOH and KOH with Ca(OH), is used as a CO absorbent.
Hydroxide
In mildly acidic solutions, the hydroxo/hydroxido complexes formed by aluminium are somewhat different from those of boron, reflecting the greater size of Al(III) vs. B(III). The concentration of the species [Al(OH)] is very dependent on the total aluminium concentration. Various other hydroxo complexes are found in crystalline compounds. Perhaps the most important is the basic hydroxide AlO(OH), a polymeric material known by the names of the mineral forms boehmite or diaspore, depending on crystal structure. Gallium hydroxide, indium hydroxide, and thallium(III) hydroxide are also amphoteric. Thallium(I) hydroxide is a strong base.