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.
Iron(III) oxide-hydroxide
Yellow iron oxide (CAS ) is used as a pigment, e.g. Pigment Yellow 42 or C.I. 77492. Pigment Yellow 42 is Food and Drug Administration (FDA) approved for use in cosmetics and is used in some tattoo inks. Solid material color ranges from yellow through dark-brown to black. Iron oxide-hydroxide is also used in aquarium water treatment as a phosphate binder.
Recently, two forms of Iron oxide-hydroxides nanoparticles were identified as very good adsorbents for lead removal from aquatic media.