Slaked lime Slightly soluble

The product, calcium hydroxide, is commonly known as slaked lime because, as calcium hydroxide, the thirst of lime for water has been quenched (slaked). Slaked lime is the form in which lime is normally sold because quicklime can set fire to moist wood and paper. In fact, the wooden boats that were once used to transport quicklime sometimes caught fire in the heat of reaction when water seeped into their holds. An aqueous solution of calcium hydroxide, which is slightly soluble in water, is called lime water. It is used as a test for carbon dioxide, with which it reacts to form a suspension of the much less soluble calcium carbonate ... 

For most applications slaked lime is sold. The hydration of lime is very exothermic and could ignite paper or wood containers of the unslaked material. Slaked lime is slightly soluble in water to give a weakly basic solution. 

The alkaline earth metal hydroxides M(OH)2 (M = Mg, Ca, Sr, or Ba) are also strong bases ( 100% dissociated), but they give lower OH- concentrations because they are less soluble. Their solubility at room temperature varies from 38 g/L for the relatively soluble Ba(OH)2 to 10-2 g/L for the relatively insoluble Mg(OH)2. Aqueous suspensions of Mg(OH)2, called milk of magnesia, are used as an antacid. The most common and least expensive alkaline earth hydroxide is Ca(OH)2, which is used in making mortars and cements. It is called slaked lime because it is made by treating lime (CaO) with water. Aqueous solutions of the slightly soluble Ca(OH)2 (solubility 1.3g/L) are known as limewater. 

In some cases, such as that of MgO, the solid is so insoluble that little change in pH is noticed when it is placed in water. CaO, however, which is known as quicklime, is sufficiently soluble to form a strongly alkaline solution with the evolution of considerable heat the result is the slightly-soluble slaked lime, Ca(OH)2. 

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