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Calcium hydroxide is moderately soluble in water, as seen for many dihydroxides. Its solubility increases from 0.66 g/L at 100 °C to 1.89 g/L at 0 °C. [8] Its solubility product K sp of 5.02 × 10 −6 at 25 °C, [1] its dissociation in water is large enough that its solutions are basic according to the following dissolution reaction:
Density: 2.2 g cm −3 [2] Solubility in H 2 O 0.160 20 g/100 g [2] pH (at 20 °C) ... -985.2 kJ/mol [4] Standard molar entropy, S o solid: 83.4 J/(mol K) [4] Heat ...
Tricalcium aluminate Ca 3 Al 2 O 6, often formulated as 3CaO·Al 2 O 3 to highlight the proportions of the oxides from which it is made, is the most basic of the calcium aluminates. It does not occur in nature, but is an important mineral phase in Portland cement .
2 Cl 2 + 2 Ca(OH) 2 → CaCl 2 + Ca(OCl) 2 + 2 H 2 O. Industrial setups allow for the reaction to be conducted in stages to give various compositions, each producing different ratios of calcium hypochlorite, unconverted lime, and calcium chloride. [3]
Pentacalcium trialuminate, 5CaO·3Al 2 O 3 (C 5 A 3), forms only under an anhydrous and oxygen free atmosphere. The crystal is orthorhombic, with a density of 3067 kg·m −3. It reacts rapidly with water. Tetracalcium trialuminate, 4CaO·3Al 2 O 3 (C 4 A 3), is a metastable phase formed by dehydrating 4CaO·3Al 2 O 3 ·3H 2 O (C 4 A 3 H 3).
The formula, Cu 2 CO 3 (OH) 2 shows that it is halfway between copper carbonate and copper hydroxide. Indeed, in the past the formula was written as CuCO 3 ·Cu(OH) 2. The crystal structure is made up of copper, carbonate and hydroxide ions. [36] The mineral atacamite is an example of a basic chloride. It has the formula Cu 2 Cl(OH) 3.
CaO (s) + H 2 O (l) ⇌ Ca(OH) 2 (aq) (ΔH r = −63.7 kJ/mol of CaO) As it hydrates, an exothermic reaction results and the solid puffs up. The hydrate can be reconverted to quicklime by removing the water by heating it to redness to reverse the hydration reaction.
Calcium peroxide or calcium dioxide is the inorganic compound with the formula CaO 2. It is the peroxide (O 2 2−) salt of Ca 2+. Commercial samples can be yellowish, but the pure compound is white. It is almost insoluble in water. [3]