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Calcium hydroxide has a high enough pH to turn the phenolphthalein a vivid purplish-pink color, thus indicating the presence of water. Chemical pulping: Calcium oxide is used to make calcium hydroxide, which is used to regenerate sodium hydroxide from sodium carbonate in the chemical recovery at kraft pulp mills.
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:
The reaction of calcium carbide with water, producing acetylene and calcium hydroxide, [5] was discovered by Friedrich Wöhler in 1862. CaC 2 + 2 H 2 O → C 2 H 2 + Ca(OH) 2 . This reaction was the basis of the industrial manufacture of acetylene, and is the major industrial use of calcium carbide.
Magnesium has a mild reaction with cold water. The reaction is short-lived because the magnesium hydroxide layer formed on the magnesium is almost insoluble in water and prevents further reaction. Mg(s) + 2H 2 O(l) Mg(OH) 2 (s) + H 2 (g) [11] A metal reacting with cold water will produce a metal hydroxide and hydrogen gas.
An example is when slaked lime (calcium hydroxide) is mixed into a thick slurry with sand and water to form mortar for building purposes. When the masonry has been laid, the slaked lime in the mortar slowly begins to react with carbon dioxide to form calcium carbonate (limestone) according to the reaction: Ca(OH) 2 + CO 2 → CaCO 3 + H 2 O.
Calcium aluminates phase diagram Crystal structure of dodecacalcium hepta-aluminate, 12CaO·7Al 2 O 3 (C 12 A 7). [1] Calcium aluminates are a range of materials [2] obtained by heating calcium oxide and aluminium oxide together at high temperatures. They are encountered in the manufacture of refractories and cements.
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]
Calcium nitride is formed along with the oxide, CaO, when calcium burns in air. It can be produced by direct reaction of the elements: [3] 3 Ca + N 2 → Ca 3 N 2. It reacts with water or even the moisture in air to give ammonia and calcium hydroxide: [4] Ca 3 N 2 + 6 H 2 O → 3 Ca(OH) 2 + 2 NH 3