How to remove calcium dihydroxide

1. Add sufficient MgCl2 solution, stir well, filter, wash and dry the sediment with water.


2. Magnesium hydroxide is insoluble in water, while calcium hydroxide is slightly soluble in water. Both are white solids; If magnesium hydroxide is mixed with calcium hydroxide, a small amount of calcium hydroxide will be obtained. Dissolve the mixture with enough water, and then filter it to remove a small amount of calcium hydroxide dissolved in water. Repeat the above experimental process for many times, and then wash the solid to obtain a relatively pure magnesium hydroxide. This impurity removal method is only applicable to magnesium hydroxide mixed with a small amount of calcium hydroxide.


Magnesium hydroxide (Mg (OH) 2, relative molecular weight 58.32), white amorphous powder. It is also called caustic magnesite, light burned magnesite, etc. The suspension of magnesium hydroxide in water is called magnesium hydroxide emulsion, which is called magnesium hydroxide in English. Magnesium hydroxide is a colorless hexagonal column crystal or white powder, which is insoluble in water and alcohol, soluble in dilute acid and ammonium salt solution, and the aqueous solution is weakly alkaline. The solubility in water is very small, but the part dissolved in water is completely ionized. The concentration of saturated aqueous solution is 1.9 mg/l (18 ℃). When heated to 350 ℃, the water will lose its magnesium oxide.


Chemical property: magnesium hydroxide is a medium strong alkali (magnesium hydroxide has a very small solubility, the solution is very weak in alkalinity, and sometimes it is treated as a weak alkali). Heating to 623K (350 ℃) means dehydration and decomposition: Mg (OH) 2 → MgO+H2O, which is easily soluble in acid or ammonium salt solutions. Like magnesium oxide, it is easy to absorb carbon dioxide in the air and gradually forms a basic carbonate composed of 5MgO · 4CO2 · xH2O. It is decomposed into magnesium oxide and water when the temperature is higher than 350 ℃, but it can be completely dehydrated only when the temperature is higher than 1800 ℃.


Calcium hydroxide is a white powder solid. The chemical formula Ca (OH) 2, commonly known as hydrated lime and slaked lime, is composed of two layers after adding water. The upper water solution is called clarified lime water, and the lower suspension is called lime milk or lime slurry. The clear lime water in the upper layer can be used to test carbon dioxide, while the turbid liquid lime milk in the lower layer is a building material. Calcium hydroxide is a white powder solid, slightly soluble in water. Calcium hydroxide is a binary medium strong alkali (calcium hydroxide is considered to be a strong alkali in middle school, but it cannot be completely ionized in water, so it is considered to be a medium strong alkali in college textbooks). It has the general property of alkali and has a corrosive effect on skin and fabrics.


chemical property:


1. Alkalinity: calcium hydroxide is a strong alkali, which is corrosive to skin and fabrics. However, due to its low solubility, it is less harmful than strong alkalis such as sodium hydroxide.


Note: Calcium hydroxide is considered as a strong alkali in middle school, but in fact it cannot be completely ionized in water, so it is considered as a medium strong alkali in college textbooks.


Formation: calcium oxide reacts with water to form calcium hydroxide: CaO+H2O=Ca (OH) 2


2. Reaction with non-metallic oxides: calcium hydroxide will react with carbon dioxide in the air when exposed to the air (it can be used to test carbon dioxide), as well as with sulfur dioxide, silicon dioxide, etc. Therefore, calcium hydroxide and its solution must be sealed to prevent deterioration and sealed with rubber plugs.