How to remove calcium

1. Add enough MgCl2 solution, stir well, filter, wash and dry the precipitated water. MgCl2+Ca(OH)2=Mg(OH)2↓+CaCl2






2. Magnesium hydroxide is difficult to dissolve in water, and calcium hydroxide is slightly soluble in water, both of which are white solid. If there is calcium hydroxide mixed in magnesium hydroxide, a small amount of calcium hydroxide will be removed. Add enough water to the mixture to dissolve it, and then filter it. Repeat the above experiment several times, and then wash the solid, then you can get a relatively pure magnesium hydroxide. This method of impurity removal Only suitable for magnesium hydroxide mixed with a small amount of calcium hydroxide.






Magnesium hydroxide (Mg (OH) 2, relative molecular weight 58.32), white amorphous powder. The suspension of magnesium hydroxide in water is called magnesium hydroxide emulsion, which is also called magnesium hydroxide. Magnesium hydroxide is a colorless hexagonal crystal or white powder, which is difficult to dissolve in water and alcohol, 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 ℃, it loses the water to form magnesium oxide.






Chemical properties: magnesium hydroxide is a medium strong base (solubility of magnesium hydroxide is very small, solution alkalinity is very weak, sometimes treated as weak base). When heated to 623k (350 ℃), it will dehydrate and decompose: Mg (OH) 2 → MgO + H2O, which is easily soluble in acid or ammonium salt solution. Like magnesium oxide, it is easy to absorb carbon dioxide in the air and gradually form basic carbonate composed of 5mg o · 4co2 · xH2O. It can be decomposed into MgO 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 hydrated lime, takes on two layers after adding water. The upper aqueous solution is called clarified lime water, and the lower suspension is called lime milk or lime slurry. Carbon dioxide can be detected by the upper clear liquid clarified lime water, and the lower turbid liquid lime milk is a kind of building material. Calcium hydroxide is a white powder solid, slightly soluble in water. Calcium hydroxide is a kind of binary medium strong alkali (in middle school, calcium hydroxide is considered as a strong alkali, but in fact, it can not be completely ionized in water, so it is considered as a medium strong alkali in University Textbooks). It has the universality of alkali and has corrosive effect on skin and fabric.






chemical property:






1. Alkali: calcium hydroxide is a strong alkali, which has corrosive effect on skin and fabric. However, due to its low solubility, the degree of harm is not as great as sodium hydroxide and other strong bases.






Note: calcium hydroxide is considered as a strong base in middle school, but in fact, it can not be completely ionized in water, so it is considered as a medium strong base in university 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), or with sulfur dioxide, silicon dioxide, etc. Therefore, calcium hydroxide and its solution must be sealed to prevent deterioration and sealed with rubber plugs.