Preparation of sodium hydroxide by caustification of carbonate


The preparation of sodium hydroxide is based on a reaction of double exchange, called “caustification of carbonate”. Calcium oxide powder is poured into a porcelain dish adding enough distilled water to form a fairly dense “whitewash”. Sodium carbonate is heated in water until it is completely dissolved. The “whitewash” is then poured while continuing to heat it for a certain time. After this time turn off the burner and let the beaker with its contents cool. The insoluble calcium carbonate (CaCO3 ) formed by the reaction will precipitate, while the supernatant will result in a solution of sodium hydroxide (NaOH). This part is collected by decantation or by filtration and the basicity of the same occurs. The solution can be made to evaporate by further heating it and by placing it in a drier to collect the crystalline sodium hydroxide which, in another stage, may be subjected to a flame test in order to show the presence of the Na+ ion (yellow colouring).

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