The preparation of hydroxides

Hydrated oxides with clearly exhibited basic and acidic properties are well soluble in water. They are prepared by the interaction of the corresponding oxides or metals with water. Weak bases, ampholytes and weak acids are practically insoluble or poorly soluble. Exchange reactions between the solutions of the corresponding salts and strong bases are used to synthesize them. 

The most pure precipitates of the mentioned hydroxides are obtained from nitrate solutions of relatively low concentrations (till 1 N) with a stoichiometric amount of the precipitating agent (sodium hydroxide or ammonia) [32]. 

The hydroxide precipitates as prepared always contain variable amounts of non-structural water (as H2O molecules) depending on precipitation conditions. Water content decreases when passing from diluted 

The dispersity of hydroxide precipitates can be governed by changing precipitation conditions. Particle size increases in the following row of salts used for precipitation sulphates - chlorides - nitrates, and with passing from fast precipitation from concentrated solutions to slow precipitation from diluted ones. 

As a rule, the fresh precipitates are X-ray amorphous. Crystallization is accelerated at increased temperature of the mother solution crystallization also takes place during precipitate ageing. 

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