Kimia Analitik Precipitation Yang Baik Dan Benar Menurut Vogel Dan Gravimetri

Precipitation Pengendapan

HKK > Ksp 

Supersaturated solution (contain more than its solubility caused of abnormal condition) potent to produce precipitate if the condition get normal.

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In a simple word supersaturated solution will produce precipitate

The purity of precipitate Impurities could be:  co precipitant 

post precipitant

Co-precipitant 

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 

Contaminant/impurities of the precipitate which are normally soluble in the mother liquor Formed during the main precipitate forming Adsorption at the surface Occlusion during the process of crystal growth.

Post precipitation 

Precipitation occurs on the surface of the main precipitate after its formation

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Sparingly soluble substance forms supersaturated solution Usually have common ion with the main precipitate

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Differs Aspect

Co precipitant Post precipitant

Forming time During the main After the main Forming process

precipitate

precipitate

Adsorption Occlusion

Super saturation at the end caused by excess prec. agent

Amount Great Digest effect Less Agitation Less

Small More More

Digesting 

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Let the precipitate in contact with the mother liquor at a certain temperature for a certain time Allowing the precipitate to stand for 1224 hours at room temperature, or sometimes by warming the precipitate for some time in contact with the solution which it was formed

Goals of digesting 

To obtain complete precipitation in a form which can be readily filtered by means : 1. large size 2. less impurities Digest is effective for crystalline precipitate but only has a little effect to amorphous or gelatinous precipitate