Kimia Gravimetri Tentang Penyaringan Endapan Yang Baik Dan Benar

FILTRATION PENYARINGAN

Filtration • Separation of the precipitate from the mother liquor • Object: • Get the precipitate and the filtering medium quantitatively free from the solution

Filtering Medium • 1. Filter paper • 2. Sintered glass filtering crucible • The choice of filtering medium controlled by : a. nature of the precipitate b. temperature of drying and igniting

Filter Paper • Size : 7, 9, 11 and 12.5 cm • Ash less, the 11cm diameter should not contain more than 0,1 mg of ash • Three porosity : very fine, medium, coarse • Special nature : hardened, greater strength in wet condition, extremely small ash, more resistant to acids and alkalis

Whatman Quantitative Paper Number

Particle size retention

Speed of filtration

Ash (%)

40

Medium

Medium

0.008

41

Coarse

Fast

0.008

42

fine

slow

0.008

Filter Crucible • 1. Sintered glass crucible Should not be heated above 2000C • 2. Silica crucible • Has a better thermal stability (could be heated at 200 -12000C)

Porosity of filter disc Number of porosity

Pore diameter Number of (micrometer) porosity

Pore diameter (micrometer)

0

200 -250

3

20-30

1

100-120

4

5-10

2

40-50

5

1-2

Filter crucible • Inert and resistant to all solution that do not attack silica • Attacked by HF, fluorides and strongly alkaline solution • The new crucible should be washed with concentrated HCl solution and then with distilled water.

Cleaning the filter crucible • Shaking out the solid as much as possible then, • Dissolving the remainder solid with hot 0,1 M EDTA solution, rinse by suction. • The solid could be removed by EDTA: • Barium sulphate, calcium oxalate, calcium phosphate, calcium oxide, lead iodate, lead oxalate, lead carbonate, magnesium ammonium phosphate