Gravimetric Determination of Zinc

Zinc ions, like many other di-and trivalent ions, are precipitated by 8-hydroxyquinoline (oxine) forming the oxinates [M(oxinate)J where n is the valence of the metal ion and the number of chelate rings formed. Precipitation starts at a characteristic pH value and is complete with in a range of higher pH s, these being pH 3.3 and 4.4 respectively for zinc oxinate. 

Pipette 25.0 cm of 0.09 M zinc sulphate solution, dilute to 100 cm with water and dissolve in the solution 5 g purest potassium acetate and 4 g glacial acetic acid. Warm the solution to 60°C and add with stirring a 2% solution of oxine in 2 M acetic acid. Boil for a few minutes to coagulate the precipitate. Check for complete precipitation, adding a slight excess of the oxine solution. Filter in a prepared G4 sinter, wash with hot water and dry at 130° to constant weight. Calculate from duplicate determinations, the average [Zn(ll)] in mol dm.  

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