General gravimetric.

P4.7, 19, 16, 14

5. A 3.667 g sample of a foot powder was wet-ashed and the zinc in it was precipitated as ZnNH₄PO₄. After filtration the precipitate was ignited to Zn₂P₂O₇ which weighed 0.2824 g. What gravimetric factor would you use in calculating the % Zn(C₁₁H₁₉O₂)₂ in the sample.

a) 3.667/.2824 b) .2824/304.7 c) 431.4/178.38 d) 2x431.4/304.68 e)2x304.7/431.4

6. The phosphate in a 1.1020 g sampe of fertilizer was precipitated as MgNH₄PO₄. Ignition at 900 ^o C converted to precipitate to Mg₂P₂O₇ which weighed 0.2416 g. What is the % P in the fertilizer. Show your work.

7. The gravimetric factor you would use for calculating the %Fe₃O₄ from the gravimetric analysis in which Fe₂O₃ results from igniting the Fe(OH)₃ precipitate is ____________.

8. What do the following terms mean when applied to a gravimetric procedure?

a) digestion

b) homogenous precipitation

c) ignition

9. Write the balanced equation for the following:

a) The precipitation of chloride in sample by adding silver nitrate.

b) The precipitation of sulfate in a sample by adding barium chloride.

c) The gelatinous precipitate of ferric hydroxide is ignited to ferric oxide.