The active ingredient in a zinc nutritional supplement is ZnSO4·7H2O (molar mass

Question

The active ingredient in a zinc nutritional supplement is ZnSO4·7H2O (molar mass = 287.58 g/mol). Ten zinc tablets containing a mix of the active ingredient and an inactive filler were ground and mixed together thoroughly. The total mass of these ten tablets was 11.960 g. A 2.470 g sample of the finely ground tablets was dissolved in an acidic solution. The solution was neutralized with ammonia and subsequently warmed in a water bath. Addition of (NH4)3PO4 to the solution resulted in the precipitation of ZnNH4PO4. The precipitate was filtered and dried, then ignited to produce 0.206 g of Zn2P2O7 (molar mass = 304.76 g/mol). What is the mass percent of ZnSO4·7H2O in each tablet? What is the average mass of the active ingredient ZnSO4·7H2O and inactive filler in each tablet?

Explanation / Answer

Molar mass of Zn2P2O7 = 304.72 g/mole

Thus, moles of Zn2P2O7 in 0.206 g of it = mass/molar mass = 0.206/304.72 = 6.76*10-4

Moles of ZnSO4·7H2O in 2.47 g of sample = 2*moles of Zn2P2O7 = 0.00135

Thus, moles of ZnSO4·7H2O in 11.96 g of the sample = 0.00135*11.96/2.47 = 0.00655

Thus, mass of ZnSO4·7H2O = moles*molar mass = 1.883 g

Thus, % of ZnSO4·7H2O in the sample of 10 tablets = (mass/mass of 10 tablets)*100 = (1.883/11.96)*100 = 15.742%

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