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 11.185 g. A 1.692 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 0.214 g of Zn2P2O7 (molar mass = 304.76 g/mol). What is the mass percent of ZnSO4·7H2O in each tablet?

1. What is the mass percent of ZnSO4 . 7H2O in each tablet?

2. What is the average mass of the active ingredient ZnSO4·7H2O and inactive filler in each tablet?

Explanation / Answer

0.236/304.76 = 0.000775 moles of Zn2P2O7

In case of zinc sulphate haptahydrate there is 1 Zn atom while in Zn2P2O7 there are 2 Zn atmos. so final sample would have twice mole of Zn in ZnSO4.7H2O

2 x 0.000774 = 0.00155 moles of ZnSO4.7H2O.

Mass of ZnSO4.7H2O

moles = weight in gm/molecular weight

weight in gm = 0.011155 x 287.53 = 0.445 gm of Zn

mass % = (mass of ZnSO4.7H2O / mass of sample) x 100

(0.445/1.634) x 100

= 27.3%

Avarage mass of ZnSO4.7H2O in each tablet can be caluclated by dividing mass of tablet/number of tablets used.

11.375/10 = 1.1375 g per tablet

Mass of ZnSO4.7H2O in each tablet

0.273 x 1.1375 = 0.310 of ZnSO4.7H2O

To find the mass of binders in each tablet

1.1375 - 0.310 = 0.827 g of binder will be present

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