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 11.890 g. A 2.242 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 0.180 g of Zn2P2O7 (molar mass = 304.76 g/mol).

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

2 and 3- What is the average mass of the active ingredient ZnSO4·7H2O and inactive filler in each tablet?

Answer 1

we know that

moles = mass / molar mass

so

moles of Zn2P207 = 0.18 / 304.76

so

moles of Zn2P207 = 5.906 x 10-4

now

moles of Zn = 2 x moles of Zn2P207

moles of Zn = 2 x 5.906 x 10- 4

moles of Zn = 1.1812 x 10-3

all the Zn should come from ZnS04.7H20

so

moles of ZnS04.7H20 = moles of Zn = 1.1812 x 10-3

now

mass of ZnS04. 7H20 = 1.1812 x 10-3 x 287.58

mass of ZnS04 . 7 H20 = 0.4 g

now

2.242 sample containes 0.4 g ZnS04. 7H20

11.89 g sample contain y g ZnS04.7H20

y = 2.1213 g

so

2.1213 grams of ZnS04 . 7 H20 in 10 tablets

mass of ZnS04. 7H20 in each tablet = 0.21213

also

mass of each tablet = 11.890/10 = 1.189

now

mass percent = mass of ZnS04.7H20 x 100 / mass of tablet

mass percent = 0.21213 x 100 / 1.189

mass percent = 17.84

so

mass percent of ZnS04.7H20 in each tablet is 17.84 %

2)

avergae mass of ZnS04 . 7H20 in each tablet is 0.21213 grams

3)

mass of inactive filler = 1.189-0.21213

mass of inactive filler in each tablet = 0.97687 grams