Predict the mass of iron (iii) sulfide produced when 3.0 g of iron filings react completely with 2.5 g of yellow sulfur solid, s8(s).
a) 1.5g fe2s3
b) 2.5g fe2s3
c) 3.5g fe2s3
d) 5.5g fe2s3

D) 5.5 g Fe₂S₃.

Explanation:

No. of moles of Fe filings (3.0 g) = mass /atomic mass = (3.0 g) / (55.845 g/mol) = 0.0537 mol.

No. of moles of yellow sulfur solid (2.5 g) = mass / molar mass = (2.5 g) / (256.52 g/mol) = 0.009746 mol.

The theoretical ratio of (Fe: S₈) is (16: 3) which is 5.333.

The actual ratio of the reactants (Fe:S₈) is (0.0537 mol: 0.009746 mol) which is 5.5.

Using cross multiplication:

3.0 moles of S₈ produces → 8.0 moles of Fe₂S₃, from the stichiometry,

0.009746 moles of S₈ produces → ??? moles of Fe₂S₃.

The mass of the the produced Fe₂S₃ =  no. of moles x molar mass = (0.026 mol)(207.9 g/mol) = 5.405 g ≅ 5.5 g.

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.