Question

The formula of a compound of iron and sulfur was determined using the method of mass measurements. A sample of iron was weighed into a crucible and covred with finely powdered sulfur. The crucible was covered and heated to allow the iron and sulfur to react. Assume all the iron reacted with the sulfur. Additional heating burned off all unreacted sulfur. The crucible was then cooled and weighed. The following data were collected.

Mass of crucible and cover, 27.889 g.

Mass of crucible, cover, and iron, 32.025 g.

Mass of crucible, cover, and compound formed, 35.587 g.

a. calculate the mass of iron reacted.

b. calculate the mass of the compound that formed.

c.calculate the mass of the sulfur reacted.

d.calculate the moles of the iron reacted.

e. calculate the number of moles of sulfur reacted.

f. find the simplest whole number ratio of the number of moles of iron to the number of moles of sulfur in the compound formed.

Answer 1

given mass of crucible= 27.889gm. mass of crucible, iron and cover= 32.025 gms

Mass of iron = 32.025-27.889=4.136 gms   mass of compound formed= 35.587-27.889=7.698gms

a) Mass of iron reacted= 4.136 gms   b) Mass of compound (Iron sulfide) formed= 7.698gm

c) Moles of iron =mass of iron/ atomic weight = 4.136/56=0.074 moles

d) Iron exists in +2 state as well as +3 state. So the following reactions are possible

The reaction is Fe+S----> FeS or 2Fe+3S---> Fe2S3 needs to be verified.

Atomic weights = Fe =56 and Sulfur =32

1 mole of Fe requires 1 mole of sulfur to give rise to 1 mole of FeS ( if Fes is formed)

0.074 mole of iron should give 0.074 moles of FeS ( but mole of FeS if FeS is formed)= 7.698/88=0.0874

so moles formed is highe than moles of iron reacted so it can't be FeS.

In the second reaction 2 mole of Fe reacts with Sulfur to give rise to 1 mole of Fe2S3)= 7.698/208= 0.037 moles

Hence product is Fe2S3.

moles of Sulfur reqruired= 0.074*3/2=0.111 moles

Moles of iron/ mole of sulfur= 0.074/0.111= 2/3