# gcse chemistry moles/mass questionWatch

#1
Iron and sulfur react according to the equation:

Fe(s) + S(s) → FeS(s)

What is left in the reaction vessel when 112 g iron and 80 g sulfur react?

Ar values: Fe = 56; S = 32

A 192 g FeS

B 176 g FeS and 16 g sulfur

C 176 g FeS only

D 192 g FeS2

The answer is B, but i am not sure how they got that.
I first worked out the moles of each element.
Moles of Iron = 2
Moles of Sulfur = 1.5

not sure what to do next
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#2
bump
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4 weeks ago
#3
Number of moles of sulfur is 2.5, not 1.5 (using relative atomic mass of sulfur as 32)
0
4 weeks ago
#4
(Original post by PencilPot!)
Iron and sulfur react according to the equation:

Fe(s) + S(s) → FeS(s)

What is left in the reaction vessel when 112 g iron and 80 g sulfur react?

Ar values: Fe = 56; S = 32

A 192 g FeS

B 176 g FeS and 16 g sulfur

C 176 g FeS only

D 192 g FeS2

The answer is B, but i am not sure how they got that.
I first worked out the moles of each element.
Moles of Iron = 2
Moles of Sulfur = 1.5

not sure what to do next
Moles of sulphur that react are 2 actually. 80 grams is 2.5 moles of sulphur however as you've worked out, there are only 2 moles of iron. As the two react in a 1:1 stoichiometric ratio, the lesser of the two determines how many moles react.

The weight of the product is quite simply the combined weight of the reactants used up in the process as there are no secondary products. And the remaining sulphur is the 0.5 moles that is not reacted.
Last edited by Kvothe the Arcane; 4 weeks ago
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