Question

In an experiment, equal weights of iron and sulphur ($1.0$ g) are heated together and react to form $FeS$. What is the weight left unreacted?

• A. $0.250$
• B. $0.579$
• C. $0.875$
• D. $0.425$

Answer 1

Answer: (D)

$0.425$

1 mole of iron ($55.85$ g/mol) reacts with one mole of sulphur ($32.1$ g/mol).
The reaction is given below:
$Fe+S\to FeS$
$1.0$ g each of iron and sulphur corresponds to $0.01791$ moles and $0.0312$ moles respectively.
Thus, sulphur is present in excess and iron is limiting reagent.
$0.01791-0.0312=0.0133$ moles of sulphur will remain unreacted.
This corresponds to $0.0133\times 32.1=0.425$ g.