Find % of Fe

Question

if a piece of iron gain 10% of its weight due to partial rusting into Fe₂o₃ the % of total iron that has rusted is ?

Answer 1

This is a limiting reactant question in a slightly different form than usual.  We are told that a sample of iron increases in weight by 10% as the result of  partial rusting and asked how much has rusted.

 

First, write the chemical equation

 

__Fe   +  __O2 ------>  __Fe2O3

 

then balance.  There is an excellent YouTube video on balancing chemical equations you might find helpful

 

www.youtube.com/watch?v=7GityTHbeKw

 

Remember that the coefficients correspond to moles or molecules, not grams

 

Second, because of the conservation of matter, the only possible source of the weight gain is O2.  So, let's assume we have a 10 gram sample of iron that gains 10% of its weight due to partial rusting.  That means 1 gram of O2 has reacted with it to form rust.

 

Third, determine how many moles of O2 are in 1 gram of O2 and use the coefficients from the balanced equation to calculate how much iron was converted to rust.  Divide the result into 10 grams, express in % and you're done!