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A compound contains 69.94 percent iron and 30.06 percent oxygen. What is its molecular formula if the molar mass of the compound is 199.55 per mole?

Answer 1

Olivia Anton

#Fe_2O_3#

As with all these problems, we ASSUME, that there is a #100*g# mass of unknown compound.

We divide this amount into its component atoms.

And, there is #(30.06*g)/(15.999*g*mol^-1)# #=# #1.88*mol# #O#.

And #(69.94*g)/(55.85*g*mol^-1)# #=# #1.25*mol# #Fe#.

If we divide thru by the lowest molar amount, we get an empirical formula of #FeO_(1.5)#, but because the empirical formula is the simplest whole number ratio defining constituent atoms in a species, we double this result to get WHOLE numbers, i.e. #Fe_2O_3," ferric oxide."#

Keep in mind that at the A level, an examiner would have every right to state that "an oxide of iron has 70% iron content" without providing the percentage of oxygen, and they would expect you to understand that oxygen makes up the remaining balance.

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Answer 2

Noah Aldrich

The compound's empirical formula is FeO.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.