Question

a compound contains 70 by mass of iron and 30 by mass of oxygen. what is its empirical formula​

Answer 1

Answer:

Fe2 03

Explanation:

Your ultimate goal here is to figure out the smallest whole number ratio that exists between iron and oxygen in this unknown compound, i.e. the empirical formula of the compound.

Start by converting the percent composition to grams by using a 100-g sample of compound.

You will have

70% Fe a100 g sampleaaa−−−−−−−−−→ 70 g Fe

30% O a100 g sampleaaa−−−−−−−−−→ 30 g O

Next, use the molar masses of the two elements to convert the masses to moles

For Fe: 70g⋅1 mole Fe55.845g=1.2535 moles Fe

For O: 30g⋅1 mole O15.9994g=1.8750 moles O

To find the mole ratio that exists between iron and oxygen, divide both values by the smallest one.

You will have

For Fe: 1.2535moles1.2535moles=1

For O: 1.8750moles1.2535moles=1.496≈1.5

Now, you are looking for the smallest whole number ratio that exists between the two elements, so multiply both values by 2 to get

Fe(2⋅1)O(2⋅1.5)

You can thus say that the empirical formula of the compound is

Fe2O3−−−−−−→ empirical formula

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