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# Empirical formula and molecular mass watch

1. Hi,
how would I go about working out the answer to this question?

One of these compounds of oxygen and fluorine has a relative molecular mass of 70.0 and contains 54.3% by mass of fluorine.
Calculate the empirical formula and the molecular formula of this compound.
Divide each % by the relative mass of each
You should get 2.85 for F and 2.85 for O
There in a ratio of 1:1 so you know the empirical formula is just FO

As for molecular formula it would be F2O2 as the molecular mass of that molecule = 70
3. (Original post by Daniel100499)
Divide each % by the relative mass of each
You should get 2.85 for F and 2.85 for O
There in a ratio of 1:1 so you know the empirical formula is just FO

As for molecular formula it would be F2O2 as the molecular mass of that molecule = 70
Where do you get the 45.7 from for oxygen? I can't seem to work it out.
4. (Original post by Chiaralia)
Where do you get the 45.7 from for oxygen? I can't seem to work it out.
It gives you %by mass of F, so the other % of mass is just oxygen 100-54.3 =45.7
5. (Original post by Daniel100499)
It gives you %by mass of F, so the other % of mass is just oxygen 100-54.3 =45.7

Thank you so much!
6. (Original post by Daniel100499)
It gives you %by mass of F, so the other % of mass is just oxygen 100-54.3 =45.7
One more quick question! How do you work out the molecular formula?
7. (Original post by Chiaralia)
One more quick question! How do you work out the molecular formula?
You look at the molecular mass it gives you and just use trial and error until you get the right mass using the elements in the ratio of 1:1

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