A salt contains 31.84% potassium, 28.98% chlorine, and 39.18% oxygen by mass. What is its empirical formula?

1 Answer
anor277
Sep 16, 2017

KClO3

Explanation:

As always with these problems, we assume an 100⋅g mass of compounds, and then interrogate the molar quantities of the constituent atoms...

Moles of potassium≡31.84⋅g39.10⋅g⋅mol−1=0.814⋅mol.

Moles of chlorine≡28.98⋅g35.45⋅g⋅mol−1=0.817⋅mol.

Moles of oxygen≡39.18⋅g16.00⋅g⋅mol−1=2.45⋅mol.

We divide thru by the lowest molar quantity to give an empirical formula of KClO3 (or close enuff to!), i.e. potassium chlorate.

And the molecular formula is always a multiple of the empirical formula.....(39.1+35.45+3×16)n⋅g⋅mol−1=122,5⋅g⋅mol−1. Clearly, n=1, and the molecular formula is KClO3, potassium chlorate.

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