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

#KClO_3#

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*g)/(39.10*g*mol^-1)=0.814*mol#.

#"Moles of chlorine"-=(28.98*g)/(35.45*g*mol^-1)=0.817*mol#.

#"Moles of oxygen"-=(39.18*g)/(16.00*g*mol^-1)=2.45*mol#.

We divide thru by the lowest molar quantity to give an empirical formula of #KClO_3# (or close enuff to!), i.e. #"potassium chlorate"#.

And the molecular formula is always a multiple of the empirical formula.....#(39.1+35.45+3xx16)_n*g*mol^-1=122,5*g*mol^-1#. Clearly, #n=1#, and the molecular formula is #KClO_3#, #"potassium chlorate"#.

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