Question

Find the empirical formula of a compound that contains 26.56% potassium, 35.41% chromium and the remainder oxygen?

Answer 1

`"Empirical formula"=K_2Cr_2O_7`

Explanation:

As with all these problems we assume a `100*g` mass of substance, and then we interrogate the molar quantities of each element: i.e.

`K_((26.56*g)/(39.10*g*mol^-1))Cr_((35.41*g)/(52.00*g*mol^-1))O_((38.03*g)/(16.00*g*mol^-1))= K_(0.681)Cr_0.681O_(2.37)`

And if we divide thru by `0.681`...we gets....

`K_((0.681)/(0.681))Cr_((0.681)/(0.681))O_((2.37)/(0.681))=KCrO_(3.5)`..

But by definition the empirical formula is WHOLE NUMBERS ONLY...and so we gets....`2xxKCrO_(3.5)-=K_2Cr_2O_7`..

i.e. we gots `"potassium dichromate"`....