Question

What are the empirical and molecular formulas of a compound that is 40.27% potassium, 26.78% chromium, and 32.95% oxygen? The molar mass of the compound is 194.2 g/mol.

Answer 1

The mass of each element is as shown below;

mass of K = 40.27g

mass of Cr = 26.78g

mass of O = 32.95g

Find the moles of each element

moles of K = $40.27/39.10=1.030$

moles of Cr = $26.78/52.00=0.5150$

moles of O = $32.95/16.00=2.059$

Let the empirical formula be $K_xCr_yO_z$

divide the number of moles of each element by the least number of moles.

$x=1.030/0.5150=2$

$y=0.5150/0.5150=1$

$z=2.059/0.5150=4$

Hence the empirical formula is $K_2CrO_4$

molecular formula $=(K_2CrO_4)n$

empirical mass =$39.1\times 2 +52\times 1 +16\times 4=194.2g/mol$

$194.2=194.2n$

$n=1$

Therefore, the molecular formula =$K_2CrO_4$