Problem: Calculate the mass percent composition of each constituent element of potassium chromate.

$\boxed{\mathbf{mass}\mathbf{ }\mathbf{percent}\mathbf{=}\frac{\mathbf{mass}\mathbf{ }\mathbf{element}}{\mathbf{total}\mathbf{ }\mathbf{mass}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{compound}}\mathbf{\times }\mathbf{100}}$

potassium chromate: K₂CrO₄

molar mass K = 39.1 g/mol

molar mass Cr = 52.0 g/mol

molar mass O = 16.00 g/mol

molar mass K₂CrO₄ = (39.1 g/mol x 2) + 52.0 g/mol + (16.00 g/mol x 4)

molar mass K₂CrO₄ = 194.2 g/mol

Mass percent of K:

total mass K = 39.1 g/mol x 2

total mass K = 78.2 g/mol