Now, to get the percent, we multiply by 100 and we get 7.14% by mass of H in ch two. So in this context, our H takes up 7.14% by mass. So now, suppose I want to find my empirical formula given percent by mass. So suppose I'm given that my compound is eleven point 11% hydrogen and 88.89% oxygen. I have to follow three steps to find the empirical formula. In my first step, I make the assumption that I have 100 grams of my compound.