Find the percent composition of C7H5N3O6

Finding percent composition is fairly easy. You only need to divide the mass of an element by the total mass of the compound. We can do this one element at a time.

First, let's find the total mass by using the masses of the elements given on the periodic table.

7 x 12.011 (mass of Carbon) = 84.077

5 x 1.008 (mass of Hydrogen) = 5.04

3 x 14.007 (mass of Nitrogen) = 42.021

6 x 15.999 (mass of Oxygen) = 95.994

Add all of those pieces together.

84.077 + 5.04 + 42.021 + 95.994 = 227.132 g/mol is your total. Since we also just found the mass of each individual element, the next step will be very easy.

Carbon: 84.077 / 227.132 = 0.37016 ≈ 37.01 %

Hydrogen: 5.04 / 227.132 = 0.022189 ≈ 2.22 %

Nitrogen: 42.021 / 227.132 = 0.185 ≈ 18.5 %

Oxygen: 95.994 / 227.132 = 0.42263 ≈ 42.26 %

You can check your work by making sure they add up to 100%. The ones I just found add up to 99.99, which is close enough. A small difference (no more than 0.03 in my experience) is just a matter of where you rounded your numbers.