Molar mass of element
Molar mass of compound
So, first lets calculate the mass of the compound as a whole. We use the atomic masses on the periodic table to determine this.
Ca: 40.078 g/mol
N2 (there is two nitrogens): 28.014 g/mol
O6 (there are six nitrogens: 3 times 2): 95.994 g/mol
When we add all of those numbers up together, we get 164.086. That is the molar mass for the whole compound. However, we are trying to figure out what percent of the compound oxygen makes up. From the molar mass, we know that 95.994 of the 164.086 is oxygen. Lets plug those numbers into our equation!
When we divide those two numbers, we get .585. When we multiply that by 100, we get 58.5.
So, the percent compostition of oxygen in Ca(NO3)2, or, calcium nitrate, is 58.5%.
Percentage Composition = (Mass of element / Mass of compound) * 100
Mass of oxygen = 16g
Molar mass of Ca(NO3)2
Ca = 40
N = 14
Molar mass = 40 + 2[14 + 3(16)] = 164
Substituting into the formular;
Percentage composition = (16 / 164) * 100
Percentage Composition = 0.0975 * 100
Percentage Composition = 9.75% ≈ 9.8 %
Correct option = A