Calculating % Mass of an Element in a Compound.
Percentage mass of an element in a compound =
(RAM x No. of Atoms (of that element) / Relative Formula Mass) x 100
E.g Find the percentage mass of sodium in sodium carbonate, Na2CO3.
% Mass = (23 x 2) / 106 x 100 = 43.4%.
Finding the Empirical Formula from Masses or Perce
1. List all elements in compound.
2. Write experimental masses/percentages.
3. Divide mass/percentage by the RAM for that particular element.
4. Turn numbers into a simple ratio by multiplying or dividing by well chosen numbers.
5. Get ratio in simplest form.
Emperical Formula Example.
E.g Find the empirical formula of iron oxide produced when 44.8g of iron reacts with 19.2g of oxygen.
1. Fe O
2. 44.8 19.2
3. 44.8/56=0.8 19.2/16=1.2
4. Times ten, Then Divde 4.
5. Therefore, Fe2O3.