Molecular and Empirical Formula - As OCR Chemistry Unit 1

Throughout my AS level chemistry i have endeavored to create a collection of my class notes and revision notes, that i will type up and folder. So i can use them for revision purposes, but then i thought how time consuming this is for me, probably why i didn't think of this sooner!
So i have decided to share all my class notes and revision resources on here for other people studying whom don't have the time to sit and type them all up :)

This Particular one is only short, stating the definitions of Molecular and Empirical Formula's and giving two worked examples.

If you would like anything requested please feel free to comment, i will be adding more and more through out the course. 

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Molly Graystone ­ Chemistry
Molecular & Empirical Formula
Empirical Formula:
o The simplest whole number ratio of atoms of each element in a compound.
3.53g of Fe (iron) reacts with 6.71g of Cl (chlorine). Find the empirical formula of the iron
o 3.53 : 6.71
56 35.5
0.063 : 0.189 FeCl3
0.063 : 0.063
1 : 3
Molecular Formula:
o The actual number of atoms of each element in a molecule of a compound.
An oxide of phosphorus contains 56.4% P (phosphorous) and 43.6% O (oxygen). Its Relative
Molecular mass is 220. Find both empirical and molecular formula of the compound.
o 56.4 : 43.6
31 16
1.819 : 2.725 P2O3 (Empirical Formula)
1.819 : 1.819
1 : 1.5
2 : 3
o P= 31
O= 16
31 +31+16+16+16= 110 220 =2
o 2(P2O3)
P4O6 (Molecular Formula)

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